keithw1975

I have been putting up with this problem for so long and while I don't want to throw anymore money at it blindly it is very irritating. My 98.5 24v has had a problem where it idles very rough and you can hear it missing from the exhaust note every few seconds. My uncle who has spent his life around diesels said it sounded like a stuck valve. It sounded to me like it was out of time or something along those lines. Now the interesting part I found by accident is this. I had a battery go bad last fall and it caused a check engine light and set a code saying the lift pump input voltage was low. While the check engine light is on the engine runs smooth as can be and doesn't have the miss. If I reset the codes the engine goes back to idling rough and missing. Then if I unhook a battery and cause the error again it will smooth out. This is easily repeatable yet the dealers I have talked to are baffled. I have on my own replaced every engine sensor there is as well as tried swapping a new ECM but nothing has made any difference. I have been told the PCM and dodge sensors have no effect on fueling.

This may be unrelated but last Summer on hot days I had a problem on a few occasions where after driving my truck on the highway for an extended period of time the truck wouldn't start until it sat for an hour or two. After that it would start right up. That hasn't happened since and it never was solved even after the dealer had it for 2 days. During that time it never set any codes.

One more thing. Is it normal for the engine idle speed to increase slightly if the truck goes faster than around 5 mph? If I am sitting on a hill with the truck idling in neutral and let it start rolling around 5 mph the engine will increase in speed about 50 rpm and will stay there until you slow back down below the 5 mph.

Keith

PaulDaisy

LP input voltage low? Do you have a shorted out LP that is pulling the ECM down and causing this headache? Try to measure voltage on the LP after a starter bump. It was 8.5 V on mine. If running, should be 12 v full I think.
-p

keithw1975

Sorry if I wasn't clear. What caused the low LP input voltage was a bad battery. The good battery couldn't handle the load of the heaters on cold mornings and would set the code. And whats crazy is it runs good with the low voltage code set but runs rough when I clear the codes.

Keith

lovinCTD59

I think most of the time when someone experiences this on a hot day its a sign of a half dead VP44. Have you tried replacing that yet?

keithw1975

Nope. That is the one thing I haven't changed. If it was at fault though would it have lasted this long, over a year?

Keith

keithw1975

Well now it has set the code again but it is still idling rough this time. I was mistaken about the code saying low LP voltage. It was P1693 and P0237. These are the same codes I am getting as of this morning. I went out to start the truck and the check engine light came on and the lift pump wouldn't cycle just like before. The LP will only run while the engine is on but won't run to prime it like usual. If you bump the starter the LP will chatter off and on about 3 times very quickly but won't run.

I don't see how the low boost sensor voltage could cause the LP not to work properly. I replaced the MAP sensor but that had no effect on the check engine light which came right back on after clearing the codes.

Any ideas?

Keith

smokin habit

sorry but sounds like the vp44 is going out the timing is controled electronicly by the pump this is a problem lately that in my opinion is due to the new fuel that is out but thats my opinion

keithw1975

Well, can anyone tell me what might be causing the problem with the LP not priming the fuel system when you bump it? I have tested the leads and it simply isn't given any power from the leads going to it. What causes it to run for a few seconds when turn the key to run or when you bump the engine normally? Every time that I get the P0237 code and the check engine light comes on the LP does this so somehow they are connected.

And yes my timing does seem to change noticeably sometimes while driving. It has been doing that ever since I got this pump 70,000 miles ago.

Keith

PaulDaisy

The LP comes on for 2 sec once you turn the key to On. Once you turn the key to Start, the LP is commanded by the ECM to run at 50% duty cycle for 25 sec to allow the engine to start. I gather the lower inlet pressure on the IP makes it easier to start.
All functions of the LP are controlled directly by the ECM, I think.
Why do you think there is no voltage to the LP? If it is making noise when starter is bumped, the ECM is doing its job, demanding fuel. If the LP is not pumping, it is because it is dead. But you're saying "not priming". It will not "prime" the injection pump, it is not self priming. This is why you must crack the injectors open when you get a lot of air in the system.
-P

keithw1975

Well, what it does when the P0237 code trips the Check Engine light is as follows:

In the morning when I turn the key to run before starting the LP will chatter but won't build any real pressure. It will run for about 1/10 of a second 3 times.

If I bump the starter it will do the same thing again but it will never run for 3 seconds like it does when I don't have the Check Engine light on.

Simply clearing the codes will cause the LP to work as normal for a few days until the code is set again. I have checked all the LP connections and can't fine anything wrong. This is my second ECM. The first was was replaced about 3 years ago. I took my truck in because the tachometer stopped working and on the way home from having the dealer replace the crank sensor the truck had several dash lights come on and when floored would only muster about 2,000 RPM. Then it would idle from around 800 RPM up to 2,000 RPM without me touching the accelerator. After limping back to the dealer they said it was a bad ECM and I bought a new one from Cummins and had them put it in. Cummins claimed they tested the old ECM and said that nothing was wrong with it.

Keith

keithw1975

Doesn't anyone have any ideas? Short of blindly throwing more money at the problem I am pretty much lost at this point.

Keith

RAM2940

What is your fuel pressure while it is idling. Also if you have any electronic performance or fueling boxes have you disconnected and returned to stock mode to very that these are not causing the problems.

keithw1975

My fuel pressure, post filter, is 11-12 psi at idle. Yes I have tried removing the fueling box and putting everything back to stock.

I am just about to try replacing the VP-44 to see if that is the problem. I just hate to spend the money on a guess.

Keith

00 big boy

I think what you are experiencing is a bad vp 44. When the electronics goe bad in them you will experience hard cranking when engine is hot or the weather is very hot. I would have guessed that you are experincing dead pedal as well. The missing that you are hearing at the exhaust could be related to a bad injector. If I were you I would put a different LP system, such as a FASS or Walbro on the truck and replace the VP.