Suburban miss fires after going up a hill?

[elorenzo39]

I thank you very much for your advise. I try it out.

thanks,

[JoleneFraser]

Originally Posted by 99subhelp

I have a 99 chevy sub with the 5.7 and I had the seal replaced under the intake manifold and now it miss fires when I climb a hill and get to peak it will missfire badly. It will never do it when your climbing the hill or on flat ground but only when the engine has been enganged on the hill and then comes off of a little. It only happens at speeds over 50 MPH. I have replaced the plugs, wires, cap & rotor, and the fuel filter. The dealer wants to replace all these parts again and charge me 500 for it. I need some Ideas. I took it to another mechanic and he sees it misfire with the scope while driving but can't pinpoint it.

Thanks

Tony

I have a 99 chevy had the same problem one of the valves in the transmission was blocked have a transmission anaylisis done

[mmoss10]

Can someone explain how cam position sensor helps this condition? It's about the only part I haven't changed on my '99 Tahoe 5.7 to try to cure this poblem. I have done plugs, wires, EGR, Dist cap, rotor, Seafoam, cleaned mass airflow, still no cure.

[Rconce01]

guys same problem misfire codes and problem here. Car misfires heavily at idle lots of black smoke poor MPG. We replaced rotor, cap, wires, a lot of plugs, coil, coil module, inatake valve seals, crank position sensor, and still the same problem. Intake gasket has been replaced 5 times. We tried the GM OEM twice one the autozone one the advance auto parts one, even a home made one out of gasket material. The car will run fine upon the change of the intake gasket (it even clears codes automatically) but within 24 to 72 hrs it will end up in the same condition.

[jtmarten]

Originally Posted by Rconce01

guys same problem misfire codes and problem here. Car misfires heavily at idle lots of black smoke poor MPG. We replaced rotor, cap, wires, a lot of plugs, coil, coil module, inatake valve seals, crank position sensor, and still the same problem. Intake gasket has been replaced 5 times. We tried the GM OEM twice one the autozone one the advance auto parts one, even a home made one out of gasket material. The car will run fine upon the change of the intake gasket (it even clears codes automatically) but within 24 to 72 hrs it will end up in the same condition.

Dead thread. But, have you checked the O2 sensor(s) and the fuel pressure regulator?

[Rconce01]

Yes fuel pressure is good and 02 are good too. The problem obviously is the intake gasket when we replace it the problems goes away then it returns as the days go past. Why this happens beats me. Why do you say the thread is dead?

Originally Posted by jtmarten

Dead thread. But, have you checked the O2 sensor(s) and the fuel pressure regulator?

[elorenzo39]

I have fixed the problem. Thanks for the SeaFoam advise. I have poured Seafoam in my crankcase and fuel tank and fixed the problem overnight. I even passed my CA smog with flying colors. I highly recommend Seafoam to everyone who has been having the same problems with their Suburban.

Thanks again.

[J-Ri]

Originally Posted by Rconce01

Yes fuel pressure is good and 02 are good too. The problem obviously is the intake gasket when we replace it the problems goes away then it returns as the days go past. Why this happens beats me. Why do you say the thread is dead?

The thread was dead because it was over a month old. When a thread is dead, start a new one.

[LastOne]

The problem will come back. Sticking valve guides in the heads is most likely your problem. Seafoam will free it up for awhile but be ready for the return of the miss or as I call it the 1500-2000 RPM Shake

[maxwedge]

We discourage continuing a thread for more than 3 months, all the topics/possibilities have been thrashed over sufficiently at this point.

[bigjake99]

Hello all I just joined here, but have read the post's. I have a 99 suburban 5.7 also. I have this problem for over a year now I have allmost tried every from Seafoam to changeing the sensor's in my throttle body to new distributor. I will try the cam sensor this weekend ,hope it works also i use Royal purple oil in my truck .

[rbnkaty]

I think there is more than 1 issue being defined, so if I may allow me to provide insight on my similar issue and I appreciate the feedback.
1998 C2500 Auto 5.7
Unrelated, within the last 3000 miles I had replaced by the local Chevrolet dealer the starter, ignition control module, the fuel pump, spark plugs, dist. cap and rotor and all 4 brakes. I am aware I have a coolant loss and suspect the intake seal that uses approximately 1/2 gallon every 2 weeks. Here's the problem . . . recently while in overdrive driving up a slight uphill grade the truck begins to miss violently "until" I drop the transmission into 3rd gear, then all is well.
I've read others suspensions, "torque convertor, distributor gear, intake manifold gasket, crankshaft sensor, etc.", with no conclusion.
Somewhere there is a GM tech that is computer savvy that knows much more than many of us.
I personally suspect the torque convertor. Ford in the mid "90's had an auto transmission shudder as the trans would shift into overdrive. Dealers were selling trans' overhauls left & right, when all it took to fix it was a small bottle of Whale Oil prescribed by Ford to be a limited slip additive. One 3 oz. bottle . . . fixed. I seem to believe my truck with over 200-K miles may be experiencing a clutch issue in the torque convertor. Any GM transmission guy online?

[j cAT]

with the mileage I would say the pressure is dropping when in OD above 45 MPH. TCC is dropping out. the A/B valves and other parts will need inspection for wear.

also these transmissions now require a synthetic transmission fluid called DEXRON VI. this is a 2006 GM TSB concerning DEXRON III that turns to acid after 30K miles.

my guess with what you just stated you will have to find a repair shop to test out and take pressures and drive train DTC failures to narrow down what is worn. what is your fluid replacing schedule ? what type dexron do you use ?

[regghook]

I had same thing happening and was told it was the throttle body that the carbon needed to be cleaned. I watched a viedo to take it apart and clean it. Now I have small mis at start of take off then all is fine. Maybe I didn't clean it good enough.