89 S10 4.3 misfire

[SoCalSlaughter]

Hello all, recently my friend bought a 89 S10 with the 4.3 and 700r4 for $800. "Running" and driving. It has a decent misfire at idle, engine shakes abit. It has close to 180K miles. Engine starts fine, no ticking, no smoke out of the exhaust. Oil looks fine, cooling system is fine. No engine light. So far we have changed the O2, fuel filter, wires and plugs, coolant temp sensor, changed the dizzy (gear was worn and shaft had some play), replaced EGR valve, cap and rotor. Triple checked firing order. Base timing with with timing connector unplugged set at 0. When accelerating from a stop the mis is more present. Any ideas or direction would be appreciated! Thanks

[ProStreet68SB]

Have you checked the coil? I had a pretty gnarly miss at idle on my truck and it turned out to be a bad coil.

[Cali72K20]

Try rebuilding the TBI, the diaphragm in the fuel regulator leaks on these and clean out the IAC orifices. It is really easy, the hardest part is getting the diaphragm screwed down while holding the spring.

Here is the kit: https://www.autozone.com/fuel-delive...82053_821751_0

YouTube: https://www.youtube.com/results?sear....3+tbi+rebuild

[SoCalSlaughter]

I've taken the throttle body off and checked, its not ripped. Haven't replaced the coil on the truck. Last night we did a compression test. Cylinder 2 and 6 have 120 psi. Cylinder 5 had 150. Cylinder 1 and 3 had about 135. I think the engine is toast.

[SoCalSlaughter]

Took the MSD coil off my Suburban and tried it on the S10, no change.

[SoCalSlaughter]

Compression readings

Cyl 1 - 130 - Wet 140
Cyl 2 - 135 - Wet 155
Cyl 3 - 120 - Wet 130
Cyl 4 - 150 - Wet 160
Cyl 5 - 140 - Wet 150
Cyl 6 - 125 - Wet 130