Engine/Transmission (1998.5 - 2002) Ecm/lift Pump Intermittent

[rattlnrench]

I noticed on a handfull of occasions in the past few months my fuel pressure gauge would read 0 after a cold start. It usually would happen with colder weather. I finally had a chance to look at my truck yesterday. I checked the voltage at the lift pump and found 9 volts which would vary up and down by 1 volt at times. I know the lift pump goes from a 25% duty when the key is first turned on to 100% when the truck is running. Shouldn't I get a full 12 volts to the lift pump while its running? I can also see my fuel pressure vary a little. At times while I was testing(had my wife bump the starter) the voltage would read 2 volts for a second & then read the 9 volts with the lift pump responding accordingly. The lift pump relay is in the ECM & I'm thinking that is my problem. The lift pump is a couple of months old and is not running when I have the 0 fuel pressure. I don't want to rig something up to cure it(switch & relay), but I also want to ensure the injection pump will last. Anyone have an ECM they could part with that's reasonable? Anyone repaired this a different way? Suggestions are appreciated.

Oh Yeah,

The truck has 106k on it so warranty is not an option.

 

[CoastyAV8R]

I had a similar thing happen to me. My fuel pressure would drop to around 0-2 psi from the 10 psi range. It would do it usually after driving it for about 30 minutes and then only intermittently. Scared the heck out of me when the needle would drop to 0. I replaced the lift pump and it has been fine since then. I tore the lift pump apart and the only thing I found was some slop in motor bearings, I guess they were just wore out. My guess is it would overheat or just get into a position and bind up and stop pumping. I know you probably don't wanna replace a lift pump on a whim, but that's what I did and it was the cause. I had 25,000 miles on mine when it died.

Hopefully others will chime in with their experiences.



Pat

 

[15w40]

The lift pump at start up produces about 7 psi because the ECM duty-cycles the 12V to the pump. The duty cycle is 50% at about a 10 Hz rate. This may be tough to measure on a meter because it is changing from 0 volts to 12 volts. Some digital volt meters will give you wild readings as they sample the voltage at 0 then 12 and don’t display the correct readings. An analog meter will average to about a 5-volt reading.



The ECM powers the lift pump directly, not using a relay. The ECM gets its power through a relay in the PDC. If this relay is intermittent, it could cause the voltage at the lift pump to vary but it would also cause the engine to stumble and possibly set codes.



Hope this helps.

 

[rattlnrench]

This lift pump probably doesn't have over 5k on it. The one I replaced before it was 1 year old. I'm thinking that I've had this voltage thing going on for a while causing the lift pumps to over work themselves from the lack of current. They have to do just as much with less. I guess if no one has a different fix I'll bite the bullet with a new ECM. BTW. I tried to open the ECM up to check the circuit boards for an intermittent connection or dirty relay & since then I'm running 1 more psi on my gauge. 15 at idle & 13. 5 at cruise. I didn't change anything else so maybe I'm on to something here with repeated lift pump failures. I haven't checked the voltage again to confirm this yet. The truck didn't act up today either.

 

[rattlnrench]

15-40



You just beat me to the punch. I know there's a relay in the PDC but if that ones bad the truck will run poorly if at all. This truck runs great & I'd like to keep it that way. When I opened the box cover slighty I could see relays inside. Now if the ECM duty cycles the lift pump my voltage will vary no doubt. I never have seen 7 psi on key on engine off. I only see a little blip on my gauge as the lift pump runs less than a second. Earlier I was talking about bumping the starter & there is a delay(pump runs,stops & runs again) to get 100% duty cycle. I can understand running the lift pump through a resistor for the 7 psi but I can't understand why you would duty cycle an electric motor to acheive 100% duty or max output. There are no DTCs. I guess I could put my Vantage on it to see what waveform I have. Maybe I'm in no mans land here but surely someone has checked this stuff before or are willing to check theirs & report.

 

[15w40]

It seems to me that your problem is in the 50-pin connector to the ECM. Taking it off and then reattaching it may have helped out the lift pump connection. I would try some dielectric grease after cleaning the connector. It is a lot cheaper than a new ECM.



Good luck!

 

[rattlnrench]

15-40



I agree anything must be cheaper than a new ECM. The pins on the ECM were pristine. I also wiggle tested the wiring harnesses I've run into that kind of thing before, I own & run an automotive shop. I've repaired computers before by repairing bad solder joints or replacing bad components. The circuit boards, 2 of them, are attached to the lid of the cover and connected by a ribbon cable between them. I got cold feet about bending the cover completely open because i was afraid of breaking a circuit board & disabling the truck. No one has an ECM around here & there would be a 3-4 day wait but I use it for the shop daily.

 

[rattlnrench]

I put the lab scope on it today & the ECM does not pulse current to the lift pump. I guess it depends on the definition of duty cycle. At key on engine off the pump runs for . 25 seconds. An interesting thing happens when you bump the starter to get the 27 second run. The voltage to the lift pump actually goes from 0 to battery voltage to 0 3 times before the voltage goes back to battery voltage & the pump runs. In an earlier post I indicated less voltage when the pump would initially start(2 volts) & corresponding lift pump actuation. What I was looking at was a rapid voltage fluctuation that the DVOM averaged out. The lab scope caught it. Still in the hunt here & I always win. My bank account may not however.

 

[2-ND TIME]

lift pumps and ECM's

What a dummy never though of checking the relay that feeds the ECM will try that soon ! Thanks They could use a Zinner diode to give 7 volts or ???? I like the info that is here will use it . What about corroded terminals would that drop the voltage enough?

 

[rattlnrench]

I think I'm going to install a temporary test light on the lift pump & run it into the cab. The pump has never failed to run while I've been checking it & has also been fine while driving it the past 4 days. Figures. I thought I was on to something about lift pump failures with the "duty cycle" thing. Research in my Alldata system has shown a initial key on duty cycle from 50%(4 seconds) to 25%(2 seconds) to 15%(1/4 second) depending on year model. My truck was reflashed last year so I'm sure I have the 1/4 second parameter set in the ECM. The only thing that still has me thinking the ECM is the culprit here is the 3 voltage "spikes" to battery voltage I get when doing the bump test. On vehicle starting it will "spike" once before the pump operates normally. BTW. According to the test procedure you run 2 pressure tests a key on & a cranking test. To run the cranking test the procedure tells you to pull the pump relay to keep the engine from starting. That would eliminate the pump relay as a cause. The pump relay must be for the injection pump alone & also according to the test can set a code. I wish the wiring diagrams were better, diagnostic information clearer, or a voltage pin out was available.

 

[Marco]

rattlnrench,

I've seen several ECM's with problems but never one with a faulty lift pump circuit. Sure there's always a first time but I doubt your problem is ECM related. Both the positive and negative sides of the juice for the lift pump come from the ECM. What did you use as a ground when you tested the voltage to the lift pump? The original ground wire?



The ECM uses a MOS-Fet transistor to power the lift pump. As you know them transistor can provide some crazy Ampere numbers. I've never seen one fail in these ECM's... .



My thought is that the lift pump has a problem. If the lift pump has a short sometimes, then the voltage would obviously go down low...



Marco

 

[Neal Cassady]

3 pulses after bumping the starter

is normal. I have seen quite a few trucks do this, including mine. I first noticed this when I installed my pusher pump. I thought I fouled something up doing the install.

 

[rattlnrench]

Neal,



Thanks for the heads up on the voltage spiking. That is of some relief.



Marco,

I appreciate your insight. I've worked on a lot of vehicles with computer controlled problems & agree that the computer is rarely the problem. You said the ground is through the ECM also. Could you tell me which pin on the ECM it is? The ground I used to check the voltage was the engine. My fault there that I did not take the ground circuit into account. But then again the truck hasn't acted up. I know I would have checked that if the pump didn't run & I had voltage to it. According to my wiring diagram the ground for the lift pump is located close to the ground for the a/c clutch ground. I didn't tear the harness apart to confirm or deny this. The weather is much warmer here now so the truck may not act up again until next winter. I'm still going to do the test light thing which will tell me for sure if the truck acts up whether I have a lift pump problem or a control problem right after I check the ground circuit for it.



Thanks to everyone... ... . I'll keep you posted.

 

[Marco]

Wiring

http://www.dodgeram.org/tech/dsl/ECM/ecm.gif



Need more?



Marco

 

[rattlnrench]

Marco,



Great wiring diagram. It's from Cummins so it's different from the one I have from Alldata. I can see that the ECM, FPCM, & Fuel Lift Pump share a ground but the ground for the Fuel Lift Pump does not go through the ECM. No big deal, the diagram is really much better than what was available to me. It seems that if I had a ground problem, with those components sharing the same ground, it should show up with a DTC or the truck running poorly. It runs great while it's acting up but I know the VP44 is having to work harder than it should. I guess that's my main concern. If the problem lies in the ECM I'd rather spend the $800 now than $800 later with another $1000 or so for an injection pump. I haven't ruled the lift pump out either. I just need to get the thing to act up again while I have something attached to it to see if it's the voltage supply or the Lift Pump itself.



Thanks Again

 

[Marco]

OK, here's the other half of the wiring diagram. #ad




Have fun!



Marco

 

[HeberRam]

Same problem

Rattlewrench... . I just started having the same problem as you, two days ago. I started the truck, started to accelerate, no prower, looked at my fuel pressure gauge "ZERO" pressure! I immediately shut it down. Two more attempts to re-start, my pusher pump and lift pump started working again. This now has happen 4-times in the last two days and is intermittent as you describe? I know its not the lift pump (new), its like the power is not getting to it on initial turn of the key? Once started, everything runs find? Keep me informed, I'm going to ask my friend at a dealership (tech) who works on nothing but Dodge diesels, if he has come across this problem.



Steve

 

[Marco]

Try a relay

To understand where the problem comes from you can try to power the pump(s) through an relay.



The ECM powers the relay which then feeds juice to the pump(s).



Since the load (pump) is now uncoupled from the ECM you can find easier if the power is missing from the ECM or if you have a faulty pump... ...



Just a thought...



Marco

 

[HeberRam]

???

Ok. . I talked to my Tech friend... #1. go into the fuse box (engine) compartment, locate the fuel pump relay fuse, lower left hand corner, approx. 1/2x1" in size and change out with another fuse, like the quad lite fuse. If the problem stops, you need another fuse. If the problem, stills happens, this tells you the fuse and the relay is "OK". #2. The lead wire to the lift pump is loose. #3. The lead wire to the lift pump is corroded, not making good contact. This is happens quite often, due to salt corrosion, or where people(like me) scotch lock on the lift pump, to run a pusher pump. His experience so far has been 1 of the above, has been the problem. He can't remember any ECM or PDC issues that has caused a similar problem.



This morning, first start-up, the problem happen again. I switched the fuses, perhaps, 15 starts & stops today no problem so far.



If it happens again soon, I will go to step #2 and so on! I don't want to get to step #4. ????:{



Thanks Marcos, keep them ideas flying.



Steve

 

[rattlnrench]

HeberRam,

I pulled every fuse that is linked to the ECM one at a time & never did get the exact symptoms my truck has. There is a fuel pump relay but that's for the VP44. I did get other components not functioning when I did this. The only problem my truck has is no fuel pressure at times. I did install a 12v(194) bulb off of the wires at the lift pump & ran it into the cab. The next time, if ever, my truck acts up I'm going to check the light first without shutting the truck down & if I have no light I'm going to pull the connector @ the lift pump to see if I get a light then, eliminating a shorted pump. My fuel system is stock with the exception of DD1 injectors & all the connections in the area of the lift pump operation have been checked.



My truck is a '99 so maybe the wiring is different. BTW, the fuse box under the hood is the PDC(Power Distribution Center).