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1999 vortec engine trouble

ZooMad75 said:
According to the service manual the pump runs off of the ecm-b fuse in the under hood fuse block. It's obviously not blowing or else it would not work after it quit.

My guess is you got a bad ground or high resistance on the ground side from the pump and it's drawing more current than the motor can handle and it's quitting.

Your new pump came with a new connector right? Make sure you didn't swap the grounds for the sender and the pump. The ECM would not like having that current come through on the signal ground. Kinda sounds like you did based on how the gauge behaves.

The schematic shows both wires are black (big help right) but the fuel pump ground is the larger of the two wires. Terminal locations on the original connector would be terminal c for the fuel pump ground and terminal d for the sender ground.
Click to expand...
It has gray, black, purple and black with white stripe.
They're all matched up on the new plug and wires.
I have done this 3 times now, the fuel gauge pegs and the engine doesn't start.
Unhook the battery for a few minutes and then the gauge works and the engine starts, runs for a few minutes then back to the same problem.
:doah:
 
imiceman44 said:
It has gray, black, purple and black with white stripe.
They're all matched up on the new plug and wires.
I have done this 3 times now, the fuel gauge pegs and the engine doesn't start.
Unhook the battery for a few minutes and then the gauge works and the engine starts, runs for a few minutes then back to the same problem.
:doah:
Click to expand...

I totally get where you are coming from. But it's got all the symptoms of the pump grounding through the ECM. If that pump has been replaced and they put a new connector on it, they could have spliced further up the harness. IF they did it wrong and you match the wires to that it's going to continue to do it. I just ran through a similar issue with my trainee tech at work this week on a 2001 S10 Blazer. Fuel gauge hadn't worked since a previous owner replaced the pump. I was pretty sure he had an open circuit on the purple wire for the sender. I had asked if the connector had been changed and he said it was different than the connector view in the manual, but couldn't find where it was spliced in. I was just glancing at it on the rack and started pulling back the conduit and found the splice he didn't see. It wasn't right. That mistake is an easy one to make (whoever did it prior to you).

I'm not doubting what you did in the least but the behavior of the engine stalling after 5 minutes is a big sign. The pump is pulling at least 10-15 amps on a 12v circuit. The sending unit is working on a 5v reference voltage with the ground coming right back to the ECM. That circuit inside the ECM is not capable of the current draw. The other thing that signals the ground is swapped is the fact that the gauge goes high before stalling. The way the sender works with the ECM is high voltage on the signal return (ground) is showing a full tank. Low voltage is a low tank. Now throw 12v on the signal return circuit (less with the voltage drop of the pump, but still higher than 5v) and the ECM is going to see that high voltage and show a full gauge reading up to the point the ECM shuts down and cuts power to everything.

I'd just go back to the connector at the pump and use an ohmmeter to check continuity to confirm the pin locations for the sender and the pump. You can confirm the ground circuits from there. You could run a new ground for the pump at that point as another option.
 
ZooMad75 said:
I totally get where you are coming from. But it's got all the symptoms of the pump grounding through the ECM. If that pump has been replaced and they put a new connector on it, they could have spliced further up the harness. IF they did it wrong and you match the wires to that it's going to continue to do it. I just ran through a similar issue with my trainee tech at work this week on a 2001 S10 Blazer. Fuel gauge hadn't worked since a previous owner replaced the pump. I was pretty sure he had an open circuit on the purple wire for the sender. I had asked if the connector had been changed and he said it was different than the connector view in the manual, but couldn't find where it was spliced in. I was just glancing at it on the rack and started pulling back the conduit and found the splice he didn't see. It wasn't right. That mistake is an easy one to make (whoever did it prior to you).

I'm not doubting what you did in the least but the behavior of the engine stalling after 5 minutes is a big sign. The pump is pulling at least 10-15 amps on a 12v circuit. The sending unit is working on a 5v reference voltage with the ground coming right back to the ECM. That circuit inside the ECM is not capable of the current draw. The other thing that signals the ground is swapped is the fact that the gauge goes high before stalling. The way the sender works with the ECM is high voltage on the signal return (ground) is showing a full tank. Low voltage is a low tank. Now throw 12v on the signal return circuit (less with the voltage drop of the pump, but still higher than 5v) and the ECM is going to see that high voltage and show a full gauge reading up to the point the ECM shuts down and cuts power to everything.

I'd just go back to the connector at the pump and use an ohmmeter to check continuity to confirm the pin locations for the sender and the pump. You can confirm the ground circuits from there. You could run a new ground for the pump at that point as another option.
Click to expand...
Never thought of that, I will be dropping the tank again tomorrow and I will uncover the wires a little further down.
Thanks for staying with me on this even when I seem like I am not listening.
I have been a little ahead of you until this so hopefully you have the cure, it's getting really frustrating and the guy who is getting it can't do his job( working on my projects) until it's running reliably
 
imiceman44 said:
Never thought of that, I will be dropping the tank again tomorrow and I will uncover the wires a little further down.
Thanks for staying with me on this even when I seem like I am not listening.
I have been a little ahead of you until this so hopefully you have the cure, it's getting really frustrating and the guy who is getting it can't do his job( working on my projects) until it's running reliably
Click to expand...

Dude I deal with this kind of fun daily. It's not uncommon to get so deep into an issue you can't see the forest for all the trees. My techs get stuck like that too. One thing I've learned over and over is never take what might have been done before as being done right to a vehicle. If you think someone has fixed the same thing we better check the work and make sure it's right. Or else you end up chasing your tail on a problem that won't be fixed until you un-phuckup someone else's mistake. This comes from customers that don't understand nor care what someone else did to it, we were the last ones to touch the car so it's our fault if it don't work right.

It's all good brother. I figured you might get the lightbulb moment after my last post.
 
ZooMad75 said:
Dude I deal with this kind of fun daily. It's not uncommon to get so deep into an issue you can't see the forest for all the trees. My techs get stuck like that too. One thing I've learned over and over is never take what might have been done before as being done right to a vehicle. If you think someone has fixed the same thing we better check the work and make sure it's right. Or else you end up chasing your tail on a problem that won't be fixed until you un-phuckup someone else's mistake. This comes from customers that don't understand nor care what someone else did to it, we were the last ones to touch the car so it's our fault if it don't work right.

It's all good brother. I figured you might get the lightbulb moment after my last post.
Click to expand...
Well nothing.
There's no wires messed up I took the tank down and pulled the pump out and checked the wires to make sure it was not a defective setup,it's happened before with my CAT engine harness brand new with crossed wires, all was where it should be.
Hooked it back up with the tank on the ground and the gauge is pegged.
I realize it's not the pump.
I have a suburban with the same engine so I grabbed the ecm and hooked it up.
It's running now, I'm going to see how long it'll run.
 
ZooMad75 said:
Good find. That's rare but we've seen ECM's fail too.
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So far it's working, it has SES flashing and security flashing but it runs.
The security goes away after a while and SES goes solid.
My obd2 scanner is not working, I have another one when I get home I can see what it is but if it's running at this point he can be mobile and I can get him to get things done.
 
So an update.
The ecm it came with worked for about 30 minutes then shut off, the only way to get it to run was to unplug the power and plug it back up.
Fuel gauge worked and it ran smooth.
The other ecm ran all the time but fuel gauge didn't work and their had a random miss and ran like crap.
Finally I opened up the case and aluminum corrosion was all over, so I cleaned it up as much as I could and flushed it with contact cleaner and it runs all the time now and it doesn't shut off.
I guess the aluminum oxide was shorting out when it got warm.
In the meantime I had a problem with bank 2 O2 sensor and replaced it.
Evap code got fixed with a new gas cap.
Now I have codes 171 and 174 condition clean on both banks.
This what it shows online .
I don't know where to start looking.

Screenshot_20200520-161508_Samsung Internet.jpg

Screenshot_20200520-161534_Samsung Internet.jpg
 
Resized_Resized_20200508_085615.jpeg Resized_Resized_20200508_090722.jpeg Those engines are prone to the spider injector fuel lines cracking or the FPR leaking. Easy enough check - hook up a fuel pressure gauge, make sure it hits at least 50 psi and stays for a few minutes. If pressure doesn't hold, you just did the fuel pump so likely it's the other end. Pull the plastic plenum off and see if there's any clean spots - fairly easy to spot. If you still have the poppet style "injectors" I would replace with the upgraded mpfi spider. Just ran through this on a friends truck and it runs MUCH better now.

Edit: Tried uploading pictures, will have to do at home.
 
Last edited:
Chevman88 said:
Those engines are prone to the spider injector fuel lines cracking or the FPR leaking. Easy enough check - hook up a fuel pressure gauge, make sure it hits at least 50 psi and stays for a few minutes. If pressure doesn't hold, you just did the fuel pump so likely it's the other end. Pull the plastic plenum off and see if there's any clean spots - fairly easy to spot. If you still have the poppet style "injectors" I would replace with the upgraded mpfi spider. Just ran through this on a friends truck and it runs MUCH better now.

Edit: Tried uploading pictures, will have to do at home.
Click to expand...
Assuming the test is with engine off ?
 
No it can be running. It should hold within 5psi that pressure for at least 1 mintue after shut down
 
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