99` Tahoe and the infamous CEL

[Weston Graham]

Hello everyone,
Getting down to the basics,
Idle: cold and hot runs perfect, couldnt be happier
Granny driving: Runs very well with no check engine light or stuttering
WOT and anytime after: Will steadily increase up until about 50mph where it will then start to lose power, then it will slowly increase. Watching the handheld scanner both fuel systems go into OL fault (open loop fault) and a Multiple Random Engine Misfire (note, when the light first came on, it was a cylinder 7 misfire but switched to this) will occur when trying to mash it going anywhere above 50mph. Produces more of a whine than the mighty 5.7L roar that typically comes with the mash. Ran seafoam through and it seemed to improve slightly, however now pulling codes with give a O2 Sensor Circuit Low voltage Bank 1 and Bank 2 sensor 1. Im not entirely sure if this is from the misfire or from seafoam or is actually the cause of all of it. MAF sensor reads about .3 lbs/sec when WOT. Fuel filter replaced, after which the fuel trim was at about -12% for all long term trims suggesting a rich condition.

Also, there is a coolant leak that cannot be found, steadily looses coolant. Possibly bad intake gasket.

This is a lot of information, trust me, I have a headache too. IF anyone can offer any ways of testing and possibly finding a solution at home that would be great, otherwise its going to be taken to the local shop.

Current possibilities:
Both O2 Sensors are bad
MAF is bad
Injectors are bad
Fuel pump is bad
Fuel pressure regulator is bad
Bad Intake gasket

 

[pro17]

Check compression?

 

[grampadirt]

How many miles on the Tahoe? Might be a candidate for a MPFI upgrade.

 

[Eveready]

Since you have replaced the fuel filter Murphy's law makes it likely to be the biggest pain in the ass...e.g. the fuel pump. Sounds like it isn't getting enough, a condition we can all sympathacize with.

 

[Weston Graham]

Check compression?

Dont have a gauge at home, clearly will need one with how many troubleshooting steps need it

How many miles on the Tahoe? Might be a candidate for a MPFI upgrade.

it's at 150k, about ready for the upgrade but it's also been garage kept it's entire life.

Since you have replaced the fuel filter Murphy's law makes it likely to be the biggest pain in the ass...e.g. the fuel pump. Sounds like it isn't getting enough, a condition we can all sympathacize with.

Ah, lucky for me it wasn't. I forget I post these threads on here and never check them.


Appreciate all the feedback and support. for anyone that does have this issue or similar check distributer. Took it to a local shop that has a scope and was able to determine that the distributor was worn to bits. At higher load it wasnt delivering a full spark and was "spark scattering". A replacement of rotor and cap solved the issue. If you do have a spark problem, get it fixed quickly. Fuel was dumped into the bank 1 cat and destroyed it. Time to do that.

 

[Lanny]

[QUOTE="

Appreciate all the feedback and support. for anyone that does have this issue or similar check distributer. Took it to a local shop that has a scope and was able to determine that the distributor was worn to bits. At higher load it wasnt delivering a full spark and was "spark scattering". A replacement of rotor and cap solved the issue. If you do have a spark problem, get it fixed quickly. Fuel was dumped into the bank 1 cat and destroyed it. Time to do that.[/QUOTE]

Dump the cats. Get some decent high flow ones or none at all. Not worth the money for stock ones if you ask me.

 

[Weston Graham]

[QUOTE="

Appreciate all the feedback and support. for anyone that does have this issue or similar check distributer. Took it to a local shop that has a scope and was able to determine that the distributor was worn to bits. At higher load it wasnt delivering a full spark and was "spark scattering". A replacement of rotor and cap solved the issue. If you do have a spark problem, get it fixed quickly. Fuel was dumped into the bank 1 cat and destroyed it. Time to do that.

Dump the cats. Get some decent high flow ones or none at all. Not worth the money for stock ones if you ask me.[/QUOTE]

Considered doing that, it's my mothers 4-door and she has a lead foot and enjoys the sound of a healthy V8. Also considered stripping my 96' 2 door of its cats and putting one on hers and then having a spare for hers. Not too worried atm, though the check engine light isnt exactly fun to always be seeing. Especially when you drive others around. What kind of effects will going catless have?

 

[Lanny]

Not really any with the stock exhaust. Might change the note a very small amount. But running no cats is healthier than running one that is plugged or 2 that are plugged. I need to replace both of mine and hopefully pull my mileage out of the single digits.

 

[kennythewelder]

Have you checked your fuel pressure ? Vortecs are very sensitive to fuel pressure. The fuel pump gets week in time, and doesn't deliver enough fuel pressure at WOT. It took me forever to figure mine out, the first time mine did it to me. Vortecs need over 60 PSI pre start, and in the 50s once they are started. You would think, that if the fuel pump is bad, that the truck would not run, but that is not the case. Here is the video I used to diagnose mine when it was failing. It is worth doing a fuel pressure test, to eliminate if you have a bad pump , or not. Also when mine was going out, I was getting some other codes too. I was so frustrated before I figured mine out that I was thinking about selling my truck. If it is your FP, then you only want to use an AC Delco, or a Delphi pump. Don't use anything else. I tried that too at one point. The other brands, dont put out the pressure that you need. I have had my truck sence 2002. I think I am on my 4th or 5th pump. If you don't have a fuel pump tester, you can rent one @ Auto Zone

 

[Weston Graham]

Have you checked your fuel pressure ? Vortecs are very sensitive to fuel pressure. The fuel pump gets week in time, and doesn't deliver enough FP at WOT. It took me forever to figure mine out, the first time mine did it to me. Vortecs need over 60 PSI pre start, and in the 50s once they are started. You would think, that if the fuel pump is bad, that the truck would not run, but that is not the case. Here is the video I used to diagnose mine when it was failing. It is worth doing a fuel pressure test, to eliminate if you have a bad pump , or not. Also when mine was going out, I was getting some other codes too. I was so frustrated before I figyred mine out that I was thing about selling my truck. If it is your FP, then you only want to use an AC Delco, or a Delphi pump. Don't use anything else. I tried that too at one point. The other brands, dont put out the pressure that you need. If you don't have a fuel pump tester, you can rent one @ Auto Zone

Appreciate the advice, turned out to be the rotor and cap on the distributer. Wasnt delivering spark under load