With the recent snow storm I was pummeled with, I had to utilize the truck today to get to work. Unfortunately, the lift pump wasn't giving me a pre start prime. Even cranked over and running, the lift pump is still not giving pressure.

 

I checked the fuse, it's good. I swapped the relay out with a different one. Nothing. I checked voltage at fuse and got nothing.

 

Any ideas? Pump dead? Some other electrical issue?

Are you getting voltage from the ECM with the key on?

Edited February 13, 20196 yr by dripley

Where test?

My wait to start light illuminates. The grid heaters cycled when I warmed the truck up. 

 

There should be battery voltage at both sides of the fuse and terminal #30 of the relay.   ECM voltage at terminal #86 when ignition switch is first turned on (5sec) and when starter motor is engaged (25sec) and battery voltage at terminal #87 at the same time.  Terminal #85 to ground should test < 5 ohms.

 

With no voltage at the fuse I'd check the wire and connection from the fuse to the power source, either the battery or PDC.

 

 

3 minutes ago, IBMobile said:

 

There should be battery voltage at both sides of the fuse and terminal #30 of the relay.   ECM voltage at terminal #86 when ignition switch is first turned on (5sec) and when starter motor is engaged (25sec) and battery voltage at terminal #87 at the same time.  Terminal #85 to ground should test < 5 ohms.

 

With no voltage at the fuse I'd check the wire and connection from the fuse to the power source, either the battery or PDC.

 

 

The schematic is fantastic reference.

 

NOTE - you can pull the relay from the Relay block (assuming it is plugged into a relay block)  and put a jumper wire from 87 to 30 - and see if the lift pump starts running.  (This can be done with the key off - because the relay gets power directly from the battery via the PDC (power distribution center).  Done with the key off - you should be able to hear the pump running.

 

Again - with the relay still pulled - connect a digital meter - one lead to Pin 86  and one lead to Ground (or 85).  Set to VOLTS - at 20VDC scale.  Turn the IGN key on and 'bump' the starter.  You should see 12 - 13 Volts on the meter if the ECM is providing the proper 'signal' to the relay to turn the lift pump on.

I like it when the better electrical minds jump in.

Check the fuse. If the fuse is blown the pump motor is locked up. Most likely the pump to motor seal failed and now there is most likely fuel leaking from the pump. 

 

WARNING: Do not install a bigger fuse. If the 20A fuse blows a second time the pump motor is locked.

Thanks guys, I'll troubleshoot it and get back. 

 

I thought maybe it was what you said, Mike, but the fuse was not blown. This is like my 4th or 5th pump, so that's what I was expecting too. 

Alright, so I went to work on the truck. Like all things in my life, I try before I pry. Lo and behold, I turn the key and the lift pump primed.

 

Well, at least I don't have to deal with fixing the lift pump! Im not sure what happened. Only thing I can speculate is that the fuel gelled up. I haven't been driving it much lately since I got myself a tdi passat for a commuter.

Im cursed. The pump is messed up or something. Occasionally only works. Going to hot wire the pump and eliminate that. Otherwise it's something else. Frustrating...

@hex0rz Did you do the W-T ground wire mod? Have you checked the alternator noise level?

 

I have not. I tried to work on it this weekend but the pump was working. So I drove it for 20 min to the fuel station. Filled up and the pump would not prime after the turn of the key. I said well, gotta get home, just take it slow. Then about a mile down the road the gauge needle jumps up to 30psi.

 

Today it did the same thing on the way to work after doing a dump run.

 

How can I troubleshoot it when it's intermittent?

Since you have already replacered the fuse and relay have you checked all the wires and connections?  

Did you check if the ECM is suppling power to relay terminal 86 when you bump the starter and the pump doesn't run?

18 minutes ago, IBMobile said:

Since you have already replacered the fuse and relay have you checked all the wires and connections?  

Did you check if the ECM is suppling power to relay terminal 86 when you bump the starter and the pump doesn't run?

 

Suggestion - (and - since IBMobile is pointing to possible problems from the ECM...) - install a temporary switch to supply 12 V - from the battery - directly to the output of the relay that supplies the Airdog.   Have the switch inside the cab.     THEN - when you are expecting the Airdog to turn on...like after key on and bumping starter - and you don't see any fuel pressure build up - flip the switch and see if the Airdog comes on.  If it didn't come on when expected...and flipping the switch does give you the pressure - you will need to troubleshoot the relay and the signal that energizes the relay.

 

IF you don't get fuel pressure under either circumstance - then the problem is likely down stream - power into the pump motor - or the motor itself.

 

AND- for good measure - you could run 2 lines from the pump connector into the cab - and connect those lines to a LED  (check for proper polarity of the LED - or use an incandescent bulb...) - and the LED will turn on when power is going to the pump motor.  If you have the LED on - but no fuel pressure - well -either your pressure gauge is faulty - or your pump just isn't pumping.  

Bump the key test the ECM lift pump connection? (Power yes or on)

 

Bump the key test the AirDog Power Relay? (Power yes or no)

 

Bump the key and test the AirDog pump motor? (Power yes or no)

 

Any odd sound will the pump is running? (Sounds typically point to bad bearing and shaft seal)

 

Any fuel leaking off the pump motor? (Signs fo bad shaft seal)

With my recent frequent usage of driving the truck, the frequency of times the pump not priming or not running has practically diminished to nothing. 

 

I have yet to encounter a time now, recently where it has not primed or ran.

 

I. Just. Don't. Get. It. ?

ECM failure?

 

Did you do the W-T ground wire mod?

Hi everyone, long time no talk. 

 

Ive resurrected this post. Funny how time passes and you forget what's transpired. Ive forgotten way too much...

 

Well, suffice to say, this issue came back to haunt me again! This time, nothing I tried solved the problem. I spent a couple hours out on the truck troubleshooting it. Without really understanding what the problem was, I wasn't able to gain much ground on it. Eventually, after going through several different posts on the web, I narrowed it down. 

 

If I had remembered this post, it would not have taken so long. Ha...

 

Well, lo and behold, it turns out my issues have all along been from too low voltage from the ECM to trigger the relay. Tested the connection and only got about 2v.

 

If I bypassed it and hot wired everything else, the pump would run. Eventually I found ibmobile article on wiring the trigger wire to the fuel relay in the PDC.

 

I took the black wire from the trigger and grounded it and then took the tan wire and stuck it in terminal 87 of the fuel relay. 

 

If I understand it correctly, I need a relay for the relay? Im not exactly sure what I need to accomplish with his article as the lift pump already has a relay. 

 

Regardless, when I switch the key to ON, the lift pump runs. When I start the truck then turn it off, the pump doesn't run. If I bump the key, it doesn't do a prime, but stays running. 

 

I guess for now it'll work? Can I get away with doing it setup like this for now?

 

How can I get it back to doing a prime with the key to ON and not run until I start the truck?

 

Im willing to deal with the way it is now, but I would hate for it to run while I'm sitting somewhere in the truck with the ignition on and the engine not running.

Did you check the voltage at the ECM? Could just be a bad wire or connection.

1 hour ago, dripley said:

Did you check the voltage at the ECM? Could just be a bad wire or connection.

 

The plug that you connect the trigger to from the ecm, yes. It was 2v.

Just to be clear I am speaking of testing at the pin on the ECM itself and not at the plug you connect to the relay. There maybe a problem between them.

 

As far as getting the prime and such back the ECM controls that. The only other way I know to control that is put a switch on it.