Intermittent Cutting Out / Misfire

[DavidM]

In my Striker I've got RAW's silvertop 4AGE 20v engine and Omex 600 ECU combination. The engine has been pretty much faultless for the last 5 years since the car was SVA'd ( is it really that long?!).

Yesterday I was doing a track day at Anglesey and we started getting a very intermittent cut out. It was generally very brief (not even long enough to think 'what's that?' before it picks up again) and feels like a complete engine cut rather than just dropping down to 3 cylinders.

The engine runs absolutely fine the rest of the time and sometimes we were able to do complete sessions with no problems, others it'd cut out 3 or 4 times in the space of a lap and we'd come back into the pits. I fiddled with a few things on the day, mainly checking for bad connections etc as I didn't have any spare bits to bolt on anyway.

My passenger noticed the tacho (fed from the ECU's RPM signal) was dropping to 0 when it cut out, which makes me think the ECU might be losing the crank signal (although I've had problems with the lambda sensor in the past I'm pretty sure that caused the tacho to drop to 0 to so it might just be when the ECU picks up some sort of condition it doesn't understand).

As it's cutting all 4 cylinders and runs perfectly the rest of the time, I think it must be ECU / sensor or electrical related rather than fuel and there are a limited number of things it could be, so far I've got coil pack, throttle position sensor and crank position sensor (or associated wiring, gaps etc).

Anyone got any other bright ideas before I start remaking connections and changing stuff at random in the hope it goes away? Kind of my nightmare scenario to track down this one, intermittent and can only be tested by driving the car for an extended period of time (and it's not MOT'ed / taxed at the moment either so testing is tricky... trying to get an MOT booked for Saturday!)

[jeffw]

New cranksensor, new leads/plugs, new coil pack. Make sure all the connections are OK and I'll bet it doesn't do it again.

[matt_gsxr]

Add to Jeffs list.

Main master switch (these can go bad).
Earthing.
Alternator leads.

[RobMsport]

Re -- Matt's alternator lead check My own ECU , albeit not an OMEX , is set to cut all functions when not receiving it's full desired electrical grunt SO , possibly the alternator isn't delivering consistantly

[David]

Have personal experience of misfire due to (very slightly) loose crankshaft position sensor, faulty FIA switch, and insufficient voltage (alternator woes).

Sudden onset followed by return to perfection does not sound like alternator; I would expect misfire to continue.

Other two possibilities are very easy to check.
With the sensor, make sure the mounting is tight and then check the gap with a feeler gauge. It's amazing how gap sensitive some of them are
If you have an FIA cut-out, simply turn on the ignition and wiggle the cut-out (in the "on" position) -- if you can make your ignition lights go out, Occam would suggest you've found your problem. Since that happened to me earlier in the year I've found at least five people who've had similar experiences (including Rob).

HTH

[DavidM]

Can't be the cut out switch as I don't have one, have heard from a few people about them causing trouble though

Don't think it's the alternator either as I've had an alternator fail (notice I said the engine has run faultlessly, plenty of other bits have broken / fallen off ) and the ECU still worked while the battery got pretty flat as I limped home.

I checked the crank position sensor hadn't come loose, but I couldn't check the gap as I didn't have feeler gauges (or remember what it should be for that matter, it's written down somewhere!). Ordered a new one anyway as it wasn't expensive. Once I'd done that, I carefully lowered the car off the jack onto my foot - which was indicative of how my day was going I think

I'll get a new coil pack, leads and plugs as Jeff suggests and properly check all the earths and other electrical connections that could be related too (rather than just looking at them and poking them a bit and deciding they're ok which is what I did yesterday!)

I like knowing what has caused something, but at the same time I don't want to spend yonks faffing about with it when changing a few (relatively) inexpensive components in one hit might just make it go away.

[DavidM]

Pretty sure the coil pack was the culprit, I changed bits as I got hold of them and it doesn't seem to have happened since I fitted a new one. The Ford coil packs that look like this



that a lot of people use don't seem the most reliable things. I found there's a Bosch version that's a different design but is a drop in replacement for the Ford type ones, it's Bosch part number 0221503490. So I went for one of those instead, who knows if it's any better or not though!

Car has a new crank position sensor, new spark plugs and tested earths for the engine and ECU too now anyway

Does anyone know of a place that makes custom HT leads though? I'd like ones that have the correct ends for my engine, trying to get a decent fit on the spark plugs when they're down quite deep wells is a bit of a pain.

Anyway off to Anglesey again on Sunday so I'll find out for sure then, it's with Circuit Days if anyone else fancies it.

[dopdog]

I think i got my leads from RAW they seem to do a good price and if correct were the 8 or 10 mm version? such a long time ago like you i just put oil and water in my car and have just treated myself to a new set of plugs

[Taff Striker]

Got some custom length leads for my tin top from these guys

http://magnecor.co.uk/customsets.htm

Took a while as it seems to be a very popular service. Can't fault the quality though