Need help! In a pickle in Nome, Alaska

[Shatmepants]

Hi guys! I apologize that I'm not a typical enthusiast who has been involved with this forum and could have contributed previously, but I'm in a bind and could use some help if possible.

The backstory is that my father in law has a 98 6.5 GMC in Nome, Alaska. He is only here for the summers. He came up last year and his truck wouldn't start. He and his buddies are very mechanically inclined, but most of their education comes from the necessity of having to fix things in the bush, not from a formal education. Anyway, at some point they determined that the injection pump was bad, so they installed a rebuilt unit, but they still couldn't get the truck to start.

Fast forward to yesterday, I flew up here to try to help him out. I got the truck running yesterday after installing a new crank position sensor, but it runs horribly. I bled the lines well and I tried to reset the crank position sensor, but it doesn't run well enough to get the thing warmed up enough to reach the 170 degree mark. We have swapped the PMD with a known good unit and tried to time the pump. But again, the thing runs horribly.

I've been handed a can of worms, have limited experience with this particular motor/system, and have limited time and resources. I'm doing my best to help, but could use some help myself if anyone can shed some light on what is going on.

Here are the symptoms:
The glow plugs work, the lift pump works, and the motor starts. As soon as the motor starts, it shakes violently, but it will remain idling while shaking in its mounts. If I increase the RPM, the motor smooths out at about 2000 RPM. However, I noticed something odd about the APP yesterday. The APP seems to have three modes...idle, 2000 RPM, and after that it seems to run away so you have to let off the pedal.

We plan to test the APP today, but I'm not convinced that is the issue. I could be wrong, but I've never seen a potentiometer fail in this kind of mode.

I realize there are lots of variables here, and I have no idea what happened during the replacement pump installation. I looked through the manual and it appears that the replacement of the pump is pretty straight forward, but I don't know how easy it is to make a mistake during assembly (like putting the pin in a hole other than the slotted hole or if it's possible that the gear could move enough to skip a took while the mess was disassembled). I do know that they followed the manual and were careful not to rotate the engine during the pump assembly, but I wasn't there to see the action.

Oh, and we have checked that the fuel is okay (no water, etc.)

I'm only up here for another four days, so if anyone can help, I would be incredibly grateful for any tips to help us figure this out. Thanks so much.

 

[WarWagon]

As soon as the motor starts, it shakes violently

Still have the old IP? Where is the "new" rebuilt or whatever IP from? Lots of krap out there being sold.

Video on youtube and link here. The exhaust will tell you, and us, a lot about what is happening. Smoke puffs etc. Remove the oil cap and check for "huffing" blowby.

Any codes present? How many miles on engine and injectors?

The glow plugs work, the lift pump works, and the motor starts. As soon as the motor starts, it shakes violently, but it will remain idling while shaking in its mounts. If I increase the RPM, the motor smooths out at about 2000 RPM.

Check fuel condition. Add a clear return line off the IP and look for air or bubbles. These things Go NUTS when starving for fuel or dealing with air. Just A possibility.

 

[Shatmepants]

Still have the old IP? Where is the "new" rebuilt or whatever IP from? Lots of krap out there being sold.

Unfortunately, the old pump got returned as a core. The rebuilt pump came from Heath Diesel out of Florida.

Video on youtube and link here. The exhaust will tell you, and us, a lot about what is happening. Smoke puffs etc. Remove the oil cap and check for "huffing" blowby.

I will do this and post asap. Only appears to have very light smoke upon light off, but nothing (or very little) while running. I did notice that there didn't seem to be any change in smoke while playing with the pump timing. Not sure if that means anything or not.

Any codes present? How many miles on engine and injectors?

Prior to getting it running, we did have a crank sensor code (hence the replacement), but nothing now. I will recheck that and report back.

Check fuel condition. Add a clear return line off the IP and look for air or bubbles. These things Go NUTS when starving for fuel or dealing with air. Just A possibility.

We did put a clear line off the return on the pump and it is 100% free of any air.

 

[Shatmepants]

Okay, here are my current codes: (I will post a video asap)

 

[Shatmepants]

 

[ak diesel driver]

I'd crack the injector lines loose while it's running, one at a time and see if one cylinder is causing the issue.

 

[Big T]

Still have the old IP? Where is the "new" rebuilt or whatever IP from? Lots of krap out there being sold.

Video on youtube and link here. The exhaust will tell you, and us, a lot about what is happening. Smoke puffs etc. Remove the oil cap and check for "huffing" blowby.

Any codes present? How many miles on engine and injectors?




Check fuel condition. Add a clear return line off the IP and look for air or bubbles. These things Go NUTS when starving for fuel or dealing with air. Just A possibility.

Damn it, you beat me to the clear return line at the injection pump!

Shudders and shakes at idle sounds like air in the fuel system. Installing the clear fuel line allow you to confirm that.

Need to confirm lift pump fuel pressure at the injection pump.

Need to address any leaks between the fuel tank and the lift pump. This is the suction side of the lift pump and a leak there will let air into the fuel system. Speaking from recent experience (twice) the o-ring seals at the fuel tank sender go bad or disintegrate at this age for the truck. The o-rings are cheap, but you have to drop the tank.

 

[Shatmepants]

Shudders and shakes at idle sounds like air in the fuel system. Installing the clear fuel line allow you to confirm that.

Yes, we did this a few times. In fact, I just went out and checked it again and the line is 100% bubble free.

So, does the fact that the line is completely bubble free definitely rule out the lift pump (and associated bits) as a culprit or should we check the pressure anyway? We don't have a pressure gauge, but I could probably round one up if necessary.

We have bled the lines several times, but yeah, from everything I know and have read, this does seem like air in the system. From the beginning of the project, with all of the bleeding we have done, nothing has changed at all. I'm happy to keep trying to bleed the thing, but it kind of feel like I'm beating my head against a wall at this point. Maybe I need more beating.

 

[Big T]

Yes, we did this a few times. In fact, I just went out and checked it again and the line is 100% bubble free.

So, does the fact that the line is completely bubble free definitely rule out the lift pump (and associated bits) as a culprit? We don't have a pressure gauge, but I could probably round one up if necessary.

We have bled the lines several times, but yeah, from everything I know and have read, this does seem like air in the system. From the beginning of the project, with all of the bleeding we have done, nothing has changed at all. I'm happy to keep trying to bleed the thing, but it kind of feel like I'm beating my head against a wall at this point. Maybe I need more beating.

No, clear line only comfirms whether there is air in the system. You need to install a fuel pressure gauge to test that.

Are there roads from Fairbanks to Nome? If so, glad I did not see them on a map, else my wife have had us out there.

 

[Shatmepants]

Are there roads from Fairbanks to Nome? If so, glad I did not see them on a map, else my wife have had us out there.

Nope, there are no roads into Nome. Thank you though. I will hunt down a pressure gauge.

 

[ak diesel driver]

He's roughly 800-1000 miles north of me.

 

[jrsavoie]

Is there some type of relearn that needs to be done?

 

[Shatmepants]

I just came in from bleeding it three more times and there has been zero change. The thing is still trying to jump out of its motor mounts and the APP is causing the strange RPM-related behavior.

We can't find a low pressure fuel gauge of any kind, so Napa is having one overnighted.

I'm kind of at a loss at this point.

 

[dbrannon79]

using the scanner you have and with the key on engine off, there should be three data readings for the APP sensor. watch them as you slowly sweep the go pedal from nothing to on the floor. again with the engine off. you should see voltage in the data stream of the scanner go from 0.5 or so to right at 5v smoothly with no drop outs or glitches. I forget which one but one of the data points will start out at 5v and slowly go to 0 as the pedal is pressed.

if this checks out then the APP sensor is good.

Now for the crank position sensor. this engine will run without it connected. it uses both the CPS and the optical sensor inside the IP to run. in a failsafe mode the engine will run with out one or the other.

you can try this... but it will introduce new codes on the scanner. write down all codes currently first.
disconnect the crank position sensor from the harness and try to start the engine. if it starts is will take a little longer cranking for it to fire up.

if it does start, then take note of how it runs at idle and attempt what you did with the pedal at 2k rpm and what not.

Not reconnect the CPS and now disconnect the optical sensor on top of the IP. it's the big 6 pin connector right on top of the IP next to the fuel shut off solenoid. Try to start the engine. again if it starts, take note of how it runs and report back to us. if for whatever reason disconnecting ether of these sensors and it's a no start condition. look at the scanner live data and see if you see an RPM signal when cranking.

remember it has to have one or the other still connected to run in safe mode.

 

[Shatmepants]

using the scanner you have and with the key on engine off, there should be three data readings for the APP sensor. watch them as you slowly sweep the go pedal from nothing to on the floor. again with the engine off. you should see voltage in the data stream of the scanner go from 0.5 or so to right at 5v smoothly with no drop outs or glitches. I forget which one but one of the data points will start out at 5v and slowly go to 0 as the pedal is pressed.

if this checks out then the APP sensor is good.

Now for the crank position sensor. this engine will run without it connected. it uses both the CPS and the optical sensor inside the IP to run. in a failsafe mode the engine will run with out one or the other.

you can try this... but it will introduce new codes on the scanner. write down all codes currently first.
disconnect the crank position sensor from the harness and try to start the engine. if it starts is will take a little longer cranking for it to fire up.

if it does start, then take note of how it runs at idle and attempt what you did with the pedal at 2k rpm and what not.

Not reconnect the CPS and now disconnect the optical sensor on top of the IP. it's the big 6 pin connector right on top of the IP next to the fuel shut off solenoid. Try to start the engine. again if it starts, take note of how it runs and report back to us. if for whatever reason disconnecting ether of these sensors and it's a no start condition. look at the scanner live data and see if you see an RPM signal when cranking.

remember it has to have one or the other still connected to run in safe mode.

Doug, thanks so much for the reply. The weather turned here so we called it a day for now. We will hit it again tomorrow and I will report back asap.

 

[dbrannon79]

Send some of that weather down here to Texas! its way too hot and humid here !!

 

[Shatmepants]

using the scanner you have and with the key on engine off, there should be three data readings for the APP sensor. watch them as you slowly sweep the go pedal from nothing to on the floor. again with the engine off. you should see voltage in the data stream of the scanner go from 0.5 or so to right at 5v smoothly with no drop outs or glitches. I forget which one but one of the data points will start out at 5v and slowly go to 0 as the pedal is pressed.

if this checks out then the APP sensor is good.

Now for the crank position sensor. this engine will run without it connected. it uses both the CPS and the optical sensor inside the IP to run. in a failsafe mode the engine will run with out one or the other.

you can try this... but it will introduce new codes on the scanner. write down all codes currently first.
disconnect the crank position sensor from the harness and try to start the engine. if it starts is will take a little longer cranking for it to fire up.

if it does start, then take note of how it runs at idle and attempt what you did with the pedal at 2k rpm and what not.

Not reconnect the CPS and now disconnect the optical sensor on top of the IP. it's the big 6 pin connector right on top of the IP next to the fuel shut off solenoid. Try to start the engine. again if it starts, take note of how it runs and report back to us. if for whatever reason disconnecting ether of these sensors and it's a no start condition. look at the scanner live data and see if you see an RPM signal when cranking.

remember it has to have one or the other still connected to run in safe mode.

Okay, there's no way I would be able to sleep tonight if I didn't get out there and check into these suggestions.

We've been playing with this thing all day, so it may account for slightly low voltage, but APP 1 0.65 volts at rest, 3.75 volts at full pedal. There do not appear to be any glitches in the entire sweep. All appears to be smooth.

There is a no start condition with the optical sensor connected and the the crank position sensor disconnected.

 

[dbrannon79]

There should be an APP 2 and 3 signal to look at. I will let others chime in on the voltages but 3.75 seems a little on the low side. you might need to check the batteries state of charge.

how long did you crank for with the CPS unplugged. did you see an RPM signal on the scanner. try this again but with the CPS connected and the optical sensor unplugged.

 

[dbrannon79]

I'm sure you already know, but the square connector circled here is the optical sensor. might be kinda hard to get to with the upper intake in place though



and I doubt this truck has one, but if you see this filter harness inline on the optical senor, pull it and toss in the trash... they will cause more grief than good.

 

[Shatmepants]

There should be an APP 2 and 3 signal to look at. I will let others chime in on the voltages but 3.75 seems a little on the low side. you might need to check the batteries state of charge.

how long did you crank for with the CPS unplugged. did you see an RPM signal on the scanner. try this again but with the CPS connected and the optical sensor unplugged.

Yes, there is the APP 2 and APP3 to look at. I will post that asap.

I completely forgot to check the RPM signal. I will do that tomorrow morning and report back.

Thanks for the info in your other post as well. I do know where the optical sensor is, but I didn't know about that filter. I will look into that as well.

I'll be back tomorrow. Thanks so much. This gives me hope.