2000 Tahoe misfire/backfire problem

[liljim]

Thats a vague description so heres a better one. Its a 2000 tahoe 5.3L with K&N cold air intake and Hypertech II programming thats both been done for about 4 years. The truck starting dying on cold startups about 2 months ago then progressed to dying hot or cold, meaning it wouldnt idle immediatly. You would have to hold the gas a little until it felt like idling on its own. My fuel consumption increased quite a bit and i kept having a rich fuel smell. I figured it was just time for a tune up so i put some new plugs and wires on with no success. Its still dying and today was much worse than its been being. It didnt want to idle today at startup for nothing in the world. If you gave it a little gas and held it, it would run all day.

Another new symptom actually falls back to the title. I think its a misfire but im told its a backfire. I think misfire due to the strong gas smell. Im told its a backfire and that chances are my fuel pump is going out.

Truth is i dont know what to call it which is why im here to begin with. I can tell you that it makes a faint "popping" in the exhaust when holding it anywhere from 1000rpm tp 2000 rpms

Another guy is trying to convince me the fuel pump is weak and im really struggling with that answer. Hopefully someone can come up with an alternate

[MT-2500]

Originally Posted by liljim

Thats a vague description so heres a better one. Its a 2000 tahoe 5.3L with K&N cold air intake and Hypertech II programming thats both been done for about 4 years. The truck starting dying on cold startups about 2 months ago then progressed to dying hot or cold, meaning it wouldnt idle immediatly. You would have to hold the gas a little until it felt like idling on its own. My fuel consumption increased quite a bit and i kept having a rich fuel smell. I figured it was just time for a tune up so i put some new plugs and wires on with no success. Its still dying and today was much worse than its been being. It didnt want to idle today at startup for nothing in the world. If you gave it a little gas and held it, it would run all day.

Another new symptom actually falls back to the title. I think its a misfire but im told its a backfire. I think misfire due to the strong gas smell. Im told its a backfire and that chances are my fuel pump is going out.

Truth is i dont know what to call it which is why im here to begin with. I can tell you that it makes a faint "popping" in the exhaust when holding it anywhere from 1000rpm tp 2000 rpms

Another guy is trying to convince me the fuel pump is weak and im really struggling with that answer. Hopefully someone can come up with an alternate

Fuel pump can be checked with a good fuel pressure test.

Back firing and miss fire can be crossed plug wire or bad dist cap and rotor.

Is the engine missing on any cylinders?
Good hot blue spark to all plugs?

[liljim]

No distributor, 8 coils. 1 coil over each cylinder with a 6" plug wire.

Yes i think one of them are missing but dont know which one, not getting any error codes and i havent manually checked each one as of yet. At least now i have a starting point.

[j cAT]

Originally Posted by liljim

No distributor, 8 coils. 1 coil over each cylinder with a 6" plug wire.

Yes i think one of them are missing but dont know which one, not getting any error codes and i havent manually checked each one as of yet. At least now i have a starting point.

the plug wires should be 500-700ohms....

you may very well have a intake manifold leak..or the fuel regulator is defective ,,,,internal diaphram has a hole in it causing fuel to get sucked into the intake,,,remove the regulator vac, line and inspect for fuel...

[lvnrel98]

I hav ea 2000 Tahoe 5.3 doing the same thing. It wasn't the coil packs. I replaced ALL of them and NOTHING changed. So I returned them. Getting ready to take it to the dealer.

[lvnrel98]

Originally Posted by liljim

Thats a vague description so heres a better one. Its a 2000 tahoe 5.3L with K&N cold air intake and Hypertech II programming thats both been done for about 4 years. The truck starting dying on cold startups about 2 months ago then progressed to dying hot or cold, meaning it wouldnt idle immediatly. You would have to hold the gas a little until it felt like idling on its own. My fuel consumption increased quite a bit and i kept having a rich fuel smell. I figured it was just time for a tune up so i put some new plugs and wires on with no success. Its still dying and today was much worse than its been being. It didnt want to idle today at startup for nothing in the world. If you gave it a little gas and held it, it would run all day.

Another new symptom actually falls back to the title. I think its a misfire but im told its a backfire. I think misfire due to the strong gas smell. Im told its a backfire and that chances are my fuel pump is going out.

Truth is i dont know what to call it which is why im here to begin with. I can tell you that it makes a faint "popping" in the exhaust when holding it anywhere from 1000rpm tp 2000 rpms

Another guy is trying to convince me the fuel pump is weak and im really struggling with that answer. Hopefully someone can come up with an alternate

Have you found out what is going on??? I'm having the same problem & I'm not that thrilled about going to the dealer over it.

[discnik]

Just a thought here, but have you checked your Mass Air Flow sensor. Since you have the Cold Air Intake oil can contaminate the sensor causing driveability concerns.

As stated just a thought.

[j cAT]

Originally Posted by lvnrel98

Have you found out what is going on??? I'm having the same problem & I'm not that thrilled about going to the dealer over it.

so have you opened the hood and inspect/test anything ?

[liljim]

Originally Posted by discnik

Just a thought here, but have you checked your Mass Air Flow sensor. Since you have the Cold Air Intake oil can contaminate the sensor causing driveability concerns.

As stated just a thought.

I did, sensor appeared clean and dry. Unplugged it with truck running and received error code as i should have. Plugged it back in and cleared it. Still running a little rough. Its just enough that if someone borrowed my truck they would never notice it but i been driving it 4 years, i know its off. The cranking is obvious but if reference to the miss. I havent had the chance to get anything else checked on it yet, personal issues jumped in the way as usual. You try to get one thing done and 100 other things fall apart, gotta love it.

[liljim]

ps, i can check plug wire ohms and vac line tomorrow myself. Will post results.

[caw333]

While your checking stuff give your alternator and battery a check. I know from past experiance that a weak alternator will cause a problem similar to yours. It cant hurt to put a mutimeter on your battery with the engine off and with the engine at idle. Bat should be around 12.5 mabe a little higher and while checking the alt with engine idleing it should be around 14.5 could also be a little higher or just a little bit lower but not much lower.

[liljim]

12.5 dead and 14.1 at idle. Wires showed to be 900 ohm average except for #1 which was over 1K for some reason. Odder than that i could unplug it and not notice a diff yet i could unplug any cyl and not see a diff. Miss was consistent all across.

Found no fuel in vac line

certainly 1k is too much resistance but is 900?

Sounds like i might have an exhaust leak right at collector flange too, tap coming from that area i think. I guess i have to crawl under there and find out

Havent had fuel pressure checked or had chance to change filter yet


i appreciate the responses, must explain that im slow at getting this done due to a ton of other things one including dental work . So, thanks for the help and sorry for the delays.

[liljim]

oh, havent pulled plugs and checked spark either but its on the list too

[liljim]

changed pressure regulator valve today on a whim, wasted $51 bucks.

Oh well, live and learn.

I was told to wait until nightfall and check to see if i have any spark jumping taking place. I guess thats next.

[j cAT]

Originally Posted by liljim

12.5 dead and 14.1 at idle. Wires showed to be 900 ohm average except for #1 which was over 1K for some reason. Odder than that i could unplug it and not notice a diff yet i could unplug any cyl and not see a diff. Miss was consistent all across.

Found no fuel in vac line

certainly 1k is too much resistance but is 900?

Sounds like i might have an exhaust leak right at collector flange too, tap coming from that area i think. I guess i have to crawl under there and find out

Havent had fuel pressure checked or had chance to change filter yet


i appreciate the responses, must explain that im slow at getting this done due to a ton of other things one including dental work . So, thanks for the help and sorry for the delays.

the plug wire resistance should be 500-650 ohms,,,900 plus is too high...
plugs should be replaced if 50,ooomi or at least checked for gap tip damage...

the fuel pressure must be above 53 psi ....60 psi is perfect and it holds pressure on shut down..

the exhaust manifold leak is common the bolts break..use a ratchet and tighten to 10 ft lbs to see if the head falls off...

all these items could cause your problem cost to check zero...