5.3l After Start Up

ac0905 · January 19, 2009

On my 99 NBS, it acts like it's not going to make it. Quick, easy start everytime, fires right up. Then after a second or two it acts like its going to die, but it doesn't. Just chokes, bogs down a bit and then runs fine.

I have to let it warm for about 15-20 seconds every morning or anytime it sits for a while. If I don't let it warm up and try to go, I won't get any throttle response. I can push the gas and it bogs down. I'll push it to the floor, and nothing. It always stays running though.

Also, related or not, as I am cruising (45-55 mph) down the road and come up on a hill or something, the rpms go up and down slightly and won't down shift until I really give it some gas. Then it gears down and goes on with no problems.

The truck has 185k miles. I bought it with 100k on it 5 yrs ago. I have not had any problems out of it, so there has not been much done to it other than maintenance, tune up, brakes, etc.

Does anyone have any ideas?

J-man67 · January 19, 2009

Might want to try cleaning the throttle body and MAF. The throttle body can accumulate carbon. It can make the butterfly valve stick. Not sure if it will fix it, but worth a shot. Also, when is the last time you did some maintenance on it? Like plugs, wires, fuel filter, all that jazz?

Spurshot · January 19, 2009

The MAF may be a culprit as Justin said.

My 99 6.0L idles a bit rough since I put Bosch plat plugs in it. I've since read about the idle issues associated with the Bosch plugs. Probably go back to AC or Autolites. I had Autolites from about 50k miles until about 200k miles and was perfectly happy with them. I'm due for plug wires on the 99 also.

Your downshift scenario may be normal. Hard to diagnose by these posts. But they tend to leave these electronically controlled transmissions in higher gears until you really mash on it. The logic behind that kind of programming probably has to do with fuel economy or emissions. On the otherhand, my 99 6.0L 2500, drops down a gear at the drop of a hat.

I'd do the usual tuneup with plugs and add plugwires, fuel and air filters for this old a truck and remove the MAF sensor and check it out, clean as necessary and reinstall.

ac0905 · January 19, 2009

I cleaned the throttle body about 2 months ago, due to the gas pedal sticking. Took care of that.

I installed new plugs around 130k, 185k now. I don't have the traditional plug wires, as you probably know. It has a coil for each plug. I replaced the fuel filter probably 3 yrs ago. Do you think it may be time for these again? New air filter last year, which is a K&N that I clean regularly.

What's the best way to clean the MAF? I looked at it when I cleaned the TB, but it didn't "look" dirty. Maybe it doesn't.

I have also read, with these motors the intake manifold gasket breaks down and can leak. As the motor heats up, the gasket seals properly, and it doesn't leak. Any possible truth to this?

ColoradoSkiCountry · January 19, 2009

You should never start a cold engine and then drive off immediatly.

At minimum give it 30 seconds for the oil to circulate. Unless you don't plan on keeping your truck a long time.

J-man67 · January 19, 2009

I cleaned the throttle body about 2 months ago, due to the gas pedal sticking. Took care of that.

I installed new plugs around 130k, 185k now. I don't have the traditional plug wires, as you probably know. It has a coil for each plug. I replaced the fuel filter probably 3 yrs ago. Do you think it may be time for these again? New air filter last year, which is a K&N that I clean regularly.

What's the best way to clean the MAF? I looked at it when I cleaned the TB, but it didn't "look" dirty. Maybe it doesn't.

Hmm. I got nothing. I would try to clean the MAF and see what that does, then go from there. Just buy some MAF cleaner from your local auto store. Take it out, and use the cleaner. Its a spray can with a straw. Just aim and squirt. Its fast drying, but leave it out for about 10 mins, then re-install. I'd wear some disposable gloves or something. The cleaner is nasty crap.

ac0905 · January 19, 2009

You should never start a cold engine and then drive off immediatly.

At minimum give it 30 seconds for the oil to circulate. Unless you don't plan on keeping your truck a long time.

Yeaaaah. That's not how I roll.

185,000 miles without a problem....

ac0905 · January 19, 2009

I cleaned the throttle body about 2 months ago, due to the gas pedal sticking. Took care of that.

I installed new plugs around 130k, 185k now. I don't have the traditional plug wires, as you probably know. It has a coil for each plug. I replaced the fuel filter probably 3 yrs ago. Do you think it may be time for these again? New air filter last year, which is a K&N that I clean regularly.

What's the best way to clean the MAF? I looked at it when I cleaned the TB, but it didn't "look" dirty. Maybe it doesn't.

Hmm. I got nothing. I would try to clean the MAF and see what that does, then go from there. Just buy some MAF cleaner from your local auto store. Take it out, and use the cleaner. Its a spray can with a straw. Just aim and squirt. Its fast drying, but leave it out for about 10 mins, then re-install. I'd wear some disposable gloves or something. The cleaner is nasty crap.

Ha. Just aim and squirt, huh? Maybe I'll give that a try.

Smitty00Z71 · January 20, 2009

may not be getting enough fuel pressure.... I just had a similar problem with my 2002, just a worse... ended up being the fuel pump. I would get the PSI checked on the fuel pump

txab · January 20, 2009

You should never start a cold engine and then drive off immediatly.

At minimum give it 30 seconds for the oil to circulate. Unless you don't plan on keeping your truck a long time.

Yeaaaah. That's not how I roll.

185,000 miles without a problem....

Oh, maybe I misread your post I thought you had a problem. You posted here for a reason...... a problem!

Check:

Fuel filter

Fuel pump

Fuel pressure regulator

Intake manifold leaks

Maf