Caprice mystery engine skip

[kevm14]

This has been happening for a month or two.

Basic symptoms:
Sometimes when the rear axle would hit a bump, the engine would skip. Sometimes it seemed like the torque converter would actually unlock. Initially I thought my foot was just moving around on the throttle over a bump, but I saw engine RPMs change more than once when the torque converter wasn't locked and I know my foot didn't move.

I was tightening my driver's side rear exhaust manifold bolt (again), when I noticed some plug wires touching my steering shaft. Not just touching but actually worn through the insulation. I zip tied the bundle which hopefully will get me by until I can replace the plug wires. I should consider split looming the individual wires. Or maybe just loom the whole bundle. Probably not enough room to loom both (too bulky).

The routing is, of course, non-stock because I am using LT1 exhaust manifolds.

I test drove the car and it did not do the skip even once. It also seems to drive a little better. Perhaps some spark energy was bleeding to ground and would occasionally short enough to cause a total misfire. I dunno.

Time will tell, because it usually happens on my commute.

[Fast_Ed]

Here's a question I shouldn't ask, but will: Is that 290000 mile fuel pump original?

Not a whole lot else in the back I'd think would cause a skip..

Any sort of crash sensor back there for the fuel pump?

[kevm14]

Here's a question I shouldn't ask, but will: Is that 290000 mile fuel pump original?

Gee, why don't you ask a little louder so my fuel pump can hear? Also, 291k now. 300k is a near-certainty (now why did I say THAT?).

The problem is instant and sharp enough that I'd not associate it with a momentary drop in fuel pressure. If I felt a power drop some moments after the bump, that would have triggered me to consider the pump, I think.

But actually, no, this is not the original pump. The original pump failed as I was driving home one weekend from WPI, so that long ago. I used an LT1 replacement and I think I replaced THAT one a couple years back (with a Napa replacement LT1 pump). TBI pump has no pressure headroom and the LT1 fuel pump can be throttled back adequately by my stock FPR so it works as a drop-in replacement for whatever slightly-higher-than-stock fuel needs my L05 may have.

Any sort of crash sensor back there for the fuel pump?

Nope. This is not a Ford!

Also, on my commute, the symptom did not appear even once. So I think that was it.

This was a nice simple fix, as usual, but I should caveat that: it goes in the ~85% of problems I've had with my Caprice that were related to my previously having "improved" something by changing the configuration from factory stock.

I should probably order plug wires so I at least have them on hand if something fails.

[Fast_Ed]

Gee, why don't you ask a little louder so my fuel pump can here? Also, 291k now. 300k is a near-certainty (now why did I say THAT?).

The problem is instant and sharp enough that I'd not associate it with a momentary drop in fuel pressure. If I felt a power drop some moments after the bump, that would have triggered me to consider the pump, I think.

This occurred to me as well.. But I still couldn't keep my mouth shut.

This was a nice simple fix, as usual, but I should caveat that: it goes in the ~85% of problems I've had with my Caprice that were related to my previously having "improved" something by changing the configuration from factory stock.

Every once in a while I think about how cool it would be to LS-swap the Roadmonster. I'm sure it would be reliable, most of the time, but other times there would be unexplained phenomena that I could troubleshoot forever. Then I realize that the car performs just fine as it is... Fixed.

Now, if it were a TBi car, different story....

[kevm14]

Yeah I mean a problem with a non-factory configuration basically has no official diagnostic procedure. You have an additional layer of complexity: is it something on the still-stock part of the car, a component/system that is part of the swapped part of the car, or just a general byproduct of having performed the swap at all?

My original fuel pump would have lasted longer, I'm sure, if I hadn't removed it, let it sit out of fuel for a while and then put it back in. It failed within a week of doing that. The reason I did that is because the LT1 pump I thought I was swapping in had been used in water (by me) to test it, and it locked up solid. So I had to drop the tank again to put the stock pump back in...this was back in the WPI days.

A related story: when I had to R&R my intake manifold many years ago due to snapping a thermostat housing stud in the intake, I bent the heater hose out of the way. The plastic coupler exploded a little while after, right when I got into the Jamestown side westbound after the Newport bridge. I thought my car was on fire.

Or my differential explosion, caused by snapping off the lock shaft retaining bolt in the carrier, putting the unbroken half back in, and driving the car for years. That bolt backed out and then the whole thing just let go.

Swapping the 94-96 9C1 brake booster caused my brakes to lock up, because the master cylinder piston was not returning fully (different actuation rod length on the 94-96 booster).

My oil pressure problem. I associate this with my exhaust conversion job, where I messed around with the oil cooler lines (lots of Teflon paste - may have gotten into the sump/engine). Or this was a coincidence (or just the first time I noticed).

How about the time I ruined my engine harness by drilling in the wrong place for my sub amp power cable?

I assume there are more things.

[kevm14]

Every once in a while I think about how cool it would be to LS-swap the Roadmonster. I'm sure it would be reliable, most of the time, but other times there would be unexplained phenomena that I could troubleshoot forever. Then I realize that the car performs just fine as it is... Fixed.

It would be reliable most of the time. What I learned over the years is just try to have a quality of workmanship that will stand the test of time. If it looks like it won't last, it probably won't. So you spend the extra time, as you are able. OR, you have conducted a free risk assessment by noting that "if I have a problem in this department, check this shoddy thing I did first."

[kevm14]

Just did the plug wires. Autozone no longer stocks the Bosch wires (on the shelf) and while Rockauto did carry them, I switched to Delphi to consolidate shipping locations. Build quality seems good and they are the standard 7mm.

I forgot to snap a pic of my solution for the rubbing but basically the difference this time around on the driver's side is large red split loom around the front 3 driver's side plug wires where it routes precariously close to the steering shaft and exhaust manifold.

I also added two aftermarket plug wire looms and zip tied those in a strategic fashion. I will try to get pics.

[kevm14]

My fanciest job yet.
Driver's side:

Passenger side:

[kevm14]

So now there's a new problem. And it's different than the one I just fixed. This one actually does feel like a fuel pump going out.

I went to merge in some traffic off the line, expecting a nice solid snap and instead I got some severe hesitation and missing. I limped the car to do the business I set out to do (get a trash permit) and then went home. But my tools are at the new house. Grr.

I put my fuel pressure gauge on the car and tried everything. I tried free revving and even some heavy/transient brake torqueing in the driveway to put a load on the engine. The fuel pressure was rock solid and no symptoms, either. Then I taped it to the windshield and drove around. Again, rock solid fuel pressure but also zero drivability symptoms.

So the fuel pressure gauge is in the trunk and when this gets more severe, I'll at least be able to rule in, or out, the fuel system.

If it IS fuel pressure, it could still be a clogged filter or an issue with the fuel pressure regulator. Could even be a wiring issue, or something screwed up with the sending unit plumbing. The latter all requires dropping the tank anyway.

This pump has been in the car for a few years now, but honestly not that long and certainly not enough miles to make me suspect it. I think it's a Napa/Carter replacement pump for an LT1 B-body.

[kevm14]

Found an e-mail from late June 2009 where I discuss my fuel pump failing. Pressure was dropping from 13 to 10 psi under load.

So about 6 years. I would be shocked if there was more than 50k on that pump.

Fuelly says I've averaged done a little over 27k since Feb 2011. So that's 7k miles per year. Which is less than 50k as I expected. That's below average for fuel pump life expectancy.