bob_442
mad scientist
I've got a mid-90s 6bt from a Dodge implanted in a 1988 Chevy V30 Dually Crew Cab. I use this rig almost exclusively with a truck camper on it. The whole thing is just shy of 12K lbs with me in it. Behind the engine is an NV5600 6-speed manual transmission and behind that is an NP205 transfer case. The truck also has an exhaust brake; it is very nice for those descents. Generally, the truck does a really good job, though it is a bit stressful after a long day of driving a very top-heavy package.
I've got a bug in the system that is ******* me that I would like to get to the bottom of. There are several symptoms that may or may not be related.
First, the performance between the right and left fuel tanks is noticeably different. The truck performs better on the right tank. Each tank has its own electric pump inside, and the 6-hose selector valve with return lines is in place. Second, often after, or during a climb, the engine gets into a funny state whereby there is a severe loss of power. In this state, it starts running rough. When increasing throttle, it does respond, a little, but only after a delay...about a second or two. If I push in the clutch and release the throttle, it dies. If I let out the clutch, it restarts, and continues misbehaving. If instead, I wait 5 seconds before releasing the clutch, it generally comes back to life -- normal operation.
This generally is more likely to happen on the left fuel tank. It is very, almost certain, to happen on modest climbs, or even on level ground if the tank is very full. Weird.
OK, so I mentioned I've been fighting this for a while. I figured I had a bad pump and have a pressure problem. So I installed a fuel pressure, pyro, and a boost gauge on the a-pillar. Really glad I did that! But, I digress. There isn't a problem with the pressure. Initially, the pressure was around 29-31 PSI. I lowered it to 25-ish (there is an adjustable regulator inside the frame rail). No change. When the engine misbehaves, you cant see it on the fuel pressure gauge. It is obvious on the boost gauge of course. I figured, well, it's not the fuel feed, it must be the fuel return. So, I put the truck on the rack and pulled the lines on the selector valve. I manually pumped fuel in and out of each tank. I blew compressed air back in the return lines (with the caps off, of course). I even tried driving with the caps on loose, to eliminate tank pressure or vacuum as an issue. I replaced the selector valve.
One more thing. I thought maybe the left tank was letting air bubbles into the system. I think I have ruled that out because when I flip the selector switch under load, there is zero delay in the exhaust note changing a bit between the tanks. If there was air getting in, I figure it would take at least a second to make it from the selector valve, thru the filter, and into the IP. And, yes, I have replaced the fuel filter.
I drove the rig last week from Morgan Hill, Ca., south to 101/58, east to Barstow & Vegas, north thru Nevada to Gardnerville, and then finally west back to Morgan Hill. Again, I suffered with this issue.
The IP does have some mods done to it. I think the springs have been replaced to raise the governor speed and/or increase the fuel supply. This was done by the PO. I have to be very careful not to let it get too hot. It can easily fly past 1100 degrees if I don't pay attention and downshift or slow down when climbing.
I'm wondering if the collective wisdom out there might be able to help me shed some light on this. Thanks for reading. Hopefully at the very least it's an entertaining story.
I've got a bug in the system that is ******* me that I would like to get to the bottom of. There are several symptoms that may or may not be related.
First, the performance between the right and left fuel tanks is noticeably different. The truck performs better on the right tank. Each tank has its own electric pump inside, and the 6-hose selector valve with return lines is in place. Second, often after, or during a climb, the engine gets into a funny state whereby there is a severe loss of power. In this state, it starts running rough. When increasing throttle, it does respond, a little, but only after a delay...about a second or two. If I push in the clutch and release the throttle, it dies. If I let out the clutch, it restarts, and continues misbehaving. If instead, I wait 5 seconds before releasing the clutch, it generally comes back to life -- normal operation.
This generally is more likely to happen on the left fuel tank. It is very, almost certain, to happen on modest climbs, or even on level ground if the tank is very full. Weird.
OK, so I mentioned I've been fighting this for a while. I figured I had a bad pump and have a pressure problem. So I installed a fuel pressure, pyro, and a boost gauge on the a-pillar. Really glad I did that! But, I digress. There isn't a problem with the pressure. Initially, the pressure was around 29-31 PSI. I lowered it to 25-ish (there is an adjustable regulator inside the frame rail). No change. When the engine misbehaves, you cant see it on the fuel pressure gauge. It is obvious on the boost gauge of course. I figured, well, it's not the fuel feed, it must be the fuel return. So, I put the truck on the rack and pulled the lines on the selector valve. I manually pumped fuel in and out of each tank. I blew compressed air back in the return lines (with the caps off, of course). I even tried driving with the caps on loose, to eliminate tank pressure or vacuum as an issue. I replaced the selector valve.
One more thing. I thought maybe the left tank was letting air bubbles into the system. I think I have ruled that out because when I flip the selector switch under load, there is zero delay in the exhaust note changing a bit between the tanks. If there was air getting in, I figure it would take at least a second to make it from the selector valve, thru the filter, and into the IP. And, yes, I have replaced the fuel filter.
I drove the rig last week from Morgan Hill, Ca., south to 101/58, east to Barstow & Vegas, north thru Nevada to Gardnerville, and then finally west back to Morgan Hill. Again, I suffered with this issue.
The IP does have some mods done to it. I think the springs have been replaced to raise the governor speed and/or increase the fuel supply. This was done by the PO. I have to be very careful not to let it get too hot. It can easily fly past 1100 degrees if I don't pay attention and downshift or slow down when climbing.
I'm wondering if the collective wisdom out there might be able to help me shed some light on this. Thanks for reading. Hopefully at the very least it's an entertaining story.
