1994 M1123 won’t start. Please help!

[Coug]

I’m starting to think it’s the new lift pump is bad. I started it this morning and it only ran for a couple of minutes before it sputtered and died.

as long as there is no air in the system, the injection pump usually has enough suction to still run. It isn't until you try to put it under a load that the lift pump is an issue. Usually also if it dies because of the lift pump, it will NOT restart until the lift pump is replaced.

Open the fuel filter drain in the front wheel well.
Crank engine.
If fuel comes out, then everything is working up to the fuel filter, and the issue is likely in the injection pump.
If no fuel comes out and engine will not start/dies, then it's lift pump most likely, though possibly check valves or fuel pickup completely blocked.
Only other option I can think of is something floating in the tank/pickup tube area that gets sucked up and blocks fuel flow, but after it sits for a while it drops back down until the next time it's run.

 

[Mogman]

I’m starting to think it’s the new lift pump is bad. I started it this morning and it only ran for a couple of minutes before it sputtered and died.

If you did not pull the cover behind the fuel pump, grease the pump rod and then put it back together than you likely broke the pump rod when you reinstalled the pump, common newbie mistake

 

[MrLucky7137]

If you did not pull the cover behind the fuel pump, grease the pump rod and then put it back together than you likely broke the pump rod when you reinstalled the pump, common newbie mistake

If that was the case, would it be running at all?

 

[Mogman]

If that was the case, would it be running at all?

Yes, possibly, there is a charge pump in the IP that will try to pull fuel.
If you did not pull the plate and grease the pump rod there is a 99% chance you broke the pump rod, it slides down inside the area the pump bolts up to when you pull the pump, if you did not address that the rod is again very likely broken, it is almost impossible to push that rod back up into the block and hold it there while mounting the pump, the only practical solution is to pull that plate and grease the rod.
EDIT, it is fortunately an easy fix, pull the pump, pull the plate, remove BOTH halves of the broken rod and then reverse greasing the rod to hold it in place.
The 6.2/6.5L uses it own rod, not just any GM pump rod will work.

 

[royg]

Yes, possibly, there is a charge pump in the IP that will try to pull fuel.
If you did not pull the plate and grease the pump rod there is a 99% chance you broke the pump rod, it slides down inside the area the pump bolts up to when you pull the pump, if you did not address that the rod is again very likely broken, it is almost impossible to push that rod back up into the block and hold it there while mounting the pump, the only practical solution is to pull that plate and grease the rod.
EDIT, it is fortunately an easy fix, pull the pump, pull the plate, remove BOTH halves of the broken rod and then reverse greasing the rod to hold it in place.
The 6.2/6.5L uses it own rod, not just any GM pump rod will work.

Removing the plate and thoroughly greasing the rod does work well but there is another practical approach. The first time I changed a lift pump it took me hours and I used up a weeks worth of swear words. Several humvees latter I've learned :

-It makes all the difference where in rotation the engine is. If you rotate it so the pump rod can fully retract it makes the pump install much easier.
-It's possible to place a finger through the plate pushing the pump rod in and simultaneously manually rotate the engine a few degrees at a time by prying on the flex plate teeth by the starter. You can feel when the rotation allows the pump rod to fully retract and you're in the sweet spot.
-you can get some grease on a finger through the plate onto the rod. Not as effective as removing the plate/rod and fully greasing but it's enough to slow the rods descent and that's all you need.
-stuff a rag in to hold the pump rod fully retracted then go prepare the new pump with gasket held in pace with a thin skim of rtv
-position the pump like you're Indiana Jones preparing to swap the idol, pull the rag like you're Houdini , and start both bolts before the rod descends.

It works.

But if you've never done it, maybe you're better off removing the plate and spreading the grease well so the rod stays while you re-install the plate.

 

[Mogman]

Removing the plate and thoroughly greasing the rod does work well but there is another practical approach. The first time I changed a lift pump it took me hours and I used up a weeks worth of swear words. Several humvees latter I've learned :

-It makes all the difference where in rotation the engine is. If you rotate it so the pump rod can fully retract it makes the pump install much easier.
-It's possible to place a finger through the plate pushing the pump rod in and simultaneously manually rotate the engine a few degrees at a time by prying on the flex plate teeth by the starter. You can feel when the rotation allows the pump rod to fully retract and you're in the sweet spot.
-you can get some grease on a finger through the plate onto the rod. Not as effective as removing the plate/rod and fully greasing but it's enough to slow the rods descent and that's all you need.
-stuff a rag in to hold the pump rod fully retracted then go prepare the new pump with gasket held in pace with a thin skim of rtv
-position the pump like you're Indiana Jones preparing to swap the idol, pull the rag like you're Houdini , and start both bolts before the rod descends.

It works.

But if you've never done it, maybe you're better off removing the plate and spreading the grease well so the rod stays while you re-install the plate.

Seems like ALLOT of work to avoid removing 2 screws...

 

[MrLucky7137]

Removing the plate and thoroughly greasing the rod does work well but there is another practical approach. The first time I changed a lift pump it took me hours and I used up a weeks worth of swear words. Several humvees latter I've learned :

-It makes all the difference where in rotation the engine is. If you rotate it so the pump rod can fully retract it makes the pump install much easier.
-It's possible to place a finger through the plate pushing the pump rod in and simultaneously manually rotate the engine a few degrees at a time by prying on the flex plate teeth by the starter. You can feel when the rotation allows the pump rod to fully retract and you're in the sweet spot.
-you can get some grease on a finger through the plate onto the rod. Not as effective as removing the plate/rod and fully greasing but it's enough to slow the rods descent and that's all you need.
-stuff a rag in to hold the pump rod fully retracted then go prepare the new pump with gasket held in pace with a thin skim of rtv
-position the pump like you're Indiana Jones preparing to swap the idol, pull the rag like you're Houdini , and start both bolts before the rod descends.

It works.

But if you've never done it, maybe you're better off removing the plate and spreading the grease well so the rod stays while you re-install the plate.

Thank you that was very helpful.

 

[TNDRIVER]

Removing the plate and thoroughly greasing the rod does work well but there is another practical approach. The first time I changed a lift pump it took me hours and I used up a weeks worth of swear words. Several humvees latter I've learned :

-It makes all the difference where in rotation the engine is. If you rotate it so the pump rod can fully retract it makes the pump install much easier.
-It's possible to place a finger through the plate pushing the pump rod in and simultaneously manually rotate the engine a few degrees at a time by prying on the flex plate teeth by the starter. You can feel when the rotation allows the pump rod to fully retract and you're in the sweet spot.
-you can get some grease on a finger through the plate onto the rod. Not as effective as removing the plate/rod and fully greasing but it's enough to slow the rods descent and that's all you need.
-stuff a rag in to hold the pump rod fully retracted then go prepare the new pump with gasket held in pace with a thin skim of rtv
-position the pump like you're Indiana Jones preparing to swap the idol, pull the rag like you're Houdini , and start both bolts before the rod descends.

It works.

But if you've never done it, maybe you're better off removing the plate and spreading the grease well so the rod stays while you re-install the plate.

The thin cutting board sheet of plastic that you sneak out of your wife's kitchen cut into a narrow strip works better than a cloth. Rotate the engine with a large wrench at the back of the damper with your finger on the pump rod at the same time, easy to do. Rod up, plastic strip under it, slide in the pump, slide out the plastic strip. Just my 2 cents.

 

[MrLucky7137]

The thin cutting board sheet of plastic that you sneak out of your wife's kitchen cut into a narrow strip works better than a cloth. Rotate the engine with a large wrench at the back of the damper with your finger on the pump rod at the same time, easy to do. Rod up, plastic strip under it, slide in the pump, slide out the plastic strip. Just my 2 cents.

Thank you. That’s great advice.

 

[MrLucky7137]

Seems like ALLOT of work to avoid removing 2 screws...

I removed the pump and the rod and the pump arm or in great condition, and the pump seems to be working fine. I have fresh fuel. I replace the fuel filter.

 

[MrLucky7137]

Removing the plate and thoroughly greasing the rod does work well but there is another practical approach. The first time I changed a lift pump it took me hours and I used up a weeks worth of swear words. Several humvees latter I've learned :

-It makes all the difference where in rotation the engine is. If you rotate it so the pump rod can fully retract it makes the pump install much easier.
-It's possible to place a finger through the plate pushing the pump rod in and simultaneously manually rotate the engine a few degrees at a time by prying on the flex plate teeth by the starter. You can feel when the rotation allows the pump rod to fully retract and you're in the sweet spot.
-you can get some grease on a finger through the plate onto the rod. Not as effective as removing the plate/rod and fully greasing but it's enough to slow the rods descent and that's all you need.
-stuff a rag in to hold the pump rod fully retracted then go prepare the new pump with gasket held in pace with a thin skim of rtv
-position the pump like you're Indiana Jones preparing to swap the idol, pull the rag like you're Houdini , and start both bolts before the rod descends.

It works.

But if you've never done it, maybe you're better off removing the plate and spreading the grease well so the rod stays while you re-install the plate.

ok. I replace the pump and did it exactly the way you said removed the plate greased the rod everything went back together smooth and I am convinced the new pump is working just fine. But I cannot get this thing to run for more than a minute before it starts to surge and die every time.

 

[Mullaney]

ok. I replace the pump and did it exactly the way you said removed the plate greased the rod everything went back together smooth and I am convinced the new pump is working just fine. But I cannot get this thing to run for more than a minute before it starts to surge and die every time.

.
Make sure it works.

Disconnect the pressure side of the pump and add a length of rubber hose that reaches over the fender and onto the ground. Get a gallon jug (maybe a clear, clean milk jug) and turn the motor over. Did the pump put a gallon of fuel into the jug?

 

[Mogman]

ok. I replace the pump and did it exactly the way you said removed the plate greased the rod everything went back together smooth and I am convinced the new pump is working just fine. But I cannot get this thing to run for more than a minute before it starts to surge and die every time.

As Mullany said you need to confirm you are getting a good flow to the IP, you could still have issues with the check valves (I do not remember you saying if they were removed) the pickup sock in the fuel tank could be plugged, you could be sucking air before the lift pump.

A plugged return line can also cause these symptoms, you can pull the return line off the top of the IP and run a small hose into a container and if you are not getting flow out of the IP when running the IP is not getting enough fuel, if it does have flow and continues to run while the return is going into a container then the return line is likely plugged.

If you do run the lift pump discharge into a container as Mullany suggested there is a time cranked/ammount of fuel pumped specification but I do not know what it is off the top of my head.

 

[MrLucky7137]

If you did not pull the cover behind the fuel pump, grease the pump rod and then put it back together than you likely broke the pump rod when you reinstalled the pump, common newbie mistake

Side question. I’m drawing 11 V at the front of the dual voltage regulator with the ignition off. Is this normal?

 

[Mogman]

Side question. I’m drawing 11 V at the front of the dual voltage regulator with the ignition off. Is this normal?

Yes, that is the connection between the batteries, the 12V source, no relay etc. disconnecting it with the ign. off.
It actually should be over 12V looks like you have dead/week batteries, check to make sure you have the same voltage between the "center" of the batteries and ground

 

[MrLucky7137]

Yes, that is the connection between the batteries, the 12V source, no relay etc. disconnecting it with the ign. off.
It actually should be over 12V looks like you have dead/week batteries, check to make sure you have the same voltage between the "center" of the batteries and ground

I have a bad draw on the batteries that will drain both batteries overnight. I’m attempting to find it right now.

 

[MrLucky7137]

Yes, possibly, there is a charge pump in the IP that will try to pull fuel.
If you did not pull the plate and grease the pump rod there is a 99% chance you broke the pump rod, it slides down inside the area the pump bolts up to when you pull the pump, if you did not address that the rod is again very likely broken, it is almost impossible to push that rod back up into the block and hold it there while mounting the pump, the only practical solution is to pull that plate and grease the rod.
EDIT, it is fortunately an easy fix, pull the pump, pull the plate, remove BOTH halves of the broken rod and then reverse greasing the rod to hold it in place.
The 6.2/6.5L uses it own rod, not just any GM pump rod will work.

oil pressure switch? Seems to be running great when it’s cold, but shuts down as soon as it warms up.

 

[Mogman]

oil pressure switch? Seems to be running great when it’s cold, but shuts down as soon as it warms up.

Oil pressure switch does not control anything

 

[Mogman]

oil pressure switch? Seems to be running great when it’s cold, but shuts down as soon as it warms up.

Again if it surges just before it shuts down it is starving for fuel.
I have seen injector pumps that are worn enough they have a hard time starting when hot but never one that dies when hot.
If it surges just before it dies that is the governor trying to maintain idle when the fuel supply runs out.
Have you tested the lift pump output when cranking the engine into a bottle?
Have you removed the return line from the IP, put a short hose to a bottle and see if you have fuel coming out of the IP return fitting?
Have you removed the check valves?
Have you removed the return fitting from the IP and made sure it is not plugged? there is a check valve in that return line fitting that can clog
How long after it shuts down until it will start again?
How long does it run before shutting down?
All the engine needs to run is fuel to the IP, voltage to the shut down solenoid and air to the intake and something to spin it over.
The pickup screen in the tank might be plugged, the return line might be plugged which will shut the engine down, why I suggested you run it with a hose from the return fitting on the IP into a bottle, that will answer two questions at the same time.
If the shutdown solenoid was bad or you have a voltage problem to the IP or IF it had a safety shutdown system (IE low oil pressure) which it does not it would simply shut down like you turned the switch off, it would not surge before dying.

 

[MrLucky7137]

If you did not pull the cover behind the fuel pump, grease the pump rod and then put it back together than you likely broke the pump rod when you reinstalled the pump, common newbie mistake

how about the fuel control module? I am told that most guys relocate it, because when it heats up it causes similar symptoms.