2001 XC70 ECM Ignition Ground failure P0301 P1367 Topic is solved

[jcb]

After two days of troubleshooting, I'm ready to send my ECM out for repair (2001 XC V70 - 98,000 miles). Although I'm 99% certain that the ECM is the problem, thought I'd run my experience by the experts to make sure I'm not missing something. If nothing else, perhaps it will help others with troubleshooting things to do, or perhaps NOT to do. After writing the third paragraph, my wife looked at it and said it was way too long and nobody will read it. I agree, and while it is also probably hard to follow, I don't know of any other way to describe a frustrating experience.

Problem showed up without any warning several days ago - P0301 = misfire cyl #1. Thought no big deal, likely coil pack, spark plug, or possibly injector or wiring. Did the obvious things first, unplugged that connector with engine idling and saw no change. Followed this by swapping plugs and coil packs twice with other good firing cylinders - problem stayed with #1 cyl. An inline light spark tester did not flash, nor did a good spare plug fire after inserting it in the coil and grounding it to the engine block. Time to check coil pack electrical plug and wiring. Both of the heavier gauge wires checked ok - using a multimeter they showed being connected to the other common colored wires that feed the other cylinder's connectors.

NOW THIS IS WHERE IT GETS INTERESTING (and results in something I can't explain) : The third thin wire is the pulsed ground signal from the ECM. With the ECM still plugged in, it checked the same as those to the other cylinder plugs - open, not grounded or shorted to any other adjacent wires. To check it completely, I pulled the ECM hoping to find that the signal wire was open between the ECM block and the coil pack plug. Unfortunately, it showed zero ohms indicating the wire had good continuity. That was the first indication of an ECM issue. So I plugged the ECM back in and decided to check the injector circuit with a simple test light. The injector hot wire turned the light on when connected to ground, and the light pulsed with the signal wire connected to battery+ - so all seemed normal electrically. For some reason I decided to use the test light on the coil pack plug wires. With the engine idling the two thick wires checked as expected, but the thin ECM wire turned the light on solid (not pulsed) with the tester connected between it and battery+. So to me there appeared to be a solid ground on the ECM/plug wire. I turned the engine off and the tester light remained lit. So I used my multimeter as I had done before between the same plug wire and ground and the ohm reading showed as open, not grounded. So why the difference between the test light and the multimeter ? Baffles me, but then again electrical things are definitely not my forte. The test light on ECM wire only turned off when the ECM was removed again (note it did not light for the same signal wire on the other cylinder plugs with the ECM plugged in).

So my conclusion is that something is wrong with the ECM signal to #1 cyl coil pack, and I have to decide where to send it - Xemodex, ARD, SIA, or others. Any input as to experience with such vendors is welcome.

Bottom Line - The most important thing to me is any input as to this being a wrong move because I missed something. Note that I didn't swap injectors, primarily because the other evidence seems too clear. Note that I also did a compression test and all cylinders were in the 145-150 psi range (note my compression gauge is not an expensive one).

One other tidbit - I always thought that the fuel injector was automatically disabled if it detected a solid misfire. Seems not to be true because of the pulsed light on the injector signal wire coupled with a somewhat damp (not soaked) spark plug on several
#1 cyl plug removals. Hope I didn't damage my cat or O2 sensors.

Thanks in advance for any input !

[abscate]

You can't test the ECM coil function this way. It's more complicated than just grounding the coil

Did you have the coil pack screw attached to the engine block when you tried the spark plug test? The 10mm M6 bolt forms the coil ground on these. You have to rig up some sort of ground strap to test like that.

[jcb]

abscate,

Thanks very much for the very prompt reply.

Your coil pack grounding requirement never occurred to me. I did several spark plug tests, but thinking back on it there are only two that fit that concern. In both cases, the coil pack was NOT attached to the block with that bolt :

1 - Probably first one was with the inline spark plug tester. Spark plug was installed in engine with tester attached by cable to coil pack sitting unattached laying on top of block = bolt not installed. Tester light did not activate. Did exactly same setup on adjacent cylinder and light flashed as expected indicating plug was firing. So I assumed this test was OK - meaning #1 was not firing for some reason.

2 - Second test was similar in that coil pack with bolt was not installed with bolt. Original plug was left in block, coil pack removed and known good plug stuck into it. End of plug was placed on engine block with engine running (grounded) and there was no spark at electrode. Did not perform exactly same test on another cylinder, but at least in the old days this was a good way of testing for spark. However, back then you had one common coil and not one for each cylinder.

I believe all the other tests were to check the wiring. In those cases the coil pack plug was obviously disconnected to access the wires. I can do the above two test again with a grounding jumper installed if you think it's worthwhile.

Your grounding concern made me think of another bolt that was disconnected during the wiring testing. To get the ECM out without the proper tool, I had to remove the bolt that secures the ECM enclosure base to the wheel well. Don't think this is a grounding bolt of any kind, but who am I to say.

Thanks Again For The Input

!

[jcb]

UPDATE :

Just completed doing a repeat of tests #1 & #2 as described above, this time with a ground jumper between the engine block and the bolt hole metal attachment plate on the coil pack (as suggested by abscate). Unfortunately got the same results - #1 cyl not firing the test light or the spark plug when held against the block. Moved to #2 cyl and the plug tester light pulsed on correctly when the plug fired. As before, it fired correctly even after removing the ground jumper, so it's questionable how important that ground connection is. I did not do the "spare spark plug laying on the block test" because the engine runs pretty badly on three cylinders.

Perhaps more telling is the repeat of checking the ECM signal wires to the coil pack plug. In order to perform the above tests, I had to reinstall the ECM. Before reinstalling I ohm checked the signal wire on all 5 cylinders and all showed open as would be expected. After putting the ECM back in, I ohm checked them all again with the same results. However, after reconnecting the battery, I used a test light (attached to battery+) on each at the plug end. Even with the key off, the light glowed brightly on #1 cyl, and showed nothing on #2 thru #5. It is that difference that leads me to suspect the ECM. It seems my ohm meter doesn't pickup a ground, but interjecting a small test light current into the ECM does. Perhaps this suggests something like blown diode, but I hate to speculate on such things for lack of electronic knowledge.

So if there are any other thoughts or options anyone would like to suggest, please please let me know a.s.a.p. - I'm just about ready to box the ECM for shipment (not certain to where at this point).

Thanks !

[RickHaleParker]

Plugs need compression to fire. Do a compression check.
Incorrect air/fuel ratios can cause misfire, Check for intake leaks around #1.

[jcb]

RickHaleParker,

Thanks for the input, but I already did one (see next to last paragraph of my first post). I understand why you probably missed it - as my wife said, it's way tooo-ooo long and most won't suffer through it !

[jcb]

RickHaleParker,

Sorry, forgot to comment on checking for intake leaks. I have a good bit of experience in that regard. I changed at least two, possibly three, intake gaskets my '86 740 turbo wagon (which I still own). While they cause some pretty nasty misfires, the spark tests I've done pretty much rule that out. To me an intake leak can cause a misfire by preventing ignition/combustion, but I've never seen it stop a spark plug from "sparking". On my good cylinders, a plug will fire/spark when totally removed from the cylinder, hooked to the coil pack and grounded to the engine block (no compression/no fuel). I can't make this happen with my #1 cyl, even with a known good coil pack and spark plug. Unless I'm missing something else (possible), that pretty much only leaves the wiring or ECM as possible culprits.

Thanks for the input - you never know when something might show up that you haven't considered. Then you know where you'll be kicking yourself !

[abscate]

I think you’ve done a good job isolating it to the ECM by elimination. Send it in!

[jcb]

abscate,

Thanks very much for your followup on my issue. It's really comforting to have an experienced Volvo guy tell you that there's not much more you can do. So I REALLY DO appreciate your comments. While I had come to the same conclusion a few days ago, I posted just to try to make sure there was not something obvious I was missing. While in the end I could still be wrong, at least I gave it my best shot. I'll need to decide who to send it to, but for sure I'll not be working with a Volvo dealership.

Thanks Again !

[RickHaleParker]

I would check for one last thing before I sent the ECM off ... ashort between the ECM line and a 12V supply line. That would keep the ECM line from going low and firing the coil pack. Disconnect the ECM and see if the ECM line on #1 still stays high. If it stays high, it not the ECM holding it high.