Hot Run Issue?

[Rebelrodder]

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:

[CUMMINSDIESELPWR]

it honestly sounds like you got a sh!t VP. When mine went out it would not start hot until cooled down.Where did you source the VP from? Is the VP refurbished with new internals and computer? If only internals the computer is on its way out. (some remans dont have new computers)Did you ensure all plugs are re-connected? Are you positive you didnt jump timing on the gear when replacing the VP?Hope this helps and sorry for the bad news. I would let other chime in as well to get a broader scope of others opinions as to the issue.good luck!

[dually]

When you turn the key but not starting it, do you here the lift pump run ? Check the tank lines to the lift pump. Check the filter out. If it burps and spits it could mean it is short on fuel.As for the vp pump the key way is the bugger on these. As well as the gear it self. Did you put the key way in correct. it has to go in one way. Did the pump shop tape the key way in place when thay shipped it ? If the gear it self moved and it is no longer dot to dot that would make it burp and spit.When it is cold and you run it how does it run ? Just like when it was new ? How does it run when you start it cold and warm it up,say on a ten mile run ? How does it run at 2000 + rpm loaded (up a big hill)?Dont rule out a bad pump. I had one. Had to send it back.

[CUMMINSDIESELPWR]

good points dually, def need more info to point to the issue

[Mopar1973Man]

Couple of things come to mind air leak in the low pressure side of the fuel system and fuel is draining back to the tank.Fuel pressure problems just because you got a AirDog doesn't mean the upper end fuel pressure is still good I've seen plenty of videos watch pressure go from 19 at idle to 0 at WOT.I would go back and do the basic test with error codes nad testing both idle and WOT pressures. Yeah you might end up building test gauge.

[Rebelrodder]

@CUMMINSDIESELPWR

I got the VP from Diesel Auto Power. I saw that they were an advertiser here and read that they had good prices. Seemed ok to me, so I went with them. I was under the impression that their pumps were rebuilt with new internals and new computers. At least that’s what their ebay storefront said anyway.

I have double checked all of the electrical connections and they appear to be in good order. I recall disconnecting just 2. One to the VP itself and the other for the APPS. I’m 99% sure I didn’t make the drive gear jump a tooth; if that was the case wouldn’t it run funny all the time?

@dually

I can hear the lift pump running when I bump the key if I stick my head down by it. It’s a pretty quiet unit. That’s one of the reasons that I don’t think it is pulling air. I could be wrong though.

They key way was in the shaft with the arrow facing the pump body as per the instructions. When I opened the box. It was stuck in there tightly so I didn’t monkey with it.

I’ll have to check the gear train alignment marks when I get some light. [i work 12 hour shifts on the back half of the week so that could take a few days! Dark when ya get up, dark when ya go home… But the long weekends are great!]

After a cold start, it runs great. I’ve only had the truck since October 2011 but it runs like it did back then. I’m not sure I have had it out for a whole 10 miles but I know I have been out far enough to get everything good and heated up. I’ll have to try the hill stress test you mention this weekend and post back. I imagine it will be fine.

To be honest, the more I think about it, the more I think it may be an old computer getting heat soaked… I need to read a few more things to see if that pans out. One thing I am not sure I got into my first post was that the truck will restart and run fine if I try within about 5 minutes or so after initial shutdown. Much after that and I’m SOL…

@mopar1973man

I thought about an air leak draining back so I triple checked everything under the truck but, I didn’t find anything that was damp or showed signs of dripping. Is it possible for a fitting to pass air but not leak fuel?

I do have one question regarding the Jiffy Tite quick connections used at the Airdog itself. How far in should those be threaded? The one that was installed by them was threaded in until flush. I stopped on the two I did at about 2/3 of the way. They felt really tight at that point and I didn’t want to strip threads or break anything.

I also checked for the tank drawing a vacuum. Sadly, that wasn’t the trouble either.

Thanks for all of your help so far. If I can get more info to help you help me, let me know.

Rebelrodder

[dripley]

DAP sells pumps with and with out new computers, just like many others. That could be an issue.

[Mopar1973Man]

I thought about an air leak draining back so I triple checked everything under the truck but, I didn’t find anything that was damp or showed signs of dripping. Is it possible for a fitting to pass air but not leak fuel?

Really common for a suction line to be dry even though its leaking air. So during running it will suck air into the fuel and make it foamy. But then shut down the engine the fitting continues to leak air into the line and drain the fuel back to the tank. The only time these kind of leaks show up is when you pressurize the fuel tank by using a blow gun and packing a rag around the blow gun. Just get about 1-2 PSI and you see the leak for sure then because now it will turn damp and can really make it stand out by using baby powder on all the joints.

I do have one question regarding the Jiffy Tite quick connections used at the Airdog itself. How far in should those be threaded? The one that was installed by them was threaded in until flush. I stopped on the two I did at about 2/3 of the way. They felt really tight at that point and I didn’t want to strip threads or break anything.

Tight is good but you don't need to be yanking on the wrench too much. The fittings are usually are 18 ft/lbs for the banjo fittings...

[Rebelrodder]

I'll try the blow gun thing as soon as I get a chance. Hopefully, this will be it. If the suction line quick connect fitting is leaking what is the best way to correct it?

[dually]

You can also park the truck down hill to see if you have drain back.

[Mopar1973Man]

I'll try the blow gun thing as soon as I get a chance. Hopefully, this will be it. If the suction line quick connect fitting is leaking what is the best way to correct it?

Give Eric a call at Vulcan Performance and ask him doe the old school push loc connectors... Looks like the connector on my AirDog. When Airdog/Raptor switch over to the quick connectors it made installation quicker and easier... But as for making a air tight seal it didn't...

[Rebelrodder]

OK, I just got back from a 15 mile run up the longest hill that is reasonably close to my house. I ran up the hill at about 2k rpm. She pulled like a train all the way up. No stumbles or any other issues. Started fine from cold and ran great the whole time. :thumbup2:When I got back, I placed a bag of ice cubes on the VP computer to test for heat soak issues. We'll see how it goes in about 20 minutes. Heat soak is making more sense to me with respect to the symptoms I am having. Namely, that it starts from cold and runs great. It will restart and run fine within about 5-10 minutes after shutdown from a hot engine state. After 10 minutes it will start and fire, then idle for a couple of seconds then die. Repeat until batteries are dead... :lmao:I have not ruled out air leaks in the quick connect fittings as yet. Gotta wait for daylight for the tank pressure test.

[CUMMINSDIESELPWR]

$10 on the vp computer stepping into the grave...

[Rebelrodder]

Update!

My heat soak test didn't work. The computer case was about room temp when I placed the bag of ice on it. After 25 minutes it was a bit cooler than that but the old starting issues were still there.

I cycled the lift pump by bumping the starter and it sounds like it might be pulling a bit of air in. I'll proceed with leak testing in a couple of days.

One more question. If air bubbles draining fuel back to the tank is the root cause of this hot start problem, then why are they not a problem when the engine is cold? Or when running?

--- Update to the previous post...

A dying/sick VP computer is still a possibility in my mind. Still no codes to report.

I'll update as I learn more. Thanks for all the help so far!

[pepsi71ocean]

try this for me, run your truck get it nice and hot then pull the fuse for the Air dog, and see if the truck starts and stays running.if it stays runnign but then fails to stay running when plugged in you have a screwed up VP-44, but we can then eliminate the fuel drainback issue, and leave it to a VP-44 internal problem.Im really disheartened to hear this was a DAP Vp-44, i know Jkidd sells good stuff, i know lemons always make their way to market.

[Rebelrodder]

@pepsi71oceanI just tried what you suggested with the fuse pull. The engine merely sputtered. I didn't try too hard for fear of trashing the pump.On a more general note, I believe I found a flaw in my test methodology from last night. I think the ice bag thing was ineffective in keeping the computer cool via the plastic case cover. I'm going to try again this time with a small stream of water from the hose on more of the pump case. I can't remember where I read that as a diagnostic tool to verify that heat soak is the problem. :smart:I'm a little disheartened too but we get machine parts at work that are DOA. It happens to everything. If the VP computer is an issue, I'm sure DAP will be cool about exchanging it for me. I know the swap will go faster for me this time!

[Rebelrodder]

I'm back with more info!I used a blowgun to leak test the push lock fittings as per Mopar's suggestion. Didn't find any leaks. I did the test three time just to be sure. I have rechecked all of the fittings on any and every connection anywhere on the fuel system including the head drain. I can't find anything at any point.I also tried removing the fuse from the LP and starting the truck. Didn't even get it to fire. Clearly, this VP doesn't like 0psi from the LP!Next I redid the heat soak test this time by letting the pump sit for 20 minutes, then verifying the start-fire-die issue was still there. Then I ran some water from a hose over the pump case for about 15 or 20 minutes. This time, with a hot engine and a cold pump, it was just like a normal cold start. She fired up and idled nicely. Drivability was normal. Now this has me focused on the VP.I then called DAP to talk to them about getting a replacement pump. They suggested that the pump may not be bad especially with the lack of error codes. They mentioned that VPs don't always like to start with high (17 psi) input pressure like I was seeing. So at their suggestion I tweaked the airdog spring a bit and got the pressure down to 14 psi. This helped a little bit as the truck will now idle for about 3 or 4 seconds before it dies as opposed to the 1 or 2 seconds before. I can put a little throttle to it and get the truck to run but it won't idle for crap.I don't really want to drop the fuel pressure much lower than I have it right now for fear of getting below 10 psi. Plus, I know some of you guys are running way more pressure than that without issues. I still think the pump computer has a problem. I do not now and never have had long crank times to get the truck to fire. It's just an idle issue.Any further ideas out there? I'll keep this thread posted until I get a resolution just for future reference. I doubt I'm going to be the last guy to experience this.

[CUMMINSDIESELPWR]

my truck starts fine with 20psi prestart lift pimp run hot cold whatever. your vp is toast and it should be warrantied.

[dripley]

I think I am inclined to believe it is a computer issue on the vp. If cooling the vp like you say is allowing you to start and run with a hot engine when it wont without the cooling, the cooling is definately affecting someting in the pump. The circuit board or something else electronic in the pump.

[CUMMINSDIESELPWR]

Direct from blue chip diesel...

http://www.bluechipdiesel.com/vp44_diagnostics.html

[h=2]HARD START HOT, LONG CRANK TIMES, and then instantly runs smoothly[/h]Hard start hot is ALWAYS an electrical issue due to heat soak, where the computer gets hot from the latent heat from the engine after the engine is shut off. Cooling the computer by either time or an outside source restores the crystallized and therefore intermittent lead free solder connection(s) on the computer circuit board, and it takes off and starts. To test for this or convince yourself that I am right, try this trick. Run cold water over the computer on the top of the injection pump for a few minutes the next time you know it will be hard to start, and if it starts right up you know you need a new pump.