fjdavid

I have a 1999 4WD Surburban with a 5.7L V8 and 130,000 miles. I purchased the vehicle late this summer and It was starting to run rough this fall so I replaced the cap, rotor, wires and spark plugs (all OEM brandparts from Autozone).3 months later I'm now having the same misfire/studder when I start the car. after running a few minutes it smooths out but you can feel the engine stumble/misfire at idle.

The codes it is throwing are as follows:
First:
P0304 cylinder misfire #4

Then if I keep driving a few times/days I get:
P0141 O2 sensor bank 1 sensor 2
P0161 O2 sensor bank 2 sensor 2

Sometimes I will get P0300 random/multiple cylinder misfire, If I reset the codes again the first one is almost always P0304

From what I can tell, the intake manifold gasket has been replaced. I have the Actron OBD II autoscanner so I can check codes as soon as they pop up. Any ideas on what to check so I don'tjust startpart swapping would be appreciated.

Thanks,
Frank

east302

What brand are the wires, cap and rotor? Some people have had problems with aftermarket parts and swear by AC Delco.

Otherwise, a fault fuel injector may be the cause or low compression.

I did see this online...it's quite a list so maybe a trip to the shop is in order so that you don't waste a lot on parts.

"A code P0300 may mean that one or more of the following has happened:
[ul][*]Faulty spark plugs or wires[*]Faulty coil (pack)[*]Faulty oxygen sensor(s)[*]Faulty fuel injector(s)[*]Burned exhaust valve[*]Faulty catalytic converter(s)[*]Stuck/blocked EGR valve / passages[*]Faulty camshaft position sensor[*]Defective computer [/ul]
Possible Solutions
If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open."

fjdavid

I replaced the cap, rotor, plugs and wires with OEM products and the truck still stumbles when cold and accelerating. once warm it is slightly noticable at idle, in gear and stopped. You can feel the engine stumble and vibrate slightly. I checked all the spark plugs and wire connections with no luck.

I haven't checked the coil packs yet and i'm not sure how to do that.

I'm concerned about the fuel delivery system. when I checked the truck cold this morning (25 degrees F this morning) the fuel pressure with engine off is 62 psi for 2-3 seconds then the pump shuts off and the pressure drops to 56psi, when I turn the engine on and running the pressure is 56psi. the specs say 60 - 68 psi but I don't know when it should be in that range. when the pump is running but the engine isn't, after the pump turns off or while running??

You said:
"Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open."

Wouldn't I be getting lean O2 sensor faults? I'm not.

Thanks,
Frank

tlarimer

I am having the same exact problem with the wifes suburban. I have to replace the plugs every 3000 miles, but the problem keeps coming back. We have 162K on the suburban now, but this has been happening since 115K. Dealer has no idea, have had it scanned every time CEL comes on, even replaced o2sensors and egr valve. Every 3K I pull the plugs and thet appear carbon/oil fouled and usually 2-3 are soaked in fuel.
I am subscribing to this thread to track your progress.

fjdavid

This weekend I did the injector cleaner and replaced the O2 sensors. I also talked to the NAPA guy and he suggested testing the idle air control valve. So I ended up replacing it as well. While the problem isn't fully resolved, it is running better. The Idle air control valve did smooth out the hesitation at idle but it still has some hesitation when the vehicle is cold. It hasn't thrown a code yet so I'm waiting for it to do that so I can determine what the next step will be.

Thanks
Frank

68poni

Hello:
If you just tune up your vehicle and still having problems look under your hood on your right side, Drivers side is an electric airpump for the emision system. This took the place of the old vaccum pumps. This supplies emison pressure in your system for smog. This unit might be out or the e-vap system could have a block in it. So check the pump with 12v and it should pump. Yes on the pump, look at the EGR with a vacuum guage and feel with your finger under the body if the plunger is coming up. Yes Clean the EGR sytem with throttle body cleaner and a round nylon bursh. You can get the brushs at Harbor Fright Tools. The throttle hes. is from the emisions not cycling through the engine. When you press on the throttle all vacuum is gone from the engine and the pump supplies the needed vacuum. Also if your at 105,000 miles have the cat and muffler look at to much back pressure can cause the samething, it kinda sound like you still have the factory exhaust on your vehicle. 68poni

fjdavid

I didn't look at those things yet, but I will. Thanks for the additional information. At least the truck is still drivable and I can do what I can as I get the information.

Yes, the exhaust looks like original. I purchased the truck this past summer and haven't had to replace the exhaust

Thanks all for your continued help
Frank

fjdavid

Everything that has been suggested is either replaced or appears to be in good working order.

I talked with someone this weekend that goes to Lincon Technical School for diesel Mechanics. He talked to his teacher who use to work at a Chevy dealership. He said that on 98 and 99 trucks with the 5.7 liter engines (like mine) they had a problem with the valve guides in the head wearing after 100,000 miles (mine has 130,000) which can cause the rough idle and studder under acceleration. I've replaced heads before, but at $300 each I don't want to and find out it wasn't the problem even thought he says he is 99% sure that is the problem. Has anyone else heard of this or had that problem and it fixed it?

It kinda sounds like it might be the issue. Once it warms up, the valve guides/valve stems could expand for a tighter fit and lessen the issue. but I'm skeptical

Frank

aeropatr82

If it is an injector there is a company called premium injector services. They remanufacture your injectors for $15 a piece. Alot cheaper than new ones. www.premiuminjectorservices.com

fjdavid

Very nice, but how do I check to confirm that I have a problem with one or all of the injectors?

Thanks,
Frank