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Ignition intermittently cutting out


neal

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My engine has started to develop the annoying habit of cutting out. It only happens intermittently (every ten minutes or so) and for a brief duration (literally a split second). Usually it just recovers by itself, otherwise a quick prod of the accelerator fixes it.

I've had misfire problems in the past because of dodgy leads but I don't think this is the case now. The misfire caused a noticable stuttering acceleration which was especially bad at a particular rpm and throttle position. This time it's only a brief blip and can happen across the rev and throttle range.

When the ignition does cut out, the tacho also flips to zero then back again but there are no warning lights. I've also checked the ECM and there are no error codes. I know the tacho feed comes from the ECM and I had presumed this used the crankshaft (rpm) sensor. So last weekend I had a close look at this sensor and the wiring but didn't see anything unual and was unable to recreate the problem by wiggling the wiring around.

However, last night about 200 miles from home the engine died and stayed dead. I tried the starter a few times but nothing. I had a quick look round the engine and by some miracle thought about checking the ignition coils fuse, only becauase I yank it when away from home for a while as a precaution. It had blown. Replaced the fuse and the engine started again fine but was still cutting out every so often.

The blown fuse would suggest the problem is with one of the coilpacks. It the insulation in the LT coil is deteriorating, it could be shorting out briefly, cutting the ignition. If shorted for long enough it would blow the fuse. But that wouldn't explain why the tacho is affected unless of course I am wrong about the tacho feed coming via the ECM from the crankshaft sensor. If the ECM is instead using the LT coil supply (similar to an old points style ignition system) that would tie in.

Any ideas?

Thanks,

Neal

May: DON'T hit it with a hammer!

Clarkson: Why?

May: Cause it's the tool of a pikey.

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Hi Neal,

Having fun, huh.

The coil packs are connected to the engine ground via the block. The engine ground (via bellhousing earth) is also a vital for the ECM. It could be that if one of the packs is shorting, then the ECM is being impacted. Is it only the tacho that is affected by the hiccup?

Cheers,

Mike S

1996 Esprit V8, 1998 Esprit V8 GT, 1999 Esprit S350 #002 (Esprit GT1 replica project), 1996 Esprit V8 GT1 (chassis 114-001), 1992 Lotus Omega (927E), 1999 Esprit V8SE, 1999 Esprit S350 #032, 1995 Esprit S4s, 1999 Esprit V8 GT (ex-5th Gear project), 1999 Esprit V8SE ('02 rear)

1999 S350 #002 Esprit GT1 replica

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Hi Neal,

Having fun, huh.

Yeah, it would probably be less of a pain if the transaxle had just fallen off. At least then you know what needs replacing.

The whole 'it might be this so we'll replace it and see what happens' scenario is the worst. I could end up replacing the coilpacks, leads, plugs, crank sensor, camshaft sensor, rough road sensor, wiring loom, ECM,... and still not get to the bottom of it.

The coil packs are connected to the engine ground via the block. The engine ground (via bellhousing earth) is also a vital for the ECM. It could be that if one of the packs is shorting, then the ECM is being impacted. Is it only the tacho that is affected by the hiccup?

Yes, all I get is the tacho flipping to zero and a slight jolt. No warning lights, CELs, nothing. It's actually one of the annoying things about having a non-US ECM since a lot of the errors are disabled. I can understand the emission errors being removed since my engine doesn't have the additional emissions components (EGR, etc.) but as I recall they also removed a lot of useful stuff such as the misfire codes.

Thinking about it even the jolt isn't that noticable, probaly less than lifting abruptly off the gas. If a coilpack is shorting it is possible that 4 cylinders are still running off the good pack. Just so happens that the tacho is getting its signal via the ECM from the bad pack...

May: DON'T hit it with a hammer!

Clarkson: Why?

May: Cause it's the tool of a pikey.

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