It runs fine when its cold. Eventually the engine starts cutting out at higher rpms (2500-3000), eventually getting worse (cutting out at increasingly lower rpms).
It used to take 50 miles of driving for this behavior to show up, now it’s about 20. It seems like it’s more inclined to start cutting out at lower rpms (2000) as well.
I haven’t been able to get it to sputter in park… unless what I think is the rev limiter is actually this behavior. I’m not sure what the rev limiter is set to though.
The plugs, wires, and fuel filter are all fairly new (~5000 miles). It has a new fuel pressure regulator.
The fuel pressure tested low (35 psi, should be 45 I think). So I replaced the fuel pump. I haven’t tested the pressure since, but this hasn’t solved the problem. Of course there’s others reasons the pressure might be low, but I think I should only be worried about problems that get worse as it gets hotter.
I’m going to replace the coil packs next, since that seems like it might fit. But I feel like I’m just guessing and throwing parts at the situation, which I don’t like.
Most likely either spark or fuel. Since it only occurs as the engine warms up, the common heat related items to consider are
fuel pump
coils
crank position sensor
exhaust heat affecting the wiring harness somewhere
I think what I’d do if I had that problem is hook up a fuel pressure gauge where I could watch it while I was driving. If it drops coincidentally with the symptom, you’d ID’s the problem as fuel related, which is a big clue.
When I said cut out, I meant sputter, not stall. It’ll continue to run normally if I keep the rpms low enough. So I think I would still see a spark once it started doing it.
Since I replaced the fuel pump, I’m disinclined to suspect it’s a fuel issue.
Is there a way to distinguish between ignition module, coils, and crank sensor problems? Or will I ultimately just have to replace them one by one?
A shop w/the scan tool specific to the vehicle (probably it is the GM scan tool) would be able to differentiate between those three possibilities. They could tell you what the problem is, then you could replace the part yourself if you like. If you want to try the diy’er approach, here’s where I would start
read out the diagnostic codes, both current and pending. post them here for opinions.
inspect the crank sensor, especially its connector. Gunk can build up in that area sometimes.
inspect the coils, any of them look like they’ve been baked?
Make sure the coils are properly attached to their mounting points, as the mount is also the heatsink.
for the IM, verify a good healthy whitish-blue spark at a spark plug during cranking. Beyond that it is difficult for a diy’er to test the IM without ignition testing shop equipment, something a diy’er usually doesn’t have. You might could connect a volt meter to the B+ power input to the IM, and monitor the volt meter as you drive the car and get a clue.
without checking the fuel pressure after the pump replacement, you are flying somewhat blind on the fuel issue. especially if an aftermarket fuel pump. I just recently installed an aftermarket starter motor that was bad right out of the box. And that wasn’t the first time such a thing had happened to me.
I think the lack of codes might suggest crankshaft position sensor. Also how long it needs to cool down before it starts acting normally again corresponds more to the thermal mass of the engine than the coils/ICM that are small and off to themselves.
On the other hand, I’m not sure why it wouldn’t cut out while revving it in park if it was the crankshaft position sensor.
Based on my limited understanding I don’t think the quality of the spark should vary with engine load, but maybe it suffers more from a lower quality spark if there’s a high load on the engine?
Regarding the fuel pump, I agree that there’s no guarantee that the new one is good. But it would seem like quite a coincidence for a new pump to be bad in this particular way.
I was thinking that the ignition components would behave the way regardless of engine load. But I guess it’s also true that it might be harder for the same voltage/amperage to flow through some conditions than others.
I won’t know for sure until I take a long trip, but I’m pretty sure replacing the coils solved the problem.
At least the test drive I did would have normally been enough to set it off lately, although it used to take longer.
I also noticed that the crankshaft position sensor wire was running pretty close to the exhaust header, and doesn’t have any protective cover. The insulation looks dark in that area (although it’s a bit hard to see).
I moved it over, although I think the coils were more likely the problem.
The only thing that seems visually off about the old coils is one of the plug wire terminals is discoloured.