Millworm
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| posted on 19/12/15 at 05:16 PM |
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Zetec missfire under load
It seems to be out to get me!  now I can acutely drive it as it don't overheat I've noticed it's missing I think it's
cylinder 2. I've replaced plugs and coil pack but no joy I also tried a know good lead on each cylinder with no luck. Any ideas? I ran fine in
the donor car? Poss injectors or a senor that's had it? Thanks
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obfripper
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| posted on 19/12/15 at 07:38 PM |
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Check for tracking marks on the lead boot or spark plug porcelin, some silicone grease on the plug and inside the boot will stop the spark tracking
temporarilly.
You can swap leads 2&3 with each other at the coil pack and see if the misfire moves with the leads to help isolate if it is a specific
cylinder.
If you use a pair of insulated tongs and lift each plug lead in turn with the engine running, you can hear the spark arcing once it is a few mm
clear(any further will cause a misfire), this sound should be the same on all 4 leads if the spark is good, if it sounds muffled and weak on one
cylinder you can investigate further.
If the spark plug is very light in colour and overly clean, you may have an injector failure or blockage, a basic electrical test for an injector is
the solenoid resistance, expect something between 10-16 ohms, anything higher would indicate a failure of the windings.
For more in depth checking if the resistance is good, an oscilliscope is needed to look at the flyback voltage waveform while the engine is running
and compare with the known good ones.
Swapping the injectors around may be a pain if there is any corrosion around the manifold seals, dont put wd40 or other oil based lubricants to free
the injector as they will cause the o-ring to swell, try a small amount of silicone lubricant spray.
My only other thought is have you changed the oil and not used 5w30, this will cause misfires on a silvertop engine.
Regarding your other post, the diag socket is taped to the loom and is either 1 of 2 different 3 pin connectors, or a single 2 pin connector with a
separate earth wire from the diag kit, any older snap on/sykes/x431 etc kit will work fine, the newer kit tends to only come with a 16pin connector
only.
I dont think it will respond to eobd diagnostics even if you did make an adaptor cable from 16 pin, only manafacturer specific equipment, as the later
cars have 16 pin connectors but dont respond to eobd diagnosis.
Dave
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Millworm
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| posted on 19/12/15 at 07:43 PM |
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Looms like i have a q day of testing ahead of me tomorrow then. I hace the genuine ford diagnostic kit at work so that shouldnt be an issue as
I'm sure I can get hold of it for a few days. I doubt anyone will be testing any pre obd cars lol. I used 5/30 ford approved stuff in it also
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Millworm
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| posted on 19/12/15 at 07:45 PM |
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I did test the spark like that and it appeared to be ok. I'll pull the plugs as they'll tell me the deal
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Millworm
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| posted on 20/12/15 at 08:28 PM |
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Narrowed it down to an injector no firing and it was no3 not no like I thought. I pulled the plugs and they where all good apart from 3 with looks
like it's been doing nothing. I beleive it is to do with the injector loom it's self as there is a perminant voltage there but no earth to
switch it. I also checked the resistance of the injector to narrow that out. I'll replace the loom or repair if I have to and report back. I
should have looked behind the electrical tap! Doh! To be fair I'm supprised it even ran!
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coozer
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| posted on 20/12/15 at 08:48 PM |
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Shared permanent 12v to all the coils and the earth side goes back to the ecu for switching. Try a continuity check on each ecu pin.
1972 V8 Jago
1980 Z750
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Millworm
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| posted on 20/12/15 at 08:52 PM |
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Ok will do that as soon as I've got the new loom, the lack of sleep led me to belive it was just under load but it's never actually been
firing, spent too long on this motor! I did do a continuity check before when I first installed as that's how I determined what was what but ill
try again later as the loom has been moved about a lot and cracked more.
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