A hard start

[hershel]

I recently replaced the injector pump on my 94 6.5 due to a missing cam
reference pulse. Before removing the pump I checked the lift pump, found
it was drawing about 2 amps and delivering 8 and 5 psi,unloaded/loaded, to the injector pump. I installed a new pump, purged the air from the fuel line and attempted to start the engine. Repeated cranking intervals failed to produce any fuel at the injectors or out of an open return connection. I returned the pump, not convinced it was bad but unable to see how an air lock could could be the problem. The pump checked good but there was no fuel in it after all that cranking. I installed the pump again, purged the air from the fuel line and cranked it one time for 30 seconds with the same results. Considering the time that was put on the starter It was time for a change.

With 4 inches of vacuum on the pump return fitting, cranking started fuel flowing in the return line and the engine tried to start on those cyclinders which had the lines tightened. I replaced the return line, tightened the remaining injector lines and the engine started right up. I had the timing checked at a dealer and was told the range was set to plus and minus .75 deg and the timing was set at TDC.
Anyone had this range setting?

The original pump on this vehicle developed a stumble (brief interrupt of power) at about 35k miles. This problem is random, very infrequent, and is more likely to occur under heavy load, like going up a grade with cruise on in fifth gear. Unfortunately, the new pump didn't correct this problem. I think the cyclinder balance check should see this problem but it doesn't.

Hope some of this helps in changing injector pumps.

[markelectric]

That sounds all too familar. I would check the fuel pressure in working conditions. I do that by unhooking the hose at the bleed pitcock and installing a test gage taped to the windshield. The gage I use reads 15 to zero vacuum to 15 psi. I would see pressure at crank but a large vacuum under acceleration. You may want to look at yours.

Good luck

[MTTwister]

so Mark - what would cause that? Plugged Fuel Filler Cap? Marginal Lift pump?

[markelectric]

Every time it was the oil pressure switch. Start gave a 12v supply to lift pump but when the key was released, no power from OPS. I initally changed a new injection pump again because of this. Just because the OPS is new out of the box does not mean it will work.

[hershel]

I see I don't do very well with details-the lift pump was delivering 8 psi to the injector pump during cranking and although the supply line had been purged of air the injector pump would not pump any fuel to the injectors or out of an open return connection. It was poor judgement on my part to return the pump but I wasn't convinced that more cranking time was the answer. This was an electronic pump which may be more difficult to get started after changing than the mechanical pumps. My experience with the old 5.7 and 6.2 pumps were nothing like this.

I just wanted to point out that cranking the engine with 4 inches of vacuum on the pump return connection cleared the air lock immediately.

[Hubert]

I don't know exact details but maybe it was a wiring connection problem. Or the Fuel shutoff solenoid was stuck and not opening allowing fuel into the IP. A missed ground connecting things back up ?????? Electronic ghost etc? 2nd install electronics were happy

I think it works like this:
The ECM controls the IP & FSD. If either the FSD has bad connection, is bad, or what ever and ECM doesn't like what it "sees" it won't allow power to the fuel shutoff solenoid and it won't deliver fuel to the IP but the lift pump will still supply fuel pressure to the IP.

A good IP will suck in fuel (but I guess it has to have prime first).

FYI
The FSD drives the fuel solenoid inside the IP that meters fuel out. But the ECM controls the IP and fuel on/off. FSD's don't set a code if things are wierd or give any indication they are bad except IP does not output any fuel (because the ECM will shut fuel off).

[hershel]

12 volts are supplied to the fuel solenoid by the igniion switch and a ground is supplid by the PCM. Both of these conditions were checked plus one could hear it cycle and feel it if you put a finger on the case. This was checked the first time the pump was installed.