Chevy K1500 P0300 & P0100

I have a 97 Chevy K1500 and I am in a bind. I started to get a rough idle and I replaced the spark plugs, that didn't help, the check engine light would come on and off intermittenly. I then discovered I had a bad converter, I replaced that. I didn't have a rough idle but it was hard to start. I noticed that after a month the muffler was bad and replaced that but also the check engine light was staying on. I had them read the code and it was P0300 misfire. I replaced the cap, rotor, wires and coil. The rough idle got worse. I pulled all the plugs again and discovered cylinder #5 was wet and all the others were good. I removed it and replaced it. It was still the same problem. I drove it for a bit with injector cleaner and no change. I pulled #5 plug again and it was normal, a little on the rich side but you can tell it was firing, not wet. I took it back up to the shop to get a quote on having the injectors cleaned or any bad replaced. While up there we hooked it up again and it had the P0300 along with the P0100 code. I am stumped! Any suggestions?

Mike

First I'll give the codes then what you may want to check out.

P0100
Mass or Volume Air Flow Circuit Malfunction

P0300
Random/Multiple Cylinder Misfire Detected

If you are 100% sure that all cylinders are getting proper spark ( especially the one that was wet, #5, then that rules out spark plugs, wires, coil, distributor, rotor & cap ). It is a good idea to test this out to be certain.

Assuming spark is getting to the cylinders, then it sounds like a leaking fuel injector on #5 ( excess fuel in the exhaust may have caused converter & muffler to overheat & burn out? ). You should get that injector changed for sure. You may also want to do a compression test?

You're also getting a MAF error. So, you may also have to replace this. But first check for vacuum leaks from hoses & intake manifold ( one of the first things to always check ). Also, you can check electrical connections under the hood & make sure they are secure. Then, maybe try disconnecting MAF & see how engine runs or clean the MAF and see if that helps.

PS The MAF error might have been set because of excess fuel in #5. So, best to fix cylinder 5 first. Reset codes and check idle. If not ok then check vacuum leaks & MAF out.

http://www.obd-codes.com/trouble_codes/ ... nction.php

Trouble codes give very limited ( basic ) information. Without using obd2 interface to laptop or hooking up to mechanic computer - then it is tougher to diagnose.

aftermarket dist caps on those engines often still throw misfire codes. If you check your ful system you'll likely find you have a fuel pressure problem. maybe the regulator or a nozzle leaking pressure. or a bad pump. Intake gaskets should be checked for a vaccum leak. I'd check all that before throwing a MAf on it.

Ok, I cleaned the MAF and replaced the air filter. It runs a lot better but still has a rough idle at times and hard to start. The #5 plug doesn't come out wet anymore, its firing. So with a rough idle and a little sluggish at times you think it could still be a fuel pressure problem and or manifold gasket? Do you suggest getting the A/C Delco cap and rotor first? I am really trying to avoid getting into it that far, the truck has 155,000 on it and just don't feel like putting that much money into it, although it looks like it is only 5 years old or less. I am still getting the P0300,not getting P0100. Hmmmmm.

Mike

You can try an AC Delco cap & rotor. I'm not sure if it'll make a difference, but if Jeff thinks so, then a good idea to try it out.

I believe Jeff is on the right track. It sounds more of a fuel related problem ( fuel pump, injector(s), old fuel filter, etc.) or vacuum leak ( vacuum hoses, or intake gaskets ).

Hard to start & sluggish sounds like fuel problem ( or vacuum leak? ).

With your first post, cylinder #5 being wet, sounded like either leaking injector or no spark to #5. Then you changed plug & it was firing but on the rich side. Sounds like injector is leaking ( malfunctioning ). Still, you should check fuel pressure too to rule out the pump.

Did you use rubbing alcohol & Q-tip to clean the MAF?