Howdy, Ya'll.

First off, let me fill you guys in on the install. I'm running a '96 12Valve with the P-Pump. I have stripped all of the electronics off of the engine...what's still in place isn't hooked up unless it's a temp/boost/pressure sending unit. For a tranny, I'm running the A518, Non Lock-up, with a toggle switch to engage the OD.

I got my Cummins Conversion on the road about 3-4 months ago, and have absolutely loved it...until today...I bed mounted the radiator when I did the build, and it appears as I have a slow leak. Well, with a bed mounted radiator, you have to bleed the air out of the top of the block because where the radiator is mounted so high, it creates an air pocket in the head.

Anyways...the truck started to overheat, so I pulled into a gas station to bleed out the air and top off the coolant...the temps continued to climb, so I shut her down and gave everything about a half hour to cool off. Topped off the coolant and brought the temps back into normal range.

Anyways...when she started to run hot, I noticed a loss in power...no smoke or anything...just a loss in power. Once I topped off the coolant, and got her running cool again, I headed back down the road, and the RPM's would drop to almost nothing, and then surge back up to normal, and then drop back down. The whole cycle (from prolly 800 RPM's, up to 2500, and back down to 800 RPM's) probably took maybe 30-45 seconds or so, and got worse the further I went. I was about 15 miles from the nearest parts store, so I limped her there with plans of putting a new fuel filter on her and fixing the issue. I swapped in a new filter that was topped off with LUCAS and she drove pretty good for about 6 or 8 miles, and then the viscious cycle started again. Fuel pedal position didn't make any difference. It would do it at half throttle or full throttle the same...boost would surge up to about 20 when the truck would take off, and drop to 0 when it would die down.

I think it is acting like the fuel pressure is dropping off, and will then build back up, and drop off again. I don't believe for a second it's related to the truck running hot...It did something very similar a few days ago, and I thought maybe I was running low on fuel...I put a tank in the bed, and don't have a gauge hooked up, so I stopped and put 10 gallons in the tank (which was NOT near empty yet) and today she had a full tank of fresh fuel (I've never had problems with the fuel from this gas station and it's all I have ran for 5 years). The tank is a bottom feed tank, and has only had about 300 gallons of fuel run through her since I installed it. Tank was cleaned before I installed it...I've probably put a few thousand miles on the truck since the build, and know she wasn't acting like this before...I did run a gallon of oil mixed with about 50 gallons of diesel a couple of weeks ago...

Would the overflow valve cause symptoms this severe? Did I destroy something with the used motor oil? I have heard of people running used motor oil in the past, and figured it'd probably help the rings, IP, etc more than it would hurt them because of the extra lubriscity.

 

If the P-pump gets too hot it can warp the DV bores causing them to stick.
Causes problems like you're having plus hard pedal and dieing at idle.
Remove the DVs and see if they're scuffed up.
If so the pump needs to be rebuilt.

 

GRRRR!!! I had a feeling that's what I was gonna hear. Is there any way to rule out the LP or the Overflow Valve before I start tearing into the pump? Would either of them even POSSIBLY cause these symptoms or am I pretty much assed out??

 

There sure is, hook up a fuel pressure gauge.
Instructions> http://www.cumminsforum.com/forum/94...-12-valve.html

After you have the gauge installed if your pressures aren't up the spec in the link pinch off the rubber return line with pliers, engine idling.
Pressure should instantly jump up to at least 60 psi, that means the lift pump is good, overflow bad.

 

Ok...just for $hit$ and giggles, I took the truck around the block this past weekend to see how she acted while cold. The cummins sounded GREAT...for about a half of a block, and then started losing power again. This time, it never re-gained it's power, and eventually died off. I towed it back to the house, and pulled the fuel filter off, and it was only half full...telling me that either the LP was not pumping, or there was a blockage in the line/tank somewhere. I pulled the line off of the tank, and it was empty. The tank is bed-mounted and is gravity fed from the bottom of the tank to the LP. I dropped the line to the ground and still, NO FUEL...I did finally get a small stream of fuel out of the line once I removed the fuel cap, but it still wasn't what it should have been...I'm guessing the tank has some crap in it that's keeping the fuel from flowin...

I THINK....and HOPE...and PRAY....that this will cure my ailments and I'm not gonna have to replace the IP after all...I'm gonna switch back over to the stock tank and see what happens...

 

Yes, it turned out that the kinked fuel line was all that was wrong. I straightened it out and she runs like new again.

 

glad to here it was a simple fix. reading your sig that thing sounds like a beast... got any pics?