6.2L LP Issue
 

Hey all!

I have a 1991 Chevy C2500 with 6.2L vin J. The electric LP is mounted on the frame rail, under the driver's seat.

Recently I've had some hard starting issues.

Here's what I have:
- Fuel pump fuse is good
- Fuel pump relay is new
- OPS is good
- LP runs while engine is running
- LP does NOT run during glow cycle
- LP continues to run a few seconds after engine is off, until oil pressure decreases

The LP used to run during the glow cycle, but has stopped. What have I overlooked in my troubleshooting?

Thanks!!!

does it start easy if you press the gas?

Negative. I've tried pressing the peddle, and not. Either way it takes about 10 seconds of cranking after it's been sitting for a while. If I'm out running errands, or if I've been driving a bit, the engine fires right back up. Let it sit for a while—right back to cranking for 10 seconds or so.

odd. let me think about that for a bit.

Wheres the PMD located. Best Buy Tweww.. J/K

Your missing the 'Fuel Supply System Checks'...... A laborious task thats routinely skipped, and always assumed good...

Condensed version.
Stanadyne Pump Diagnostic Troubleshooting


Educational materials...
Stanadyne DB2 Injection Pump - How It Works

Stanadyne Operation and Instruction Manual Model DB2 Pump


I suspect your losing prime when parked for extended periods, and while you 'crank' the engine, the lift pump must 'reprime' the fuel supply system.
Once engine starts, the OPS powers the lift pump.
Unless I am mistaken or youve done some modifications, the 'pre-prime' feature (liftpump works w/ glowplugs) didnt begin until '96.....

Here are a couple student handbooks.. Download it all to your PC for future ref, excellent educational material and most helpful with diagnostics when you dont have the appropriate 'factory authorized service manual(s) readily available.

The 6.2 Liter Diesel Engine, 386pg pdf

6.5 Liter V8 Turbo Diesel Engine, 344pg pdf

Thank you for the great info!

I've made no mods, but that doesn't mean they weren't added prior to my buying the truck; I'm the third owner. It's definitely losing prime, which never used to happen.

-could be helpful-

#87-65-25: EXTENDED ENGINE CRANKING TIME DURING HOT ENGINE RESTART IN - (Sep 22, 1998)
SUBJECT: EXTENDED ENGINE CRANKING TIME DURING HOT ENGINE RESTART IN HIGH AMBIENT TEMPERATURE CONDITIONS (ALLOW ENGINE TO IDLE PRIOR TO SHUTDOWN)

MODELS: 1996-99 CHEVROLET, GMC C/K, G, P MODELS WITH 6.5L DIESEL ENGINE (VINS F, S, Y - RPOS L65, L56, L57)

CONDITION:

SOME OWNERS OF DIESEL EQUIPPED VEHICLES MAY COMMENT ON AN EXTENDED ENGINE CRANKING TIME DURING A HOT RESTART IN HIGH AMBIENT TEMPERATURES OF 38 C (100 F), ESPECIALLY WHEN PULLING A LOAD. THIS CONDITION NORMALLY WILL OCCUR AFTER THE VEHICLE HAS BEEN SHUT OFF AT FULL OPERATING TEMPERATURE AND THEN RESTARTED AFTER APPROXIMATELY 15-90 MINUTES. IT IS SOMETIMES CALLED A "HOT SOAK". NO OTHER DRIVEABILITY SYMPTOMS HAVE BEEN NOTED AND THE MIL IS NOT ILLUMINATED.

CAUSE:

VISCOSITY OF THE DIESEL FUEL FOLLOWING A HOT SOAK BECOMES TOO LOW TO BE PROPERLY PRESSURIZED BY THE FUEL INJECTION PUMP ON RESTART DURING THESE PERIODS OF HIGH UNDERHOOD TEMPERATURES. THIS LOWER PRESSURE IS INSUFFICIENT TO POP THE FUEL INJECTION NOZZLES AND PROPERLY DELIVER FUEL TO THE ENGINE.

CORRECTION:

IF THE AMBIENT TEMPERATURE IS 38 C (100 F) OR GREATER, ESPECIALLY WHEN PULLING A LOAD, CUSTOMERS SHOULD ALLOW THE VHEICLE TO IDLE FOR 5-10 MINUTES PRIOR TO SHUTTING OFF THE ENGINE. THIS WILL ALLOW THE ENGINE TEMPERATURE TO STABILIZE AND MINIMIZE HOT RESTARTING TIME.

Josh, that TSB applies to '96-'99 models. Gator has a '91 model.


However the liftpump doesnt know what year it is..
Lift pump has 2 spring loaded check valves that get lax if not lazy in there old age.
Its in this relaxed state, LP OFF that fuel will drain back to the tank PROVIDED an air leak 'somewhere' in order to displace (replace) the fuel as it drains. Provided an air-tight system, air cant get in so the fuel will remain 'suspended' in the FFM due to vacuum.

Air leaks and fuel leaks are not synonymous, rarely found together, often dont exhibit wet spots. If it were only that easy..


Proper liftpump testing requires inserting a tee before the IP inlet and monitoring fuel pressure during normal OPERATIONS. not just idling in the driveway..

Recently 'restored' my fuel supply system.
Dropped, cleaned and inspected my fuel tank.
Replaced Fuel Sender, Fuel Strainer, Lift Pump, FFM, OPS, along with all new OEM repop steel fuel lines and hoses...

Been closely monitoring fuel supply system operating pressures and although not important to DB2, been simultaniously monitoring PMD all while summoning, playin' and slayin' PMD goblins AT WILL for over 4 months now.
1- Vacuum Restriction Indicator* mounted pre lift pump in the LP 'suction' line.
1- Fuel Pressure Gage (0-15psi) mounted post-LP, pre FFM.
1- Fuel Pressure Gage (0-15psi) mounted post FFM, pre IP.

*Will replace the spendy vacuum gage w/ pointer asap.

Should have at least 6psi at idle (minimum fuel flow, maximum fuel pressure) if your to ever maintain 3psi minimum during WOT (max fuel flow, minimum fuel pressure) operations.

My ACDelco EP158 lift pump is producing nearly 10psi at idle, and the system when not in use will slooooowly drop before holding at and maintaining 4-5psi indefinitely, several days anyhow...

For more details, you'll have to wait for the report.

yea just posted it to turn some gears. Old parts can do funny things it was for later pumps but the information should be valid for all years. I agree with you a 100% though that proper fuel system diagnosis should be undertaken to find the cause. If no cause is found that bulletin provides a simple test/resolution to attempt.

Losing prime can happen all the way back at the tank sender. Definitely need to figure out where the leak is through diagnosis.

If you come to checking for leaks. I'd start at the fuel lines under the intake, then to the filter housing, and keep working your way back.

The lines under the intake are easy to replace and have a habit of cracking around the hose clamp

The running during wait to start is not factory in that year. Start by checking for a jumper wire over to the glow plug relay and follow it.