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2004 XC70 Misfire on cylinder #4, wrong spark plugs

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shiloh51933
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2004 XC70 Misfire on cylinder #4, wrong spark plugs

Post by shiloh51933 »

20161102_160238.jpg
So I've been trying to track down this intermittent misfire for the longest. I thought I had it yesterday when I found a vacuum hose that totally collapsed when motor is pulling vacuum. I replaced hose and it ran great until this afternoon. Anyway after quite a bit of diagnostic work i found an issue with the coil packs harness/plug wiring to cylinder #4.
20161102_160238.jpg
The outer wiring loom was brittle and fell apart during removal. If you can see in the pic the actual insulation on each wire has hardened over time is breaking apart leaving the wiring to cross each other and short out that circuit. Anyway has anyone ever purchased the coil packs harness? How much did you pay and where'd you find it?
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abscate
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Re: 2004 XC70 Misfire on cylinder #4,

Post by abscate »

You should get to the PnP and buy couple of coil connectors for a buck or two, then splice them in with either good crimps or solder.

That harness new will break your 401k
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shiloh51933
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Re: 2004 XC70 Misfire on cylinder #4,

Post by shiloh51933 »

abscate wrote:You should get to the PnP and buy couple of coil connectors for a buck or two, then splice them in with either good crimps or solder.

That harness new will break your 401k
That's a good one .
I repaired the connector wiring, covered in high temp electrical tape and the replaced the wiring loom that was falling apart around the coil pack harness. Unfortunately I'm still having an issue with cylinder #4 and cylinder #5 has a slight miss with a random misfire code. Only other thing I could scan was a Volvo factory code 928c, the definition was vague control module communication problems. I'm not sure what that means, I hope it doesn't mean the control module is failing. Any clue?
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Re: 2004 XC70 Misfire on cylinder #4,

Post by abscate »

Cleat the codes and see if they come back before worrying too much, Shiloh.
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shiloh51933
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Re: 2004 XC70 Misfire on cylinder #4,

Post by shiloh51933 »

abscate wrote:Cleat the codes and see if they come back before worrying too much, Shiloh.
thanks for your reply.
Unfortunately the miss is still very present on cylinder #4 and #5 isn't as bad but still present. I tried disconnecting both +/- cables @ the battery for an hour to reset everything to no avail. The coil pack are new, the spark plugs are new, timing belt/TB tensioner/idler/water pump & TB cover clips are all new factory parts from about 8 months ago. Anyway she has good fuel pressure at the rail, she has good spark, the fuel injector ohm out within spec and the are firing. I found one bad vacuum hose that was collapsing when pulling vacuum so I replaced(hose that plugs onto IM nipple.
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abscate
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Re: 2004 XC70 Misfire on cylinder #4,

Post by abscate »

Check that wiring for multiple faults on 4 and 5

The coils fire by grounding at the ECU, and have constant 12 V in them, check that too

Move your coils to new cylinders to eliminate them as bad parts, even if new.
Empty Nester
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shiloh51933
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Re: 2004 XC70 Misfire on cylinder #4,

Post by shiloh51933 »

abscate wrote:Check that wiring for multiple faults on 4 and 5

The coils fire by grounding at the ECU, and have constant 12 V in them, check that too

Move your coils to new cylinders to eliminate them as bad parts, even if new.
Yes thank you. I tried swapping coil packs around, checked FP, ohm out injectors, only thing I could find is faulty brake pedal position sensor after realizing cruise control didn't work. I know that will fuck up vacuum with brake booster so I ordered a new one.
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Re: 2004 XC70 Misfire on cylinder #4,

Post by abscate »

The esoteric check list is:

intake manifold gasket failure leaking air into cylinders 4,5
Head gasket leak
Two chipped valves..the Swedish gods hate you if this it..compression test finds this one
Empty Nester
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shiloh51933
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Re: 2004 XC70 Misfire on cylinder #4,

Post by shiloh51933 »

abscate wrote:The esoteric check list is:

intake manifold gasket failure leaking air into cylinders 4,5
Head gasket leak
Two chipped valves..the Swedish gods hate you if this it..compression test finds this one
I should have mentioned I did a compression test, everything is within spec.
My wife finally mentioned that a couple of times she had an issu with dash cluster going off while running and the RPM needle staying at 4000 after cranking motor trying to start her but she wouldn't start first try. After another attempt of starting as she keyed on RPM needle went down and she started.
Sounds like ECM or CEM maybe.
Should I try getting a software update?
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shiloh51933
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Re: 2004 XC70 Misfire on cylinder #4,

Post by shiloh51933 »

I still can't believe it but it was the plugs, 6 month old NGK 's spec for this XC70. They didn't looked fouled up when i pulled them , light tan color. I went and got the Bosch dbl platinum iridium like suggested in the book and swapped them in. It runs great now. I'm happy but WTF!!
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