Caprice mystery engine skip

[kevm14]

Pulled some Gs going around an exit ramp and the symptom seemed to return, at least while I was cornering. Still need to have the gauge on it when this happens so I can rule in/out fuel delivery.

[kevm14]

And it's getting worse. Won't do much more than a very easy acceleration. It idles fine. Attempt at driving to work this morning failed.

Limped it home, put the fuel pressure gauge on it and....pressure is rock solid even when the engine breaks up. So it isn't anything fuel pressure related.

I am actually thinking ignition by the way it behaves. I think I will start with a cap/rotor (was done 2 years ago with the plugs). Could also be coil or ICM. It's something that affects the whole engine, not just one cylinder. And it is very load-dependent. I think I heard a backfire pop which I admit would normally indicate lean. But it really won't be lean unless one of the injectors was intermittent. But the fuel trims don't indicate that.

[kevm14]

I started the Caprice last night to continue diagnosis. It seemed fine. Revved cleanly. Then I got a spray bottle and soaked the coil and distributor. It still idled fine but upon revving it was starting to do that breakup thing. So, I think I do have some kind of ignition/moisture issue. It was particularly foggy/humid yesterday morning when I tried to take it to work, also.

I have a new cap and rotor that I'll try to put on soon, though the cap isn't really sealed so I don't see why that would fix anything. I may need to do a coil. At least I think I am zoning in on the problem.

[kevm14]

Finally got around to doing the cap and rotor. The dist hold down bolts use a tiny 7/32" socket (or Philips).

Anyway, here are the old parts, for show and tell:

Looks a little gunky for how few miles were on them.

I sprayed water at the coil and nothing happened. Went for a test drive, and it drives well (best throttle response of my entire fleet, that's for sure).

Now I just need a very foggy morning to know for sure.

In the mean time, I need to get it inspected and the new tires mounted. So that will happen Saturday.

[Adam]

How few miles were on them? That's got a lot of gunk.

[kevm14]

Probably around 15k.

[kevm14]

Pulled some Gs going around an exit ramp and the symptom seemed to return, at least while I was cornering. Still need to have the gauge on it when this happens so I can rule in/out fuel delivery.

This happened yesterday. I actually got it to completely die. As if I shut the ignition off while driving. Then it came back. Let's recap:

1) Plug wire(s) shorting on steering shaft, causing intermittent misfires. Symptoms presented mainly when hitting bumps. [fixed, new wires, loom, hasn't returned]
2) Seemingly moist weather causing a more severe loss of power, liked to present when trying to merge into busy traffic. [fixed, new cap/rotor, hasn't returned but hasn't been very long, either]
3) Total engine power loss during G loads. Maybe related to #2, or not. This isn't totally new as you can see from the quote. May be one of those classic harness issues that I've had before. Going to be tough to track down. Will have to wait for it to get worse. In the meantime, I really need the car to get through emissions.

Speaking of, they haven't called me back yet after telling me they couldn't run the car due to the entire system being down. The only good news is they said safety was fine. I should check the base timing after replacing the cap/rotor and also check the calibration to see if it's the same tune that I passed with 2 years ago (extra spark advance at 2500rpm free rev).

[kevm14]

I ran to Home Depot this evening and it was raining, so I thought it would be a good test.

No issues at all.

[kevm14]

I continue to drive in some wet conditions and I've had no issues. Haven't pulled enough Gs to repeat that other thing. It probably still does it.

[kevm14]

3) Total engine power loss during G loads. Maybe related to #2, or not. This isn't totally new as you can see from the quote. May be one of those classic harness issues that I've had before. Going to be tough to track down. Will have to wait for it to get worse. In the meantime, I really need the car to get through emissions.

As predicted, this one is rearing its ugly head again in a more serious way. Certain bumps are doing it. Pulling Gs to the right is doing it. It was bad enough this morning that AFTER I went around a corner quickly at about 65-70mph, it was dead to the throttle even after I straightened out for a few seconds. That's as bad as it's ever been.

At work I spent a few minutes in the parking lot to dig into this. A few weeks back, I did a very aggressive maneuver where I turned hard to the right and then to the left (pulling in a parking lot to turn around). I actually got the SES light. It was Code 34, MAP sensor low. Ah, that's something.

So when I opened the hood, I aimed immediately for the MAP sensor harness. Last year I had a problem where the old MAP sensor actually was failing and tapping on it caused the car to die. I tapped on it. No issues. I grabbed the harness and wiggled it. Oh man, bingo. Of course it runs under the windshield wiper motor, under some spark plug wires and behind the passenger side valve cover. Perhaps it is contacting something and getting burned or abraded. Either way, I know where I need to concentrate next time I get to this at home.

It wish I could duplicate results and see something on my scan tool, like MAP voltage going to zero (which would certainly cause the engine to die as it would be completely starved of fuel by the ECM). If I get that far, it will probably be easiest to just run new wires to the MAP sensor from the ECM, as per the usual routine for harness issues on this car (O2 sensor and TPS to name two).

I did reroute a plug wire that was actually touching the bare MAP harness thinking maybe there was interference but that didn't seem to help. Maybe if I zip tie the MAP harness in a certain direction, it will temporarily resolve the issue until I can look at it closely.

This just makes me want to LQ9 swap, as THAT would fix this issue.