Surge 5 minutes after start, advance solenoid disconnected

[FnFilthy]

I am completely baffled. I have a 92 7.3idi. The motor has only 30k miles, but the fuel pump may have over 500k miles.
Symptoms are that about 5 minutes after start I get a surge with hard dieseling, like the pump is advanced. There is a noticeable surge in power along with the increased "rattle". I have disconnected the wire to the advance solenoid, but still have the high idle solenoid connected. I don't think its air in the line because it doesn't happen until after driving for some time and only happens once. The surge only lasts around 5 seconds or so, but its definitely noticeable. It never does this at any other time and never does it if the engine is warm. Any ideas?

 

[chillman88]

Not sure, certainly SOUNDS like air in the lines. Maybe you have a very small leak that only leaks enough to be a problem after sitting all night?

 

[FnFilthy]

Chillman88 - That's what I had been thinking, but it seems like the lift pump and return lines would have cleared any air from the system by that time, but stranger things have been known to happen! When I get a chance, I will go through the hoses and check. I wish I could loop a long bit of clear hose up into the cab so I could see if there was any air circulating. I guess I could still do that with it just sitting at idle. Hmmm. Maybe that's a thought. Anyhow, thanks for the reply.
After over 500k miles on that pump I keep my fingers crossed that I don't have to replace it.

 

[chillman88]

but it seems like the lift pump and return lines would have cleared any air from the system by that time

Well I would think so as well, but

Have you ever changed your lift pump? Just out of curiosity. If you have a weak lift pump the injection pump will still "pull" fuel although not near as fast as a working lift pump would. Although if that's the case your fuel filter light should be on, assuming it's functional.

 

[FnFilthy]

Chillman88 ... So... I parked uphill in the driveway last night. Started up this morning and made it as far as backing out before she fell on her face. So somewhere I am getting air in and it allowed the fuel to roll back into the tank.
I didn't change the lift pump when I put in the new motor. And it may be a bad assumption, but I'd think that if it was allowing air, I'd find diesel in the oil or on the ground. But I dunno. Stranger things have happened!

 

[chillman88]

I didn't change the lift pump when I put in the new motor. And it may be a bad assumption, but I'd think that if it was allowing air, I'd find diesel in the oil or on the ground. But I dunno. Stranger things have happened!

I have heard it said that air being "thinner" than fuel, that it's possible for air to get in places that fuel can't get out. I've never had that happen to me, but food for thought anyway.

 

[riphip]

Chillman88 ... So... I parked uphill in the driveway last night. Started up this morning and made it as far as backing out before she fell on her face. So somewhere I am getting air in and it allowed the fuel to roll back into the tank.
I didn't change the lift pump when I put in the new motor. And it may be a bad assumption, but I'd think that if it was allowing air, I'd find diesel in the oil or on the ground. But I dunno. Stranger things have happened!

Another reason I went to electric pusher pump.

 

[IDIBRONCO]

And it may be a bad assumption, but I'd think that if it was allowing air, I'd find diesel in the oil or on the ground.

Not necessarily. It's entirely possible to have the lift pump allow air into the fuel system while keeping all of the fuel in. I think that there's a check valve in the lift pump that can fail and let the fuel drain back.

 

[The_Josh_Bear]

If you have the stock fuel filter header check the line going to #1 injector. The fitting inside the header has a check valve, they fail.

Also, the fuel heater port on top or the factory filter base will leak/allow air to enter the fuel filter.