sudden engine misfire and self cure

[cureton]

Strange one this. While driving, suddenly engine shows kind of misfire, still runs and idles but feels and sounds like running on 4 cylinders only. Stopped, switched off engine, started engine and everythings fine again. Happend twice now, once while stopping at a traffic light, second while driving along country road. Changed ignition coil as it looked a bit dodgy (black stuff leaking out)Thought problem cured but came back while driving on motorway. Drove off to car park, switched engine off, back on and fine. Any ideas where to take a deeper look? Many thanks in advance!

[carsy]

Difficult to say really. Can you say if it feels like a fueling problem or definate spark missfire. Ignition amp as well coil can cause misfires. With you saying it cures itself after ignition off / on might well be fuel/ecu related. For a start check the connection at the ecu.

[FlipFlopGriff]

I've got the same issue. It overfuels like hell when it happens and you lose power, runs like a dog. Like you I turn off, start again and all is fine. Possibly injector earthing as I've been told they splice into an earth cable. But could be a range of other things too but best to check the cheap things first. Not had chance to play with mine yet. By the way mines also a 430, ie 20+ years old.

Also have an annoying stalling issue but unsure if its related. Doesn't do it all the time but seems to happen when i start it from hot (petrol stations) and I can't get it to idle and everytime I dip the clutch it stalls, which is a nightmare (and extremely dangerous) especially at islands.

Be interested to hear if you solve it.

FFG

[Rob_the_Sparky]

As it is fixed by a switch off/switch on it seems highly likely that the ECU is getting its knickers in a twist and the power cycle clears this. However, what is causing this could be quite complex. I'd guess at an intermittant sensor somewhere or something intermittant in the ECU itself. I don't see how an injector gnd could be fixed by a power cycle and not obvious how it could cause the ECU to throw a wobbly.

Could the ECU be thinking the engine is cold? This would cause it to add extra fuel.

Mind you these are only educated guesses so I could be wrong...

[FlipFlopGriff]

I changed my ECU and it still happens.
FFG

[ESDavey]

Gents, Ive suggested this before but try disconnecting the AFM and see if the problem goes away. I had a really 'orrid running issue which turned out to be a duff / contaminated AFM.

(I suspect my fault for covering the air filter in non-standard oil which got sucked into the AFM mesh - doh!)

[EGB]

Paul. Stalling at islands and in my case, also at traffic light stops. I had this annoying habit. I put it down to the lazy GM stepper motor. Fixed it by inserting and sticking a 2mm thick piece of plastic (see pics) under the throttle stop next to the plenum. This keeps the plenum butterfly just slightly open on closed throttle. Cured mine %100. Good old SU and Webber carbs had a simple screw to do this.
Adjusting the plenum air bleed valve should do this but it did not work for me. Either blocked or not drilled. We have got to sort out your everfuelling. Have you done tests with the SH ECUmate?

Edited by EGB on Saturday 29th September 23:29

[gavgavgav]

FlipFlopGriff said:

Also have an annoying stalling issue but unsure if its related. Doesn't do it all the time but seems to happen when i start it from hot (petrol stations) and I can't get it to idle and everytime I dip the clutch it stalls, which is a nightmare (and extremely dangerous) especially at islands.

FFG

If you have a spare ignition module to try I would suggest that. (thats what was the cure for me)

[FlipFlopGriff]

gavgavgav said:

If you have a spare ignition module to try I would suggest that. (thats what was the cure for me)

I've changed that too.
FFG

[blitzracing]

I think an ECU mate permanatley plugged into the diagnostic port would be a good idea, then you can scan all the sensor data when it happens- the important bits being stepper position, cars idle status, and lambda cycling. Its small enough to keep in the footwell.

[FlipFlopGriff]

blitzracing said:

I think an ECU mate permanatley plugged into the diagnostic port would be a good idea, then you can scan all the sensor data when it happens- the important bits being stepper position, cars idle status, and lambda cycling. Its small enough to keep in the footwell.

I've bought one now but not had the time to use it yet. Car still in garage blocked in by a load of stuff. Renovating a listed property which is taking all (and more) of my time.
FFG

[Rob_the_Sparky]

FlipFlopGriff said:

I changed my ECU and it still happens.
FFG

Fine but if one of the sensors is doing something odd that the ECU reacts to then changing the ECU will not help. I'd go with the constant monitoring.

Rob

P.S. Does the LUCAS have some sort of idle switch? Could the stepper motor be being driven fully closed and back to normal after a power cycle?

[FlipFlopGriff]

Temp sensor also changed. Yes, I do have fair few spare items. Will change AFM next but been through a couple on the 500 and they tend to get worse over a short period of time with lots of crap thrown out the back so easy to tell when on the way out, so I'm not expecting that to be a problem. ECU mate is next - if I can find it.
FFG

[blitzracing]

Rob_the_Sparky said:

Fine but if one of the sensors is doing something odd that the ECU reacts to then changing the ECU will not help. I'd go with the constant monitoring.

Rob

P.S. Does the LUCAS have some sort of idle switch? Could the stepper motor be being driven fully closed and back to normal after a power cycle?

There is a lot going on with the ECU during idle- Steve heath has spent a lot of time explaining it in the users manual and putting functions into the ECU mate to monitor whats happening.

Have a read- its not so simple!

http://ecumate.com/docs/Ecumate%20inst.pdf

[davep]

The 'crap out the back' has been cured on my pre-cat with new valve guides, heads cleaned up and some minor adjustment to ignition timing. I suspected the AFM, but once the hotwire was cleaned up with carb cleaner it was found to be working just fine.

[EGB]

davep said:

The 'crap out the back' has been cured on my pre-cat with new valve guides, heads cleaned up and some minor adjustment to ignition timing. I suspected the AFM, but once the hotwire was cleaned up with carb cleaner it was found to be working just fine.

Nice action pic of your Griff Dave. Mask the jack next time lol. How did you clean up your hotwire. Spray or cotton buds?

[davep]

Remove the inlet port clip and air turbulence grill. Aim a short spray of carb cleaner at the air flow aperture and clean with very gentle applications of a small cotton bud, do not damage the hotwire element or the thermistor behind. Turn the AFM over and let the unit dry. Gently clean the grill with carb cleaner and lint free cloth.

I've also fitted an AFM heat shield.

With the AFM refitted I used a DVM and ECUMate or RoverGuage to verify that output voltages are correct.

That's not me in the profile pic, it's a support mechanic doing fine shocker adjustment and trusting very much in his jack.

[Rob_the_Sparky]

From the ECU Mate manual:

"IDL
This signal indicates that the ECU is an idle mode and should only state ON when the car is stationary. It should reflect the ROAD signal in that it will be on when ROAD is 0 and off when it is greater than 0. If not, this indicates a fault with the road speed. If it is permanently zero then the idle mode will be permanently on and the car may stall when lifting off at a junction. If teh road speed is greater than zero, then idle mode will be permanently off and idle speed may stay high."

"...may stall when lifting off at a junction." That sounds like it might be the issue.

Rob

P.S. Thanks for ECU mate link - very interesting.

[FlipFlopGriff]

Thanks Rob.
May stall - should be will stall.
I've printed the ECU Mate pdf which is 100 ish pages. Certainly plenty to go at and I'm sure I'll get my moneys worth.
Given the car is 20+ years old and done 250k miles the electrics are a constanct cause of concern.
FFG

[cureton]

Trouble is I cannot reproduce the fault, so I'll just have to wait until its happening again. Will check ECU connection in the meantime. ECUmate is on order now as it seems sensible to leave it plugged in for the case. Might well be a problem with the road speed signal telling the ecu to switch into idle mode when car is still moving. But then, would the car not properly idle when stationary? I think mine doesn't. Keep you posted.