Ok...I'm working on a 95 chevy 3/4 ton with the 6.5 L diesel.
The customer said he was plowing and it just quit as if the key was turned off.
Of course I assumed it would be the black box. (PMD?)
So I got a test part and sure enough...I was wrong.
It turns out the pump was bad. The customer ordered a rebuilt that came with the new black box. I installed it, bled the system and it fired right up. It ran for about 15 minutes at an idle and quit...as if the key was turned off. This time it turned out to be the lift pump's relay. I replaced the relay, bled the fuel system, it started up but has a bit of a miss. I clears out at about 2000 rpms. To be expected for a minute until ALL the air is gone from the system. But the miss returns when at an idle. The "Service engine soon" light is on at an idle but goes out when you hold the idle up for a couple of seconds. Unfortunately, being a 95 and an OBD1 system, my scanner won't scan it so I have no idea what the code is. However When it stalled the light that says, "service throttle soon" came on just before it quit. It restarted but again, if left to run at an idle, that light comes on and stalls.
In the process of diagnosing the problem I meticulously checked every wire in the harness from the plug to the ends. I'm referring to the harness that sits under the intake. I figured I was onto something because the drain hole in the valley was plugged up with debris and the harness was submerged in 2 inches of fuel. I cleared the hole, cleaned the valley, meticulously inspected and cleaned the wires and connectors and thoroughly taped up the wires. I also applied di-electric grease to all connections. It had been blowing the fuse that breaks the ignition. That problem was solved. But, again, the problem proved to be the pump.
So, the pump, pmd box, lift pump relay have been replaced. The valley harness has been cleaned and taped up very well and it runs. BUT I've still got the service engine light at low rpms and the service throttle soon light that comes on just prior to stalling.
I have a new lift pump but did not install it once I found the relay was bad.
Is there any chance that the lift pump is weak or shorted inside, not only causing the failure of the relay but possibly the shaky idle?
As for the "service THROTTLE soon" light. The only throttle I'm aware of is the rheostat at the pedal. IE, no linkage.
What does that light typically mean?
The owner has a friend with an old scanner that if push comes to shove I can get to come over and scan it. I don't know that it's actually throwing a code because the light goes out when the rpm's are increased.
I'm looking for any hints as soon as possible as this heap has been tying up my shop for far too long. And the customer would kinda really like to get his truck back too. LOL
So any and all ideas would be very welcomed and as soon as possible would be greatly appreciated. I'm in a real bind here, several cars waiting to be worked on and a heap of...stuff...truck on the hoist tying up the shop. I've GOT to get this thing done and out FAST!
Thanks,
Wayne
The customer said he was plowing and it just quit as if the key was turned off.
Of course I assumed it would be the black box. (PMD?)
So I got a test part and sure enough...I was wrong.
It turns out the pump was bad. The customer ordered a rebuilt that came with the new black box. I installed it, bled the system and it fired right up. It ran for about 15 minutes at an idle and quit...as if the key was turned off. This time it turned out to be the lift pump's relay. I replaced the relay, bled the fuel system, it started up but has a bit of a miss. I clears out at about 2000 rpms. To be expected for a minute until ALL the air is gone from the system. But the miss returns when at an idle. The "Service engine soon" light is on at an idle but goes out when you hold the idle up for a couple of seconds. Unfortunately, being a 95 and an OBD1 system, my scanner won't scan it so I have no idea what the code is. However When it stalled the light that says, "service throttle soon" came on just before it quit. It restarted but again, if left to run at an idle, that light comes on and stalls.
In the process of diagnosing the problem I meticulously checked every wire in the harness from the plug to the ends. I'm referring to the harness that sits under the intake. I figured I was onto something because the drain hole in the valley was plugged up with debris and the harness was submerged in 2 inches of fuel. I cleared the hole, cleaned the valley, meticulously inspected and cleaned the wires and connectors and thoroughly taped up the wires. I also applied di-electric grease to all connections. It had been blowing the fuse that breaks the ignition. That problem was solved. But, again, the problem proved to be the pump.
So, the pump, pmd box, lift pump relay have been replaced. The valley harness has been cleaned and taped up very well and it runs. BUT I've still got the service engine light at low rpms and the service throttle soon light that comes on just prior to stalling.
I have a new lift pump but did not install it once I found the relay was bad.
Is there any chance that the lift pump is weak or shorted inside, not only causing the failure of the relay but possibly the shaky idle?
As for the "service THROTTLE soon" light. The only throttle I'm aware of is the rheostat at the pedal. IE, no linkage.
What does that light typically mean?
The owner has a friend with an old scanner that if push comes to shove I can get to come over and scan it. I don't know that it's actually throwing a code because the light goes out when the rpm's are increased.
I'm looking for any hints as soon as possible as this heap has been tying up my shop for far too long. And the customer would kinda really like to get his truck back too. LOL
So any and all ideas would be very welcomed and as soon as possible would be greatly appreciated. I'm in a real bind here, several cars waiting to be worked on and a heap of...stuff...truck on the hoist tying up the shop. I've GOT to get this thing done and out FAST!
Thanks,
Wayne