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My first diesel, 1994 Chevy 3500HD, 160k+miles, been sitting in a non-running condition for a bit before I purchased it (previous owner purchased it non-running and got it going before selling it for a truck with a dump bed), so I'm going to be doing a pile of work to refresh it.

One of the big items is an exhaust manifold leak, it's got a broken bolt (first one on the manifold, drivers side) and there's a gap that it's coming out of, it looks to me like the gasket has blown out because of the lack of pressure. The fun bit is that the dealership doesn't list an exhaust gasket, neither do the manuals I have (PDFs), but NAPA shows an exhaust manifold gasket, and it looks like there currently is a gasket that is blown out. I have the gasket on order (along with a full set of bolts), and I can return to Napa if I don't end up using it, just wondering what the experts think of gasket or no gasket for the exhaust.

Second question is about the injectors, for the most part it runs ok, doesn't seem to have much power (I suspect pre-turbo exhaust leaks) and it starts hard (I blame glow plugs which I'm replacing, chugs with clouds of smoke, then kicks in and idles just fine). There is at least one injector that is leaking (looks like the copper crush washer is bad?), but otherwise it seems to run ok. So I don't destroy my budget, I'd like to replace the injectors (and injector lines) later and just clean them now (disassemble and clean in an ultrasonic cleaner). Is that reasonable or should I just go to replacing them now? The ancillary items (gaskets, crush washers, etc) seem cheep enough that I wouldn't mind a second round of them as long as I don't need to replace the $400 injectors and $250 lines this round of work.

Finally, are there any suggestions for a super-sensitive throttle? When cruising along, maintaining speed, the throttle is super touchy between engine accelerating and engine decelerating (engine breaking). At low speeds (25mph to 40mph) it's bad enough that it'll be bouncing me back and forth (run/decel/run/decel/run/decel) till I give up and either give it throttle or push the clutch in and coast for a bit. I've checked codes and once got a 'throttle voltage high' code, but otherwise none that seem to be major culprits. Any ideas before I replace the throttle?

Thank you for your time.
 

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My first diesel, 1994 Chevy 3500HD, 160k+miles, been sitting in a non-running condition for a bit before I purchased it (previous owner purchased it non-running and got it going before selling it for a truck with a dump bed), so I'm going to be doing a pile of work to refresh it.

One of the big items is an exhaust manifold leak, it's got a broken bolt (first one on the manifold, drivers side) and there's a gap that it's coming out of, it looks to me like the gasket has blown out because of the lack of pressure. The fun bit is that the dealership doesn't list an exhaust gasket, neither do the manuals I have (PDFs), but NAPA shows an exhaust manifold gasket, and it looks like there currently is a gasket that is blown out. I have the gasket on order (along with a full set of bolts), and I can return to Napa if I don't end up using it, just wondering what the experts think of gasket or no gasket for the exhaust.

Second question is about the injectors, for the most part it runs ok, doesn't seem to have much power (I suspect pre-turbo exhaust leaks) and it starts hard (I blame glow plugs which I'm replacing, chugs with clouds of smoke, then kicks in and idles just fine). There is at least one injector that is leaking (looks like the copper crush washer is bad?), but otherwise it seems to run ok. So I don't destroy my budget, I'd like to replace the injectors (and injector lines) later and just clean them now (disassemble and clean in an ultrasonic cleaner). Is that reasonable or should I just go to replacing them now? The ancillary items (gaskets, crush washers, etc) seem cheep enough that I wouldn't mind a second round of them as long as I don't need to replace the $400 injectors and $250 lines this round of work.

Finally, are there any suggestions for a super-sensitive throttle? When cruising along, maintaining speed, the throttle is super touchy between engine accelerating and engine decelerating (engine breaking). At low speeds (25mph to 40mph) it's bad enough that it'll be bouncing me back and forth (run/decel/run/decel/run/decel) till I give up and either give it throttle or push the clutch in and coast for a bit. I've checked codes and once got a 'throttle voltage high' code, but otherwise none that seem to be major culprits. Any ideas before I replace the throttle?

Thank you for your time.
Welcome to DieselPlace

Exhaust leaks will affect performance. Everything pre-turbo must be leak free.
Looking on a GM Parts site I do not see a part number for an exhaust manifold gasket.

Injectors and return line kits can be found through a couple of our supporting vendors:
Unique Diesel Welcome to Unique Diesel - GM Truck - High Quality 6.2 6.5 Parts Source
Kennedy Diesel Kennedy Diesel
The hard lines that feed the injectors shouldn't need to be replaced unless they are damaged/leaking.

The super-sensitive throttle can be a few things.
Air in fuel issues
Faulty PMD
Armature in the Injection pump is worn = replace the Injection pump

I would go through your fuel system from tank to Injection pump
The fuel system needs to be leak-free and solid
Once you have the Fuel system squared away then concentrate on the PMD
Install a "Known working" PMD w/ resistor installed and see if things improve
 
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Discussion Starter · #3 · (Edited)
Welcome to DieselPlace

The super-sensitive throttle can be a few things.
Air in fuel issues
Faulty PMD
Armature in the Injection pump is worn = replace the Injection pump

I would go through your fuel system from tank to Injection pump
The fuel system needs to be leak-free and solid
Once you have the Fuel system squared away then concentrate on the PMD
Install a "Known working" PMD w/ resistor installed and see if things improve
The fuel system from the tank right up to the injector pump (but not including the injector pump itself) is all new, new tank, sender, lift pump, rubber lines, etc. The Fuel Pump Relay mod has been installed (relay runs directly off of the ignition circuit) and the PMD Relocation kit has been installed, both by previous owner before I picked it up. I plan on checking the fuel system for leaks before I tear it apart for the other work that I'm going to do.

EDIT: The PMD was the issue causing it to be non-running, they replaced the fuel system in their attempt to figure out the issue before they figured out that it was the PMD and replaced/relocated it.
 

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The fuel system from the tank right up to the injector pump (but not including the injector pump itself) is all new, new tank, sender, lift pump, rubber lines, etc. The Fuel Pump Relay mod has been installed (relay runs directly off of the ignition circuit) and the PMD Relocation kit has been installed, both by previous owner before I picked it up. I plan on checking the fuel system for leaks before I tear it apart for the other work that I'm going to do.

EDIT: The PMD was the issue causing it to be non-running, they replaced the fuel system in their attempt to figure out the issue before they figured out that it was the PMD and replaced/relocated it.
PMD's can last 5 minutes or 5+years depending on fuel system condition. We always recommend that you carry a couple of "Known working" spares in the vehicle.
There are a lot of China-made PMD relocation kits that are junk. Make sure the relocation kit has quality AC/Delco connectors with wire...
One way to rule out a bad relocation harness is to remove the PMD from the relocation harness and connect the PMD to the OEM harness on the Injection Pump and see if conditions change.
 

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Welcome. 1994 has the " inj. pump has to match the PCM eprom " possible problem.
Get the IP numbers and the numbers on the eprom inside the PCM and post them.
The numbers on the outside of the PCM will not do.
IP example # DS4831-5521
Eprom could have a 4 digit code such as BDFG and an 8 digit part number.
I have experienced exactly what you are describing in the same rig, no fun at all.
An out of town dealer was working on it and I never saw it again.
 
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Discussion Starter · #6 ·
Welcome. 1994 has the " inj. pump has to match the PCM eprom " possible problem.
Get the IP numbers and the numbers on the eprom inside the PCM and post them.
The numbers on the outside of the PCM will not do.
IP example # DS4831-5521
Eprom could have a 4 digit code such as BDFG and an 8 digit part number.
I have experienced exactly what you are describing in the same rig, no fun at all.
An out of town dealer was working on it and I never saw it again.
EEPROM code: BNTC1621-5256

while we’re on the topic, is the EEPROM a GM/Chevy special or is it fairly standard 80s-90s eeprom? (AKA, are the EEPROMs I have bouncing around my parts bin compatible)
 

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BNTC is not for the HD inj. pump, and is for your 3500HD w/man tranny.
As long as your IP is not DS4831-5068 you should be OK.
 
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