M998 air in fuel line

Steel Soldiers is supported by:

BSLogic

New member
9
1
3
Location
Cedar Park, TX
Driving home from work one day at a stop light when she puttered out and died on me. After a tow home, did some basic looking and found nothing. Started right up and drove around the neighborhood. Couple days later, start off to work. Realize I forgot something at home and turned around. Lucky for me (i guess), at that point I started losing power. Kept moving until I got home and again died on me.

I found I have air building up in the fuel filter. When I purge it, I can get about 30-60 seconds of idle time before dying again. I've replaced the rubber supply hoses before the lift pump, the lift pump itself (one of which had a hole worn in it - TM shows it should have a guard on it, probably to prevent that), had the injection pump rebuilt, replaced fuel filter and water separator (both clean and in good shape from what I could see). Filled up the tank all the way to see if the problem went away, no luck. Blew out the return line just in case it was clogged, air came out into tank fine. Pulled filler cap to see if maybe the tank was going under vacuum - still no luck.

Anyone else have any ideas?
 

papakb

Well-known member
1,421
41
48
Location
San Jose, Ca
Did you check to make sure the O-ring in the separator housing was good? Just had a similar problem on a friends truck after replacing the filter. You could also have air leaking in thru the water separator pressure switch. You might put one of those glass body fuel filters in the line after the mech pump to see if you have air bubbles there.
 

NDT

Well-known member
Steel Soldiers Supporter
7,531
93
48
Location
Camp Wood/LC, TX
There is some kind of retrofit kit to add an access panel in the truck floor right above the fuel pickup, I don’t know any details on this.
 

Retiredwarhorses

Active member
Steel Soldiers Supporter
2,430
23
38
Location
Brentwood, Calif
Start simple....check that you have good solid hose connections on your fuel lines from the fuel tank to the injection pump, especially at the fuel filter. Check your fuel tank vent and blow out the vent line from the tank forward to the filter.
if you open the fuel cap, is it hissing ? Have you changed your fuel filter?
 

BSLogic

New member
9
1
3
Location
Cedar Park, TX
Quick update:
Dropped the tank - only took about an hour, so not too bad.
I didn't find any obvious problems, but I'm thinking that the supply line connection on top of the tank might be the culprit. The baffle in the bottom of the tank had come loose and may have bumped the internal supply tube hard enough to unseat the connection at the top (it is sitting off at a slight angle).
I'm going to replace the tank and all the hard supply lines just to be sure (rubber hoses already new).
 

BSLogic

New member
9
1
3
Location
Cedar Park, TX
Got new parts delivered. I was moving all the old stuff that didn't need to be replaced to the new tank and I ran into a stuck plug of some sort. Looked in the TM, but part 41 has nothing listed. Anyone know about this thing? It's just an allen head plug as far as I can tell. I've tried lots of stuff to get it out, so even if it does come loose I'm not going to use it again.
pic.PNGlist.PNG
 

BSLogic

New member
9
1
3
Location
Cedar Park, TX
Everything is put back together. Runs perfect now. Could not find the actual problem, but it really seems like it was probably the baffle hitting the supply suction tube.
I appreciate everyone trying to help.
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks