OVER FUELLING ON COLD START

[blitzracing]

The resistor needs to go in parrallel across the sensor wires. I made up a plug in unit with an old mini timer connection that would plug "inline" with the current loom, so I did not need to cut any wires. If you want to give it a try, pop me your postal address.

[chimyellow]

The adapter arrived in the post this morning.
I will be fitting it at the weekend (possibly before) and will report back.

[blitzracing]

Start with cold engine, and see what RoverGauge is reading for the engine temp- I set it up at 14'C ambient to read 24' engine temp- although Im sure you could raise the "fake" temp a bit further. I tried to get stable readings for the injector pulse width with and without the resistor to see the effect, but as the engine heats up so quickly if difficult to get a stable platform. Id suggest you start with a stone cold engine then wind the temp up to say 30' and see if it starts and runs well. If not wind it down so it reads cooler and try again. I have no idea of the ratio of extra fuel per'c cold start is applied so this is guess work but I believe that some extra fuel is added to around 70'C. If you wind the temp up too far, the mixture will lean out to much, and you could end up with flat spots in the power delivery when the car is driven. Happy tweaking.

[s3c chris]

I await with interest the outcome of this one!
Before doing anything to mine I though tit wise to test it all first.I am waiting for the postman to drop a "Rovergauge" lead through the door and will let you know what, if anything,itsays.
Good luck with the resistor...
Chris.

[chimyellow]

Ok, new bit for Car, must fit and try as soon as possible syndrome kicked in.

I plugged in RoverGauge and it showed a temperature of 10C (which at the time was correct according to various sources)
I then plugged in the resistor/adapter sent to me by Mark.
RoverGauge now showed 22C (i.e. it added about 12C)

I started the car and it quickly settled into a good tickover (much better than normal).
I did not use any throttle.
So that I could do a review I videoed it
https://youtu.be/L7zWZSEsCh4
I only let it run for about 10 seconds so as not to let the engine get too warm.

I then removed the removed the resistor and started it again, without any throttle.
https://youtu.be/7njjIEXPfCA
I think that you can notice a definite difference with this configuration (without resistor) struggling to maintain the tickover.
If I had not turned it off I think it would have cut out soon.

After this test I re-fitted the resistor and started it again. For a couple seconds it struggled but then settled down nicely. I think this was because of the without test almost flooding it.

I have not taken it out on the road with the resistor as I have a leaking manifold gasket (you may be able to hear the tick on the without resistor video) and therefore don't want to use it if I can avoid it. Tomorrows job it to do the manifold so all going well will be able to report back on this aspect later this (longer) weekend.

I have also not played about with the resistor because of the manifold and also that there is, in my opinion, such an improvement that it wouldn't do much better.
I might do this at some point and if I do I will update again.

[chimyellow]

OK, service and manifold done.
It started and settled to idle again without the need for ant throttle.
Tickover when hot is not affected and when out driving I can't tell any difference either with my foot down or in town.
I would say this is overall a massive improvement.

[ChimpOnGas]

chimyellow said:

OK, service and manifold done.
It started and settled to idle again without the need for ant throttle.
Tickover when hot is not affected and when out driving I can't tell any difference either with my foot down or in town.
I would say this is overall a massive improvement.

Great news, but not massive surprise to me if I'm honest.

ChimpOnGas said:

I'd put money on the OP solving his cold start problem if he adds the Blitz ECU temp resister

ChimpOnGas said:

The other thing I'd encourage the OP to do is bin the unsuitable shrouded NGK B7ECS spark plugs, I recommend switching to the projected electrode NGK BPR6ES or better still NGK BPR6EIX iridium plugs.

Immediately after fitting these plugs (still on 14CUX & distributor at the time) I enjoyed a noticeably smoother idle, better cold starting, and a smoother drive at lower RPMs.

Read about the plug switch here in my 2012 post when my pre-gas name was ChimpOfDarkness

http://www.pistonheads.com/gassing/topic.asp?h=1&a...

ChimpOnGas said:

The other thing that will help is to bin the cats (especially the big main one), removing the restrictions the cats impose will help the engine breath more efficiently and will have the added benefit of releasing 5-10hp.

[chimyellow]

I have to admit I am playing devils advocate here...

If the NGK BPR6ES are so good what don't the Specalists recommend these or people like Powers Performance supply them as standard as part of their service it?

The Chimaera is the only car that my family has that I know that I don't have to worry about the imissions test at MOT time (one of five, including two post 2011 vehicles). It is plenty quick enough for what we use it for (family days out and touring).
Why would I want to jepodise that by removing any of the catalysts?

[blitzracing]

Interesting plots from a post on MS cold start;




The response is as near as dammit 1% increase in fuel per 2'degrees in drop in temp so the resistor will give around a 6% drop in fuelling if the 14CUX uses the same response.

[NZ fan]

just tried this on a 1995 4.0 hc that was suffering from this exact problem i.e. running very rich for the first minute or so from cold start. i first tried a 5k ohm resistor which didn't seem to make much difference so i then went to a 3k ohm resistor and it completely transformed the running of the car. with rover gauge on the car first thing in the morning i had a reading of 6 deg. on both the fuel and engine temps. plugged in the 3k ohm resistor and the engine temp. showed 27 deg. started the car and it ran beautifully. the resistor has been on now for about three weeks and its running great. Thanks heaps to Blitzracing for this suggestion and his continued valuable input to this forum.
i must add this was a last resort for me after first checking plugs, leads, cap, rotor, changed temp and air flow sensors for a known good units.

Edited by NZ fan on Tuesday 20th October 09:59

[QBee]

chimyellow said:

I have to admit I am playing devils advocate here...

If the NGK BPR6ES are so good what don't the Specalists recommend these or people like Powers Performance supply them as standard as part of their service it?

The Chimaera is the only car that my family has that I know that I don't have to worry about the imissions test at MOT time (one of five, including two post 2011 vehicles). It is plenty quick enough for what we use it for (family days out and touring).
Why would I want to jepodise that by removing any of the catalysts?

I followed Chimpongas’s advice after experiencing fouled 7 plugs. My TVR expert was already fed up with replacing similarly fouled plugs and liked what he saw with the 6s (I used the iridium variant). He now fits 6s at all Chimaera and Griff services.

[Classic Chim]

QBee said:

I followed Chimpongas’s advice after experiencing fouled 7 plugs. My TVR expert was already fed up with replacing similarly fouled plugs and liked what he saw with the 6s (I used the iridium variant). He now fits 6s at all Chimaera and Griff services.

The manual for my 1978 two stroke bike says
Use a 6 grade plug in winter months or where short journeys are often encountered.
7 being standard.
8 can be used in hot summer months or where long journeys at high revs are endured

I map it with a Screw driver effecting both idle and high revs mixture and judge it by plug colour and sound which I have not done for decades.
Our climate suggests a 6 grade plug will warm engine quicker and help burn off sooty deposits better.

The 7 plug is a safe place to be from a mappers position and does a decent allround job. High lift Cams, power maps and plenty of slow running suggest a 6 grade plug is indeed a good idea on these cars. The CUX I don’t think can advance the ignition enough to make a 6 risky so they can be used to run the car at high revs no problem too so not a lot to lose.

As my bike manual demonstrates from all those years ago, it was once considered quite normal to change plugs for the driving conditions.
I bet most of us rarely get past 80 mph on most occasions so using a 7 grade plug not necessary as it’s just a safe guard against pinking at 6000 revs and as a manufacturer TVR had to do that and why most service centres still recommend it I should think.

I use the Iridium tipped 6 grade and my plug colour as a lovely light grey which in today’s climate absolutely upto date.
I do run a bespoke ecu but the 6 grade plug does exactly what it’s supposed to do, warms up quicker and runs smooth from cold which 7’s rarely did.

90% of the time contrary to how hot it all seems the engines are often running a bit cool as the cooling systems are actually very efficient on Tvr. The 6 grade helps to hold some heat in the engine and combats this tendency to run cool when on the move.
It’s not a drastic change to go one grade up or down in truth so nothing to worry about unless you run in very hot conditions for hours on end which is when you might choose an 8 grade to help reduce heat transmitting through to cylinder heads.

[Penelope Stopit]

NZ fan said:

just tried this on a 1995 4.0 hc that was suffering from this exact problem i.e. running very rich for the first minute or so from cold start. i first tried a 5k ohm resistor which didn't seem to make much difference so i then went to a 3k ohm resistor and it completely transformed the running of the car. with rover gauge on the car first thing in the morning i had a reading of 6 deg. on both the fuel and engine temps. plugged in the 3k ohm resistor and the engine temp. showed 27 deg. started the car and it ran beautifully. the resistor has been on now for about three weeks and its running great. Thanks heaps to Blitzracing for this suggestion and his continued valuable input to this forum.
i must add this was a last resort for me after first checking plugs, leads, cap, rotor, changed temp and air flow sensors for a known good units.

Edited by NZ fan on Tuesday 20th October 09:59

What about BHP and fuel consumption when warmed up

Surely a timer relay activated by the crank signal is the way forward

[spitfire4v8]

There's something you can buy (I forget the info) whereby you can alter the apparent output of a thermistor for re-aligning a temperature gauge needle on non-standard engine/car installs .. I don't know if it's for bi-metallic strip style gauges so could be a pwm output though or whether it does provide an output that an ecu can see as true thermistor emulation .. if it did then you could set your effective thermistor curve to whatever you wanted.
Forgive me if it doesn't do what's required, it just popped into my head when reading PS's post ^^

[Steve_D]

spitfire4v8 said:

There's something you can buy (I forget the info) whereby you can alter the apparent output of a thermistor for re-aligning a temperature gauge needle on non-standard engine/car installs .. I don't know if it's for bi-metallic strip style gauges so could be a pwm output though or whether it does provide an output that an ecu can see as true thermistor emulation .. if it did then you could set your effective thermistor curve to whatever you wanted.
Forgive me if it doesn't do what's required, it just popped into my head when reading PS's post ^^

You are thinking of the Gauge Wizard. https://www.spiyda.com/fuel-gauge-wizard-mk3.html
And yes it just takes a resistance from the sender and modifies it to a different resistance for the gauge or in this case the ECU.

Steve

[NZ fan]

Penelope Stopit said:

What about BHP and fuel consumption when warmed up

Surely a timer relay activated by the crank signal is the way forward

apparently the ecu no longer uses the input from the temp sender for fueling [or stops adding extra fuel] once the engine reaches 70deg. C.

Edited by NZ fan on Wednesday 21st October 09:39

Edited by NZ fan on Wednesday 21st October 09:46

[blitzracing]

All this talk of relays- why would you do something so complex? If you look at the temperature coefficient curve of the thermistor it goes from a few hundred ohms when hot over 6 k freezing - so lets say we use a 3 k resistor across the sensor.

0'c value 5.8k ohms with 3.3 k in parallel- = 2.13k or about 15'c uplift when cold

80'0c 350 ohms with 3.3k in parallel =316 ohms

This resistance shift when hot is so low when hot it does not even fall outside the tolerance of of a new sensor.

Or pop one of Steve Sprints ECU chips in, he has done a lot of work on the cold start fuelling.

Edited by blitzracing on Thursday 22 October 10:32

[Zener]

May be of use

[Penelope Stopit]

Good post, converted online to text

Time to do some maths

TEMPERATURE RESISTANCE 0
[°C) [OHM]
-40 45,313
-30 26,114
-20 15,462
-10 9,397
0 5,896
10 3,792
20 2,500
30 1,707
40 1,175
50 834
60 596
70 436
80 323
90 243
100 187
110 144
120 113
130 89

[Penelope Stopit]

Reckon a timer relay plus summer/winter switch is needed

Underfueling in the winter doesn't come across as a bright idea

Have never needed to do this modification

Cold start modification is simple, wire a relay to switch in a resistor when cranking, fuel can be increased or decreased at start-up

If a resistor is being permanently wired into the circuit there is an obvious downside

Easy mistake for some to forget about summer and winter temperatures