Re: 1996 GMC 6.5L Diesel troubleshooting
The OPS (oil pressure switch) sends power to the fuel lift pump that is mounted on the driver's side fram rail underneath the cab. When the OPS fails, the lift pump stops operating, causing hard starts, stalling, and poor acceleration. You can check the fuel pump itself by placing the transmission in drive, and turning the key to 'start.' This will not engage the starter, but will engage the fuel pump. You should be able to hear it. Then go ahead and start the engine and place your hand on the fuel pump...you should be able to feel it operating. If not, leave the engine running, and then open the fuel bleeder valve at the front of the engine. The engine should stay running and fuel should be squirting out the drain hose. If the engine dies, the lift pump is not working. Replace the OPS.
There are mods available to prevent this from occuring again (common problem on the Chevy trucks). I suggest www.thedieselpage.com
for more information.
Another problem associated with the OPS is that the lift pump is supposed to send fuel through the IP and back to the tank, helping to cool the IP and the FSD= fuel solenoid driver, the little black box mounted on the driver's side of the IP. This is basically the brain of the electronic IP. If the lift pump has been non-functioning for some time, it can cause an early death for the FSD.
I had to replace the OPS and FSD on my '95 when I bought it. I upgraded the OPS with an aftermarket relay harness, and relocated the new FSD to a heatsink mounted off the engine. Now it's very reliable.
1996 E-350 Van Cutaway, 7.3L PSD, E4OD, Dana 70 dually with 4.10 gears, Reading enclosed utility body, 160K miles....
1995 Chevy K1500 Tahoe, 6.5L TD, NP241, 4L80E, 3.42 gears, Kennedy Diesel OPS harness and FSD cooler kit.
1981 Chevy 3/4 ton converted to 6.2L TURBO DIESEL, bored .040" over, 6.5L pump, turbo injectors, DSG timing gears, lowered compression w/ceramic-coated pistons, 17 lbs of boost....4 speed auto, custom built 4" exhaust, 4.10's, keyless entry, etc. etc....
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