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Code P0302 #6 Misfire. Need Help! Changed Plugs and Coil.

22K views 39 replies 13 participants last post by  WOOLUF1952 
#1 ·
Car just started running really Rough when I was driving it. (2002 Trailblazer 140,000 miles)

I changed all the plugs first (they were still the factory plugs) Then still had the same code. It said cyl. #6 missfire. I then changed the cold for that cyl.

Still get same code and it still runs like crap.

Anyhelp??????

Thanks so much!
 
#9 ·
Make sure that you're changing the coil for the right cylinder. a lot of people get the #1 and #6 cylinder's confused. if its still misfiring and shooting codes, then yea, it's most likely the fuel injector. i'm not really sure how to change that since i haven't done it before. but as a tip. every now and then run a bottle of techron. makes a BIG difference.
 
#12 ·
What I would do, disconnect the neg terminal for the battery (some 30 min), change coils 5 for 6 and 1 for 2, and take it for a drive.

See if any thing changes and if the code comes back be sure to confirm which cylinder is.

Because P0302 is for #2

keep us posted.
 
#16 ·
The only thing I can think of is that you have a broken connection in the wire harness to coil #6, I know you should have negative, pulse signal and positive.

I had the same thing happened to my IAT wire harness, one of the wires broke inside(copper).
 
#17 ·
Hope this helps you from Chilton Manual:

Check for battery voltage to the ignition coils from the ignition switch. Attach a 12 volt test light to the battery negative (-) terminal or other good ground. Disconnect the electrical connector from one of the ignition coils and check for power at the pink wire terminal. Battery voltage should be available with the ignition key on. if there is no battery voltage present, check the wiring and/or circuit between the under hood electrical center and ignition coil connector (don't forget to check the fuses). Also check the black wire terminal for continuity to the battery ground. If there is battery voltage at the coil, but there is no spark from the coil, the coil, crankshaft position sensor, PCM or wiring are likely culprits.

Check for a trigger signal from the PCM. Attach the lead of a test light to the positive battery terminal and touch the probe of the test light to the ignition control circuit terminal (it's the center terminal in the connector). Crank the engine. The test light should blink with the engine cranking if a trigger signal is present. Check each coil, if necessary. If a trigger signal is present at the coil, the power and ground circuits are good and there is no spark, replace the ignition coil. If a trigger signal is not present, check the crankshaft position sensor. If good, check the circuits from the coil to the PCM. If circuits are good have the PCM checked by a dealer or qualified shop.
 
#23 ·
It is possible that the fuel injector caused the code. You can buy the automotive stethoscopes and put it on the fuel injector #6 to see if it is work proper. Maybe you can try take it to a local shop to use the emissions sniffer to see which it is running rich or lean. If it is running rich then it is the ignition problem. If it is running rich then it is the fuel injectors problem.
 
#27 ·
Well, I changed the injector and dont have that missfire code now.

But I have 2 more codes. PO300 and I believe PO1514 (Maf sensor code)

Car chugs when started and goes into limp mode (engine power reduced mode) and wont move more then 1mph.

Im hoping its a vaccuum leak, gonna check tonight.

I just did this all yesterday.

Im about to throw it off a bridge.

Joe
 
#28 · (Edited)
P0300-RANDOM/MULTIPLE CYLINDER MISFIRE DETECTED
P1514-AIR FLOW TO TP SENSOR CORRELATION HIGH

i'm guessing that since one injector is new, the PCM senses that the other injectors are not up to par with the new one. any other ideas???i
the way i check for vacuum leakes is take off the resonator, intake, and start the car with the throttle body exposed. then just put your hand over the throttle body (make a tight seal!!!) and wait for the car to stall. if it stalls, then no vacuum leaks. If it tries to stall but comes back up, then there's a vacuum leak somewhere.
 
#30 ·
I will try that now.

Well, over the weekend I ended up taking it apart 5 more times over about 20 hours. I could not get the intake manifold to seal properly for some reason. Then loosening it one time I broke off 2 bolts from the intake into the head. Talk about a PITA!!! Got them out and re-torqued the intake again.

Started it up and still ran like ****. Reached under the intake and felt gas coming out. Dont think it sealed again. Im going to put extra rtv sealant on it tomorrow night.

Also, took out all the injectors again and getting them rebuilt today. Going to put all new ones in and try to get that intake to set. I bought new bolts also.

Wish me luck. Im about done with this thing.
 
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