Sudden no start

[CheaperJeeper]

I have a 95 3/4 ton Suburban, had it for a couple of months now, no issues (except for replacing the batteries). Truck is bone stock as far as I've been able to determine.

48 hours ago the wife drove it to haul a load of stuff to the recycling place. Started and ran just fine. Today she cranks it and cranks it and cranks it some more, no start. I even tried a tiny whiff of ether and it tried to fire a lick or two, but that was all. Stll no start. No smoke, no nothin'. GPs are cycling normally (10-15 seconds when you first turn the key to on, and then they come back on for a couple of seconds every 5 seconds or so while cranking. But no go, it just won't even try to start.

I don't get it. What could cause an easy-starting, good running truck to suddenly just refuse to start like that? OPS? Lift pump? PMD?
I'm at a loss where to even begin troubleshooting here, with no other symptoms to go on...

H-E-L-P!

 

[Drago]

My son's 95 did the same thing, turned out to be the PMD.

 

[hookedup50]

Others will chime in, but I would be plugging in a spare pmd. Be careful of the ether use though.

 

[CheaperJeeper]

OK, 2 new discoveries to report. I took the fiberglass "shroud" off the top of the engine and between the pump and the firewall is a black filter housing abour 3" in daimeter. It has a knob on top that I unscrewed and removed. the knob has about a 1" long x 3/8" diameter tube on the bottom side of it. On the assumption that this is a fuel filter I figured if the OPS is powering the lift pump, and it is working fuel should come out of the filter when cranking the engine. Cranked it over and about the second rev fuel started welling up out of the top of the filter housing. From that I'm thinking the OPS and fuel pump are working.'

Next I loosened the nut on one of the injector lines and had my kid crank it over. No fuel at all - bupkis. Tightened that one back down and loosened the nut on a different line. Cranked it over, and again, no fuel at this injector line either. So it looks like there is fuel from the tank to the pump, but not from the pump to the injectors. Probable sign of PMD failure?

Assuming it is the PMD, how in the heck do you unplug the cable from it? Looks like you have to remove the entire intake manifiold! I can feel the plug, and even see the lock tab on the side of it, so I MIGHT be able to push the plug out of the PMD, but then what? I can't seem to find where the PMD cable goes in under the manifold. Where does the cable to the PMD come FROM? Where is the other end? Is it necessary to remove the intake manifold to unplug and re-route the cable?

 

[CheaperJeeper]

Yeah, I know. Ether is downright dangerous with these high compression motors. That is why I only gave it a little whiff - like a quarter to a half second blast at a time.

The only spare PMD I have is a grey one, and from what I understand they aren't plug-n-play compatible with the black one that is on my truck.

 

[WarWagon]

Glow plugs must be disabled with starting aids or they will disable themselves permanently. Best to throw away the starting fluid as it is usually cheaper to tow her than fix damage from it. And most of the time it doesn't start the engine anyway!

Check all fuses.

Do you get a Service Engine Soon and Service Throttle Soon at key on? this indicates the ECM is getting power and operational to some extent. Wait 60 seconds with key off and try again to be sure the bulb check is working as the ECM stays on for 30 seconds after key off and the lights do not test properly after a short key off-on.

 

[ak diesel driver]

get a remote pmd kit like the one Leroy sells and when you get it you can take a straight bladed screwdriver and push the connector free with it, then use a piece of wire and use it like a sheperds hook and fish it out of there. there will be enough slack to plug it into your new extention cable.

 

[CheaperJeeper]

Glow plugs must be disabled with starting aids or they will disable themselves permanently. Best to throw away the starting fluid as it is usually cheaper to tow her than fix damage from it. And most of the time it doesn't start the engine anyway!

Yeah, I'm well-versed in the evils of demon ether. I waited until the GPs cycled off before giving it a half second blast, let it crank a few seconds before giving another little blast, etc. I've found that with the proper juducious application a little ether can be very helpful starting a hesitant diesel. You just have to be VERY sparing in your use of it...

Check all fuses.

Done that too

Do you get a Service Engine Soon and Service Throttle Soon at key on? this indicates the ECM is getting power and operational to some extent. Wait 60 seconds with key off and try again to be sure the bulb check is working as the ECM stays on for 30 seconds after key off and the lights do not test properly after a short key off-on.

Yup, all the idiot lights come on as they should.

 

[CheaperJeeper]

get a remote pmd kit like the one Leroy sells and when you get it you can take a straight bladed screwdriver and push the connector free with it, then use a piece of wire and use it like a sheperds hook and fish it out of there. there will be enough slack to plug it into your new extention cable.

So just pull the plug up and out over the top of the original PMD?

 

[ak diesel driver]

pretty much

 

[CheaperJeeper]

Anybody in the greater Seattle area (or better yet, south King/north Pierce county) area with a spare PMD I could try?

 

[JMJNet]

OK, 2 new discoveries to report. I took the fiberglass "shroud" off the top of the engine and between the pump and the firewall is a black filter housing abour 3" in daimeter. It has a knob on top that I unscrewed and removed. the knob has about a 1" long x 3/8" diameter tube on the bottom side of it. On the assumption that this is a fuel filter I figured if the OPS is powering the lift pump, and it is working fuel should come out of the filter when cranking the engine. Cranked it over and about the second rev fuel started welling up out of the top of the filter housing. From that I'm thinking the OPS and fuel pump are working.'

Next I loosened the nut on one of the injector lines and had my kid crank it over. No fuel at all - bupkis. Tightened that one back down and loosened the nut on a different line. Cranked it over, and again, no fuel at this injector line either. So it looks like there is fuel from the tank to the pump, but not from the pump to the injectors. Probable sign of PMD failure?

Assuming it is the PMD, how in the heck do you unplug the cable from it? Looks like you have to remove the entire intake manifiold! I can feel the plug, and even see the lock tab on the side of it, so I MIGHT be able to push the plug out of the PMD, but then what? I can't seem to find where the PMD cable goes in under the manifold. Where does the cable to the PMD come FROM? Where is the other end? Is it necessary to remove the intake manifold to unplug and re-route the cable?

That first test is still not definitive on whether the LP and OPS are working.

The OPS runs the LP WHEN ENGINE IS RUNNING, during crank the OPS is NOT RUNNING the LP.
So, you need to test a little further, try to put 12V direct source to the LP and see if you can start.
Make sure there is fuel at the t-valve when open and it keeps running. If you do, the OPS is bad.

When replacing OPS, use ACDelco OPS ONLY.

 

[DieselSlug]

There is a fuel pump relay on the passenger side firewall under. You can use a paperclip to jump the relay and run the lift pump. Unscrew the valve on the top of the filter housing and jump the relay, you should get fuel squirting out after the air.

Just took this pic for you: (Jump the pins that i have painted yellow for my memory)

[/URL]
After you get fuel out the top of the filter try to start the rig.

 

[JMJNet]

On a 95, the relay is on a nice box.

There is a way to jump it there but I don't remember.
If you jump it on the wrong pin, it will blow the ECM-B fuse.

 

[DieselSlug]

On a 95, the relay is on a nice box.

There is a way to jump it there but I don't remember.
If you jump it on the wrong pin, it will blow the ECM-B fuse.

Oh i read that wrong, i thought he had a 94'. I saw a thread for a 99' 6.5 truck wonder if its the same?

 

[DieselSlug]

This is from the gmt-400 website for a 99' 6.5 truck. Check to see if you have this.

Take the cover off the panel and remove the fuel pump relay. As your looking at the picture like a U shape you want to jump the pin in the top right corner, with the bottom left corner. As looking at the picture.

 

[CheaperJeeper]

This is from the gmt-400 website for a 99' 6.5 truck. Check to see if you have this.

Take the cover off the panel and remove the fuel pump relay. As your looking at the picture like a U shape you want to jump the pin in the top right corner, with the bottom left corner. As looking at the picture.

This is the setup I have in my truck.

So, I'm thinking that if I jumper this relay, and it pumps fuel, that rules out the pump being the problem, right? If so, and it starts I have an OPS problem, but if it still doesn't start, then we're back to a PMD issue.

 

[JMJNet]

This is the setup I have in my truck.

So, I'm thinking that if I jumper this relay, and it pumps fuel, that rules out the pump being the problem, right? If so, and it starts I have an OPS problem, but if it still doesn't start, then we're back to a PMD issue.

Yes. It can be both the PMD and OPS or all three.
They all share the same symptoms and OPS is another weak link in addition to the PMD.

It can be cause and effect also since they are part of the fuel delivery.
Bad OPS causes non-running LP causes the IP to suck fuel all the way from the tank causes PMD/IP to fail due to heat.

 

[handcannon]

There is a fuel pump relay on the passenger side firewall under. You can use a paperclip to jump the relay and run the lift pump. Unscrew the valve on the top of the filter housing and jump the relay, you should get fuel squirting out after the air.

Just took this pic for you: (Jump the pins that i have painted yellow for my memory)

[/URL]
After you get fuel out the top of the filter try to start the rig.

For those with an OBD 1 system there is another way to temporarily get the lift pump running. You will have to manually make the connection so this is just a temporary way to get power. If you look along the left side of the pic dieselslug posted you'll see a small black covered fuse container. Pop the fuse out of the socket and move it over to the left and re-insert the fuse into the holder. This leaves one blade of the fuse exposed. Touch the exposed blade to one of the hot studs to the right of where the fuse cover is mounted to apply power to the lift pump.

Don

 

[CheaperJeeper]

Well, now I don't know what to think. I jumpered the relay and had good fuel flow. Started right up. Then I put the relay back in and re-started it again - no problem - like nothing ever happened.

The reason I find this so confusing is that I had already pulled and reinserted the relay a couple of times yesterday to make sure it wasn't just bad conections at the relay. It made no difference yesterday, but today everything is back to normal again.

Could it be that there was just air in the filter somehow?

So it would appear I have the worst of all possible scenarios - an intermittent problem with 3 or 4 possible causes.

GREAT - just what I need....