1999 24V Cummins with 138k miles. Just replaced the injection pump, fuel filter, oil and air filter. Lift pump is pushing about ~8psi at idle and cranking. Not sure what it's doing at WOT.

9 out of 10 times when trying to start, it will idle VERY lopey for about 5 seconds, then die. Peddle does nothing. The next minute it will fire up and run perfect. Sometimes it will idle with that big lope until I kill it. The accelerator still does nothing.

Also, when it is "loping" the relay for the lift pump (on the firewall in the engine bay)is constantly clicking on and off. Not sure if that is normal or not. I've replaced it with a known good relay and it still does it.

Any suggestions?

 

not sure what is going on but 8psi at idle is not good.

 

Could that cause these issues or cause it to not start at all? It seems like 8psi should be plenty to at least start the engine?

 

I can't believe this isn't a common problem that someone else has had to deal with. I can't be the only one this has ever happened to?

 

Have you checked for codes? Do you have an edge product installed?

Yes, I had that problem when my edge ez went bad. It was causing no communication between ECM and Vp.

 

8 psi of fuel pressure at idle is enough for a smooth running engine. Since you mention the lift pump relay on the fire wall clicking on and off, I’ll assume you have an aftermarket lift pump triggered from the factory lift pump wires. If this relay is going on and off, the ECM on the engine block might be receiving intermittent power from the fuel pump relay in the PDC. Try swapping it with another.

Does the lope happen only with a cold engine? Maybe you have weak batteries and the cycling grid heaters are pulling the voltage down causing the lift pump relay to drop out. Try testing the batteries or cleaning the battery connections.

A signature with your truck info will help others to respond to your questions.

 

The truck is a 99 24v with 138k miles. Bone stock. Brand new batteries, oil, filters and VP44.

No codes, both batteries are brand new and connections are clean. Grounds are all clean and secure. No mods are done to the truck. It's stock.

What is a "PDC"?

I would say the problem happens more often when it's cold. Usually when it's fully warmed up it starts just about every time.

 

A completely stock truck does not have a relay for the lift pump on the firewall unless it has been retrofitted with an in-tank pump by the dealer. If this is the case, the relay on the firewall is triggered by the ECM.

Look in the Power Distribution Center (PDC) on the driver’s side fender well for a relay labeled “Fuel System” or “Fuel Pump”. I can’t remember how it is labeled on the cover of the PDC. Anyway, try swapping it with another one like the “Horn” relay. If that stops the lope you have found the problem.

 

Yup, tried that. Swapped each one over and over. Still no dice. The horn worked with each relay.

The dealer must have installed the in-tank pump. It has -0- aftermarket parts installed(unless you consider the pump aftermarket). It is STOCK.

 

OK, the fuel pump relay is not causing the problem. My guess is that there is an electrical problem causing the lope and it could be anywhere between the ignition key and the ECM. I base this on your comment that the fire wall mounted relay cycles on and off when the engine is misbehaving. Have you tried wiggling on the engine harness to see if you can cause the engine to lope? Or maybe a connector (ECM or PDC) is not making a reliable connection. Removing and reconnecting them may help.

I’m out of ideas. Good luck.

 

Im dealing with this also on a customers ride. Swapped out the new pump for another new one. There was no comm between vp and ecm code 1689. Took 3 days of running before it threw that code.

 

So the second new pump fixed the problem? I'd hate to have to swap another pump in.

 

Had the same problem at 13?k turned out to be the APPS

 

It caused this exact problem? I've adjusted the APPS and it seems to be functioning correctly. I never thought the APPS could cause such a large problem, especially the consistant stalling after 5 seconds. I'll have to look into that a bit closer.

 

The APPS was replaced at the dealer before I worked on it. Still had the problem. The APPS may have had 10-15 miles and was in adjustment. The dealer told the customer, sorry we thought it was that but we were wrong. Thats why he brought it to me. Still waitin truck to come back today to put on new new pump.