O.T. Calling jdemaris for 6.5 diesel fuel problems

Having some more fuel problems with our 95 6.5 diesel. Engine has 247k miles on it and it starts up and runs like the day we bought it. Always used Rotella 15-40 with oil changes at about 4500 miles. The first few years (when the vehicle was still under warranty) several injection pumps & lift pumps changed out by factory. I had to get a new pump about 15k miles ago. I clean out the filter housing once a year or so and change the fuel filter between 10 & 15 k miles. So here's what's happening:

Made a 3 hour road trip yesterday and with the tank about half empty, the engine started bucking pretty badly. Limped into a truck stop, filled up the tank and bled quite a bit of air out of the filter. I noticed the pressure on the lift pump was much lower than normal by the fact that the fuel barely flowed out of the vent. (I also confirmed the lift pump was running.) At the truck stop I went ahead & changed the fuel filter and reprimed the system and started up. Drove home last night and made a half-way stop and noticed the filter housing was not full. Bled more air and made it home OK.

As to the cause, I'm thinking either the stainless steel sock in-tank strainer is clogged or maybe the lift pump is getting weak? I have no way to measure fuel pressure off the lift pump but by observation I know the pressure is marginal in getting fuel through the filter. In the past, the electric lift pump either ran or it didn't and also, the fuel would flow at least an inch or two above vent when engine running and vent valve opened. This is the first time I seen it running but not delivering a good pressure. So I go back to the SS strainer being clogged....do you have any ideas as to what else could be causing the problem??

Thanks in advance and sorry for the long post!!

There are entire website forums dedicated to the 6.5L Detroit diesel. Have you searched any of these out yet? I know the personalities on those sites can be a bit immature at times, but they know their stuff and could probably tell you in a snap what's wrong. You wouldn't have to depend on one guy for your advice either.

FWIW, in the browsing I did on those sites, it seemed that the lift pump was a common affliction in these trucks. Has it been replaced ever? If not time for a new one at 247K.

Several lift pump replacements...I keep a spare onboard...what's throwing me off is that in the past the pump just quits running and then I know to replace it...this is the first time the pump continues to run but the system is showing low pressure to the filter housing. Another common problem is the oil pressure sending unit failure which provides power to the pump once the engine is running. Since the pump is running with engine running, that's not the issue so I keep going back to the strainer in the tank. Planning to pull it tonight.... thanks for the reply and I'll check out the diesel sites tonight. I use the one for the Ford trucks for our F350..

Sounds like that Delco electric lift-pump to me. Note though I have had a few trucks with an intake-sock plugged, inside the tank -with diesel-bacteria. Both of them were farm trucks. Hopefully that's not very common with trucks run on fresh highway diesel.

The Delco EP-309, EP-158,GM 25115224, Carter P74001 pumps, etc. used OEM are known for such problems. I know a few people that carry spares.

I don't use either anymore. Walbro makes one that is a totally different design much more rugged. #1 choice for people using "questionable" fuels, as well as good highway fuel. Walbro FRB-5.
It costs more, but worth it - in my opinion.

I'm not trying to get you to change pump designs; just mentioning my personal choice. I'd take a mechanical pump, or the Walbro over any of those frame-rail mounted vane-pumps.

WORKED ON A 93 THAT KEPT DYING for lack of fuel the oil pressure switch only gave the lift pump 6 volts and so the pump was turning too slow.i think you should check the voltage at the lift pump,however, the only place to get air in the system is between the tank and the lift pump.after the lift pump the fuel is under pressure,there fore,your problem may well be in the tank

Might bee a lift pump, but I would bee looking for a rusted out fuel line or something, sounds like air getting in there somehow.

Had a '95 that did something similar. Would starve for fuel wide open. Lift pump would run but apparently not pump very well. Cut the old one open after I replaced it and the check valve part of it had failed and wasn't sealing. Aparently was moving some fuel, but not much.

Jeff

Sounds like a good option...is the Walbro FRB-5 a mechanical pump (if so, how is it driven?) or is it a more rugged electric pump that bolts in where the factory rail pump goes??

I'll still remove the tank sometime this week. Might have to drive wife's Cherokee the rest of the week....

Thanks!!

It's an electric pump, just more HD. Often used in HD truck applications and diesel boats. The OEM pump you have now is a a rotary-high-speed electric pump. The Walbro is a low-speed diaphram-type pump. I know it's been tested for endurance and greatly outlasts the rotary pumps. It is rated for a life of 18,000 hours under constant running, and it does not run all the time in a car or truck. That equates to around 1,000,000 road miles. Also has a removeable fuel-screen in it. I paid $130 for the last one I got.

http://www.fuel-pumps.net/frb51.html

I'm not saying the pump is your problem, though. When you get air at the filter, it means your pump is sucking air from somewhere. A bad pump can suck air from itself, and a questionable pump can work OK until the intake line or strainer gets plugged - and that pump will leak and draw air.

If you live in a winter-road-salt area, you might have a broken or rusted intake line on top of the fuel-tank.

I've got a 92 diesel Suburban sitting here that pumps air no matter what I do - if I use the fuel tank that's in it. I'm stripping it anyway, so I stuck a 5 gallon out-board motor tank in the back, and have it hooked with a rubber hose to the engine. Runs fine that way. Obviously there is break or rust-hole in the intake line on top of the tank somewhere.

The OPS on these trucks have a history of failing as well.On a 95 the OPS alone is supplying power to the LP on a running engine it could be intermittently drive the pump or not at all.
If you supply batt power directly to the LP and it pumps strong,then the OPS is faulty

twopop has the right answer this is the same thing happened to my 93 6.5 at about the same amount of miles oil pressure sendig unit

Would it be to hard to just type the thing your talking about What is an OPE or AN LPQ GMAB Give me a break

My '83 6.2 Diesel had a similar problem. Fuel filter would slowly fill with air, preventing fuel from getting thru. Stock filter was replaced by a Racor filter years ago, so I could se air in filter bowl. Finally traced problem to pinhole on upper part of metal fuel line between sock and tank outlet WITHIN THE FUEL TANK.
That caused a lot of consternation. This unit has a mechanical fuel pump downline from the tank, fuel lines and filter, just before the injector pump....

Update. Had an idea tonight--before of pulling the tank I removed the fuel cap, disconnected the supply line at the pump (inlet or suction side) and then applied about 40 PSI to the line back into the tank. Heard some noise when the air finally released through the tank fill pipe. Then I hot-wired the pump and opened the vent on the filter housing and observed the fuel gushing high like normal. Bled off all air, then reconnected the pump and started the engine and it's running steady and also checked fuel flow and it's gushing high (about 1 1/2") above the vent valve..

So....good news is that the pump seems to be good but bad news is that something was probably piled up on the SS strainer--maybe some algae or ???. So I likely bought some time, but will still need to remove the tank and either clean or replace the SS strainer.