OK fellow Cummins fans, I've got a big problem that many days of web searching has not found an answer to.I recently replaced the VP$$ and added an Airdog 100. Now my truck will start fine when cold and runs great. The trouble comes when I try to start it when hot. The engine will fire immediately and idle for a couple of seconds then it stumbles and dies. I can re-fire it immediately with the same result. If I try to start it within 5 minutes of shutdown all is well. Beyond that it's a no go until the engine is cold again. Does this condition fall under the hot start banner? Would the LP cutoff relay mod help me? Idle PSI is about 17psi on my test gauge. I don't have an in cab gauge yet since i had to blow my gauge fund on repair parts. I did plumb in a needle valve in prep for a gauge. :thumbup2:I have checked all points along the fuel lines where there is a connection and found everything to be tight. All high pressure lines are tight with no visible signs of leaks. I also checked the return fitting at the back of the head which did have a loose connection but did not solve the problem. I checked for codes and found none. I did not have this problem before the VP died.I'm at a loss here! Any thoughts? :banghead:

@PepsiIt sputtered and never started with the LP fuse pulled. Kinda like there was enough stored fuel in the pump for 5 of 6 cylinders then nothing.I kinda figured that the LP pressure wasn't the problem but I tried anyway just in the interest of being through.I have tried to pull codes twice now. Once with a cold engine and once hot when it was acting up. No codes either time. I am using an Actron scanner I borrowed from Autozone. Gotta love their tool rental program!Update!!I pulled the pump out and shipped it off for testing. We'll see what happens from here. I suspect that the computer is sick. Through all of this, DAP customer service has been very good. Everyone I have talked to has been courteous and helpful!

good to hear that they are workin with ya

I am a little late with this, but is your lift pump connected thru the ecm? As long as the ecm is working right and you are wired thru it, the pressure is lowered during starting to avoid a high pressure starting issue.I am happy that DAP is helping you woork thru it.

Good to hear, I think DAP does well.Jacob will do you good mate. Hope to hear good news, and it reminds me to make sure i get one that is rebuilt with a new computer when i can (afford) mine.

I'm back!!!Here is the latest update on my VP saga. It turns out there were two problems with my VP; one was my fault the other wasn't. When I took the pump out I noticed that the keyway was a bit damaged and I had dinged the shaft a little bit. I know what I did to the keyway but I'm not sure how the shaft got involved. In any case, I'm almost too embarassed to admit that I made a mess out of it! Needless to say, this time will be different! :)The problem that wasn't my fault was that IAT sensor inside the pump was faulty. The rebuilding facility said that the pump was throwing a code for it. Apparently, it's not a code that gets forwarded to the ECM because I never had a code to pull.In the end, they are going to replace the sensor under warranty and replace the shaft and keyway for me. I just had to buy those 2 parts. They are not charging labor to replace them because they have to come out to fix the sensor anyway. All in all, this is about the best way it all could have worked out! Could been much worse! The parts were not a terribly expensive lesson in being a ham fisted mechanic... Whew!The VP should be in my hot little hands on Wednesday. Hopefully the UPS guy will roll through early in the day so I can get the pump in my truck since that is the last day I'm off. :pray:I'll update when I get her back up and running. Hot or cold!Thanks to everyone who helped me work through this. This is a wonderful resource for shadetree mechanic types like me!

Glad you got an answer to your problem hopefully this time you'll take your time installing the pump...

No worries there! I know exactly where I went wrong and I'll never do that again! :banghead::banghead::banghead::banghead:Any tips from the brain trust with respect to aligning the key with the keyway in the gear? Thought I had that handled last time... Apparently not!

edit (try to get the gear running the vp to have the keyway in the up position this will make life easier before taking out the vp you can turn the engine over by hand with it out you must hold the gear to the ajoining gear to keep timing)when i replaced my vp i had a friend hold the flashlight to the mirror and direct me to go up down, passenger side or driver side, also where the key on the vp sat in relation to the gear. I would first look myself and try to orientate the vp housing as it would sit on the engine, then orientate the shaft of the vp to where the keyway was. when installing i used both hands and my friend guided me where to move it so it would slip right into the gear and not move the gear. once i got the shaft into the gear slightly i grabbed the gear and held it to the ajoining gear so it wouldnt move as i pushed the shaft into the gear (i know sounds like a ____ novel...)basically once the vp was sitting on the studs i too the nuts and loosly tightened them first. Then i took the shaft nut and put a little torque on the gear to the vp to keep it from moving. then i torqued the nuts on the vp and then torqued the gear nut on the front. then hook up the fuel lines and plug in.If this is what you were looking for i hope it helps, if not need more specific as to what you are asking

As I remember once you have the keyway lined up the shaft should slide right in. the pump and engine mating surfaces should come evenly together. Dont use the bolts to pull the pump up to the engine. I lined the keyway up by eye and then rotated a little until I felt is slip in. Id idnot have much trouble with that part. I just sweated dropping the key. Seemed everything i read about had a big warning for that. Had me nervous as hell.

As I remember once you have the keyway lined up the shaft should slide right in. the pump and engine mating surfaces should come evenly together. Dont use the bolts to pull the pump up to the engine. I lined the keyway up by eye and then rotated a little until I felt is slip in. Id idnot have much trouble with that part. I just sweated dropping the key. Seemed everything i read about had a big warning for that. Had me nervous as hell.

i should have put that in there, the shaft did slide right in to a point, i then put the nuts on the vp to hold the vp to where i could get the nut on the gear and get it tighted down a bit. i too was sweating my bawlz off not wanting to skip a tooth or drop the key... bad day if that happens.

It can lenghten the install time considerably. I think I was sweating that one when i read the instructions the first time.

i remember reading somewhere that when you have the pumps out, take the new pump and rotate the shaft until it matches the key way on the old pump. then put some loc tite on it or motor oil and it will stay in place. but then again if you use the alternator pulley to rotate the engine assembly, make sure your key way is up on the VP gear, this (i believe marks the position of the Key way on the VP-44)

yes best to get the keyway at 12oclock first then remove the pump. makes life so much easier!

yes best to get the keyway at 12oclock first then remove the pump. makes life so much easier!

He's right...

do i get a cookie?

Good news!!I got my new pump installed and everything works great! No more hot idle issues! Yay! :thumbup2::thumbup2:I knew about aligning the key slot in the gear to 12 oclock but my sticking point the first time was in making sure that the key was going into the slot. This time I spent a lot of time with a flashlight and a mirror checking and re-checking trying to make sure that everything was lined up perfectly before tightening anything. I'll know if it paid off when I wear this VP out!Next up, gauges!Thanks again for all of the great advice and helpful articles!Rebelrodder

good to hear man!!nuther satisfied customer.(send money for the bill to me )