Discussion
...or pre-cat idle. All of a sudden my 4.3 won't idle at constant revs - goes up and down between 500 and 1500 rpm, but only once its hot (90-95 degrees), which makes driving in traffic difficult to say the least. Car feels 'sick' when hot also, until revs have built up - could the ECU be defaulting to 'limp-home mode' straightaway? Its got a (newish) clean stepper motor thats doing its job, 'cos when unplugged the idle stays where the stepper left it, if you see what I mean. New dizzy cap, rotor arm and recent posh leads, the airflow meter voltage ramps up as per the bible (early car/airflow meter so only up to 3 volts, not 5?), and the coolant and fuel temp sensors are giving the right readings cold to hot. Throttle pot voltage ok at idle (0.3ish volts) and upwards etc. Base idle seems right, 'cos it idles at 500 rpm-ish when cool, and the idle speed screw is still capped off as from new? Throttle flap thingy clean also. ECU reset X lots to no effect. I've been having loads of 'fun' with my voltmeter...
What I want to know is does the road speed sensor only tell the ECU to control the idle when it thinks the car comes to a standstill - this is the only thing left that I can think of that has an effect on the idle speed. Bible well and truly read...
The speedo works ok as well. Help!!
Worst thing about it is because its a precat car, there apparently isn't a diagnostic reader for the ECU - the 500s have a black rectangular plug for it, whereas my pre(historic?)cat has a white roundish 5 pin plug like wot Noah used wiring up the Ark...is no diagnostics correct or can the reader be adapted to read the early ECUs ?
Edited to mention its got a new fuel filter as well...but no pressure test point on the injector fuel rail like the later cars...I feel a headache coming on...
>>> Edited by andy43 on Monday 18th August 19:01
What I want to know is does the road speed sensor only tell the ECU to control the idle when it thinks the car comes to a standstill - this is the only thing left that I can think of that has an effect on the idle speed. Bible well and truly read...
The speedo works ok as well. Help!!
Worst thing about it is because its a precat car, there apparently isn't a diagnostic reader for the ECU - the 500s have a black rectangular plug for it, whereas my pre(historic?)cat has a white roundish 5 pin plug like wot Noah used wiring up the Ark...is no diagnostics correct or can the reader be adapted to read the early ECUs ?
Edited to mention its got a new fuel filter as well...but no pressure test point on the injector fuel rail like the later cars...I feel a headache coming on...
>>> Edited by andy43 on Monday 18th August 19:01
could try speedo sensor - this seems to be very capable of bug**rinG up idle speed - worth changing. also you should be able to get a fault meter connected. david beer kindly lent me his and it did find a fault code and fitted fine on my 4.3 pre cat. if not try a land rover/ranger rover delaer - they may have one that fits - same engine!
Ta for that! Looks like the road speed/speedo sensor could be at fault - bleedin' hope so after all the messing about I've done... thank God there is a diagnostic tester that fits - just need to find one with a 5 pin plug instead of 4. Just need an oscilloscope now to test it. Or maybe a hammer... 
AFAIK the road speed sensor should only come into play as you are coming to rest, once you are stationary assuming it hasn't stalled it should then settle down to idle at the usual 1K(ish), even with a duff sensor.
Not sure what you mean about you 'disconnect the stepper and idle stays the same', if you are disconnecting whilst the engine is running I think you may blow something, even the ECU itself
, rule of thumb I apply is that if you are disconnecting anything that may be connected to the ECU make sure the igniton is switched off (btw it takes about ten seconds from switching off to power coming off the ECU).
Haven't got the griff bible
, so I'm not sure about the AFM going up to 3V variants so may be totally wrong on this bit, but I thought that, assuming if its 5AM type, that it should be around 1.5-2V for idle and around 4.5 V full load 
.
There is also a CO adjuster on the AFM which is adjusted to give different values for cat and non-cat cars 1.8v cat/1.1v non cat, this obviously affects tick over as well. Apparently every adjustment of timing/CO/base idle screw should be finished with a ECU reset so that the adaptive mapping can re-adjust to the new idle, which can take a couple of hundered miles of driving.
Not sure if any of the above helps, I assume you've probably done it anyway but you never know.
Harry
Not sure what you mean about you 'disconnect the stepper and idle stays the same', if you are disconnecting whilst the engine is running I think you may blow something, even the ECU itself
, rule of thumb I apply is that if you are disconnecting anything that may be connected to the ECU make sure the igniton is switched off (btw it takes about ten seconds from switching off to power coming off the ECU). Haven't got the griff bible
, so I'm not sure about the AFM going up to 3V variants so may be totally wrong on this bit, but I thought that, assuming if its 5AM type, that it should be around 1.5-2V for idle and around 4.5 V full load . There is also a CO adjuster on the AFM which is adjusted to give different values for cat and non-cat cars 1.8v cat/1.1v non cat, this obviously affects tick over as well. Apparently every adjustment of timing/CO/base idle screw should be finished with a ECU reset so that the adaptive mapping can re-adjust to the new idle, which can take a couple of hundered miles of driving.
Not sure if any of the above helps, I assume you've probably done it anyway but you never know.
Harry
Thats the thing - if the speed sensors knackered, would it screw the idle up? Or would the sensor being knackered just tell the ECU that the car never moves..? And, yes I have been disconnecting the stepper while the engines running...whoops... but as far as I can tell no lasting damage. Won't being doing it again tho'! The airflow meter is a 3AM (obviously made earlier than the 5am by 2 hours...) the 3 or 5 must mean volts - we've had a spare 3 V meter on it anyway - no joy - but the CO etc is dead on what it should be according to the Crypton machine. Next step I think is to find one of these elusive precat ECU fault readers and get it to look into it's crystal ball for me.... Thanks for the info.
Edited to say the 'S' looks a beauty!
>> Edited by andy43 on Monday 18th August 22:26
Edited to say the 'S' looks a beauty!
>> Edited by andy43 on Monday 18th August 22:26
If the speed sensor is knackered it should not affect the idle when you switch on. It's there to let the ECU know the cars moving when you slow down, foot off the accelerator, it recognises the engine RPM above normal idle is down to engine braking, so it doesn't try to fight it with adjusting the stepper to lower the RPM.
When the speed sensor is duff it gives no output on the move so this time when you slow down (foot off the gas) it doesn't know you are still moving and compensates the fuel to reduce the apparently high RPM it is seeing for a statinary vehicle!
When you then stop it catches the ECU out because the engine slows (engine braking again) too fast. This is why with a duff speed sensor and or steper motor it can stall under heavy deceleration to a halt.
When you do stop normally (not hard braking) sometimes it stalls and some times it recovers with a quick rise in RPM above normal tickover, before settling down again.
I hope that helps the understanding of the stepper/speed sensor/ECU relationship.
All IMHO and in my limited understanding of things remotley complicated.
harry
When the speed sensor is duff it gives no output on the move so this time when you slow down (foot off the gas) it doesn't know you are still moving and compensates the fuel to reduce the apparently high RPM it is seeing for a statinary vehicle!
When you then stop it catches the ECU out because the engine slows (engine braking again) too fast. This is why with a duff speed sensor and or steper motor it can stall under heavy deceleration to a halt.
When you do stop normally (not hard braking) sometimes it stalls and some times it recovers with a quick rise in RPM above normal tickover, before settling down again.
I hope that helps the understanding of the stepper/speed sensor/ECU relationship.
All IMHO and in my limited understanding of things remotley complicated
. harry
It has done this in the past - coasting to a standstill in neutral, the revs stay about 1200-1500 until maybe a second or two after the car is stood, then dropping down to the correct idle - this is apparently normal control.
What it does now, only when warmed up (perfect idle control until 90 degC) is go up and down, 500 to 1500/2000 rpm, and it'll sit there pretty much all day like this - up and down, stuttering down to almost stalling then revving up to compensate the stall, then back down again, taking maybe 5 or so seconds to do a cycle of 500 - 1500 -500 again. Wierd. I fink I need an ECU tester that fits!
Doing searches in this and the Chim forums does give out a heck of a lot of info, but also almost too muany possibilities to check - could be engine earth strap on LH cylinder head(but mine doesn't have one?!) or poor injector bank earthing or wiring etc etc the list goes on... I have got the car booked in to a place called WGT in Northwich next week, who Steve Reid recommended as being good for fault finding electronically - so hopefully they'll go straight to the problem and save me another few days with ECU plugs and bits of wire... I'm convinced its something electrickeral somwhere. I was thinking I might stand a chance of sorting it before the car goes in to WGT, but the more involved you get in something like this, the more you realise why people who know about these things charge so much to fix 'em! I might just go and have one more play with it tho'....
What it does now, only when warmed up (perfect idle control until 90 degC) is go up and down, 500 to 1500/2000 rpm, and it'll sit there pretty much all day like this - up and down, stuttering down to almost stalling then revving up to compensate the stall, then back down again, taking maybe 5 or so seconds to do a cycle of 500 - 1500 -500 again. Wierd. I fink I need an ECU tester that fits!
Doing searches in this and the Chim forums does give out a heck of a lot of info, but also almost too muany possibilities to check - could be engine earth strap on LH cylinder head(but mine doesn't have one?!) or poor injector bank earthing or wiring etc etc the list goes on... I have got the car booked in to a place called WGT in Northwich next week, who Steve Reid recommended as being good for fault finding electronically - so hopefully they'll go straight to the problem and save me another few days with ECU plugs and bits of wire... I'm convinced its something electrickeral somwhere. I was thinking I might stand a chance of sorting it before the car goes in to WGT, but the more involved you get in something like this, the more you realise why people who know about these things charge so much to fix 'em! I might just go and have one more play with it tho'....
... and its now fixed, just in time for winter...BUGGER 
If you get the above symptoms on a car with the ignition amplifier mounted on the dizzy (this includes precat cars and probably V8S, wedges etc, but not 500s as far as I am aware) i.e crap idle, hunting and generally sick running, the ignition amplifier may need remote mounting - my 4.3 suddenly started playing up - solution was to
1 - remote mount the ignition amp away from the HT leads and any possible interference,
2 - add an extra earth to the ignition amp (new earth to alternator housing),
3 - close up the 'pick-up air gap' on the dizzy to the correct 0.015"
Car now runs perfect.
At last.
One zillion brownie points to Guy and Bruce at Camco (01925 445688), who sorted it without breaking a sweat as far as I could tell. They do a lot of ECU-type work and have had similar faults on Range Rovers - later Rangies have ignition amps remote mounted to cure this. Thanks also to Shane at SFR and Steve Reid for putting me on to Camco.
This week I shall mostly be driving the nuts off it....
Roll on next summer....
Hope this may be of use to someone with similar probs..
>> Edited by andy43 on Thursday 30th October 19:25
If you get the above symptoms on a car with the ignition amplifier mounted on the dizzy (this includes precat cars and probably V8S, wedges etc, but not 500s as far as I am aware) i.e crap idle, hunting and generally sick running, the ignition amplifier may need remote mounting - my 4.3 suddenly started playing up - solution was to
1 - remote mount the ignition amp away from the HT leads and any possible interference,
2 - add an extra earth to the ignition amp (new earth to alternator housing),
3 - close up the 'pick-up air gap' on the dizzy to the correct 0.015"
Car now runs perfect.
At last.
One zillion brownie points to Guy and Bruce at Camco (01925 445688), who sorted it without breaking a sweat as far as I could tell. They do a lot of ECU-type work and have had similar faults on Range Rovers - later Rangies have ignition amps remote mounted to cure this. Thanks also to Shane at SFR and Steve Reid for putting me on to Camco.
This week I shall mostly be driving the nuts off it....
Roll on next summer....
Hope this may be of use to someone with similar probs..
>> Edited by andy43 on Thursday 30th October 19:25
No chance - can only just suss simple computer stuff out (like the on/off button) let alone digital cameras, but the ignition amp's a little black box normally bolted to the right side of the dizzy... mines now on a custom ally plate (to act as heat sink) bent up by Camco and bolted to the chassis x-member between the engine and exhaust Y-piece.
A 2-core connecting cable has been made up to link the back of the amp to the dizzy input, and an extra earth cable routes round the wiring loom in front of the dizzy to the alternator body mounting bolt.
And it runs great.
Ta to Harry as well for giving me stuff to mentally chew over when I first had the fault.
I'll be doing some more 'testing' miles tomorrow morning, just to make sure the fault hasn't re-appeared....
A 2-core connecting cable has been made up to link the back of the amp to the dizzy input, and an extra earth cable routes round the wiring loom in front of the dizzy to the alternator body mounting bolt.
And it runs great.
Ta to Harry as well for giving me stuff to mentally chew over when I first had the fault.
I'll be doing some more 'testing' miles tomorrow morning, just to make sure the fault hasn't re-appeared....
So is the sensor which senses the position of the distributor shaft, and feeds the signal to the ignition amplifier not an integral part of the amplifier?
I had assumed that it was, because Lucas/Land Rover offer an expensive 'remote mount' kit, including, I think, a new amplifier. I assumed that this kit split the amplifier and position sensor...but your solution sounds cheaper, and I like cheap
I had assumed that it was, because Lucas/Land Rover offer an expensive 'remote mount' kit, including, I think, a new amplifier. I assumed that this kit split the amplifier and position sensor...but your solution sounds cheaper, and I like cheap
I hate to be a pessimist but the problem of the ignition amp dying is not solved by the remote mounting. They are still susceptible to it.
TVR moved the ignition amp to a heatsink on the plenum. The problem is that the unit now gets heat soak from the plenum and exhausts. It still happens on the later cars that have had there.
The change was brought about when Land Rover changed the distributor. The remote ones have a different distributor which does not have the cut out for the ignition amplifier. This change had certainly happened by 1995 and I suspect came in with the serp engines.
The ignition module is the same but it may have different connectors but Lucas do a cable kit where there is a mismatch.
>> Edited by shpub on Friday 31st October 09:36
TVR moved the ignition amp to a heatsink on the plenum. The problem is that the unit now gets heat soak from the plenum and exhausts. It still happens on the later cars that have had there.
The change was brought about when Land Rover changed the distributor. The remote ones have a different distributor which does not have the cut out for the ignition amplifier. This change had certainly happened by 1995 and I suspect came in with the serp engines.
The ignition module is the same but it may have different connectors but Lucas do a cable kit where there is a mismatch.
>> Edited by shpub on Friday 31st October 09:36
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