05 Tahoe no cats

[Dcolli9881]

Have a massive drop in mpg
Smoke from exhaust on start up
Goes away after you start to drive
Rough idle at start up stops after so long rough idle starts back when you go to park


Replaced 02 sensors 2/3 times before doing a cat delete cats were bad
Gas problem was before cats got deleted

Replaced fuel injectors
Coil packs
Spark plugs and wires

Long term fuel trim reading 25
Short term fuel trim reading 55

Any insight on what might be the problem

 

[Scottydoggs]

ltft reading 55 in what? never seen a device that reads over mid 20's. most will show a - aka neg if no - its pos.

when neg its adding fuel, when pos its taking fuel away via the pcm trying to make it right.

normal is -5 to 10 at idle.

 

[Dcolli9881]

ltft reading 55 in what? never seen a device that reads over mid 20's. most will show a - aka neg if no - its pos.

when neg its adding fuel, when pos its taking fuel away via the pcm trying to make it right.

normal is -5 to 10 at idle.

It’s a blue driver plug in that read it being at 55

 

[Scottydoggs]

will either way, its pig rich. like a injector is stuck open. that could have clogged the cats in the first place.

what injectors? lets hope you didnt get china clones that suck.

 

[Dcolli9881]

will either way, its pig rich. like a injector is stuck open. that could have clogged the cats in the first place.

what injectors? lets hope you didnt get china clones that suck.

Got some from a premium haven’t had a issues with ones I’ve used in previous cars

 

[Scottydoggs]

you could pull the plugs to see if one comes out wet with gas, or pull the rails off and leave the fuel line on and the injectors plugged in, turn key to run. they should all spray for a couple seconds then turn off. if one keeps spraying its stuck open.

 

[Fless]

Negative fuel trims means the ECM is taking away fuel -- the O2 sensors are reporting a rich mix in the exhaust and the ECU is trying to compensate.

Positive numbers (like yours, if I read that right) means the exhaust is lean and the ECM is adding fuel.

Does the fuel system go into closed loop? If the trims are extremely positive like this on both banks, suspect a large vacuum leak, or a mis-reporting mass airflow (MAF) sensor, or a leak between the MAF and throttle body, or exhaust leaks around or before the upstream O2 sensors. Other causes may be present, but with trims like that it's something relatively big or a combination of some of the above.

 

[Dcolli9881]

Negative fuel trims means the ECM is taking away fuel -- the O2 sensors are reporting a rich mix in the exhaust and the ECU is trying to compensate.

Positive numbers (like yours, if I read that right) means the exhaust is lean and the ECM is adding fuel.

Does the fuel system go into closed loop? If the trims are extremely positive like this on both banks, suspect a large vacuum leak, or a mis-reporting mass airflow (MAF) sensor, or a leak between the MAF and throttle body, or exhaust leaks around or before the upstream O2 sensors. Other causes may be present, but with trims like that it's something relatively big or a combination of some of the above.

Maf goes between .6/.-9

 

[Dcolli9881]

Negative fuel trims means the ECM is taking away fuel -- the O2 sensors are reporting a rich mix in the exhaust and the ECU is trying to compensate.

Positive numbers (like yours, if I read that right) means the exhaust is lean and the ECM is adding fuel.

Does the fuel system go into closed loop? If the trims are extremely positive like this on both banks, suspect a large vacuum leak, or a mis-reporting mass airflow (MAF) sensor, or a leak between the MAF and throttle body, or exhaust leaks around or before the upstream O2 sensors. Other causes may be present, but with trims like that it's something relatively big or a combination of some of the above.

This is at idle

 

[Fless]

All that gas that was being added probably caused the cats to go bad.

What color is your startup smoke? Blue or black? Probably blacker than my java...

If your scan dongle and app can read it, when it's warmed up and at idle speed, what is the MAF reporting in grams/sec? Has the MAF been cleaned recently? Is the intake tube intact from the MAF to the throttle body, with no leaks? All vacuum lines connected and in good condition?

Do a standard fuel pressure test (key on, engine off, turn the key to "on" but don't start the engine). Then what is the fuel pressure at idle speed?

 

[Dcolli9881]

All that gas that was being added probably caused the cats to go bad.

What color is your startup smoke? Blue or black? Probably blacker than my java...

If your scan dongle and app can read it, when it's warmed up and at idle speed, what is the MAF reporting in grams/sec? Has the MAF been cleaned recently? Is the intake tube intact from the MAF to the throttle body, with no leaks? All vacuum lines connected and in good condition?

Do a standard fuel pressure test (key on, engine off, turn the key to "on" but don't start the engine). Then what is the fuel pressure at idle speed?

Freeze frame say maf is 2.8lb A minute
Fuel test was good when I did fuel injectors and after a couple of days
Everything is connected to my knowledge
Maf has been cleaned and no known leaks any where planning on doing a smoke test when the kit gets here

Smoke is white
Only problem I’ve had with it is evap but it’s just been on fill up clicks off every few seconds but the lines are clogged with bbs from canister just gotta drop the tank and clean them (plan on replacing fuel pump and canister etc when I drop tank ) wouldn’t think this would effect mileage cause it hasn’t for about 7k

 

[ivin74]

Have a massive drop in mpg
Smoke from exhaust on start up
Goes away after you start to drive
Rough idle at start up stops after so long rough idle starts back when you go to park


Replaced 02 sensors 2/3 times before doing a cat delete cats were bad
Gas problem was before cats got deleted

Replaced fuel injectors
Coil packs
Spark plugs and wires

Long term fuel trim reading 25
Short term fuel trim reading 55

Any insight on what might be the problem

Did you use oem parts?

 

[Dcolli9881]

Everything but fuel injectors 2/3 fuel injectors were slightly black on the bottom thought that was the problem helped some but not allot

 

[Fless]

You should see if your app can be changed to read g/s, but if my conversion is correct the MAF appears to be a problem:

The MAF value -- in g/sec -- at hot idle should be close to what your engine displacement is. I assume that's a 5.3L engine, but the ECU thinks it's a 21L engine (!) based on the MAF, so that would 'need' more fuel.

Unplug the MAF for a test to see if it runs any better without it.

So I'd recommend to replace that MAF with a GM OE one, or a known good one, to see if the issue is alleviated. Re-read the MAF reporting value after that.

Hope you saved your OE injectors; they're probably much better than something bought online (if that's what happened).

 

[Dcolli9881]

Everything but fuel injectors fuel injectors were 2/3 injectors were slightly black on the bottom thought that was the problem helped some but not allot

Ivin

Did you use oem parts?

 

[Dcolli9881]

You should see if your app can be changed to read g/s, but if my conversion is correct the MAF appears to be a problem:

View attachment 449319

The MAF value -- in g/sec -- at hot idle should be close to what your engine displacement is. I assume that's a 5.3L engine, but the ECU thinks it's a 21L engine (!) based on the MAF, so that would 'need' more fuel.

Unplug the MAF for a test to see if it runs any better without it.

So I'd recommend to replace that MAF with a GM OE one, or a known good one, to see if the issue is alleviated. Re-read the MAF reporting value after that.

Hope you saved your OE injectors; they're probably much better than something bought online (if that's what happened).

Will be my next change i got some from a premium I’ve used them once before in a pinch and they never gave me trouble before on another vehicle

 

[Fless]

This is how your engine feels:

 

[Fless]

Backing up a bit, was the freeze frame data at idle? If not, we need to see what the MAF is reporting at hot idle.

 

[Dcolli9881]

Backing up a bit, was the freeze frame data at idle? If not, we need to see what the MAF is reporting at hot idle.

Yes it was

 

[Dcolli9881]

Will be my next change i got some from a premium I’ve used them once before in a pinch and they never gave me trouble before on another vehicle

Backing up a bit, was the freeze frame data at idle? If not, we need to see what the MAF is reporting at hot idle.

Changed maf sensor still getting the same readings