Express 1997 runs bad after warmup

[FVM]

Hi all: (I'll keep this short = my patience is near gone on this)

1997 Express V6 @115,000K. Pro-rebuilt trans @97K, I did R&R.
I'm #2 owner, PO did proper maintenance.
Regular gas (Non-Ethanol) in tank. (this stuff should be banned! and politicians heads examined )

Was out driving, then on a warm restart, it dies. It starts but dies quickly unless the throttle is feathered.
It's like fuel pump is bad but it's not. After cool down it runs fine until warm.
Checked for vac leaks. None in general visual and with (2 different) Carb-Cleaner trick, none.
Checked codes, replaced MAF & TPS but codes return. Rechecked old (were bad) and new parts good.
*** 1st time running on new parts, ran normal 20 minutes & no codes. Restart, codes returned. Retested MAF TPS still good.
Checked ECU wires for voltage and continuity, all good.
Possible borderline fuel pump pressure? While cold, drove in 1st gear at high RPM's, runs fine until warm. Eliminates pump & delivery system.

Anyone got ideas? Otherwise this is for sale $2200 (or trade for Wing, GL1500)
THANKS:
Floyd

[MT-2500]

Originally Posted by FVM

Hi all: (I'll keep this short = my patience is near gone on this)

1997 Express V6 @115,000K. Pro-rebuilt trans @97K, I did R&R.
I'm #2 owner, PO did proper maintenance.
Regular gas (Non-Ethanol) in tank. (this stuff should be banned! and politicians heads examined )

Was out driving, then on a warm restart, it dies. It starts but dies quickly unless the throttle is feathered.
It's like fuel pump is bad but it's not. After cool down it runs fine until warm.
Checked for vac leaks. None in general visual and with (2 different) Carb-Cleaner trick, none.
Checked codes, replaced MAF & TPS but codes return. Rechecked old (were bad) and new parts good.
*** 1st time running on new parts, ran normal 20 minutes & no codes. Restart, codes returned. Retested MAF TPS still good.
Checked ECU wires for voltage and continuity, all good.
Possible borderline fuel pump pressure? While cold, drove in 1st gear at high RPM's, runs fine until warm. Eliminates pump & delivery system.

Anyone got ideas? Otherwise this is for sale $2200 (or trade for Wing, GL1500)
THANKS:
Floyd

My idea is you need to do some proper testing.
Start with a full fuel pressure test.
Then work on codes.
The codes you have could and may give starting problems.
Codes do not say replace sensor but test and test untill you find out why it is setting codes.

And also confirm good hot blue spark to all plugs when no start.

You have answered your own questions.

Quotes from first post.

Possible borderline fuel pump pressure? While cold, drove in 1st gear at high RPM's, runs fine until warm. Eliminates pump & delivery system.

codes returned

runs fine until warm. Eliminates pump & delivery system.

End of quotes.

If you have codes.
What was the code no. ????
If you have codes you have problem with what the codes are telling you.
Get repair flow chart for the code and go all of the way threw it.

The only way to test fuel pump or eliminate fuel delivery problems.


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 95-105 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 or hot and fuel pressure testing guide lines.
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 95-105 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

[FVM]

It appears I didn't quite say this right, "Possible borderline fuel pump pressure? While cold, drove in 1st gear at high RPM's, runs fine until warm. Eliminates pump & delivery system."
I'll rephrase.
I thought it might be a possible borderline fuel pump pressure problem. As a common sense test I performed the following. While cold, drove in 1st gear at high RPM's as to place the highest fuel use demand on the system. It ran fine until it warmed up. That is why I said it eliminates pump & delivery system.
I'd love a miraculous first time answer but with all the (to me, disgusting) paraphernalia of sensors and computers etc., I know this isn't going to be a simple fix, but I can hope.

I did clear the codes after the MAF and TPS were replaced. Started it, no codes. Restarted it, still no codes. that is when I took it out on the high RPM test. Shut the vehicle off and restarted then the same MAF, TPS codes came back.
Also, I don't have tons of test equipment, THAT is ridiculously expensive. All I have is the U380 OBD 2 II reader/scanner and a digital multimeter.
I really feel sorry for modern day mechanics, vehicles should be simple to repair, not the money-monsters they've become.

For what tests I have performed, it can not be a fuel delevery problem.
I'm not here to disagree, just looking for a direction. I'm sure someone had a similar problem as mine.
Thanks!

[MT-2500]

Originally Posted by FVM

It appears I didn't quite say this right, "Possible borderline fuel pump pressure? While cold, drove in 1st gear at high RPM's, runs fine until warm. Eliminates pump & delivery system."
I'll rephrase.
I thought it might be a possible borderline fuel pump pressure problem. As a common sense test I performed the following. While cold, drove in 1st gear at high RPM's as to place the highest fuel use demand on the system. It ran fine until it warmed up. That is why I said it eliminates pump & delivery system.
I'd love a miraculous first time answer but with all the (to me, disgusting) paraphernalia of sensors and computers etc., I know this isn't going to be a simple fix, but I can hope.

I did clear the codes after the MAF and TPS were replaced. Started it, no codes. Restarted it, still no codes. that is when I took it out on the high RPM test. Shut the vehicle off and restarted then the same MAF, TPS codes came back.
Also, I don't have tons of test equipment, THAT is ridiculously expensive. All I have is the U380 OBD 2 II reader/scanner and a digital multimeter.
I really feel sorry for modern day mechanics, vehicles should be simple to repair, not the money-monsters they've become.

For what tests I have performed, it can not be a fuel delevery problem.
I'm not here to disagree, just looking for a direction. I'm sure someone had a similar problem as mine.
Thanks!

To get a direction to go for you need to run some proper testing.
Someones problems a usually different than yours.
And if you try to follow them you will wind up repacing some expensive parts that where not bad.

I would run the full fuel pressure test to elimate fuel pump.
If Maf an TPS codes come back after driving you will need to get a repair flow chart for them codes and go threw the repair flow chart.

[FVM]

I would like to thank those who DID NOT help me on THIS issue.

I found the issue... lack of solid contact at the temperature sender.
EVEN THOUGH I tested it's connection by hand it was not making full contact. That caused this vehicle to stall out after warmup.

Again THANKS for NOT HELPING!