Fuel Gremlins

[MEdlin]

I've been having sporatic problems with my 6.5TD Suburban stalling. I have read through the step by step trouble shooting guide on The Diesel Page. I replaced the filter and everthing was great for about two weeks. I think I may have bacteria in my fuel tank. Here's why... When I park my truck in a level driveway over night, I don't have a problem. At work, if I park with the backend lower than the front, within 5 miles from the office the engine will stumble or even quit on the way home. When I park the other way around, I don't have the problem. Could this be due to Algae, Bacteria, or Fungus being pulled into the fuel system when I start the engine at work, and it taking a few miles before it hits the filter?

How do I determine if I need a Biocide and what's the best way to clean up the mess? Would an additional external filter be advised?

[Marty Lau]

Did you check the lift pump and or OPS? If you really think it's bactria, I dump biocide in and change fuel filter again and then again in after 4 or 5 tanks or drain the fuel from the tank put fresh fuel in with biocide and change filter after a 4-5 tanks.
But.... I'd check the lift pump make sure it's working.

[DmaxMaverick]

Your problem sounds more like a drain-back issue. My '85 6.2L will do the same thing if the fuel level is below 1/4 tank. There are check valves in the system that are supposed to prevent this. Failed injectors can cause a similar issue, but they will usually prevent starts, not cause stalling after it starts. Another possibility would be a leaking fuel pick-up line in the tank. Some models had a bypass valve built into the fuel pick-up line that helped with extreme cold climates. You could have this feature, that has now failed, or the sock at the lower end of the pick-up line has become fouled.

If you have critters growin' in your tank, the problem won't be intermittent. A plugged filter will stay plugged. I doesn't hurt to use preventive measures in any case. Most additives will help to prevent them from growing in the tank, but most of the time they get there from the pump at the filling station, dead and alive. Using a biocide will kill the critters in your tank, if you have living algae. Either way, once they are in your tank, they will find their way to the fuel filter, and plug it up in a hurry. The best remedy is to clean the fuel tank and flush the entire fuel system. This is not practical in most cases, so most folks just keep replacing fuel filters until the problem goes away. Draining and flushing the fuel tank speeds the process. A good indication of a biologic contamination is black, or dark sludge in the filter housing. If your filter and fuel is clean when you change the filter, you probably don't have fuel gremlins.

[tom.mcinerney]

Most bases covered above. Might check fuel tank cap for clogging; might try blowing out fuel lines. Keep in mind may need to clean out tank, and renew fuel pickup assy...no rush.

[MEdlin]

Thanks for the feedback. I'm looking into replacing the Fuel Lift Pump. Diesel Injection Service sells a pump made by Delphi for $95, NAPA sells a pump made by Federal Mougal for $79,
and of course I could buy the AC Delco pump for $159. Anybody have experience with the OEM pumps?

[charliepeterson]

With the truck running make sure you have 12 volts coming down to the lift pump. You could also have a bad lift pump even if you can hear it running. I recently went through this with a newer lift pump. It could have been a voltage thing but the pump locked up causing a stall issue with difficult restarts.

[MEdlin]

Charlie, what brand pump did you use? As far as I can tell, my original AC Delco pump has 177000 miles on it. If I can get that out of another AC Delco pump, I won't mind paying $159 for a new one.

[charliepeterson]

I used AC Delco.

[tom.mcinerney]

MEdlin--
TDP advertiser Gomer's/U.S.Diesel
www.usdieselparts.com (http://www.usdieselparts.com) is a Delphi distributor. Delphi is the manufacturing arm of Delco(i think), as Visteon manufacturers for Motorcraft.
Gomer's sells the right pump at a discount to TDP members.
As 16Gauge indicates, the LP is limited by the OPS.

[MEdlin]

Well, I went with NAPA for the Fuel Lift Pump. It's made in the USA by Carter. After replacing the pump, everything was great for two weeks. Friday the truck died and restarted as I was trucking down the interstate. I'm now changing the Oil Pressure Switch and checking and cleaning all the connections.

[rjwest]

MEdlin, what year truck, 96 up different lift pump
conrol. Go back a few mounths, many posts on ;ift pumps. FSD's etc.

Suggest fuel pressure check by using drain when running..,,,,
Also, did you do all the filters etc..?
start with the easy stuff first,,,
If you really think bad fuel, change filter, open up the filter and see whats in it,,,,,

[MEdlin]

Well, now as I lay across the top of my engine to check all the connections and grounds, I think I've found the problem. The ground stud on the back passenger side of the engine was loose. Not only is it loose, but the hole in the head was rusted because the gasket for the water jacket cover had failed and antifreeze leaked into the hole. Why did GM design this very important ground to go through a water jacket cover plate? :rolleyes: This stud also holds the automatic transmission dip tube in place. I had fun trying to find the gasket from the dealership. They acted as if the cover didn't exist and I was nuts! :D

[MEdlin]

Now that I've replaced the Fuel Lift Pump, the Oil Pressure Sensor, cleaned and tightened the grounds, the truck would not start. :confused:

I start back through the trouble shooting and find the problem is with my Fuel Pump Relay. I took the relay out of the little plastic box, cleaned and burnished the contacts on the relay, and everything is back up and running!!! :D

So what, I've got a couple new parts installed... smile.gif

[Turbine Doc]

Medlin,
I also have been bitten by GM hiding the ground strap in the past, what I did to prevent it from happening again is use a #4 double ring lug battery cable, 1 lug connected to the alternator mount stud and the other end to a frame rail bolt, that way I can monitor it real regular like.

I also check the starter bolts from time to time about every other oil change or so when I'm checking the GM factory ground strap.

Another preventative I'd recommend is a frame mounted pre-filter prior to the lift pump I use a Racor 660 20 mic with aquabloc element, keeps crud & water from tank or an away from normal home fuel stop from putting junk to the lift pump.

[MEdlin]

tbogemirep,

Great suggestions. I'll look into these.

Thanks smile.gif