I have 1993 4.3 vin W that recently has started missing on a couple cylinders at around 1500-3000 rpm... I have cleaned the EGR, replaced the spark plugs, plug wires, distributor cap and rotor, ignition coil and now am at a loss... I do have both haynes and chiltons books.. but i figured i'd look to people who have possibly had this same issue

 

Suggestion #1. Put the Haynes & Chilton books back where they belong, on the shelf. Half of the information is wrong, the other half is missing If you want a shop manual, Ebay usually has used GM dealer issue shop manuals at a reasonable price.

Have you checked fuel pressure and leakdown at the service port and at the fuel filter outlet?

 

yes i have checked both and both were good, i'll look into the GM book thanks.

 

What were the pressures?

 

it hit 59 psi and after turning off the motor it held it somewhere in the time of about 5-10 seconds before it started to drop.

It is a vin W with that retarded first gen CPI but I put a brand new one in about 7 months ago. I know i also need an O2 censer but i wouldnt think this rig is new enough for the ecu to freak out and try to adjust the electrical timing...

 

Checking fuel pressure and leakdown at the service port tells you the LOWER of regulated pressure or fuel pump maximum output pressure. 59psi regulated is perfect for your CPI, but if that's all the pump can build, it's a big problem. Really need to check it at the fuel filter outlet, with all pressure and flow ending at the pressure tester.

To check base ignition timing, the EST wire must be disconnected. It is behind the top of the carpet by the passengers feet.

 

I checked the pressure at the fuel filter and it was 62... not sure why the pressure there vs at the intake is 3lbs different but i'll tackel that later... still trying to find that est wire

Edit: found the wire. the miss went away afterward but it wouldn't idle right so i hooked it back up but it is whats causing the miss...

 

"Deadhead" pressure at the fuel filter needs to be at least approx 20psi higher than regulated at the service port.

Did you check and adjust timing with the wire disconnected?

 

oh dang time for a new fuel pump. yes the mechanical timing is spot on, but the miss comes back when i hook the wire back up.

 

The outer ring on the vibration dampener likes to slip on these engines, which is where the timing marks are. If it slips, and you set timing according to the marks, ignition timing will be off, might want to check it