Help with a 6.5 non turbo

[rfree82]

I just bought a 1997 Chevy P30 van with a 6.5 L non turbo engine. The truck will not run over 50 mph on flat ground. I've changed the fuel filter but it didn't help. Like I said it won't run over 50 and will not go into overdrive. If I go down a hill the truck will shift to overdrive and run about 65 mph. The engine will not build any heat, only runs around 160 degrees. Could this cause it not shift to overdrive? The tranny is a 4L80e. Any ideas? Thanks in advance.

[bmoeller]

Lift pump working?

[DmaxMaverick]

First, VERIFY the fuel in your tank is, in fact, 100% clean #2 Diesel. Beyond about 25% gasoline, power drops significantly, and cold starts become difficult. More is worse.

Sounds like a significant fuel shortage. The anticipated fuel delivery, and power output, is not matching the pedal input, for whatever reason. This causes several symptoms, including low power, (very) late tranny shifts, and low ECT. This could be, as suggested, the lift pump (mechanical or electric?), fuel filter, damaged/deteriorated fuel lines, and/or fuel flow restriction at the tank sender unit (sock) due to contaminated fuel.

To check mechanical fuel pump operation, idle the engine and open the filter bleed valve. Fuel should flow (into a container) and the engine should idle normally. Repeat with someone running the RPM's up to the governor for a few seconds. Also check the weep hole at the bottom of the fuel pump pod. Any fuel wetness is a failed LP.

To check an electrical fuel pump, repeat the test as above. Verify battery voltage to the pump, and that the pump is actually pumping. Also, the pump should produce between 4 and 12 PSI at engine idle. If voltage is present but the pump doesn't pump, replace the pump. If voltage is not present, suspect the OPS (Oil Pressure Switch).

If all the above checks out, suspect the injection pump.

[rfree82]

Thanks for the advice. I will check the fuel in the tank and fuel pressure as soon as I can, probably a few days. The truck has an electric pump on the frame rail and a mechanical pump on the engine. I thought it to be strange that it has two lift pumps, maybe because the tank is almost 16 ft from the engine.? Where is the best place to check fuel pressure? I drove the truck again to day and if you really get down on the accelerator it will not shift until you lift the pedal. If you ease on the throttle like normal driving it will shift normal until it hits 50 mph and it flattens out if you lift at 50 mph the truck just slows down and will not shift to OD.

[DmaxMaverick]

The "extra" fuel lift pump is not unusual in the vans. Even the latest Duramax vans have them. The reason for the latter is for priming the fuel system and after filter changes, and not specifically for fuel supply (they don't run full time).

Your symptom of shifting is VERY indicative of a mild to moderate fuel restriction, the same as I would initially diagnose as the need for a fuel filter service. Anything that can produce a similar symptom would be suspect. Any condition that could allow the engine to produce less than anticipated power for the pedal position is suspect. Unfortunately, the list is long. Good luck!

[rfree82]

Here's an update. I had to change the harmonic balancer so it was first today. Then I dropped the tank and checked the fuel and fuel strainer. The strainer was very dirty so I cleaned it in an ultrasonic cleaner and reinstalled. The fuel looked good ( no water) and the pickup assembly was clean and free of rust. I ran the truck after this with no change in my problem. I then started to suspect the pumps. I noticed the electric pump has been "hot wired" to, I assume, key on power. I connected a pressure gauge and it had 7-8 psi at idle I then unhooked the "hot wired" power wire to the pump and the pressure dropped and started drawing a slight vacuum. I stopped there for the day. As I stated earlier the mechanical pump looks new so I'm going to pull the pump and make sure the push rod is there because I'm having serious doubts about the previous owners mechanical skill. What was more alarmig was the oil pressure. I drove it for a good while and when I would stop the gauge would go to zero! No knocking noise when it did but I guess I should get a mechanical gauge and check that too.

[brandongarnold02]

For the shift issue you are having the throttle position sensor could just need adusting. These can fail also and cause shift issues but if the pump was recently replaced an adjustment will most likely fix the issue.

[sctrailrider]

Have you checked to see if any codes are stored???