Now What

[balsip]

I think you are "hot on it" with the idea of exhaust gases getting back to the tank. I had the exact same problem when Dodge dealer changed VE44 in my 91.5 in 1996. Cummins used to have very brittle black-blue paint that was sprayed over the engine AFTER final assembly that came off when working with wrenches. The Dodge mechanic was so careless he got some flakes in an injector and it prevented the injector pintle from closing after "pop off". The symptom was milder surging (than yours)at idle only as the mechanical governor tried to compensate. I think the VP44 electronic governor might be more sensitive and cause the extreme surging you have as it tries to get correct idle RPM. I put in clear PVC tubing on both supply and return lines and I could see the bubbles start in the return line (exhaust gases from injectors) and then suddenly re-appear in the supply side due to the small pick-up chamber in the tank. You can imagine the the foamy diesel in the pickup chamber in the tank with exhaust gases getting in there.

There is a small 3 inch section of rubber fuel line on the supply side of the VP44 that you could substitute a loop of 12 inches of clear PVC temporarily. I only tested in the driveway since PVC was not rated for fuel and I was afraid of diesel fire while driving. The rubber piece in the return on the 24V is of no use since only the VP44 overflow portion is accessible there - the injector return flow joins in a T connector at the very back of the engine before going to the tank pick-up.

There is more to my story about the incompetence of that mechanic at a 5 star facility but I will leave that for now. It cost Dodge two injection pumps and at 2 dealers, a mechanic's job(I surmize since he was gone quickly), over 25 hours labour and finally re-imbursement to me for my own final repairs when they could not handle it.

--- Update to the previous post...

JLWelder, I put a file under downloads, "Other Manuals and Documents", called "VP44 Smart Digital Governor" that is used for gensets, pumps etc. It is probably functionally equivalent to what Cummins implemented in the ECM of the 24 V and gives a lot of insight to the Cummins ECM functionality. This governor works with 12V or 24 systems. One item of interest to you is on page 17 under Troubleshooting with a symptom of "Engine Unstable" with a cycle of 0.5 sec to 1.0 sec caused by the battery being less than 20 V on a 24 V system (or less than 10V on our 12V system). Look at the wiring to the VP44 and it shows only six conductors to the ECM: CAN H&L(serial communication), +V, GND, DZG(timing derived from Crank, cam teeth), MAS (master shutdown). I would measure voltage with safety pins piercing +V & GND with a DVM just before the final VP44 connection to see if there is a bad connection or ground and compare to voltage accross battery while it is surging. I believe surging as described above is more likely but this write-up saved 3 months ago caught my attention to your problem.

Good luck, I love your persistence in this.

[rburks]

Richie

JL...did you find out where the crack is at... Very curious as to if it was cracked through the retutn gallery or through the injector bore in the head.. You Know i was thinking that its Odd that with that much pressure in the return that you did not have fuel leaking out around the connector tube bore..I mean that an O-ring should have give out by now and be weeping fuel.. subscribed!!! Richie

[ISX]

Jlwelding, I drove a long ways this past weekend and at every fillup I had a lot of pressure at the fuel tank cap.. I know you asked anyone else if they had the same thing but I hadn't noticed til this trip. Not sure why it has pressure but it does I might have to see where it is supposed to vent at.