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6.5 frustration!

B

Blacksmoke Chevy

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Hey, what's up truck stop folks?! I have a '94 K2500 Suburban that's been kinda giving me a fit. Last summer PMD finally crapped out for good and I just now got around to installing a new one along with a relocation kit. Truck fired up and then I noticed fuel dripping off bell housing. Long story short, I found the fuel heater was loose on the bottom of filter housing. Tightened that and it cured the leak, but now it's a freakin' bear to start, and when it does start it misfires and "service engine soon" comes on when I throttle past 1500 rpm, goes off below that. To come to a point, could a bad coolant sensor be causing this? My gut says I have a breach in the fuel system, but not sure. Advice appreciated, I really like the truck and she's great when she's running right. I don't have cash to pony up to a shop, this is on me!
 
Sounds like air in fuel to me. Get a piece of 1/4" clear tubing and install it on the return line coming out of the injection pump. Look for bubbles. It's OK to have a small stationary bubble at the top but that's it,any other bubbles at all is a problem. If you find bubbles you need to start looking at the fuel lines. You can have air intrusion without it leaking because of suction.
Next get yourself a fuel pressure gauge and make sure your lift pump is working. You can hook it to the water drain line for testing.
If the lift pump isn't working there's a pretty good chance the oil pressure sending unit has failed. It controls the lift pump via a second set of contacts so just because your oil pressure gauge is working doesn't mean your OPS is working properly. Good luck
 
I read somewhere I should be able to open water separator valve and get clean fuel while engine continues to run. This does not happen; opening the valve yields no fuel at all and engine stalls after about thirty seconds. I'll try the clear tubing, and thanks!
 
This indicates that the lift pump is not running. It is an electric fuel pump mounted to the frame rail below the drivers door. it looks like an inline fuel filter. Get a volt meter to check if it has voltage getting to it as AK said above the oil pressure sensor could be bad and not supplying power to it.
 
When I touch the pump fuse to "hot" connector with air bleed open, clean fuel pumps out. Had no clue OPS had any connection to lift pump. Will check it tomorrow. I love that ol' boat, not crazy bout workin on it!
 
The oil pressure sensor is on the back drivers side of the engine valley behind the filter housing. If it ran great till you messed with it and then immediately started giving you a problem I would also look at the wiring coming out of the sensor to see if there was a bad connection that you inadvertently made worse when you were in there.
 
Looks like you found your problem. It is advisable to do a relay mod to reduce the frequency of the OPS going bad. Also get the good OEM OPS not a cheap knock off.
 
Yeah, the idea is to do some mods(as I can afford it) to overcome some of the design flaws that seem to be part of an otherwise great mill. I really appreciate the advice. I'll do some testing and post what I come up with! Many thanks!
 
One thing to keep in mind is "air". It's the #1, NUMBER 1 THING, to start troubleshooting with not only because it is the first thing in the GM shop manual to troubleshoot, but, it simply is due to the design and failure modes of the system.

Next thing after air is take apart and clean grounds.

After you have fine tooth combed the above then you can consider throwing expensive new parts at it. And the fun of that is New parts are not always Good parts. Replace part and then completely start troubleshooting over.

Keep in mind these are a Light Duty diesel in a Heavy Duty application. Life be limited for odd reasons, but, parts are cheap vs. modern HPCR diesel engine.

The above said in your case I would get new O rings for the FFM from Leroy Diesel and inspect the fuel heater for pinholes burnt into it. I am suggesting replacing the orings because they were leaking. Air leaks do not always leak fuel. The 'bad' heaters will leak even from the power connector wires! peninsulardiesel is a place to check for new take off parts now and then, but, they list out of stock for new FFM's at the moment.

Note some 6.5 DS4/DB2 systems won't run without a working lift pump. It appears the Lift pump pressure seals off enough of the air leaks on those systems to keep em running, but, the second the lift pump quits so does the engine. Normally the engine keeps going with reduced full power on a leak free system. Fuel filter changes are when good systems notice a bad lift pump.

For in depth lift pump troubleshooting check out the "Lift Pumps & OPS operation and troubleshooting" under the technical reference library http://www.thetruckstop.us/forum/forums/6-2-and-6-5-technical-reference-library.218/
 
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