Engine/Transmission (1998.5 - 2002) Intermittent lift pump

[BoeingDiesel]

A couple of months back the lift didn't always activate when turning on the key. It had been many years so I replaced the pump...problem solved.
A few weeks back the same thing happened and after about 10 seconds the pump activated but the truck took about 8 seconds of cranking to start which is atypical of this truck and the same thing happened again today.
Would that point to the ECM or..?
Any thoughts or recommendations are greatly appreciated.

 

[Bob4x4]

Wire a volt meter to the leads at the pump so you can monitor what is happening real time

 

[BoeingDiesel]

Thanks Bob, is there a specific voltage range that should be present under normal operation?

 

[klcammie]

Also check the big connector on the fire wall. It's the one with the white bale. The bale has to be all the way to the left. Mine would shut off lift pump while driving.

 

[BoeingDiesel]

Thanks Klcammie...When I started the truck this morning everything was normal, however, I intentionally drove the truck about 50 miles and periodically shut it down and the pump activated as it should. The last 20 or so miles I made two stops and the pump took about ten seconds to activate but then started without any hitches. I'm beginning to think there may be a heat issue causing increased resistance in the ECM communicating with the lift pump. Does that sound like a possibility? I'm perplexed so next step will be to check the voltage as Bob recommend and have a look at the loom at the top. I suppose I could pull the plug on the ECM but I have no idea in what I'm looking for.

 

[hcole]

BD, check this thread out. https://www.turbodieselregister.com...lem-on-1999-2500-that-mechanic-can-t-diagnose

 

[BoeingDiesel]

Thanks HCole. I think I'm going to replace the ECM as it is the original. Doing some checking there are a lot of companies out there offering remanf units but gives me reason for concern when reading customer reviews. Anyone have a recommendation as to a good source for ECM replacement?
thanks
gregg

 

[Bob4x4]

Before replacing the ecm I would run the pump off a relay.I see too many flakey rebuilt ecms to want to go that route if you can avoid it

 

[BoeingDiesel]

Before replacing the ecm I would run the pump off a relay.I see too many flakey rebuilt ecms to want to go that route if you can avoid it

I totally agree and after reading many reviews of remanf ECM's I will avoid that if possible.
Question; is there a wiring diagram available to wire the lift pump with a dedicated relay as I'm not real savy on wiring.
thanks

 

[Bob4x4]

I totally agree and after reading many reviews of remanf ECM's I will avoid that if possible.
Question; is there a wiring diagram available to wire the lift pump with a dedicated relay as I'm not real savy on wiring.
thanks

If you can get your dealer to order the wiring from the fuel pump retrofit kit It will a piece of cake

 

[BoeingDiesel]

I didn't have much luck in ordering a wiring setup from the dealer in Long beach so I guess I'll run a relay off the ignition.
Thanks all for your input.

 

[klcammie]

Here is a good wiring pix that I just used last weekend. Easy to follow. Got it from another site from a fellow that was having same trouble.

 

[BoeingDiesel]

Thanks KLcammie, but I’m not sure this would resolve the problem. If I understand the schematic it looks as though relay pin 86 is reliant upon the ECU to activate the relay and I think that is where the problem originates. Is that correct?

 

[JR]

It relies on the ecm to trigger the relay. The important thing is the load is removed from the ecm and placed directly on the battery. This is how aftermarket lift pumps like FASS and Air Dog are wired also

 

[klcammie]

That is correct. But as JR. says it removes the load. Also it is an easy thing to do and you never know maybe the ECM jst needs a little relief and there is no down side, if it doesn't work you can tigger the relay with another key on power supply.

 

[BoeingDiesel]

Thanks, I'll give it a try and report back.
Strange thing tho'...last weekend I disconnected the batteries and cleaned all contacts and the pump has only lagged once since then.

 

[BoeingDiesel]

Here is a good wiring pix that I just used last weekend. Easy to follow. Got it from another site from a fellow that was having same trouble.

Well I thought I was done and over with the intermittent lift pump activation as it’s been almost a month since it last happened, until yesterday. Same scenario and had to wait close to ten seconds before the lift pump activated. I didn’t do any re-wire as the issue just seemed to go away. I can tolerate the pump delay but what concerns me is that the pump will shut down when driving. I’ve read many related posts on the TDR as with some other forums and I noticed that some have said bypassing the ECM with a dedicated relay will cause fault codes as the ECM needs to see a load on the pump. In looking at KLcammies’ rewire diagram I’m wondering as to the location of the “Red wire to ECU.” Is this the red wire lead on the pump connector? Just want to be sure as electrical is certainly not my forte’.
Thanks gregg

 

[hcole]

It will not set a code.My truck has been hooked up to just a terminal in the fuse and relay box under the hood that is hot on ignition on for app. 5-6 years and has never set a code.

 

[klcammie]

In looking at KLcammies’ rewire diagram I’m wondering as to the location of the “Red wire to ECU.” Is this the red wire lead on the pump connector?
Yes. When I did mine I cut the red wire Spliced in a wire to the relay. Then back down to the other side of the red wire from the relay.

 

[BoeingDiesel]

Thanks guys for the feedback, I'll do the rewire and hopefully will resolve the problem