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97 Blazer 4.3. random misfire

OK.. 97 Blazer, 4.3, 2dr, 2wd, auto. 127k miles.

Following symptoms: Hard starting - must crank for 4-6 seconds, wait, crank agian, then it starts. Sometimes have to apply a bit of throgtle to get it to start. Rough idle, first 2-3 minutes of running. Gets better. But at idle even when temp gauge gets to normal, still rough.

"Soot" on the end of tailpipe.

P0300 multiple random misfires, occasionally SES light comes on for 1 driving cycle. Had it read at Autozone.

Recent things done: Was getting a misfire on cyl 5 & 6. "Injector Service", PCV Valve, fuel filter, spark plugs, distributor cap, rotor. 25000 miles ago new fuel pump - old one had gotten noisy and then stopped working. No noise at present time that I can detect.

Thoughts? Coil? Low fuel pressure?

It runs fine going down the freeway. The roughness is sitting at idle at a traffic light, or foot on brake waiting in line. If I put it in N it is somewhat better but still not idling smoothly.

Would like some idea before throwing more $ at it.

Reply to
Merlin
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Pull the air cleaner assembly off the engine intake and shine a flashlight down inside the plenum. It should be all sooty or layered with deposits. If you see any clean sections, you've got fuel washdown from a leak in the fuel delivery system. The ECU can't adjust for the fuel leak, and you get a rich mixture at idle. At highway speeds, there is more incoming air to mix with the excess fuel, so the problem does not seem as bad.

Solution? Find and repair the fuel leak. Get this fixed before it ruins your O2 sensors and catalytic converter (from all the unburned fuel).

Also, have you checked your EGR valve (as well as the IAC) for carbon deposits that clog the orfices?

Keep us posted on your findings!

Not Dead Yet

Reply to
NotDeadYet

Either the FPR or the CPI itself, make sure to get a "nut kit" when you replace them. (that is the kit with new fuel lines and seals that goes inside the plenum and feeds the CPI/FPR unit. Hope your sitting down when they hand you the bill....

Reply to
Steve W.

how many miles has it been since you put a new o2 sensor in? they're usually recommended at 30 to 50k miles so, a bad one could leave your computer thinking you're running too rich or lean & over-richening (or over leaning) - either too rich or lean will cause excess carbon deposits & hard starting, rough idle, etc -- so if what merlin suggested checks & you don't find anything, & it's been 30k or more miles since you've had a new o2 sensor, then i'd probably think about replacing it.

Reply to
superchuckles

Well, got the fuel pressure regulator replaced, and while expensive (labor, mostly).. wow. It now runs correctly. Starts easily. They chagned the oil also, as one poster noted should be done.

Merl>OK.. 97 Blazer, 4.3, 2dr, 2wd, auto. 127k miles.

Reply to
Merlin

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