LPG Cold Start - Let's See How It's Done

LPG Cold Start - Let's See How It's Done

Author
Discussion

ChimpOnGas

Original Poster:

8,416 posts

117 months

Sunday 10th February
quotequote all
OK Gas Sniffers, this one's a bit geeky but I feel I'm in good company.......... so here it is:

https://www.youtube.com/watch?v=cL42OiTNjYo

Who says you can't cold start on LPG... wink

Dave thumbup

carsy

3,011 posts

103 months

Sunday 10th February
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Good work Dave. I enjoyed that.

ChimpOnGas

Original Poster:

8,416 posts

117 months

Sunday 10th February
quotequote all
carsy said:
Good work Dave. I enjoyed that.
Cheers mate, is a bit geeky and specific to LPG but one element that's relevant to anyone running a petrol Chimaera is my manual idle vale demo, I fitted the manual idle valve because of an electrical issue, an earth loop, an earth loop the ECU installers themselves failed to resolve!

An earth loop is a potential difference between two earthing points causing electromagnetic interference, in effect you are creating a transmitter, in my case the fake Bosch idle air control valve that came with the Canems system is causing the Canems ECU to continually loop the priming pulse feature explained in my YouTube clip.

To be clear earth loops are common on cars with composite bodies, the fault is not within the Canems ECU but how it is wired to the car, more specifically it's an issue with how the Canems ECU is interacting with the Canems loom in relation to the poor earthing TVR gave these cars. I will fix this in the spring to prove my point, until then I will retain my spare ECU kindly supplied by David Hampshire of Canems Engine management systems as I'm no longer prepared to leave the car with the installers for three weeks at a time only discover when they say "it's fixed"... the truth is its far from fixed!

A looping priming pulse is actually dangerous situation, if you just left the ignition on or 'heavens forbid' I ever ended up in a ditch unconscious after an accident.... as the looping issue would just end up pumping gas into the inlet manifold and plenum effectively creating a rather effective bomb... yikes.

This is no different to the fire risk a looping priming pulse would introduce on petrol and is why the 14CUX ECU, my Canems ECU (when there's no earth loop), and all other ECUs only run the fuel pump for a few seconds. After just a first few seconds of running the pump the ECU is designed only reinstate the live feed to the fuel pump (or LPG safety solenoids) when it sees a cranking or engine running signal.

So this is why I was forced to fit my manual idle valve, its cable operated so with zero electrical activity involved so there can be no earth loop, it's a simple solution to a complex electrical issue but it works and it makes the car safe once more. What it teaches us is just how little a Chimaera actually needs extra air, this brings us full circle to the 14CUX stepper motor and why I believe it's the completely unnecessary source of so many drivability issues.

The key word here is unnecessary, even without the help of scatter spark ignition timing closed loop idle control I have conclusively proven just how little this engine needs an idle valve of any kind, in many ways my discovery was born from an ironic twist of fate but the results are undeniable. It also teaches us why the clever people who designed the MBE system for our cars chose to omit an idle valve altogether, I don't believe they were skimping on cost here..... I think it's highly likely by leaving the idle valve on the bench they were actually making the system simpler but better.

I was formerly trained in automotive engineering over three years in an academic environment (Norwich City College), but the people who really taught me how to tune an engine came later. I rejected my scholarship at Hethel and chose restoration as my path, people thought I was mad to turn up this opportunity but I was actually the winner.

The path I chose meant I was privileged to work with a group of inspirational and highly experienced mechanics who learned their trade over many years on the job, they had zero classroom education but boat loads of real world knowledge. These guys taught me many first principle lessons, and one of them that will stay with me forever was...."you can't tune an engine with a vacuum leak.

OK so they were teaching me carburetor tuning, but lets not forget a spark ignition internal combustion engine operates to exactly the same principles and rules no matter if its fed by a carb or injection wink Make no mistake an air bleed from any type of idle valve (including a 14CUX stepper motor) is still a vacuum leak, idle valves are fine but their behavior must be controlled properly, and I'm damn sure my Canems controlled pattern part PWM idle valve was not behaving properly!

I fitted my manual idle valve to solve a complex earth loop issue, but what it taught me was simple, it taught me just how little this engine actually needs extra air, it also reminded me of that lesson those old experienced mechanics drummed into me all those years ago....

IE.. "you can't tune an engine with a vacuum leak!

What I really like about my manual idle valve is how much it teaches us about what the engine actually needs (and doesn't need) in the way of extra air, I also love the fact that when I push my air valve knob fully home I know 100% for sure there is zero extra air entering the engine. You can't say that about the Canems controlled PWM idle valve I had before, and you certainly can't say that about the 14CUX stepper motor either!

I don't care if it's an engine on a carb or injection, the lesson I was taught all those years ago is still as 100% relevant today as it was 25 years ago when it was drummed into me by those clever old boys I had the privilege to be educated by.....

IE.....

"YOU CAN'T TUNE AN ENGINE WITH (ANY SORT OF) A VACUUM LEAK!... nono

Think about it wink

Classic Chim

8,737 posts

87 months

Sunday 10th February
quotequote all
So you don’t really need an idle valve on an RV8.
I think that’s why my MBE equipped car doesn’t have one smile
Ive argued for ages it’s an unnecessary arrangement.
Carb engined RV tickover at 600 revs
850/900 should be easily manageable from a decent Ecu cold start map
They run cleaner on initial take up
They warm up quicker
And use less fuel as it’s not needlessly revvin.
My car was used almost daily so cold starts were never much more than a day or two inbetween which does help but I found the car warmed upto a useable temp within a minute or so and quicker than on the CUX.
These modern Ecu, like putting icing on the engine cake and giving it the healthiest intake of fuel / air / timing you can muster.




ChimpOnGas

Original Poster:

8,416 posts

117 months

Monday 11th February
quotequote all
Exactly Alun!

Well actually for the ultimate turn key results on cold start the engine does need a little extra air, this is why I like to refer to my setup as an extra air valve not an idle valve, its purpose is to precisely add just a touch of additional air for cold starts and warm up only, it does not manage the idle because after 40c coolant temp it is pushed home and so is fully closed.

I get that modern cars with sophisticated engine managements systems do it but my opinion on our cars trying to use any type of extra air/idle valve to manage idle above 40c is the wrong approach, because on the Rover V8 I've proved such a valve is just not required and indeed can often be more trouble than it's worth. The truth is if the engine is setup correctly after 40c coolant temp, you want a completely closed extra air valve, anything else is either going to give trouble or is masking a poorly adjusted base idle setting.

What I like about my manual extra air valve is when I push it home I know its shut, of course I can configure my Canems system so the electric PWM idle valve supposedly steps out at 40c, that's easy, but the truth is even like this it still represents a significant air bleed. I discovered the idle valve is never actually 100% shut so to compensate for this you end up running less air via the base idle screw to hit your idle target, now you might think this is the same thing as far as the engine is concerned but my experience has been that's just not the case!

While the displayed valve duty remains the same on my Canems software the air bleed through my pattern part Bosch valve was in fact changing constantly, it seems in my case engine vacuum is either acting on the valve or EMI was causing it to behave erratically, TBH this caused no end of tuning issues and confusion until I discovered it.

So although you don't see it on the laptop there are definitely fluctuations in the volume of air passing through the valve into the engine, with all this in mind and the fact the pattern part Bosch PWM idle valve supplied with my Canems system was causing the ECU priming pulse feature to loop I elected to go back to basics with a cable operated extra air valve that once pushed fully home is definitely 100% fully closed and allows zero air to pass into the engine.

After the engine has been started from stone cold even on the coldest day I can push my extra air knob in completely at 40c coolant temp, the engine idles perfectly like this, after that you can start the car all day long and I never need to touch extra air control at all, and in warmer weather I don't actually need to use the system at all, even on the first of the morning cold start!

Like I say all this evidence proves just how little the engine (if set up correctly) needs an extra air/idle valve, indeed if I was still on the 14CUX I'd definitely bin off the troublesome Lucas stepper motor in favor of my manual extra air valve setup as there will likely be drivability benefits to come, as indeed I've experienced myself.

With the engine proving to us just how little it needs extra air, and given the issues idle valves can introduce, I may even stick with my manual system as it's hardly inconvenient to use and I only ever use it once a day anyway, and then only in cold weather.

If I had an MBE system I'd also definitely fit my manual extra air valve idea as it will make those cold starts turn key OEM perfect, I also feel it's just nice to have a simple system that precisely allows you to increase the idle speed at the pull of a control knob, rather than pressing the pedal and holding the throttle open with your foot.

The system cost me just £30, it works a treat, and completely eliminated the damn priming pulse looping issue that plagued me for over a year and could not be corrected by the installers, TBH this was disappointing as it was clearly a safety issue. My manual idle valve also taught me more about what the engine does and doesn't need in the way of extra air in 10 minutes than I learned in four years of chasing my tail trying to fine tune the engine with that problematic fake Bosch idle valve fitted..mad

Often going back to basics and simplifying a system is by far the best approach.. yes








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Sardonicus

15,765 posts

159 months

Monday 11th February
quotequote all
I am doing away with my wasted spark ignition and going back to a clockwork dizzy with points and condenser in spring hehe maybe a pair of SU's or Stromberg's shortly after scratchchin manual choke of course whistle

ChimpOnGas

Original Poster:

8,416 posts

117 months

Monday 11th February
quotequote all
Sardonicus said:
I am doing away with my wasted spark ignition and going back to a clockwork dizzy with points and condenser in spring hehe maybe a pair of SU's or Stromberg's shortly after scratchchin manual choke of course whistle
Come on Simon it's hardly the same thing now is it, and have a little sympathy for my situation which is an earth loop not of my making that only revealed itself on my Mk5 (fifth replacement) ECU.

I've solved a problem in my own way for £30, a problem that the installers failed to fix themselves after having the car for some three weeks. Of course it's ridiculous I had to remove my idle valve on what is an engine management system specifically designed to run one, but trust me I didn't bring this situation on myself.

I was merely sent yet another replacement ECU after yet another failure only to be told it was not compatible with my early Canems wiring loom, I'm merely the victim here. I'm disappointed and saddened I was forced to find my own solution but while the installers did agree to fix the problem (only after a barrage of emails) my biggest disappointment was after three weeks with the car they tell me I can collect as the looping issue was now fixed only to discover it was still doing it.

Off I go taking more time off work to collect the car (200 mile round trip) only for the problem to return the very next day! Faced with the serious safety issue of potentially one day finding myself in an accident and unable to switch the key off, I feared I would be sat there hearing the priming pulse looping knowing it was continually pumping either petrol or LPG into the inlet manifold and the fuel pump could potentially be spraying petrol on the hot engine.

So as always when faced with a challenge and after giving others enough chances to solve it for me I created my own solution, which not only works brilliantly but makes the car safe once more.

My final point on all this is there's no argument MBE is a very respected system and it runs no idle valve of any type (electric or manual), for many months I've been running the exact same arrangements with only a tickle of throttle required on cold start but many othere benefits so I can see why they made this choice.

I think we need to accept the people at MBE and the guy who developed the setup for Chims and Griffs on behalf of Powers knows a thing or two about engine management installations, it's not a cheap system or intended to be cheap either. As such I very much doubt the omission of an idle valve was a cost cutting exercise, I am certain in fact from my own experiences and tests there is way more to it than saving a paltry £80 - £100 on fitting a genuine Bosch idle valve.


Edited by ChimpOnGas on Monday 11th February 15:51

ric355

124 posts

87 months

Monday 11th February
quotequote all
ChimpOnGas said:
I think we need to accept the people at MBE and the guy who developed the setup for Chims and Griffs on behalf of Powers knows a thing or two about engine management installations, it's not a cheap system or intended to be cheap either. As such I very much doubt the omission of an idle valve was a cost cutting exercise, I am certain in fact from my own experiences and tests there is way more to it than saving a paltry £80 - £100 on fitting a genuine Bosch idle valve.
As is proven, you can get a car to run without any sort of idle valve but cold starts are more difficult and the idle is always a bit lumpy unless you up the revs, even with spark advance control added in to the mix. I had a Caterham done once (Rover K series) with an Emerald, and the person who built the engine deleted the idle valve. When tuning the idle, the very well respected person doing the mapping told me he "that's as good as it'll get without the idle valve". It just hunted a lot. Never really bothered me but there is a point to having one.

I think it's more important when you want to meet emissions standards, where you need to have some closed loop control to keep the AFR lean enough to pass MOT checks. Without that need you can just run it richer and add a bit of extra advance as needed.

I've just finished my ECU conversion and I kept the idle valve as I want it to be turn-key. I don't want to be messing around holding the throttle open and getting it warm so it'll idle OK. I just need to be able to get in it and drive away from cold so I don't upset the neighbours. And I want to be able to get it through an MOT with an MOT map.


ChimpOnGas

Original Poster:

8,416 posts

117 months

Monday 11th February
quotequote all
ric355 said:
ChimpOnGas said:
I think we need to accept the people at MBE and the guy who developed the setup for Chims and Griffs on behalf of Powers knows a thing or two about engine management installations, it's not a cheap system or intended to be cheap either. As such I very much doubt the omission of an idle valve was a cost cutting exercise, I am certain in fact from my own experiences and tests there is way more to it than saving a paltry £80 - £100 on fitting a genuine Bosch idle valve.
As is proven, you can get a car to run without any sort of idle valve but cold starts are more difficult and the idle is always a bit lumpy unless you up the revs, even with spark advance control added in to the mix. I had a Caterham done once (Rover K series) with an Emerald, and the person who built the engine deleted the idle valve. When tuning the idle, the very well respected person doing the mapping told me he "that's as good as it'll get without the idle valve". It just hunted a lot. Never really bothered me but there is a point to having one.

I think it's more important when you want to meet emissions standards, where you need to have some closed loop control to keep the AFR lean enough to pass MOT checks. Without that need you can just run it richer and add a bit of extra advance as needed.

I've just finished my ECU conversion and I kept the idle valve as I want it to be turn-key. I don't want to be messing around holding the throttle open and getting it warm so it'll idle OK. I just need to be able to get in it and drive away from cold so I don't upset the neighbours. And I want to be able to get it through an MOT with an MOT map.
For these reasons and more I fitted my simple manual solution, it;s easy to use, highly effective and only needed for the first 120 seconds or so of cold start, and only then on the coldest day.







Once the control knob is pushed home the engine returns to idle falling back purely on my base idle screw and throttle butterfly settings, oh and a sniff of the nasty stuff from the crankcase but I have that PCV valve controlled now to tame the rather aggressive vacuum draw of the original crude un-valved arrangement.

Its a simple solution I freely admit I shouldn't have been forced to implement, but there's no denying it delivers OEM cold starts every time and even on LPG, after the coolant reaches 40c the extra air knob stays firmly pushed home all day and ensures a zero air bleed through the valve.

This 'it's definitely fully shut' feature is something I like a lot, because TBH I never did feel I could 100% trust what my Canems controlled PWM idle valve was really up to, I admit a feeling is one thing..... but all the evidence I subsequently gathered eventually proved I was absolutely right to mistrust it wink

Sardonicus

15,765 posts

159 months

Monday 11th February
quotequote all
ChimpOnGas said:
Come on Simon it's hardly the same thing now is it, and have a little sympathy for my situation which is an earth loop not of my making that only revealed itself on my Mk5 (fifth replacement) ECU.

I've solved a problem in my own way for £30, a problem that the installers failed to fix themselves after having the car for some three weeks. Of course it's ridiculous I had to remove my idle valve on what is an engine management system specifically designed to run one, but trust me I didn't bring this situation on myself.

I was merely sent yet another replacement ECU after yet another failure only to be told it was not compatible with my early Canems wiring loom, I'm merely the victim here. I'm disappointed and saddened I was forced to find my own solution but while the installers did agree to fix the problem (only after a barrage of emails) my biggest disappointment was after three weeks with the car they tell me I can collect as the looping issue was now fixed only to discover it was still doing it.

Off I go taking more time off work to collect the car (200 mile round trip) only for the problem to return the very next day! Faced with the serious safety issue of potentially one day finding myself in an accident and unable to switch the key off, I feared I would be sat there hearing the priming pulse looping knowing it was continually pumping either petrol or LPG into the inlet manifold and the fuel pump could potentially be spraying petrol on the hot engine.

So as always when faced with a challenge and after giving others enough chances to solve it for me I created my own solution, which not only works brilliantly but makes the car safe once more.

My final point on all this is there's no argument MBE is a very respected system and it runs no idle valve of any type (electric or manual), for many months I've been running the exact same arrangements with only a tickle of throttle required on cold start but many othere benefits so I can see why they made this choice.

I think we need to accept the people at MBE and the guy who developed the setup for Chims and Griffs on behalf of Powers knows a thing or two about engine management installations, it's not a cheap system or intended to be cheap either. As such I very much doubt the omission of an idle valve was a cost cutting exercise, I am certain in fact from my own experiences and tests there is way more to it than saving a paltry £80 - £100 on fitting a genuine Bosch idle valve.


Edited by ChimpOnGas on Monday 11th February 15:51
Dave Dave Dave laugh I am only fking around fella tongue out I know of your issues previously you got a system there thats working for you whats not to like? its simple and works and your happy thumbup I only wanted to see you jump on my comment hence why I went dark ages stylee with my intended mods hehe

ChimpOnGas

Original Poster:

8,416 posts

117 months

Monday 11th February
quotequote all
Sardonicus said:
Dave Dave Dave laugh I am only fking around fella tongue out I know of your issues previously you got a system there thats working for you whats not to like? its simple and works and your happy thumbup I only wanted to see you jump on my comment hence why I went dark ages stylee with my intended mods hehe
thumbup

To be fair I am a bit dark ages mate, most of my training and all my experience was on vintage and 50's/60's stuff, the most modern training I got was on K-Jetronic tongue out

In fact I'm a secret magneto and Wilson Pre-Selector fan boy biggrin

Here I am looking over one of these newfangled Japanese engines....



How those Japs fit 16 vales in there is all well beyond me confused

Luv ya... laugh


ed_crouch

1,091 posts

180 months

Tuesday 12th February
quotequote all
You'd LOVE the Lycoming O-360.... Impulse coupled magnetos (well, one of them's got a impulse coupling), manual mixture control on the red lever in the cockpit, and a battery so small that if it's cold you have to pull the propellor through a couple of blades to break the stiction on the crank bearings or the battery won't supply enough current to crank the engine...........

Mind you, I'd like to see a modern car engine do 2,000 hrs (about 200k miles if you like) at 75% of its max rated power without breaking!

Ed.



lancelin

80 posts

59 months

Tuesday 12th February
quotequote all
Well, I have a similar setup. I’m using a solenoid valve which allows a bit of extra air to the plenum on a cold start. I manually switch the valve using a relay and switch in the cab but could also use a temperature operated switch to make it automatic. The extra air it gives produces an idle of about 1100 rpm. When the engine temp reaches about 50 degrees I switch it off and the engine idles perfectly at 950rpm with the just the main butterfly idle adjustment. Easy. No PWM valve rubbish messing with my deceleration and inconsistent starts from hot. The car also runs better at low rpm. I only need the extra air valve when starting from stone cold. I also don’t need spark scatter or any other idle control.

Classic Chim

8,737 posts

87 months

Tuesday 12th February
quotequote all
Ive ran my car through 3 winters since having MBE that does not use any kind of idle valve.
All I can say is the car bursts into life and after about 15 seconds of careful revs at 1200 it will tickover! . I started it -10 and it was all unremarkable, just the same really other than the heavy oil.
I totally agree, I don’t want a stepper or idle motor interfering with my downshifts and engine braking, that’s my job with my foot.
I regularly used mine for work and early starts, I was able to leave it ticking over while I wiped windows etc literally seconds after starting it. Using 10/40 semi helps as the oil is thin by nature and cold does’nt effect its dexterity much.
I can’t imagine I’d ever need a raised idle as we are talking a matter of seconds and in that time I’m listening and controlling bringing the revs up gently myself which is what I much prefer to do.
My view is even cold if a modern Ecu can’t run your engine properly as soon as it’s cleared its throat it’s not doing its job. Mapped fuelling and Ignition for any condition is something the sensors should pick up and have prevision for within the cold start map.
Of course iridium tipped plugs don’t half help wink




spitfire4v8

2,741 posts

119 months

Wednesday 13th February
quotequote all
Point 1) good video!

Point 2) All this idle valve stuff is a conflict if as Dave points out you don't have one that shuts off completely.
I'm absolutely 110 percent an idle valve fanboy, on my ecu installs it's a default fit, and a customer-delete option if they don't want it.
BUT
the magnetti marelli idle valve I fit is a proper stepper style, it shuts off completely when the engine warms .. and as such is really the best of both worlds .. automatic control, and full shut off when hot.

I suspect Dave that if you had a similar idle valve arrangement you'd be over the moon because it would give you exactly what you want .. automatic idle enhancement for cold running, full shut off when hot so no leaks.

I find it strange that the MBE people didn't choose to implement a similar system, I can't believe it's because they think it's better to have an engine that you can't start up and leave idling from a very cold start, that makes no sense to me.

ric355

124 posts

87 months

Wednesday 13th February
quotequote all
spitfire4v8 said:
Point 1) good video!

Point 2) All this idle valve stuff is a conflict if as Dave points out you don't have one that shuts off completely.
I'm absolutely 110 percent an idle valve fanboy, on my ecu installs it's a default fit, and a customer-delete option if they don't want it.
BUT
the magnetti marelli idle valve I fit is a proper stepper style, it shuts off completely when the engine warms .. and as such is really the best of both worlds .. automatic control, and full shut off when hot.

I suspect Dave that if you had a similar idle valve arrangement you'd be over the moon because it would give you exactly what you want .. automatic idle enhancement for cold running, full shut off when hot so no leaks.

I find it strange that the MBE people didn't choose to implement a similar system, I can't believe it's because they think it's better to have an engine that you can't start up and leave idling from a very cold start, that makes no sense to me.
Do you always tune for a fully closed stepper at hot idle, or do you tend to adjust the base idle screw down so that the stepper needs to be opened a little to get the idle at the right speed (as per the original Lucas behaviour)? I have mine set to fully closed when hot at the moment in terms of open loop settings, but I imagine this might limit the ability of closed loop idle to keep the revs around the target, since it lacks a bit of 'headroom' to work within.

spitfire4v8

2,741 posts

119 months

Wednesday 13th February
quotequote all
I run it fully closed at hot idle. it's not a closed loop feedback system so there's no point in having it open when hot, the stepper won't move as the target idle is achieved with spark adjustments, provided you have that set correctly of course.

Matthew Poxon

5,183 posts

111 months

Wednesday 13th February
quotequote all
Very impressive CoG. In LPG terms it would seem you have achieved the impossible.

Food for thought.... if you upgrade to the Drive by wire throttle you can do away with your IACV / manual valve system and configure the ECU to use the throttle to increase the revs where needed.

spitfire4v8

2,741 posts

119 months

Wednesday 13th February
quotequote all
Matthew Poxon said:
Very impressive CoG. In LPG terms it would seem you have achieved the impossible.

Food for thought.... if you upgrade to the Drive by wire throttle you can do away with your IACV / manual valve system and configure the ECU to use the throttle to increase the revs where needed.
Yes to this. I'm a big fan of drive by wire.

ChimpOnGas

Original Poster:

8,416 posts

117 months

Thursday 14th February
quotequote all
spitfire4v8 said:
Point 1) good video!

Point 2) All this idle valve stuff is a conflict if as Dave points out you don't have one that shuts off completely.
I'm absolutely 110 percent an idle valve fanboy, on my ecu installs it's a default fit, and a customer-delete option if they don't want it.
BUT
the magnetti marelli idle valve I fit is a proper stepper style, it shuts off completely when the engine warms .. and as such is really the best of both worlds .. automatic control, and full shut off when hot.

I suspect Dave that if you had a similar idle valve arrangement you'd be over the moon because it would give you exactly what you want .. automatic idle enhancement for cold running, full shut off when hot so no leaks.

I find it strange that the MBE people didn't choose to implement a similar system, I can't believe it's because they think it's better to have an engine that you can't start up and leave idling from a very cold start, that makes no sense to me.
Thanks for your contribution, very interesting, especially this bit...

spitfire4v8 said:
The magnetti marelli idle valve I fit is a proper stepper style, it shuts off completely when the engine warms .. and as such is really the best of both worlds .. automatic control, and full shut off when hot.
The above is exactly what I set out to create with my manual system, because to my mind the above is the logical and correct way to build an extra air system. My background is carburetor tuning but I can tell you I would have been properly disciplined if I let a car go out with a poorly adjusted choke with it's fast idle cam stuck on.

Sorry to keep going back to carbs but a poorly adjusted fast idle cam was effectively what I had with my Canems controlled pattern part PWM Bosch idle valve! In my personal opinion people really shouldn't get involved in engine management before understanding and tuning basic fuel and ignition systems, and then spending a few years only doing that so they get a feel for all the scenarios.

The trouble is these days so many mechanics completely skip the carburetor and distributor lessons and jump straight to fault code readers and laptops, without the grounding in how to tune a basic spark ignition internal combustion engine they are left to stare blankly into their screens without any hope of applying true wisdom to solve what is often a very basic first principle issue.

In my case I had a looping priming pulse issues that the installers themselves failed to fix, it's clearly an earth loop or poor shielding of the crank signal cable or poor shielding of the ECU itself, I will nail this myself in the spring mark my words! Now, while not the route cause I traced the key culprit initiating the looping fault myself in 20 minutes, as it turned out I could turn the fault on and off at will simply by disconnecting and reconnecting the pattern part PWM Bosch idle valve at its connector, it was hardly a rocket science discovery so how it was missed after being with the installers for three weeks is still beyond me confused

After disconnecting the pattern part PWM Bosch idle valve I blocked it's hoses which obviously forced me to re-tune my idle the old school way, and what amazed me was just how much better the car behaved after I'd done so. Both idle quality and drivability were noticeably improved, also and just like the all hundreds of other engines I've set up (all be them carb fed ones), my TVR engine was perfectly happy to idle beautifully on butterfly rest position and base idle settings alone.

In the past I'd often suspected a vacuum leak on the engine and boy did I have one, ironically the source of this vacuum leak turned our to be one of the engine management's own control systems, an errant pattern part PWM Bosch idle valve based vacuum leak rolleyes.

Realising I did actually still need an extra air device for cold starts I solved this issue in my stone age way which (as I knew it would) worked an absolute treat. The above comments from spitfire4v8 and his arrangement make perfect sense, like that fast idle cam on the side of a carb a system that's shut is what you must achieve on a warmed engine, COMPLETELY SHUT!, sadly this is most definitely not what I had on my Canems controlled pattern part PWM Bosch idle valve arrangement.

Being an old skool kinda guy I have no issue with pulling out my extra air control knob and pushing it home again at 40c, at least this way when I push the knob in I 100% know the valve is shut. Of course a little extra air on cold start is a basic fundamental requirement of all spark ignition internal combustion engines, it always was, and it always will be. I solved this requirement in a very simple way, but given this is the world of engine management where one of the key benefits is all systems are automated it's also ridiculous I've had to resort to such a stone age solution!

The inarguable truth is the Magnetti Marelli stepper motor setup from spitfire4v8 is a way superior solution and as he quite rightly says it would give me a best of both worlds solution, however I'm not sure this is an option for me as all the choice I have in the Canems idle valve settings is 80Hz, 160Hz, and 320Hz and from what I can tell all the other software features relating to the idle valve are designed for a PWM valve not a stepper motor type valve.

Dave.