2001 Tahoe 5.3 Runs Rough at times, At my ropes end!

[MrFleming007]

What the flashing CEL is usually telling you its that the system thinks that catalytic converter damage may occur if you keep driving. Misfires are a sure way to set this off. Here's my thought process. You say that the exhaust system is pretty much new, so I think we can rule that out. I also think we can rule out air delivery and vacuum leaks. Cleaning the MAF is a good maintenance item and might solve this, if not, you know its clean (I clean mine every other oil change). A vacuum leak would do this, but not at highway speeds when pressure in the intake would be near barometric pressure. Ecm getting hot and acting up? Maybe, but I would think that once it got hot it would do it all the time, the act normal when it was cooled down. It sounds like some misfires going on, which should set a P0300 code. With misfires, I would suspect the fuel delivery and ignition system. With new plugs and wires, I would just check to make sure they are seated correctly and not chaffed, then rule them out. This leaves coil packs. If you could narrow down misfires to certain cylinders, then you could take the coil packs for those cylinders and move them to a non mis-firing cylinder. If the problem follows, you've got a bad coil pack. If it doesn't, suspect ecm or fuel delivery.

To be honest, I cheaped out with my data reader. Since I already have an Android smart phone, I just got a cheap obd2 Bluetooth reader and bought Torque from the Android market. Data refreshes might be a little slower that a quality dedicated reader, but it does do everything that the quality readers do. For a total investment of around $40, its already paid for itself in diagnosing my fuel trims and p0171 and p0174 codes. Good luck!

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[Vinniety]

Everyone has great ideas and i would like to contribute a few more of mine. As we are talking about the Catalytic converter i would recommend to look at it when the problem happens and see if its RED or like someone said get a infrared temp and see what the temp is on the exhaust before and after the cat. The catch there is when that cat gets hot and is bad the truck will continue to ride bad it wont happen to ride bad then 2 minutes later run good.......unless the o2 sensor is getting the heat and going haywire. Also if the coil pack has a misfire you have to get a code. If you dont then the item which im thinking is the ecm is not working well and that why your not getting the code. You never know it might try to put you in safe mode i think that's what its called. Thats when you get a check engine light on and the ecm makes the vehicle run lean in the sense to get to a safe spot or to a mechanic. I remember reading something like that. Thats why when that check engine light is on you waste more gas. Anyway just more thinking keep this thread posted on what you find out and how it gets fixed!!

 

[Sprayed99]

If it were 1 bad coil, plug, or injector it would isolate that and give you a known misfire code by bank (side). A P0300 is a random misfire code and flashing CEL means that is requires immediate attention because it is a high risk for catastrophic failure. The flashing CEL only means that GM programmed the PCM to flash when it detects certain codes... the random misfire being one of them. I have dealt with this damn code many many times. Most times it is a wiring issue. I have seen the following.

Wires rubbing and shorting to cause injector failure
Ground wires corroded or loose
Battery voltage low (either battery or alternator)

The MAF should be cleaned just to rule it out and it is a cheap job.

---------- Post added at 10:06 AM ---------- Previous post was at 10:04 AM ----------

Thats why when that check engine light is on you waste more gas. QUOTE]

 

[MrFleming007]

Also, check for corroded/ loose engine grounds. I suppose its possible that the crankshaft position sensor is going out, but I doubt it, though I've heard of them cracking and doing all sorts of wierd stuff.

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[plsmith86]

Hey Yall,

Today I went to the parts store, and purchased some MAF cleaner, Throttle Cleaner, and for giggles a new air filter, along with a new EGR gasket. I pulled off my intake, and did find a kink in the rubber boot.. I doubt that would have anything to do with this, but I re-formed it and set it aside. Took off the MAF sensor, sprayed it down several times, and let it air dry. I took off the air box cover and removed my filter... it was not bad, but was dirty, so I put in the new one anyhow. I then took apart my EGR. After closer look, it did have some carbon, but I can not see any manufacture name on it anywhere, Usually GM has GM on it, AC/Delco, Delphi or Valeo. So, I am not sure if it is junk aftermarket but I did bench test it and the solenoid does work... Any way I douced it with TB cleaner, several times, scraped the old gasket off, and cleaned out as much carbon with Q-Tips as I could, and used a 20MM Hex driver and made sure the valve was seated and moving freely. I then sprayed down the TB, it was not dirty by any means and very little carbon came out of it, but everything was apart, so I figured I might as well do it. I let it all dry, put it back together. When I started the truck, it cranked over for a good 10 seconds, I stopped and did it again, when it kicked over, it ran rough for a few seconds and cleared right up. I suspect that it was doing some sort of calibration. I was able to get a friends scanner and pulled history - It had multipul misfire codes but nothing else. I do have a lazer thermometer and did check the exhaust, everything is fine there. I really hope I find some slack in my rope! I will keep every one posted and let them know how it runs. I sure hope this fixes it, the truck gets great fuel economy, and is in excelent condition. Thanks for all the input everyone!!

 

[Bedore]

I suspect when you first started it, it ran rough because it no doubt had a bunch of TB cleaner to digest. When I cleaned my TB my truck did the same thing. I wouldn't worry about that in particular since it eventually cleared up.

As for the rest of the issues, it's hard to tell. My truck ran great, but would occasionally flash the CEL. I ended up needing a crank relearn done at the dealer, and it was fixed. My brothers 03 GMC Sierra 1500 ran like you describe, and it finally got to the point that it was not drivable, but his ended up being plugged up cats. Wish I could help you more.

 

[plsmith86]

Well, I am not going to say its fixed, but knock on wood it has been running fine all week. I drove close to 400 miles this week and it has not given me any problems. I really dont know what else it could be, if this did not take care of the problem, but so far so good. I thought about the crank sensor, but I dont know of any 5.3's having any problems. I know on the 6.0 and 8.1 they would heat up and crack and do all sorts of weird crap. I suppose this is possible, but normally when they crack, the engine would just cut out all together with no warnings. While working for GM, I seen this at least a dozen times. But I never came across this problem that I am having which is why I was / am stumped. I have 22 chrysler techs working for me, and I have stumped every one of them as well! It's such a stupid problem and I knew it would be something easy, but the wild card is "something" Hope this one can be put to rest, Thanks Yall.

 

[shelyjo13]

help is here

it could be the fuel pressure regulater or the egr

 

[NavyVet1]

I have a cold air intake with a K&N oiled filter on it. would that cause problems with my throttle body? I also used a fuel system cleaner (Royal Purple) in my fuel tank. About a month later the problems started. I have replaced the MAF sensor, catalytic converters, spark plugs, plug wires, the computer and the o2 sensors. Which did not solve the idle or cutting out issues. Tomorrow, I am going to try cleaning out the throttle body (again) and replacing the idle air control valve, crank position sensor, & cam position sensor. Hopefully that does it!!! Any other suggestions would be welcome.

 

[JoeM5952]

Maybe TPS sensor?