Ok one I'm new to this fourm and to I've looked for help everywhere. I've got a 1996 s-10 blazer w/ 4.3l, the cel light is on and the truck has had a misfire for awhile and its was missing all the time, like a dead misfire. I've changed dist. Cap, rotor, plugs, wires, and put in a whole new spider injector. Now its seems to be fine when its cold and idleing but when its driven it starts missing again on that cylinder. I also check compression and its at 150 psi, there's no arching on the wires, and I've hooked up a vacume gauge to a main soruce and there's on fluttering of the gauge. I'm not sure where to go from here but any suggestions would be great, thanks.

 

Man I really wish someone had an answer to this problem! Because Im going threw the same sh$$ and its get Expencive Quick and Im loosing my mind

 

What have you checked?

 

I have a misfire p0306 cylinder #6 misfire. good compression. changed plugs, wires, cap & rotor. still misfires. found old fuel residue on plugs #1 & #5. I was told that if the fuel pressure regulator on the rear of the spider goes bad that excess fuel dumps into cylinder #1 or #5 or both... I forgot. I'm going to pull the spider to replace the pressure regulator and check the condition of the injectors. we'll see what happens....






***2000 ZR2 Blazer***

 

so the injectors and regulator appear to be in good condition. there was some fuel wash on the lower intake manifold on cylinders 6,1,5. maybe the pressure regulator is bad? cleaned what I could and sewed her back up but still p0306 and p0102. by the way I have a spare mass air flow sensor so I swapped them and still have the P0102 code, but I read in the Haynes manual that it can take up to 40 warm up cycles to clear this. I was just reading about camshaft retard and I'm going to play around with the position of the distributor tomorrow. I replaced my intake manifold gaskets about 7 months ago. she's ran perfect until last week when this dreaded p0306 and misfire started.

 

well I revisited my compression test results and found 90psi in cylinder 6. put a few drops of oil in and got 120psi. according to the Haynes manual my piston rings are blown. and thinking back to my last oil change I remember finding a small piece of metal on my plug. so is it possible that a piece of piston ring fell out of the bottom without destroying my cylinder???

 

P0306 and a P0102 together sounds like a vacuum leak... Yes it is possible for the ring to break and fall into the pan, but not likely. your wording suggests you fixed the P0306 with the plugs and wires. P0102 could have been fixed with the Mass Airflow and the computer just hasn't run the proper test yet. you may be sweating something that is fixed. if the two codes persist try doing a Full Compression test. don't forget WOT during cranking. i have done a short compression test in frustration before and forgot WOT and the results are usually a low reading. did you use the plastic gaskets or the updated steel Fel-Pro perma dry plus? i have seen the plastic gaskets fail in as little as 30 days. some mechanics use a 1-1/2" wizzer wheel to scrape gaskets and it can cause uneven surfaces that allow the plastic gaskets to crack. i block sand all intake surfaces with a 180 grit air board or good quality knife sharping stone. i paid $25 for mine. the harbor freight ones are crap
if you scan it and only have the p0102 left please understand the following...
Codes do not go out just because a part was changed. the computer must see the function of the part to be good. the computer must run the test for the code and it must pass 3+ consecutive ignition cycles before the light will go out. if it has a wire connector in the harness that does not have adequate tension on the terminal it may never go out. i replace alot of GM mass air flow pigtails. anything wrong under the hood and the mass airflow connecter is one of the first to be removed. Most library's have a subscription to all-data (our tax dollars at work for us) pull the code definition and what sets it. that will give you a better understanding of when it will go out.
clearing codes even with a scan tool resets ready-ness monitors then it requires all those monitors to run their respective tests with more drive time. a battery disconnect resets all monitors then requires even more drive time.

hope this helps
ASE Master-Tech Tranzman

 

Hers a link to a great site on how to test your mass airflow circuits.
requires a DVOM with a Hertz setting...

Part 1 -GM MAF Sensor Test (P0101, P0102, P0103). BAD MAF Symptoms.

keep us posted...
Tranzman

 

thanks for the feedback Tranz. my mass air problem went away since I cleared the codes. as for p0306...
my dry compression test results were 90psi first rotation and 120 with two rotations. my wet test had 120psi on the first rotation. both tests with the throttle wide open. I cleared the code then swapped spark plug wires with cylinder #4 and it came right back. I moved the distributor a little and got a p01351 but that went away after I cleared it. also I fired the injector into a bottle. right now I have 140psi of air on the cylinder via air compressor. no bubbles in the coolant. I cant hear anything either. I'm gonna go out and see if the pressure held. like I said earlier I found a piece of metel on my drain plug last oil change and it looked like a piece of piston ring to me. but the motor ran perfectly fine for a few weeks even after I found it. also if I have bad rings.. the cylinder should not hold air right? also shouldn't I have smoke from the exhaust? the exhaust smells a little sweet to me and has plenty of moisture. I know water is a byproduct of combustion... but how much? also as for the intake manifold gaskets I bought the edlebrock ones from advance auto parts. which is a composite gasket. no rubber or plastic.
I bought this blazer less than a year ago with 119k on it. one thing I have always noticed is that the motor warms up in like 5 minutes even in the dead of winter. my 97 blazer took about 15 minutes.

 

alright I just did another compression test because my air pressure from my air compressor was not moving. the motor is cold, I only did dry tests and the upper intake manifold is off. but I got 120psi on cylinder#6 and 90psi on cylinder#4 WTF? because the motor is cold I would expect to see a lower psi due to contraction. and now that I think about it my misfire only becomes apparent when the motor starts warming up.