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98 Expedition


pt_fixer's Avatar
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08-30-04, 03:51 PM   #1  
98 Expedition

I'm working on a 98 Expedition with a 5.4L. It runs with a miss in cylinder 4 and its got the codes P0354(ignition primary/secondary circuit failure) and P0304(engine miss cylinder 4). I swapped coils between cyl. 1 and 4, no change. Swapped spark plugs between 1 and 4, no change. Checked both the coil and injector on 4 for pulse with a noid light. Both were good. Figured it was a plugged injector and replaced it today, no luck. Still has a miss in 4. I also checked that the coil was firing, and checked the voltage to the coil. Both were ok.

I'm thinking that if it was a mechanical failure in 4 that it wouldnt be throwing the code P0354. But if its getting fuel and spark, wouldnt it have to be a mechanical failure? And according to Mitchell on Demand, only 4 things can throw that code, one of which is the computer. I dont want to condemn the computer so quickly, but after checking the other 3 possibilities, its looking like its at fault.

Anyone have any suggesions or comments?

 
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08-30-04, 04:51 PM   #2  
Is this a dead miss or is it intermittant? I might suspect the trigger wire from the PCM. Can you try just running an external wire spliced from that PCM pin to the injector plug just to eliminate a bulkhead connector or other wiring problem. I would also try running a voltage drop test on that line after unplugging it from the PCM. It sounds like you've already eliminated the coil and plug. That only leaves the wiring and the PCM. Also check for vacuum leaks or sticking egr. Are you experiencing any coolant loss? If so, intake gasket is a possibility.

 
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08-30-04, 08:22 PM   #3  
Its a dead miss.

Forgot to mention that I did check for a vacuum leak, couldnt find one.
The next step I was planning on doing tomorrow was as you suggested, checking the wiring between pcm and coil. If I was reading correctly today, then the coil has a constant supply of >10.5 volts and the ground is the trigger. I was getting a reading of 11.6 volts, so the supply should not be the problem. But I will doublecheck these readings tomorrow. I'll also check the coolant and egr. Thanks for the tips. Hopefully with a fresh mind and some new ideas, I will get through this pain....
Thanks for the tips Desi.

 
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08-31-04, 11:54 AM   #4  
If you've got a dead miss, then why can't you just plug a noid light into it? That's cut and dry on power and ground wiring. It should be pretty easy to isolate if the miss is constant. Check the coolant leak idea too.

 
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08-31-04, 02:56 PM   #5  
If you have a circuit failure which the code states it's electrical.The pcm detected a short or open in(including internal circuits)the pcm,related wiring or the ignition coil.A mechanical fault will not cause an electrical circuit code.Check the terminals for tension and for being backed out at both ends also.Very possible you have a wire broken inside the insulation and hidden from sight.Might not hurt to check all the grounds for the engine and pcm.You could however repair the electrical fault and still get the misfire code from a mechanical fault but I don't think that's the case.

 
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09-05-04, 06:55 AM   #6  
Well, the next morning when I got in the shop, I was told to put the car back the way we got it and that we were giving it back to the customer to take to the Ford dealer. We ate the injector and time. We were talking to the owner just yesterday (saturday), and he said that the dealer told him they have to replace cylinder number 4. I have no idea what that means, but when he picks up the car, he is going to bring the bill in so we can see what was done.

I guess I forgot to mention that I did use a noid light on both the injector and coil, and both pulsed fine. And to make sure there was a good connector going to the coil, I put a spark plug in the coil grounding it to the intake and it fired fine. And there was no coolant loss.

I am curious to see what the dealer comes up with. I will post back when I find out.

 
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