Major misfire

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SBDJ

New Member
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Hi all,

New member here, recently purchased a P38 4.6 and have been enjoying it. A few niggles to sort but nothing major. Plenty of information here to help with those issues!

Unfortunately on Monday when whilst driving down a dual carriageway and I suddenly lost power. She still runs but misfires and then around 1500RPM misfires so badly it can't rev any higher.

I pulled a few plugs and confirmed spark up until the 1500RPM mark when the spark stops. Having had this on another vehicle I replaced the crank position sensor which made no difference. Next suspect is the MAF - I managed to source another (albeit a Lucas one rather than the Sagem one I have, same part number) and she won't idle or rev on that one at all so I suspect it's duff.

Is this likely to be a faulty MAF or am I heading down the wrong route? Replacing components one by one could get expensive!

Thanks,

Scott
 
As per my OP I've already replaced that with a brand new Lucas one with no improvement unfortunately.

Just a couple of other things, checked from inspection cover that crank position teeth on flywheel are intact, not loose or bent and that the sensor is positioned nicely between them.

TPS appears to be fine too.
 
Had a look at the cam sensor - made absolutely no difference to the running of the engine when I unplugged it so its a good suspect.

Out of interest I hooked a scope up to it. I'm assuming it's a hall sensor and as such I expected a nice square wave signal. I got a signal but it was very noisy so I think I'm going to try this as my next port of call.

I'm slightly confused though. According to britishparts.co.uk my VIN (WA4xxxxx) should be an ERR6169. Looking at the car it appears to have an NSC500610 fitted, with another cable plugged into it, the end chopped off and another connector from an ERR6169 crimped on which then plugs into the loom connector.

I'm guessing someone has bodged that on? Are they the same sensor but with different connectors?
 
Replaced cam sensor, and... nothing. Tested all connections to it as well which checked out OK.

Pulled each lead in turn - two of the them stop sparking at about 1500RPM, all others carry on. When I disconnect the two that stop sparking then the engine revs much better. Swapped leads out, made no difference.

Coil pack now?
 
You'll need to get someone who know's what they're doing & get some diagnostics on the vehicle.

It will be cheaper than replacing everything.

You'll need to clear the faults & you replace parts.

A compression test is needed to rule out, valves & camshafts.
 
Trying! There's quite a wait to see someone who has appropriate diagnostics. Main dealer can see me next week which will have to do I guess - in the meantime if I can rule out things then it all helps.

I'll break out the compression tester tomorrow to be sure.

I've spoken with a few LR guys and they gave me some testing to do. I've scoped the crank sensor which seemed OK. Some of the cylinders stop sparking when you hit 1500RPM, some don't. I swapped the coilpacks between an always working and non-always-working cylinder and the fault stayed with the cylinder. Swapped the leads and the fault stayed with the cylinder. Continuity is good on all wires from coilpack to ECU.

This says to me that it's likely to be a problem with a sensor input to the ECU.
 
Where are you mate? There's bound to be an independent specialist in your locality. I've 3 near me in Durham, they are a whole lot cheaper and generally better. It does sound like an ecu fault to me, but I haven't heard of this on a p38 before
 
hi , sounds like the maf to me where are u based ??? maybe one of us can help , have a look at other thread on this page as to what i did and give it a try with yurs , cheers mozz
 
I've got a few round here (Tring area) but they are all booked up, if I can find it in the meantime then it's less time car sharing with the OH.

If I warm it up and disconnect the MAF then the misfire still occurs.
 
Hmm, just had a similar issue. A while back the P38 developed a misfire, sometimes disappeared when I gunned the engine, but mostly quite consistently annoying. Replaced both coils which I had never done. Ran sweetly for half a day then same same (sorry, local lingo). Took it to local guy and he hooked up his diagnostic machine which showed cylinder #2 out of action. No power going down the plug lead, so new coil (again!) and new plug lead justincase. Ran sweetly for half a day then same same:mad: Back to local guy, and it really was same cylinder even. We then traced fault to ECM tucked snugly away behind the cruise control vacuum. Fault: there is no drain in the bottom of the plastic ECM housing, so any a/c condensation or water draining into the housing doesn't drain out, and the bottom of the ECM with all the power connections, is happily swimming in 2cm of water! Solution: angle grinder out :D and cut two slots in plastic ECM casing to drain water when the local garage steam cleans the engine or I take her for a bath.
 
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