Yet another issue pops up

[runaway!]

Doesn't surprise me, while the mileage is low - the truck didn't see intensive maintenance for a while.

So I pulled the truck into my garage so I don't freeze while doing the brakes later this year - started to run funny...

First it started missing, okay I just replaced injectors so I figured a seal was damaged on the return lines...

Then the bizarre event, truck would change idle from barely running to my guess of 1k. Every 2 seconds like clockwork the idle would shift.

I'm thinking it's the IP, would explain the initial missing that occurred.

Also didn't want to shut off until after the same 2 second cycle.

Anyone else have some insight?

 

[punkmechanic]

if it was cold it could be the gp's cycling and a short from the ip hot circuit to the gp circuit could "juice" the solenoid, keeping the truck on when commanded off, and possible allowing more fuel when the truck is running.

my best guess off the top of my head.

punk

 

[runaway!]

if it was cold it could be the gp's cycling and a short from the ip hot circuit to the gp circuit could "juice" the solenoid, keeping the truck on when commanded off, and possible allowing more fuel when the truck is running.

my best guess off the top of my head.

punk

It was plenty warm at the time, just doesn't make sense on a mechanical fuel system... I've seen this on gassers with EFI, but that's a totally different beast.

 

[typ4]

A little air intrusion would do this also.

 

[runaway!]

A little air intrusion would do this also.

Thanks, I will check all the return lines.

 

[sootman73]

return lines would not cause this. more likely to be the lift pump supply line or something under vacuum. i think we've discovered that the return lines will only let air enter if the truck is off and sitting to let the fuel drain back. air wont get into the injection system with pressure in the lines. check hard lines and fuel filter for leaks first.

or maybe its just telling you its a pulling truck and wants to hook up to the sled!

 

[hesutton]

How much fuel is in the tanks? 1/4 or so? If that's the case, you may be sucking air from the tanks. The fuel pickup/screen on the bottom of the sending unit is notorious for breaking off and causing fuel issues at about a quarter tank.

Heath

 

[runaway!]

I'll put some more fuel in to see if that helps, just replaced the front tank and all the hardware looked ok.

Vacuum system is solid, just went through the whole system and inspected everything - even behind the dash. It will hold a vac charge for days on end without starting it.

I bypassed the old water separator and put in a second fuel filter with a water separator a few months ago, maybe something shook loose. Will check that too.

Thanks for your input!

 

[runaway!]

Well, first time trying to start the beast since yesterday's issues...

Takes quite a bit of cranking and WOT to get it started, very rough start - only firing on a few. I'm amazed it could keep chugging along.

Playing with the throttle can get them all firing, then shortly after it starts to die. Even WOT won't save it from snuffing out.

There is a manifold leak on the motor, where LOTS of white smoke pours out when dies under WOT. Smells of diesel.

There is no smoke when it dies without WOT.

I see no fuel leaks anywhere on the hard lines, they aren't perfect nor pretty - but they are solid.

There is fuel under pressure at the Schrader valve, even after sitting all night. Would this indicate nothing is wrong with the fuel lines before the IP.

The high pressure fuel lines from the IP ever cause issues? I cleaned them up with a flap wheel due to some pitting on certain areas, then painted them.

Still gotta get to the gas station to get a bit of diesel to see if the tank is drawing air.