Intermittent misfire/stall

[PhilNW 40]

Quote

 

Looks like fuel  pump and AFM not an issue.

 

Does it misfire/stall when stood still and being revved?

 

Think you will have wait for it to "fail" and check if no spark or injectors and go from there. 

 

 

[MarkKehoe 1]

Thanks Phil, yes I don't think it's either pump/reg or afm. I'm trying to rule out things systematically. I do think it's a fuelling issue rather than spark though. It's only loom, injectors or ecu left? Might be worth going after injectors next, the car was in storage for a long time? I've listened to them with a screwdriver and coil resistance is OK but perhaps they're gummed up or coil breaking down with heat?

[PhilNW 40]

Hi Mark 

 

Try to establish the exact circumstances when the thing happen.

 

if you are hearing the ticking of the injectors then I would not be too worried about clogging. 

 

The way you have described it suggests it affects all 4 cylinders and then dies, Have you checked things like the voltages and resistance of the earths etc which would affect common items to all cylinders. 

 

Just had a problem with dim headlights, the voltage at them was down to 12 volts (through the loom) rather than the 14.5 ish voltages at the battery when charging. Ended up rewiring them direct from battery as the general consensus on the forum thread was that the existing wiring loom does deteriorate quite a bit after +30 years. 

[MarkKehoe 1]

Thanks Phil, I'll focus on earths/loom next and report back. The circumstances have varied quite a bit, but never any issues when stood stilI always out on the road but sometimes after a long drive other times shortly after taking off. I have a spare ECU that I could swap out to knock off the list, do they ever give trouble? I'd of thought it's pretty unlikely?

[PhilNW 40]

Swapping the ecu is a good idea, as pretty unlikely 2 ecus will have exact same problem.

 

Edit 

 

If you have not already, might be worth identifying all the power and earth wires at each component now as it might be easier/quicker to identify where problem is when it happens.

Edited June 8, 2023 by PhilNW

[Tom Fenton 1,524]

I have never known a Jetronic ECU to go wrong. Most people have a pile of them as there is no demand for second hand ones as they don't go wrong.

[MarkKehoe 1]

Thanks Tom, good to know. I cleaned the earth connections on the top of the gearbox last night. There was fairly heavy oxidation so that may have been the source of my intermittent issues. I won't know until I can bring it for a decent drive this evening. 

[DamirGTI 323]

Seems to me like spark/ignition problem .. or loose "make-and-break" wiring connection somewhere with the engine movement .

 

I'd take a good look at the coil , ignition leads (coil to cap HT lead especially) , dizzy cap and rotor arm (unplug leads and check terminals internally with an flashlight for "carbon tracking") 

 

Also , try to wiggle the key in the ignition barrel while driving it .. might be ignition barrel going bad .

 

Does this problem manifest whilst the engine is cold or after warm up ?

 

If it does it only whilst driving , i'd lift it up and put it on axle stands , and "drive it"/shift gears engage/disengage the clutch in order to rock the engine backwards/forwards on the mounts .. ie. mimic driving it whilst up on the axle stands - ask someone to wiggle various connections cables wiring while doing so .

 

Might also try to wait till the nite time , start it up at night with no light on near so it's nice and dark , and look around the engine for spark jumping from either the coil (coil tower usually) , cap or leads .. in that case you'll also hear clicking sound whilst spark jumps around any particular area .

 

New parts unfortunately doesn't guarantee they're good too ...

If it's too hard to pinpoint now , i'd drive it till it gets worse/more intense then it'll be (should be) easier to find what's up .

 

D

Edited June 9, 2023 by DamirGTI

[MarkKehoe 1]

Just a quick update, the car is running well. I brought for a long drive this evening and no issues to report. I cleaned the earth on top of the gearbox a few days ago and although I didn't have any bad hesitation I wasn't fully convinced. I reset the ignition timing to 5 deg at 700 which required me to retard the timing by 2 degrees and I increased the co2 at idle from 1.5 to 2%. The car behaves very well off idle and no issues out on the road. Leaving well enough alone for now... 

[MarkKehoe 1]

Got a wash and polish too! Thanks for all of the help!

[PhilNW 40]

8 hours ago, MarkKehoe said:

Just a quick update, the car is running well. I brought for a long drive this evening and no issues to report. I cleaned the earth on top of the gearbox a few days ago and although I didn't have any bad hesitation I wasn't fully convinced. I reset the ignition timing to 5 deg at 700 which required me to retard the timing by 2 degrees and I increased the co2 at idle from 1.5 to 2%. The car behaves very well off idle and no issues out on the road. Leaving well enough alone for now... 

Hopefully it was just a dodgy earth. fingers crossed. Now have some fun!!

 

I watch  south main auto channel on YouTube, he is a mechanic/technician in New York State, USA, a lot of the problems he diagnoses are down to earthing issues as corrosion is a big problem there.

Edited June 16, 2023 by PhilNW