FFmike

I did a search before posting but couldn't find a similar situation, other than on the iATN which i'm not qualified for, so I'm reaching out to you guys for some help.

After replacing three LP's over the last three years, this last one finally took out my original VP44 of 180k after throwing codes 0252, 1693, and 1689, which were cleared. Now I have the Airtex that replace the Carter feeding my reman VP, and I was very impressed with 18psi at idle and 15 under speed.... for about 15 minutes. Seems like when I hit a bump in the road I drastically lose pressure within a few seconds. Gauge reads down to critical and warning light going off just as designed. So I shut er down and coast to the sholder, restart, and all is fine for about another five or ten minutes, then it repeats.

This was the reason I was replacing the previous LP's after thinking it was premature filter failure and replacing that as well, and now starting to wonder if all the past pumps were good. The original LP lasted over 100K and these last three for just over a year each? Reason being, this time I crawled under when the pressure started to drop down to 10, and measured voltage at the frame and saw only 12.5v Isn't that kind of low? I did put an extra ground right there on the last LP thinking it was a ground issue, but now not sure. I'm thinking that's why the pressure drops due to loss of power, but I didn't measure at startup when 18, sorry. I now have all new components from back to front and can't understand this sudden drop that goes away with an engine restart. I checked what grounds I could find, but I may have missed one or two.

Sorry for the novel but I didn't want to leave anything out. Do you think the PCM is going South and not feeding the LP with enough juice? Still throwing the 1689 with everything replaced. Is there an actual LP relay, the only one I found in the PDC was for "fuel system", and when i pulled it, the LP would still work so that's not it ( I do hear it click in the IP ). Any guesses?

I really appreciate your help,
Thanks,
Mike

nitrousn

Remove your edge or super chip, clear the codes and rerun it and see what happens. That 1689 seems do be a communication problem/buss problem.

FFmike

I took my edge off when the VP went out thinking that was the cause. No dice. All codes were cleared prior to replacing both LP and IP. Running bone stock right now, and code still shows up. Is there a circuit to check for LP power?

Diesel Doc

I have had that code for 2 years now I have begun to ignore it

FFmike

Did you have any problem with fuel pressure? That's my big concern right now as that relates to you know what. If the code was my only problem, I'd ignore it also.

Diesel Doc

no. I am running a fass full setup with about16-17psi all the time. The truck had that code after I got it and has had it ever since I clear it and it comes rite back. I was told it is a intermitent comunication problem between ecm and pcm.

00 CTD

It's a communication problem between the ECM and VP-44. Most of the time the VP is the culprit.

FFmike

Would this code be the cause of the drop in voltage to the LP? As in miscommunication resulting in not enough voltage being sent? 12.5 seems low considering the alternator is putting out 14. I still couldn't find a relay for the LP itself to check if it was bad. I know that FASS uses its own relay and is wired different. Just trying to trace the LP back to its power supply.

00 CTD

12.5V is fine at the L/P. In fact, Cummins states that it can be between 8 and 14V.

FFmike

Wanting to eliminate voltage drop, I installed a relay using the factory harness as the switching wire and sourced the supply from a fuse in the PDC. Still losing pressure when I open up to gain highway speed. Not full-out quarter mile pass acceleration, but moderate everyday 0-60 to get into traffic. So either the voltage drop from the factory LP wire is shutting off the relay ( below 12v de-energizing relay coil ), there is a problem with the rebuilt VP44 ( which doesn't even have fifty miles on it yet ), or the new LP is not keeping up. I'm leaning more towards this voltage drop issue which I will test by moving the switch wire to an ign-on source when the weather from Dolly clears up.

Are there any known issues with one of the controllers ( ECU, PCM, ECM ) that would indicate it's going bad and causing this kind of problem?

BTW, the code (1689) went away on it's own.

nickg

maybe try hooking your multimeter to the lift pump and running the cables into the truck, and monitoring voltage as you drive. This should help eliminate the voltage loss theory. Or maybe you have a vacuum issue in the tank which is starving the LP fuel. (bad fuel cap/or mud plugged vent on the fuel sending unit assy.)
or if you have a leak in the fuel line that allows air into the fuel line. it will not show as a fuel leak, ie wet spot on the line. If the "leak" is between the fuel tank and the inlet of your lift pump.
you say it seems to act up when you hit a bump...the leaking line theory might be compounded by the "bump" (

or how about a restricted fuel line, pinched line or plugged fuel strainer.

maybe re-route the fuel line from the LP into a fuel can for testing purposes, just to eliminate any issues from the LP back to the tank

FFmike

Thanks Nick, those are some good ideas. I'll monitor the voltage like you suggested before moving any more wires to be sure.

I did drop my tank over a year ago when I thought one of the last LP's was being starved like you mentioned. The tank was spotless, however the strainer had some sort of black stuff built up on most of the plastic screen. Almost looked like melted plastic, but like I said the tank was clean. I yanked that off and put an inline Wix strainer, and when I asked one of the dealers about this he said he had a customer who found the same stuff on his strainer. He was waiting for it to be analyzed and said he would call me with the findings, but I never heard back from him.

The tank vent works properly plus I took the filler cap off when it last happened to be sure, but it made no difference. It's weird that once I would replace a LP, it was fine for just over another year. But now you got me wondering about the intake leak. There's only a short section of hose ( less than a foot total ) from the steel tank line into the LP at the frame, and the clamps there were wrenched down good. I can't remember, and correct me if I'm wrong, but does the basket assembly in the tank ( the one they replace with an in-tank pump unit ) collapse? If it is, does the fuel pickup line that was attached to the strainer have a sliding tube? I was thinking that may be where it's sucking air if fuel was below that point, but right now I can't see that happening since my tank is nearly full.

As soon as TS Dolly gives me break from the rain I'll check my wires and get back. Thanks again Nick.

mini14

the black stuff is asphaltenes in the fuel, i see 13.2 volts at my pusher pump using a relay. u might have a weak ground, or a battery on its way out.

FFmike

Finally got a chance to check this out after 5" of rain. The voltage at the LP wire from factory harness floating around from 13.9 to 13.7 Drove around for an hour trying to find every bump n the road to get it to happen and now it's working fine. Even tracked the route I took the day I installed the pumps hoping to get a repeat and still nothin. It's looking like that 12.5v I saw may be where this is heading. That was when it went down and stayed at 10psi idle, where as now it's at 18psi idle.

I'll have to hook my edge back up on my next day off and try again to see if the extra fuel demand will trigger it, and also monitor voltage again to see if it drops or possibly the intake leak Nick mentioned.