2000 S10 4.3L Rough Idle PO304

I'm trying to figure out just what the heck is wrong with this truck...

It's a 4.3L with 169K on it. I've changed out the following (in hopes of getting it to stop idling so poorly and throwing the code)

- Replacement spider (fuel injectors/fuel pressure regulator... weren't new but vehicle is doing the same thing so I imagine it's not the injectors)

- Replacement spark plugs (delco), spark plug wires, new distributor, cap, and rotor.

- Replacement oxygen sensors

- Replacement TPS, IAC, MAP, MAF... (I have a perfectly good working 96 blazer with the same engine and am able to swap parts for testing purposes.)


The fuel pump is having issues (sending unit doesn't work and I have rough starts... in general I believe it's an issue but I don't think it would cause the engine to idle rough or cause cylinder 4 to misfire)

The catalytic converter is shot... needs a replacement but I do not want to replace it until I fix the other issue (don't want to ruin a new cat... unless it's clogged and could be causing the problem?)

I'm going to be putting in a new fuel pump however if that does not resolve the issue I might take it to the dealer...

Any ideas? I want to put the new MFI injectors into it however I'd rather not spend that kind of money on the upgrade kit if it didn't resolve the problem.

Thanks!

the #4 cylinder missfires so I would check the compression and see how the cylinders compare.

check plug color for determining how #4 is working.

coolant/excessive fuel/vacuum leak.

I forgot to mention that I had just replaced the water pump/radiator and whatnot so that's clear.

I took it to the dealership and unfortunately compression was low on #4 (they also said fuel pressure was low as well which I figured as the fuel pump isn't working as it should be.)

If I get fuel pressure to where it should be (will be changing out the fuel pump) do you think it'd help at all?

The dealer wanted around $1700 to tear the engine apart and fix it, $3600 for a used engine with 120K on it or $5500 for a reman engine.

I've found a replacement engine with 82K on it for $550 however I don't know how much it'd be to have a decent mechanic install it (I'd do so myself but I don't have a lift or a way to hoist the engine out.

Thanks

since your not working on vehicles when they get this old just buy a new or newer vehicle.


when the engine or transmission fails and your looking at more than a thousand to repair a vehicle worth a couple of thousand is not wise.


you may just need a new head or head gasket. possibly a bad valve or just a weak spring.

measure the fuel pressure . If it starts good pressure should be good. bad idle missfires are from the #4 low compression.