2000 k 3500 runs bad when warm

Hi... I have a 2000 k 3500 that terrible when the engine is warmed up. The engine starts fine, runs good cold, no misfires detected, clean computer scan, no codes. I am thinking intake manfold gaskets. Any ideas.

Thanks
Mark

What mileage and what engine and tune up history?
Any blinking check engine light when running bad?
What is the engine vacuum reading atidle and at 2K RPM?
Did you put it on a engine capable scanner and read out all engine running data?
And check for past present and history and pending codes?

This thread is repeated in the C/K section...to which I replied the same way. They should be combined.

Hi... thanks for the response, the engine is a 5.7 ltr with 162,000 miles on it. There is no blinking check engine light, i have not checked engine vaccum at idle or 2000 rpm. I do believe they cheched for all codes past present and pending but i am not sure. the engine running data is as follows.

MAF in LBS 1.51
MAP in HG 8.9
IAT 37
IGN ADV 21.5
LT FTRM1(%) 0.0
ST FTRM1(%) -6.3t to -9.4
LT FTRM2(%) -1.6
ST FTRM2(%) -8.6 TO -10.2
FUEL SYS 1 OPEN
FUEL SYS 2 OPEN
O2S11(V) 0.160 TO 0.835
ST FTRM 11(%) -10.2 TO -11.7
O2S22(V) 0.490 TO 0.525
PTO STATUS DISEN

Thanks again for your help, the truck also started cutting in and out during acceleration like the ignition or fuel pump is cutting in and out.

Thanks again
Mark

Ya i didn't realize i had posted in the wrong spot. How do i combine them?

Thanks
Mark

Make sure fuel pressure is up to specs.
Always check on the road and after warmeed up good.
Check secandary ign . good
Plugs wires cap and rotor coil .
Good Hot blue spark to all plugs?
Ac delco plugs?

Watch the camshaft retard reading on scanner.
Watch fuel trims and tempt sensors.

Does it lope idle when warm?

The engine does lope when warm, it sputters shakes, when reved a bit in park its like its missing, stumbling. I will check through the ignition system plugs, wires rotor coil. I will also have a fuel pressure test performed in the next day or so and let you guys know what i find out.

Thanks again for all help i really do appreciate it.
Mark

The engine does lope when warm, ...

Loping idle is vacuum leak. 30 year old lawnmower, or a new car on the lot. If it sucks air where it ain't supposed to, it lopes.

Brick on pedal, block TB arm, anything to get a STEADY rpm (not necessarily no MIS-fire, you just want STEADY rpm) 1200rpms or so... Feed starting fluid spray, A LITTLE AT A TIME, EVERYWHERE. Rev increase is the leak.

In a tough spot to pinpoint? Light a book of matches, blow it out while the heads are burnin', and feed the smoke to the leak.

ok i'll check it for vaccum leaks, just checked fuel pressure its 56 psi through the rpm range i think this is in spec. i will also tune up the ignition system and let you guys know it turns out.

Thanks
Mark

i will also tune up the ignition system and let you guys know it turns out.


Maybe it's a better idea to do the free diagnostic tests, instead of spending money blindly.

Unless you're rich and got $$$ to waste, then feel free to send me some ...

I had one done and the guys didn't see anything out of the ordinary, maybe i should find another shop to do it or take it to the general, although i've been trying to avoid paying the price there. There where no vacuum leaks that i could detect and no misfires showed up on the scan but it can't hurt to tune it up it doesn't cost that much. If that doen't work i guess i'll have to take it to gm.

Mark

ok i'll check it for vaccum leaks, just checked fuel pressure its 56 psi through the rpm range i think this is in spec. i will also tune up the ignition system and let you guys know it turns out.

Thanks
Mark

Fuel pressure specs are 60/66.
What is the engine vacuum readings?

Fuel pump/pressure testing.
And always test after running a hr.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold and fuel pressure testing guide line.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

ok i'll check as much of this stuff as i can on my own in the next day or two and let you know what i find out. Just tried the truck again now its running like hell will still start but its impossible to drive. I can here it popping in the the tail pipe sounds like an ignition miss but it could be a fuel issue too.

Thanks
Mark