97 960 Won't start with (recent) history

[jaxomlong]

Long history with this car- Dad bought it off lease, sold it to me with 147K on it, at 189K on it now. Been remarkably trouble free. Knew I was in for hell when I touched the harness over the engine. Had a miss, P300, P305 & P303.

Hired a mechanic at Just Answer and troubleshot it to for front ignition control module and it ran great. Changed the spark plugs along the way. Threw a code for #3 coil after thirty miles. I'll copy and paste what I said to the mechanic at just answer:
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"Hi Chad-

I'm coming off six weeks of 65 hour weeks (project ended Friday night). We left off waiting for the wiring harness that goes on top of the engine on a 1997 Volvo 960. I spliced in the new section of harness and continued the trouble shoot of ignition, replaced #3 coil.

Ran fine for 30 miles, back in the driveway with bad splice on #4, repaired that and got another thirty miles- thought I had it.

Started throwing a code for #1, #2, and multiple cylinders (301, 302, 300). Parked it for a week, laid off Friday night, got to it today (yesterday). Opened up the splice, didn't like the common, redid that splice. Still throwing same codes (added 303). Swapped 1 & 2 coils for 5 & 6. Got worse. Swapped back, did not get better. Now I can't start the car at all to get a code.

I'm going to check common to ground for 12v and wiggle the splices without starting it.

As a reminder, the car has a new Bosche ignition control module, new spark plugs and one new injector. I can upload the previous conversation if you want it.

David"

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He had me check for fowled plugs, "THE FAULT IS MOVING AND EVER TIME U MESS WITH HARNESSES IT CHANGES".

Plugs had less than 100 miles on them and looked it. Continuity check from ICMs to common good on six lines. Since starting the job I got a ratcheting crimper and while they weren't perfect I'm confident of the splices now.

Got a wrecking yard ECM. No joy.

Ignition doesn't come on until you crank (it was several days before I realized that). Chad gave up, another guy at Just Answer picked it up. Most lately had me run these tests (had to break up the old harness to do with starter cranking:

cylinder 1 2 3 4 5 6
Ressitence
of coil .5 .5 .5 .5 .5 .5
Static voltage
through coil 12.58 12.58 12.58 12.58 12.58 12.58
common at coil 10 10 10 10 10.4 10.4
after coil 9.8 9.8 9.5 9.5 9.8 9.8

Went to boost on the battery charger for #5 & #6

I'm going to put a test light on it (after dark), but at this point I just don't believe it's ignition.

I'd still be willing to believe I screwed up somehow, but how?

Oh, I was an aircraft mechanic and inspector- rusty, but when I say I'm confident I am. At the moment this is what I've got to say to the mechanic, but I haven't uploaded it:

"It's been fixed to working twice, once replacing the front Ignition Control Module, and later troubleshot to one of the coils. In between the harness came apart, expected when I just had to touch it. Both times it worked well for 10-20 miles awhile. It failed the last time when I got a hesitation sort of limped home and parked. It failed totally, parked.

There can't be a voltage drop without current flow, and I've pretty much got the same voltage drop across all six cylinders. That says to me the harness repair is good, and for sure not a point source failure."

I've pulled the cover off the fuel pump, and I'll listen for that to pressurize when I've got help.

David

[jaxomlong]

Got a project that has me working ten hour days and gave it to a mechanic- fuel pump! A little more to it- looks like the fuel gauge was not registering, and the pump was running with all the trouble shooting of the other stuff. Ran dry, and killed itself.

Too damn humble. This mechanic is good, and he kept it for 24 hours before admitting it and I know he checked compression on the way, so he didn't believe me.

So add to your diagnosis- if cylinder 1 & 2 are miss-firing it just might be fuel pressure.