My trailblazer has the 4.2 I6. It started missing bad last week, and the check engine light came on. I went and had it scanned. It came up with a misfire on cylinder 4, a code for the map sensor, and something with an open pump circuit. He didn't print the codes for me, but told me it was possible it was the fuel pump, fuel injector, map sensor, or spark plugs. I bought some injector cleaner, and was gonna run a tank of gas through it to see if it helped anything. I put the injector cleaner in, and filled the tank up. The problem went away as soon as I started the car after putting the gas in. The engine light even went off. It drove great. Well it drove great until I got to a 1/4 tank. It started doing the same thing. Missing real bad, and popped the same codes. I Just figured I would have to take it to a shop. So I stopped and put $20 dollars in gas in it. It put the gauge just over 3/4 tank, and again it immediately stopped missing, and the engine light went off again. I made a couple stops, and it would always run perfect after every stop and no engine light. Is there something that could be causing it to run crappy and pop those codes when it gets down to a 1/4 tank of gas or below?
NEED HELP 2002 chevy trailblazer 4.2 weird problem
- Thread starter deerslayer1985
- Start date
littleblazer
Member
- Jul 6, 2014
- 9,267
Well that to me would sound like fuel starvation... First things first, have you ever replaced the fuel filter? While unlikely, it could be enough of a restriction that it is leaning it out. If you bring it to a quarter tank and fill it up, how many gallons does it take? Also mileage and any other maintenance history would be nice for a starting point. 
It has 128,000 miles on it. I have never replaced the fuel filter. I don't know if the previous owner did or not. The previous owner did not have complete maintenance history on it. They said they have never had any issues with it, and showed where they changed the oil regularly. It takes around 10 gallons give or take a gallon usually when it is down to around 1/4 tank.
Is there a way you can see if it is the original fuel filter?
Is there a way you can see if it is the original fuel filter?
Last edited by a moderator:
littleblazer
Member
- Jul 6, 2014
- 9,267
If you look in the front of the tank where the filter is, if it's kinda cruddy looking it's probably original. You could also check the fuel pressure when it's doing it. If the pump is bad it could bleed off pressure when it's not submerged. IE sucking air. Either way, it wouldn't be bad to replace the filter.
ChrisinVictoria
Member
- Apr 26, 2014
- 53
Most common reason for a random misfire would be a plug or coil. #4 cylinder is the one that gets wet from cowl overflow. You need codes to properly diagnose, but I would pop off #4 coil and look for water. Given no history, I would put plugs in it.
Mooseman
Moderator
And switch #4 coil with another (I.e. #1) and if the problem goes to #1, it's bad.
Ziggy
Member
- Feb 8, 2015
- 207
It doesn't make sense to me that there would be a coil, plug, or injector issue if adding fuel to the tank restores proper operation. I would look at the fuel pump as the primary source of the issue, a hole in the pickup tube on the in-tank fuel pump maybe? The misfire code on #4 is probably a secondary issue. Possible that losing fuel pressure in the line is allowing a #4 injector to not fire properly. "never had a problem" spoken by a previous owner usually equals "didn't know I should have been maintaining that"...
I got the car about a year ago, and haven't had any problems with it misfiring or running bad until now. Its kinda ironic, but I got a letter in the mail today about a extended warranty for a fuel tank inlet check valve. I talked to a mechanic. He thinks thats what is causing my issue. Cause you can smell fuel after I fuel up, and he said it might be getting low fuel pressure from this...? I dunno, but its free to replace so I have an appointment to get it done. Hopefully this fixes it. I am still going to do a full tune-up too. Has anyone had a problem similar to that with it being that fuel inlet check valve?
littleblazer
Member
- Jul 6, 2014
- 9,267
I ended up changing the fuel filter today. The old one was rusted all the way around. It was a pain to get off. I don't know how long its been on there, but it looked old.....Then I changed the spark plugs. I started at the front of the car doing 1 at a time. The first was a little difficult because of the plastic wire shroud thing. Then I got to the 2nd, and 3rd, and they had some oil in the coil pack hole. All the rest were fine. I read about it being the valve cover gasket, and the o rings. Someone said to try and snug up the valve cover bolts very slightly. I did just a tad on them. They all felt loose in my opinion, but I didnt put too much on them. The spark plugs say AC 41-965 25319566. Are these the originals plugs that came in it? I switched to the acdelco iridiums. Hopefully this solves the problems. I still plan on a new air filter, cleaning the throttle body, and getting the fuel tank icv checked.
Mooseman
Moderator
I think those were originals. 41-103 Iridium are now the ones to use. A little oil in the plug wells is considered kind of normal. Just torque the bolts properly for the coil packs as the also snug up the valve cover gasket for the plug well.
UPDATE! I changed all the plugs, and fuel filter like I just told you. Well it started missing still. I got it scanned, and it said cylinder 4 misfire again. So I switched the coils from 4 and 3. It stopped missing after I started it back up. It is starting to miss on a pattern now.......It will miss for about 3 trips of starting and shutting off the car, and then drive fine not missing for the same time frame. I got it scanned 2 times in the last week. The first scan was right after I switched the coils. the cel was still on from before I switched them though. It said
C0267: Pump motor circuit open
P0105: MAP circuit
P0302: cylinder 4 misfire
Then I got it scanned after I waited for the cel to finally clear, and then come on again to have it scanned again. Then the only code it showed was a random misfire. Anybody got any ideas?
C0267: Pump motor circuit open
P0105: MAP circuit
P0302: cylinder 4 misfire
Then I got it scanned after I waited for the cel to finally clear, and then come on again to have it scanned again. Then the only code it showed was a random misfire. Anybody got any ideas?
Blckshdw
Moderator
Usually, after a few drive cycles, the PCM will determine which cylinder is misfiring, and change the code. Since you changed the suspect coil, in theory if it was bad, you should get a new code pointing to the cylinder with the relocated suspect coil (P0303). If that's the case, you'd want to replace that coil.
I was hoping it would just show cylinder 3 misfire so I would know it was the coil, but it confused me when it said random misfire. So your saying it could still be learning(basically) which cylinder is misfiring? It could take a few cycles of the cel coming on and going off before it says cylinder 3 misfire if it does? I hope thats the case. What about the other codes that showed the time before last when I got it scanned? Are those just codes that were triggered by the misfire or something? They were p0105 map citcuit, and c0267 pump motor circuit open.
Being as I have had it scanned probably 7-8 times and it showed cylinder 4 misfire every time, and now after switching the number 4 coil with the number 3 coil it is showing a random misfire would you guys think that probably points to the coil? I wanna get this thing fixed so bad. It is driving me nuts, but I hate to just start throwing money at it not knowing exactly what it is. lol
Blckshdw
Moderator
Give the PCM some time to figure out what changed and to report back to you. Hopefully it's just the coil got damaged from some water intrusion. If it still says cylinder #4, then more troubleshooting would be needed.Well, got the car scanned again........It showed cylinder 3 misfire. I was so pumped about that...That means its probably the coil. So gonna fix that. Another issue though....We've been smelling fuel when it was missing. Which I just thought it was because it was missing. My wife tells me thiere is an oily puddle under that gas tank yesterday morning. It was at the mall, so I told her it was probably already there. She told me just a few minutes ago she parked in a clean spot at a different store, and when she came out there was more oil under the tank, and it was dripping off the middle of the gas tank? I haven't seen it yet, but she said it is thick, and black like old oil, and smells like gas. What could cause this?
Sparky
Member
- Dec 4, 2011
- 12,927
Gas + road grime = gunky looking gas smelling funk maybe?
There was a notice that got mailed out to a lot of 02 owners about a possible check valve crack that they would replace if you were having a problem with it, up to 150k miles. Did you get that notice by chance? Maybe that is related.
Go ahead and replace that coil though, at least you tracked that down!
There was a notice that got mailed out to a lot of 02 owners about a possible check valve crack that they would replace if you were having a problem with it, up to 150k miles. Did you get that notice by chance? Maybe that is related.
Go ahead and replace that coil though, at least you tracked that down!
Thats kinda what I was thinking, and I did get that notice. I haven't seen it yet I'm just going on the wifes description. lol We had an appointment to get that extended warranty for the check valve crack, but she had something come up, and canceled it. So have to get another appointment. Thanks for all the help guys.
Update! I got the coil pack, and that fixed the misfire. I also finally got the car taken into the dealer. It was the technical service bulletin that was listed for it. They said it was the worst one they had seen as far as gas coming out......It has gotten very bad in the last couple weeks. I am losing between 50-100 miles per tank. So it is all setup to get fixed. Just waiting on them to get the parts from gm. They said it could take up to 2 months.......Oh well at least Everything is going be fixed. Thanks to everyone for the help!