99 Silverado 4.3 stuttering/starting problems.

[mseriously]

The truck is giving me more and more problems as of late...I have codes P0102, P0300 and P0420 showing up. P0102 is MAF code. Installed new MAF. New air filter. Noticed that previous owner cut out the bottom of air box for more air flow??

P0300 is the random/multiple misfire. This is probably because of the rough starting. It's specifically harder to start when colder and more so when it's damp. I recently replaced the intake manifold gasket because it blew out on the rear side (common problem), new distributor, plugs and wires to boot. The misfiring/stuttering while driving has been a problem for the past few years, so it was before the gasket blew.

P0420 has to do with the catalytic converter and possible o2 sensors...all that I've read says to deal with other codes first...

Any ideas? I'm going insane chasing this one down...basically it will start real hard, no stuttering, just turns over for about 5-7 seconds then fires off. Once I have it driving it will stutter and putter through the first 3 gears...but once it warms up it stops, and if it's warmed up it will also start fine too.

ANY ideas?

[truckdude239]

Bad o2 sensers will cause a miss or your cats m,ay be stoped up

[mseriously]

Originally Posted by truckdude239

Bad o2 sensers will cause a miss or your cats m,ay be stoped up

Any way to clean the cats up? Or am I stuck buying new? O2 sensors I can replace I'm sure...probably not cost effective I'm sure.

[bighaas79]

Without actually testing the truck this is what i'm seein. You have a cat goin bad and is plugged up, which is probably causing your misfire and the maf code. I would venture a guess that you may have started on the wrong end. I would have checked the cat and o2's first, based on the fact that the other codes can be resultant codes of other problems. And again without bein able to do tests, I'd venture a bet that your maf sensor was probably ok too. And to answer your other question, no cleaning up of cats they need to be replaced if bad. A warning they aren't cheap, and i would recommend factory cats, but if you go with aftermarkets, make sure you are getting a quality one that will work for the vehicle. Some of the real cheap universal cats can cause you just as many problems as the junk originals.

Just reread your o.p. when you did the gaskets, did you set the timing with a scan tool? Out of spec cam retard from the distributer can also cause these issues. Would make sure of that first i guess then proceed with the checking of the cat and o2's.

[mseriously]

Originally Posted by bighaas79

Without actually testing the truck this is what i'm seein. You have a cat goin bad and is plugged up, which is probably causing your misfire and the maf code. I would venture a guess that you may have started on the wrong end. I would have checked the cat and o2's first, based on the fact that the other codes can be resultant codes of other problems. And again without bein able to do tests, I'd venture a bet that your maf sensor was probably ok too. And to answer your other question, no cleaning up of cats they need to be replaced if bad. A warning they aren't cheap, and i would recommend factory cats, but if you go with aftermarkets, make sure you are getting a quality one that will work for the vehicle. Some of the real cheap universal cats can cause you just as many problems as the junk originals.

Just reread your o.p. when you did the gaskets, did you set the timing with a scan tool? Out of spec cam retard from the distributer can also cause these issues. Would make sure of that first i guess then proceed with the checking of the cat and o2's.

As far as the distributor goes, I thought it could only go in one way...line up the marks and the computer sets it...perhaps I'm wrong? Might have to get that checked first then...have a mechanic friend who has scanner tool. I'll keep this thread updated. I've seen TONS of stuff out there about this particular problem.

[truckdude239]

Pull the 2 front sensors out and drive it and see if it make a difference

[mseriously]

Well, I pulled the plug on the MAF sensor out of curiosity and the truck fired right up. No hard starting. It didn't stutter either like it normally does when I drive it down the road, but it did shift harder...not even sure if this means anything...

[truckdude239]

sounds like you new maf is bad

[mseriously]

tried pulling maf again today and it stuttered this time. will be pulling the sensors and getting a hold of a scan tool soon...

[bighaas79]

Originally Posted by truckdude239

Pull the 2 front sensors out and drive it and see if it make a difference

Originally Posted by mseriously

Well, I pulled the plug on the MAF sensor out of curiosity and the truck fired right up. No hard starting. It didn't stutter either like it normally does when I drive it down the road, but it did shift harder...not even sure if this means anything...

This is not a good or reliable method of testing these components. Scan tool data and possibly some other testing is needed to correctly find the issue without throwing parts at it.

[mseriously]

Originally Posted by bighaas79

This is not a good or reliable method of testing these components. Scan tool data and possibly some other testing is needed to correctly find the issue without throwing parts at it.

Agreed. I'll drive myself friggin nuts otherwise. I figured the MAF was a long shot anyway...

[truckdude239]

Pull the 2 front sensors out and drive it and see if it make a difference I SAY THIS TO TEST IF THE CONVERTORS ARE STOPED UP

[bighaas79]

Originally Posted by truckdude239

Pull the 2 front sensors out and drive it and see if it make a difference I SAY THIS TO TEST IF THE CONVERTORS ARE STOPED UP

I got that. And not to say it might give you some evidence that the cats may be bad, but there are tests that would show without a doubt that they are bad so why mess with a test that may not give accurate results. Backpressure tests, scan tool data in graphing mode (if you have a high speed, quality scan tool), lab scope back probed into the signal wire of the o2 sensor, or a gas anylizer test, would all give you accurate results when you did the testing. And I understand that not everyone may have access to the needed equipment to do these tests, I was just trying to get across it may not give you a definite result.

[mseriously]

Small update. Have it at the shop. They've had it one full day and want to keep it over the weekend. They have 4 other GM vehicles with similar problems. This surprised and further perplexed me. The shop in question has a reputation for being one of the best and have always been there for my brother and other family...he told me he is actually in touch with GM techs on this one...

[mseriously]

Narrowed it down to the injectors...they did a leak down test, or that's how they seemed to explain it, between the fuel pressure regulator and then from there to the fuel pump/gas tank. Nothing was leaking through when the key was shut off, but from the fuel regulator to the injectors, the pressure dropped off almost immediately from the normal 55psi. It explains the hard starts and the possibility of my cats being ruined will all that pure gas barreling through on starts and sitting around...

So, new injectors, or he suggested this mixture he gets direct from GM to try and douche them out. It's heavy duty stuff and GM recommends only using it sparingly as it could cause some damage...haven't picked up the truck yet, but plan on running this stuff through a tank of gas and seeing what it does. He mentioned that this style of Fuel Injection sucks...

The MAF is another story. Code still shows, he thinks I should try another one possibly AC Delco brand as he's got a TON of stories where they are always the last thing you'd think is wrong...

[bighaas79]

If you are changing out the injectors makes sure they put in the updated version, that gets rid of the poppet and replaces them with a multec style.

[mseriously]

Originally Posted by bighaas79

If you are changing out the injectors makes sure they put in the updated version, that gets rid of the poppet and replaces them with a multec style.

Thanks for the tip...might be changing them out myself, I've already replaced the intake manifold gasket, so I'm not too nervous about changing them out...need to do a flow test on the exhaust. All of this crap could end up costing me upwards of 800 dollars when I'm done. Cats, injectors...and that's doing it all myself.

[truckdude239]

advance auto sells the updated injectors for under 300 dollars