If you want to satisfy your curiosity, you could remove a plug and borrow somebody’s inspection to check out the top of the piston(s)
But I wouldn’t advise spending any money investigating possible carbon buildup
As for the noisey fuel pump, that’s not a good sign. I will say one thing . . . it’s much harder dropping the tank on your Blazer, versus a full size Chevy truck. It all has to do with the way the tank is attached to the frame. If you wind up doing it, you’ll know what I mean
I took the o2 sensor off and just tested #1.
It read about 185, before it was 210.
This is with rest of the plugs still in and warm engine. Does this have any significance?
You’re doing a good job there narrowing down the problems one by one. If I had the above symptoms on my Corolla (similar vintage to your truck) I’d focus on
spark plugs
spark plug wires
dist cap or ignition rotor
engine air filter
valve clearances
pcv valve and associated hoses
exhaust restriction
I have an o-scope so I’d also use that to look at the ignition system waveforms, see if I noticed anything unusual there. That method gets to the bottom of ignition system problems quickly. You probably don’t have that equipment yourself, but another method, you could look at the engine running in total dark, see if you notice any sparks jumping around.
Thanks for the help George. No, I don’t have any fancy test equipment. I’m pretty sure it’s not plugs, wires, cap, pcv or hoses. Everything is fairly new. I’ve looked at it in the dark several times. I haven’t looked at valves or ruled out exhaust.
A compression drop from 210 to 185 seems quite a bit simply by partially bypassing the exhaust system with the O2 sensor hole. I wouldn’t have expected that much. On the other hand I’ve never done that experiment before, so not sure. You’d probably have to temporarily remove the cat and see if that cured any of the drivability problems.
Mechanics do a cat back pressure test to check for exhaust restriction. They plug an air pressure gauge in where you’ve removed the cat I think. If it reads over a certain psi, that indicates there’s an exhaust restriction. Googling might show exactly how it is done. A simple intake manifold vacuum test can show up exhaust restrictions too. Have you tried that? You should be seeing intake manifold vacuum at warm idle on the order of 17-22 inch of Hg. Anything less than 15 usually indicates a problem of some kind, possibly exhaust restriction.
Alright. Engine was warm both times, I just didn’t take all the plugs out the second time. I would think having the plugs in would raise the compression, so the 185 would be even lower with the plugs out. I’ll look into the exhaust more.
Okay, I made some progress. I feel really stupid but I’ve been doing the timing wrong the whole time. I’m totally color blind so the wire colors are meaningless, I’ve been disconnecting the right knock sensor wire instead of the ESC. They’re both single wires coming out of the looms on passenger side in engine compartment. The shop spliced the knock sensor wire when they put the engine in. I didn’t even know I had 2 knock sensors. Plus the knock sensor shows the exact same ESC code when it’s disconnected.
Anyway I figured this out and there is nothing wrong with the timing at all. Mark is solid at idle and it’s set to zero. So my only indication now is the negative fuel trim at idle. The injectors/regulator are not leaking. I do not smell rich exhaust.
Bought vacuum gauge and tested, shows steady 20 psi, no fluctuating needle at higher rpm. needle sharply drops to zero then goes back normal when hitting throttle repeatedly. I’m gathering this means the exhaust is not clogged.
Tested each plug wire with ohm meter while flexing, nothing abnormal. All I can think now is maybe the cheap fuel pump is to blame. If that was clogged or not enough pressure, wouldn’t I see a leaner condition? Unless it’s too high pressure, if that’s possible? I still don’t have a fuel pressure tester and there’s no test port on this. Or maybe I have a chafed wire somewhere in the primary ignition circuit.
lol … reminds me of the time I was trying to replace my Corolla’s radiator fan temp switch but without realizing it was actually replacing the cold start fuel injector coolant temp sensor instead. As you might imagine, I couldn’t get the radiator fan to ever work by replacing that part !!! Took me several trips to the parts store to straighten that one out.
Yes, the intake manifold vacuum measurement looks very good. I think you are right, exhaust restriction unlikely.
You’re still getting an iffy idle & a little loss of power on rapid accelerations? Besides the fuel pressure & fuel pump, of these – spark plugs, spark plug wires, dist cap, ignition rotor, engine air filter, valve clearances, pcv valve and associated hoses … what all have you eliminated?
Does this engine have the spider gadget in the fuel delivery path? If so that’s a commonly reported problem item here. @db4690 seems to have quite a bit of experience with it. Might make sense to just replace it.
If it has the spider type of fuel injection, this would be a very early version. These do have a fuel pressure test port, but it’s way in the back of the engine bay
But I believe this year also had tbi as an option, and afaik, that setup didn’t have a fuel pressure test port. To test pressure on those, you need to tee in with your gauge and adapters
When you think how crudely basic and practical the TBI system was and then consider the spider sytem you can recognize just how determined GM could be in there efforts to turn mediocre into abysmal.
It still has slightly rough idle and lack of power. It’s not sputtering or hesitating, just a general reduced power. I’ve eliminated everything you mentioned except valve clearances. I might just change the fuel pump anyway because this cheap one is too noisy and I don’t trust it. I’ll invest in a fuel gauge at some point. This is just plain TBI, no spider injectors.
Valve clearance wouldn’t explain a rough idle usually, but might explain lack of power if the valves are a little on the loose side. If one valve’s clearance was much different from the others it could explain a rough idle maybe.
My thinking however, given what you way, is you still got some problem with the fuel delivery system. After all replacing the injectors was the main reason you got it running as good as it is running, which is pretty good. You just want to go from pretty good to like new, which should be possible with the compression and vacuum readings you’ve got.
Do you still got those big negative fuel trim readings? If so, that’s a loose end, and whatever’s causing that could be the source of the remaining problems. Most likely causes for weird fuel trims are the map or maf sensor, engine coolant temp sensor, ambient temp sensor, ecm problems, or the scan tool you are using isn’t compatible with your ecm. For a 1995 I’m guessing it is the latter, and the fuel trim isn’t really an issue. A Chevy Dealership shop could presumably rule fuel trim out for certain. ECM compatibility problems seem unlikely b/c it ran fine after the engine install, for another 10k miles.
hmmm … at this point I’m guessing you are close to solving what’s left. It’s just a matter of what order to test stuff. I guess if I had that problem myself I’d focus on figuring out a way to have an o’scope test on the ignition system performed, and test the fuel pressure as the next steps. Given all the parts you’ve replace on the ignition system, I’d probably put the fuel pressure test as the higher priority.
Sorry to keep pestering with this but I did a fuel pressure test today. I tapped in right after the fuel filter on the supply line. Normal pressure is supposed to be 9-13 psi.
With just the key on it goes to 14 psi then sharply
drops to zero when the relay clicks off. It stays at zero whenever the pump isn’t running. I’ve read some models have a bleed off somewhere in the fuel system and this might be normal, I’m not sure though.
With the truck running I’m getting 15 psi, maybe a hair under 15. This seems a little high but again I’m not sure.
Right before I went to the mechanic I was trying to test fuel pressure with a filter adapter. The lines were all stuck on. I cracked the return line and I noticed today the supply line is a little twisted at the filter. The mechanic spliced the return line with a section of rubber hose. So I was thinking one of these defects in the lines might explain the rough idle, neg. fuel trim and the noisy fuel pump.
Just want to see what you guys think about the fuel pressure numbers before I go through replacing fuel lines and the pump.
