I have a 4x4 1998 Chevy blazer that is having multiple cylinder misfire. The blazer has no trouble starting or stalling. When you start gaining speed you can feel the cylinders not firing with some pretty hard jerks.

I believe these misfires have been occurring intermittently over the last few years and some times gone away entirely. Back when this issue was still intermittent it seemed like cold and/or wet weather made the issue more noticeable.

Now the blazer is not driveable. I have had it with a mechanic for several weeks and he is at a loss on what is causing multiple cylinders to misfire.

He said cylinders 1,3,5 where consistently misfiring. He swapped the 02 censors to see if the other side of the engine misfired but it didn't.

The following has been done:

-crankshaft sensor replaced
-camshaft sensor
-checked fuel pump
-replaced spark plugs
-cleaned injectors
-checked some grounds

Our next step is to replace the computer. Does anyone have any suggestions? I'm not exactly sure what to do next.

 

i would check fuel pressure leak down first as it sounds like there could be a problem with the spider unit leaking. if that checks out ok than i would do a major tune up, plugs, wires, cap, rotor, and check for play in the dizzy. You could tell if the computer was shot, if said mechanic hooked a capable scanner up to the car and checked the value of the sensors.

 

Start with just looking at the distributor cap contacts and rotor. Not much sense in changing the plugs and not looking at the distributor cap. & rotor. Looking is free

 

P0300, (random cylinder misfire) is almost always caused by faults in secondary ignition: plugs, wires, cap, rotor and ignition coil. Low fuel pressure can also cause it but usually will have cold start problems also. 1996 & newer CSFI, (Central Sequential Fuel Injection) is very fussy when it comes to tune up parts, especially cap, rotor and plugs. Best to use AC Delco, and put a dab of silicone dielectric grease on each terminal of the cap, both inside and out. Fuel pressure: key on, engine off, fuel pump running; pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off.