Glad you found the source of the problem OP. At least most of it. Good detective work there. The remainder of your problem could be that all the injectors are slightly clogged, but clogged at a point beyond the screen, probably near the end, the pintle. If you don’t want to pop for all new ones, maybe there’s a method to clean them to the “good enough” state some body here knows, or posted on u-tube somewhere. You’d think a combination of soaking in a solvent and after they dry blown clean w/some compressed air could do a pretty good job. What else might work? hmmm … one of those water-pick gadgets, a water-jet spray might be able to force gunk you from the injector’s innards? Might need to power them up to their open state in brief bursts while doing this.
re: timing marks jumping around. I have one old truck, 45 years old, so I read up on articles on engines of that vintage. And it is a pretty common thing to hear there about a defective harmonic balancer causing this symptom. Seems unlikely in a 95 like yours, but anything’s possible.
Yeah, some of the HF stuff leaves a lot to be desired. I don’t know if the loaner tool compression testers are that great either but at least you aren’t out any money if it doesn’t work. You just take it back and tell them it was junk. I have come across some broken loaner tools myself.
While I have never used a loaner compression tester I have trashed several and all had check valves that failed. And now, looking back I wonder if a replacement check valve was available and cheap? But the internet has made some great improvements in the availability of seemingly insignificant parts to insignicifant devices.
Two things to consider, send your injectors out to be rebuilt/cleaned with ultrasound and check the wiring for the detonation sensor and the sensor itself.
I did a compression test today. Bought an Actron from the parts store, seems to work good. First time I did this but the engine was warm, all plugs out and throttle open. I didn’t test cylinder #3 because the steering shaft is in the way.
1-210
2-200
3-?
4-210
5-195
6-190
The Haynes manual doesn’t list compression specs for some reason, just says lower numbers should be within 70%. I’m assuming these numbers aren’t too bad?
I found out all the plugs the garage put in were not gapped right. They had the gap at like .028, they’re supposed to be .045. The plugs had some black soot on the base ring but nothing else.
Yes, those compression numbers look pretty good. Almost maybe a little higher than I’d expect. You must have got a very good used engine there. Installing a set of new and properly gapped plugs seems in order for the next step.
The other thing is I bought rebuilt injectors. They didn’t make much difference after I cleaned the old ones. I guess the old ones just had some debris but weren’t malfunctioning.
So the truck is running about 80-90% now. It lacks a slight bit of power and it occasionally idles slightly rough. It’s much better than when I picked it up from the garage though.
So what I got is a truck running okay with the timing advanced and it’s still showing a rich condition at idle on my scanner. It doesn’t have a terrible exhaust smell though. Should I just leave it like this and not worry about it?
Well that’s interesting you guys both think it’s high. I guess I should try taking off the cat. I did try wacking it with a hammer before and it doesn’t rattle. It’s an aftermarket cat about 10 years old.
I’ll look into the compression numbers more. This engine does burn about a quart of oil every 3k miles. It’s also very rusty, must have come from the northeast, I’m in NH. Not that that would affect the compression but it’s definitely used.
You mean by the fuel trim readings? I may have already mentioned this to you, but “rich” fuel trims don’t necessarily mean the engine is actually running rich. How rich or lean a modern electronic-injection engine runs depends for the most part only on the O2 sensor reading. The fuel trim values reported by the scanner is what the engine computer thinks the fuel injection rate (in pounds per hour) should be based on the maf/map/ect/tps sensors vs the rate it is actually injecting based on the o2 sensor. If one of those three sensors are faulty the computer will report a non-zero fuel trim. Or if an injector is faulty or not the proper one for the vehicle, same thing will happen. The computer calculates how much fuel is being injected based on its programmed “on”/“off” time and that the injectors are rated at a specific amount of fuel per hour delivery rate. So if the injectors are rated at 10 pounds per hour, and they are on 10% of the time, the computer calculates it is injecting 1 pound of gasoline per hour. But it doesn’t actually know that for certain. The o2 sensor is where the buck stops, b/c if the o2 sensor reading is correct and there are no air leaks the fuel mixture must be correct.
Compression has rarely been above 150psi when testing a cold Cevrolet V8 or V6 for me @db4690. And hot I don’t think I’ve ever seen pressure above 180. The only engine that I ever saw 210+ pressure on had a plugged cat.
I don’t see too much info on compression specs on the internet. Some people saying 140-180 is normal, some saying 200-210 is good. Someone else saying over 220 is too high. I guess I am on the higher end anyway. From what I read it could be from carbon build up on the pistons also. My temperature is always normal. I’ll try taking the o2 sensor off later.
Like I said, the MAF is a main input to the fuel trim. If the MAF is wacky, it’ll command too rich or too lean right down to the limits of what the computer can adjust for. I never had a bad injector in over a million miles, but had a few bad MAF sensors.
It doesn’t have a MAF sensor, just a MAP. I really don’t want to take all the plugs out again for another compression test without the o2 sensor. It’s not fun.
The other thing I’ve noticed is the new fuel pump makes a lot of noise. Like a loud high pitch buzzer. I can hear it yards away from the car. I looked up the part # 402-P3902 and it’s some generic chinese pump they sell online called Precise. They cost like $15. I would have never bought this, there’s several name brands readily available at parts stores. I’m sorry I’m all over the place with this.