Strange Near Cut-Out Conundrum

[Andy JB]

My 500 has exhibited a new tickover issue when hot which isn't problematic but has potential to be....

When hot the tickover is normal then it will start dropping suddenly and either nearly cut out then recover or cut out completely but then starts fine again.

This year its had most electricals replaced as regular maintenance (coil, leads, dizzy cap rotor etc) new plugs annually and a Lambda sensor on n/s bank.

So i'm at a loss at what could be causing this & want it resolved as its due to be parked up for a few months.

Anyone experience this?

[ianwayne]

Mine used to do this occasionally, but also idle very fast at 2k rpm now and and again for a few seconds at junctions. Turned out to be the stepper motor. Yes I know it's a cliché but in my case it really was.

[seeby]

My 400 suffers from both the above comments (low to no tickover and then 2000 revs). This only seems to happen when the fuel is getting low (1/4 tank). Im still experimenting with the answers to my thread on here a couple of weeks ago . (Petrol pump question) .Could yours be a fuel problem OP ?

[ChimpOnGas]

This one comes up from time to time on here, so it seems the issue isn't that uncommon on our cars.

If the car was stalling at junctions after slowing from speed I'd definitely say suspect the TVR speed signal box, been there..had that one.

very occasionally my Chimaera had the cut-out problem the OP is describing when I was on the old Lucas system, but for me it tended to happen when cruising at speed on the motorway so perhaps not quite the same as the OP's issue

TBH with my fault I always suspected the Meta immobiliser that switches the live feed to the ECU but it did seem more like a momentary loss of ignition rather than fuel as it was an immediate and sharp cut of power with normal service resumed just a few milliseconds later.

Suffice to say when I converted to Canems the issue never once reappeared, I can only assume the fault was somewhere within the 17 year old wiring for ECU or distributor?

I can't see how (in my case) it could have been anything to do with the stepper motor as it doesn't play any part at the speeds my fault exhibited itself, I guess it could have been the TVR speed signal box but the reality is I'll never know.

All I can say with 100% confidence is... once all that 17 year old birds nest TVR wiring and spliced into Range Rover loom was removed along with the 14CUX ECU & Lucas distributor the issue never repeated itself.




NB: One final question to the OP... is it typically raining or wet when your momentary cut of power occurs?

I had some very occasional moisture related misfires during very wet weather when I was on the distributor, my mate also had this with his 5.0 litre on the way to Le Mans in heavy driving rain.

[CHEF_GOLF]

I replaced my stepper motor and it helped the problem but I have recently changed the engine temp sensor. And it has made the world of difference to the running and the wanting to cut out and die all the time. A £12 well spent and 10 mins of my life

[QBee]

Mine was the stepper motor. It had become temperature sensitive, which showed up worse after de-catting.
Tried everything else, then Rob (V8D) realised it "had to be the stepper". Swapped it for another one off a TVR (ie not a cheapo from the Wok and Chopsticks) and no problems whatsoever since.

[Andy JB]

Thanks for replies & confirm suggestions as follows:-

-Engine temp sensor replaced this year so newish
-Stepper Motor done every 2k - due now but usually looks very clean at this interval - worth a try though...
-Not used in wet unless it rains while i'm out - it did this year in France religiously & ran smooth as a nut despite constant damp & standing water for 3 days!!
- Immob had new relay fitted this year & isn't original one anyway Meta 2 now fitted

Owned car for 10 years so pretty familiar with most aspects. The revs don't rise they only fall. The only other odd thing exhibited is there is a slight air type whine at tickover not noticed before but its slight & nothing jumps out with AFM or associated rubber leads leading to any air loss - its unikley to be intermittant too if it was this.

Looks like i may need an Indy to fault diagnose - but i hate to be beaten....

[BeastMaster]

Got so fed up with mine I have just blanked off the stepper. OK so a bit fiddly to hold on the throttle at cold start up but no more intermittent sitting at lights with 2k tick-over or just plain stalling. If you want to give it a try just disconnect stepper when you have a stable tick-over by pulling off the connector.
I decided to keep the stepper connected for long term use as the ECU may require feedback for other systems, so blanked off the bypass so the stepper movement has no effect, the tick-over can be set manually using the bleed screw.
For me I prefer this setup, as revs instantly die when lift off, making the throttle feel more connected in some way, I believe that the ECU may have been smoothing out lift off by opening the stepper a little thus avoiding rear wheel lock up when braking and changing down a gear ?
Have been using this for the last 2 years.

[EGB]

BeastMaster said:

Got so fed up with mine I have just blanked off the stepper. OK so a bit fiddly to hold on the throttle at cold start up but no more intermittent sitting at lights with 2k tick-over or just plain stalling. If you want to give it a try just disconnect stepper when you have a stable tick-over by pulling off the connector.
I decided to keep the stepper connected for long term use as the ECU may require feedback for other systems, so blanked off the bypass so the stepper movement has no effect, the tick-over can be set manually using the bleed screw.
For me I prefer this setup, as revs instantly die when lift off, making the throttle feel more connected in some way, I believe that the ECU may have been smoothing out lift off by opening the stepper a little thus avoiding rear wheel lock up when braking and changing down a gear ?
Have been using this for the last 2 years.

Have you tried 'old school' A 2mm plastic insert on throttle stop at the Plenum. Keeps the butterfly very slightly open to stop stalling. Done in the days of Webber & SU carbs. No electronics in those days.

[ianwayne]

Andy JB said:

Thanks for replies & confirm suggestions as follows:-

-Engine temp sensor replaced this year so newish
-Stepper Motor done every 2k - due now but usually looks very clean at this interval - worth a try though...
-Not used in wet unless it rains while i'm out - it did this year in France religiously & ran smooth as a nut despite constant damp & standing water for 3 days!!
- Immob had new relay fitted this year & isn't original one anyway Meta 2 now fitted

Owned car for 10 years so pretty familiar with most aspects. The revs don't rise they only fall. The only other odd thing exhibited is there is a slight air type whine at tickover not noticed before but its slight & nothing jumps out with AFM or associated rubber leads leading to any air loss - its unikley to be intermittant too if it was this.

Looks like i may need an Indy to fault diagnose - but i hate to be beaten....

Is the stepper motor actually working? If it is cleaned using soapy water (yes people do!), water can get into the motor and it will seize. When you turn the engine off, you should hear a noise as the plunger is retracted fully in. The last entry of this thread explains how you can ensure it is moving out as demanded:

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[BeastMaster]

EGB said:

BeastMaster said:

Got so fed up with mine I have just blanked off the stepper. OK so a bit fiddly to hold on the throttle at cold start up but no more intermittent sitting at lights with 2k tick-over or just plain stalling. If you want to give it a try just disconnect stepper when you have a stable tick-over by pulling off the connector.
I decided to keep the stepper connected for long term use as the ECU may require feedback for other systems, so blanked off the bypass so the stepper movement has no effect, the tick-over can be set manually using the bleed screw.
For me I prefer this setup, as revs instantly die when lift off, making the throttle feel more connected in some way, I believe that the ECU may have been smoothing out lift off by opening the stepper a little thus avoiding rear wheel lock up when braking and changing down a gear ?
Have been using this for the last 2 years.

Have you tried 'old school' A 2mm plastic insert on throttle stop at the Plenum. Keeps the butterfly very slightly open to stop stalling. Done in the days of Webber & SU carbs. No electronics in those days.

Yes, thanks have tried this trick, which meant putting a new shim in each time I started from cold, as soon as the throttle was then opened it dropped out putting the tickover back to normal. Did experiment with adding a tether so the engine bay would not fill up with shims, and fitted a cable operating it from under the dash, but decided that it was a bit hairy having bits hanging around the linkage.Did plan on making a hit miss hole in the stepper blanking plate, operated by a cable or actuator, but have since mastered the art of heel / toe which is also usefull skill for other driving situations.

[Hooperthon]

Unless it has recently been replaced with other electrical items, it would also be worth changing the Ignition Module. I had a similar problem and replaced the usual; coil, leads stepper etc but replacing the ignition module fixed the problem straight away. They are relatively inexpensive and easy to swap yourself.

[aerospoke]

Exact same Problem here. Have since gone for a 123-Ignition and nothing changed. So deffintely not ignition.
My next step will be to connect my laptop with Rovergauge and see what exactly happens when the revs fall. But the car is still at the bodyshop after a stupid (me) parking-incident.

Cheers Jens

[Andy JB]

Yes ignition module replaced last year <5k since

Only clean stepper tip with white spirit - not sure soapy water would be a conducive approach

I'll try the stepper as an approach - never heard it close off before so i would be interested to note this

I do wonder if the lambda sensors tend to go at a similar time - i replaced offside bank ls this year so i wonder if near side bank has given up, in hindsight it does need some throttle on start up for a few moments until running smoothly which went away when lambda sensor replaced this year

[Andy JB]

Yes ignition module replaced last year <5k since

Only clean stepper tip with white spirit - not sure soapy water would be a conducive approach

I'll try the stepper as an approach - never heard it close off before so i would be interested to note this

I do wonder if the lambda sensors tend to go at a similar time - i replaced offside bank ls this year so i wonder if near side bank has given up, in hindsight it does need some throttle on start up for a few moments until running smoothly which went away when lambda sensor replaced this year

[Barreti]

Andy, I have an ECUMate if you want to borrow it. You can force the stepper in and out using it so its a useful test for that alone.

I see you're in Staffs so possibly not a million miles away.
I'm the other end of the A50 at M1 J24

Drop me a line if you're interested.
IanB