Jump to content

Lift pump diagnostic help needed


Recommended Posts

I have a lift pump issue I am chasing. Now before you tell me Raptor is junk, get a FASS I switched to my spare pump today and still the same symptoms so I'm ruling the pump out for now. Most of the time when cold I'll key on, hear the 1sec pump run and away we go as normal. Pump always holds 18 psi once it's running. When the truck is warmed up and I shut it off for a few mins. and go to restart, most of the time I hear a clunk, clunk, clunk from the LP. After that sometimes it will run and sometimes not. I usually bump the starter until it does run and then start. Once running it never shuts off and hold good pressure. What makes it hard to diagnose is that it does not always repeat. Today after switching pumps out I went for a drive to warm up, brought it back shut off and bumped the starter and clunk,clunk,clunk. Till I got my meter set up and went under to check for voltage I bumped the starter again and the it worked fine. I'm thinking either bad relay or ECM not triggering as it should? Thoughts and how to test?

 

Link to comment
Share on other sites

+1 ^^^

 

You sure the clunking is  from the  lp itself?      Can you    grab the  relay   while someone is   cranking?      you'd feel a  'thunk'    when it  engages.

 

Most  'bad' relays   would be   their   ground,  (does yours have a dedicated  ground wire,  or is it   grounded through the  case?)      Then the  relay itself, (internally, coil related)   then  the    signal wire.

 

This is  where a  indicator light  in the cab  would come in handy.   it'd tell you   what  the lp is seeing for  current.  

Is  the  noise  sporadic,  or  kinda  evenly spaced?       if  sporadic,   I'd  think  it's   loose/corroded  type  connections....  more evenly   spaced  could be   'heat/load induced'  open circuit  scenario.

Link to comment
Share on other sites

I have been chasing a similar issue with my Raptor/Air Dog conversion. Almost the same exact symptoms as you describe, but when mine doesn't run its dead silent. I've pretty much narrowed it down to either brushes in the motor or the motor itself going bad, because I'll give it a good tap on the end of the motor and away it goes. Next time it acts up, be ready to give the motor a lite tap or two with a small hammer or breaker bar or something similar and see if it takes off. You will have to do it in the time frame the lift pump should still be seeing voltage, IE within 15-20 seconds of bumping the starter.

I realize your on your spare pump and are dealing with the same problem, but its worth a shot especially if your "spare" has had some use on it. These motors are not good quality motors at all. I'm really torn what to do with mine, either put a new motor on it or shell out $600+ on something totally different and be done with it. I keep hearing Air Dog supposedly cleaned their acts up on their low quality parts but at this point I don't have much faith.

Link to comment
Share on other sites

Thanks for the replies. I was hoping nobody said ECM!. The clunking is so uniform you could sing a tune to it. It's either 3 or 4 clunks every time. While stretching my arm as far as I can to reach the key and getting my ear as close as I can to the pump it sure sounds like the clunk is in the pump. Like diesel4life says, it seems like bad brushes, worn bushings, or otherwise dead spot in the motor but I kinda threw that idea out after the other pump does the exact same thing. I'd like to just replace the relay but the one they use is nice in the way it snaps into the mount and seals tight so I'd like to go with the same one if I could to avoid more cutting and splicing to put another brand in. I'll try to get it to repeat it's clunk and then jump the hot pins and see if it runs then. That should rule out the relay.

Link to comment
Share on other sites

  • Administrator

ECM is in direct control of the lift pump there is no relays for it.

ecm6.jpg

 

But if you using a after market fuel system like AirDog, Raptor or FASS then they all have a trigger relay for the fuel pump. Is the fuel pump under warranty yet? I would say look at returning the pump for warranty if so. If not I would open the pump up and inspect for damage parts.

Link to comment
Share on other sites

That's right. The trigger relay is what I was referring to. I should have a lifetime warranty but I want to check everything else out before I call because I'm sure they will tell me to do so. I did have the pump itself apart and all is good inside. Did not look at the motor yet. Just wondering does Raptor use a brushless motor?

Link to comment
Share on other sites

all brushless motors need a controller. And they use 3 wires. our LP's are all brushed.

Fuelab is brushless and doesnt use a controller

I wonder if running your signal wire to the wiper fuse would help. I have been doing this lately and has been fixing hard start issues. I know this isnt your problem but you never know

Edited by mopartechnician
  • Like 1
Link to comment
Share on other sites

Got some answers today. I swapped relay out with a known good one, no luck. Checked/greased all connections, no luck. I then got it to do the clunk, clunk and no run. Quickly, before the free 25 sec pump run timed out I checked trigger wire and no power. Worked the key for awhile until clunk, clunk, pump run and checked the trigger and now power at trigger wire from ECM.Then I put 12+ to the trigger and the LP runs instantly smoothly with no clunk at all. Thanks for the suggestion Mopartech. I now have the trigger wired to the wiper fuse which I don't like for safety reasons but I can trust it to turn on now. So for some reason the ECM is giving sporadic signals to the relay trigger. What can I do about that other than throw a $2000 ECM at it?

Link to comment
Share on other sites

Being we are one the lift pump subject. I have a question about the time the lift pump is receiving power from the trigger wire.I had my ecm rebuilt about a year ago by AES in Fl. when I got it back I couldn't get it to power up (no wait to start light). I

talked to them on the phone and told them that I was going to dispute the charges on my credit card. They said the problem had to be with my truck but they would be glad to check it out. When they got it back I got a phone call saying there was nothing wrong with it and sent it back. When I installed it,it would power up, but the lift pump trigger would only power up for about 1 sec.

I could jump the relay on my Fass pump and get it started initially .After that the lift pump would would run for the 1 sec ,and as soon as the engine started pressure would come up to 18#.The truck runs good starts good, but still has only power to trigger wire for that 1 sec when I first turn the key to run or start ,It fires right up and pressure comes up. I have noticed my milage has dropped since. I didn't have my ecm flashed after it was rebuilt. Could this be some of the reason for the lack of power to the trigger wire ,or is a problem with the ecm? I kinda figure If it works don' mess with it.

Edited by hodag56
Link to comment
Share on other sites

Fuelab is brushless and doesnt use a controller

I wonder if running your signal wire to the wiper fuse would help. I have been doing this lately and has been fixing hard start issues. I know this isnt your problem but you never know

well,  someone is lying then.

A  brushless  motor needs  some sort of   controller   to convert   dc  to ac,   either  digitally or  analog.      So  fuel lab's  either internal   controlled,    or  they  are full of  crap.

Link to comment
Share on other sites

Being we are one the lift pump subject. I have a question about the time the lift pump is receiving power from the trigger wire.I had my ecm rebuilt about a year ago by AES in Fl. when I got it back I couldn't get it to power up (no wait to start light). I

talked to them on the phone and told them that I was going to dispute the charges on my credit card. They said the problem had to be with my truck but they would be glad to check it out. When they got it back I got a phone call saying there was nothing wrong with it and sent it back. When I installed it,it would power up, but the lift pump trigger would only power up for about 1 sec.

I could jump the relay on my Fass pump and get it started initially .After that the lift pump would would run for the 1 sec ,and as soon as the engine started pressure would come up to 18#.The truck runs good starts good, but still has only power to trigger wire for that 1 sec when I first turn the key to run or start ,It fires right up and pressure comes up. I have noticed my milage has dropped since. I didn't have my ecm flashed after it was rebuilt. Could this be some of the reason for the lack of power to the trigger wire ,or is a problem with the ecm? I kinda figure If it works don' mess with it.

It's normal for the pump to only run for a second when you turn the key to acc. Try bumping the starter it should run for about 20 sec, if it does all is well on the LP circuit.

Link to comment
Share on other sites

The only time I  get power is for 1 sec ,Till the engine fires.I would not have thought any thing was out of the ordinary ,if  it did that before I had the ecm rebuilt. The dodge  FSM list the sequence of the starting events like it was before I had it rebuilt,  maybe I'm overthinking this .My dad used to tell me if it aint broke ,don't fix it.

Thanks for your help, I'm just trying to understand a little more about how the ecm functions, all the computer stuff goes over my head.

Link to comment
Share on other sites

Got some answers today. I swapped relay out with a known good one, no luck. Checked/greased all connections, no luck. I then got it to do the clunk, clunk and no run. Quickly, before the free 25 sec pump run timed out I checked trigger wire and no power. Worked the key for awhile until clunk, clunk, pump run and checked the trigger and now power at trigger wire from ECM.Then I put 12+ to the trigger and the LP runs instantly smoothly with no clunk at all. Thanks for the suggestion Mopartech. I now have the trigger wired to the wiper fuse which I don't like for safety reasons but I can trust it to turn on now. So for some reason the ECM is giving sporadic signals to the relay trigger. What can I do about that other than throw a $2000 ECM at it?

Make sure you hooked your jumper to the upper plug on the fuse that way the fuse is protecting the relay and you will have nothing to worry about

Link to comment
Share on other sites

I was thinking in the event of an accident the LP will continue to run and fuel the fire as long as the key is on. And if I'm knocked out and can't key it off....... ouch. I used a double fuse tap ( if that's what you call it ). Plugs into where the existing fuse was an has place for 2 fuses. One to replace original and the other to fuse whatever you are hooking it to. Comes with a short lead. Kinda expensive but nice to use.

Link to comment
Share on other sites

I was thinking in the event of an accident the LP will continue to run and fuel the fire as long as the key is on. And if I'm knocked out and can't key it off....... ouch.

If the ECM stays powered up you have the same thing happening.

Link to comment
Share on other sites

×
×
  • Create New...