I’ve posted about this before. It’s a 1995 S10 4.3 TBI Vin Z engine. 237k miles. I had a used engine installed over a year ago and around 10k miles on it so far (engine supposedly had 100k miles on it). It ran good, burned a little oil but no noticeable problems. A month ago it started bogging down badly when stepping on the gas, it was idling fine though. I took it back to the shop that put the engine in.
They replaced the fuel pump, ignition module, ignition coil and the spark plugs for $800.00. They had it for over a week. Picked it up and it idles very rough and has reduced power. Exhaust chugs like a race car. I took it back, they had it over a week again and they said they can’t get it to run any better.
So I plugged in my scanner, it’s running very rich. The long term fuel trim is 108, which is the lowest it will go, the normal is supposed to be 128. The short term is around 110. The numbers jump up when hitting the throttle then fall back at idle. The fuel trims looked fairly normal before I took it to the shop.
I checked the timing with a light and it’s advanced quite a bit.I tried to set the base timing back to zero and it barely runs. The timing mark is jumping around also. I have the computer advance unplugged and it makes no difference, the mark jumps back and forth. I checked the rotor position with the crank mark aligned and it seems to be lined up with no. 1 plug. I ended up advancing the timing back to where they put it.
I took the distributor out to check the gear and it doesn’t look worn. The distributor is about 2 years old, cap and wires are 1 year old. So what causes timing to be off this much and jump around like this? I’m thinking timing chain or distributor might be faulty or off a tooth in the gear? Can this be bad valves or low compression? The mechanic had practically zero communication with me. They said they ran diagnostics but I have no idea what that entailed. They pretty much just wanted my truck gone and don’t come back.