VP/APPS codes

[skyhigh4by]

Ive been chasing down problems with this new to me 98 24v and just got a pretty big indicator I think. First I diagnosed alternator AC problems causing TC lock/unlock issues,  and then narrowed down my TC not unlocking  to a couple things but now I was just out for a drive, stopped at a buddies house and we figured it was idling a little high 900rpm(ish) and the CEL kicked on while I was there. I was going to try an APPS reset when I got home but on my way home cruising down the highway my throttle pedal went dead and I had to be towed home. Pulled the codes and got P0121, P0122, P0216, P0234, and of course a P1693 to go with it all. I know what the definition of each code is but what is the actual underlying message here? Truck has 100k miles and is all original besides alternator and lift pump. Generally the truck drives fine and seems like it runs pretty good but sometimes it has been hard starting lately and I think Ive notice very brief dead pedal a couple times before. Before I just got buy an IP is there anything else I should be checking? 

[dripley]

Do you have anyway to check your fuel pressure? Weak fuel pressure can kill the VP, hence the 216 code. Dead pedal and hard starts can go hand in hand with that also. If you go the articles section, 24v, engine, obd error codes you can look the codes up and do some diagnostics to help narrow it down.

[skyhigh4by]

I assume you mean fuel pressure before the IP? I am quite capable of checking it but Im not familiar with the cummins fuel system at all. Where and how would I check it, and what pressures should I hope to see? 

[gassernomore]

14 psi is minimum. Anything lower than that contributes to the death of a vp. My truck runs at 18 psi and 15 psi at WOT. 

[dripley]

I believe on the 98s you would do it on the fuel filter canister. My 02 has a Schrader valve on the inlet fitting of the VP. Ideally you are looking for 14 psi minimum. That is not easy for a stock pump. You need to check it at idle and WOT. You need good pressure there also. The fuel cools and lubricates the VP that's why the pressure is so important. The timing piston in the can seize and cause the 216 code. 2 stroke oil helps with that also with today's ULSD. Most of us hear use it or a few other products to Add Lubricity to the fuel.

Edited January 14, 2018 by JAG1

[gassernomore]

Do you still have the factory fuel filter? If so, there should be locations on the top that you could use as a test port. BTW when was the last time the fuel filter was changed?

[skyhigh4by]

It has factory fuel filter canister. I was told that the lift pump and filter were changed very shortly before I got it. It looks to be a carter replacement pump. Ill take a look for some kind of test port on the canister 

[dripley]

Hopefully you can get the test gauge in the cab or at least visible so you can check it under load.

[Mopar1973Man]

Here is the fuel pressure article.