Engine quits..Electrical or IP?

[raunch]

Here's the syptoms: This may be unrelated, but during a road trip, I noticed as I was cruising down the freeway, a slight drop in rpms. This drop was intermittent and very slight. Have not noticed the rpm drop since the road trip. Also, I noticed a fluctuation in my voltmeter, from about 10-13volts.

The main syptoms are--2 times, within 1/2 block, the engine quit as I let up on the pedal. Both times it started right back up. After this I took it to my mechanic. He thought it may be the pump losing pressure from pieces of seals within the pump getting stuck in the little glass ball check valve out the return at the top of the pump. This seemed logical, as I have been running biodiesel which could eat away at the rubber seals in the pump. He checked it out, could not duplicate the problem, but did replace a bad battery cable--voltage drop solved.

For about a week all was well until it quit on the decel again. All three times now have been at low speeds and low rpms. The interesting part of the third time the engine quit, was that it would not start again as I turned the key to 'start' position. I had to turn the key back to the 'off' position then to 'start' and it fired right up.

Still the symptoms lead to the check valve, at least it is a cheap an easy way to begin the problem solving. So last night I was preparing to install the valve, and before I started, the mecahanic thought it wouldn't hurt to pinch of the return line out the top of the IP to duplicate the sypmtom. I did that, the engine quit right away, and what's interesting here is that I did not need to reset the ignition back to the 'off' position at the key. I simply went from the 'on' postion to 'start' and it fired right up. So, given the strange things with the ignition, I'm wondering if the problem is an electrical one, causing a voltage drop in the system and shutting down the fuel solenoid on the IP. Any ideas?
Thanks.

[raunch]

Through searches here, and thoughts from two different mechanics, the symptoms point to sucking air in from somewhere. I fixed the most likely spot in my system---the Racor secondary and all the fittings for it. There has been some weeping from the fittings. I think the teflon sealant has been dissolved by running biodiesel. I cleaned the whole thing up and used a bio diesel compatible sealant. After a test drive this morning, the symptoms did not show up.

There was also a return line that had a little leak in it. It was a roadside repair when the end nipple nearest the drivers side firewall blew the plug off. Fixed it too.

Keeping my fingers crossed.
Raunch

[john8662]

Very likely it is an air issue.

Another thing to verify is that your mechanical lift pump is functioning properly as well. When they die they will cause the engine to stall under light throttle or stepping off the throttle.

J

[raunch]

I was wondering about the lift pump, for no reason other than it is part of the system. I did not know the symptoms I am experiencing could be directly related to the lift pump. Is there a way to verify it is working properly, or should I just replace it? BTW, the filter fix-up did not solve the problem. Just got back from a test run and RPM's dropped 2x during about a ten mile trip down the freeway.

[john8662]

The only way I know of is to "T" into the output hose off the pump. You'll find a place where the hose is rubber and you can do that. Then you'll need a fuel pressure gauge that can be used mechanically to measure the pressure. For this, you'll search online, or look and see what they have at the local parts house.

You should see around 7psi fuel pressure.

Replacing the lift pump is a little bit of a chore and involves also removing the plate on the side of the block that the pump mounts to (not just the two bolts that hold the pump to the block). The lift pump rod always falls down after removing the pump, so you need the plate removed to be able to push it back up into the block with some grease on it (to keep it in place).

J

[john8662]

Find a pressure connection on a hard line in between the final fuel filter and the injection pump. With the engine running you should be able to crack that line open and observe fuel leaking. If it doesn't leak/spray a little and the engine stalls, your lift pump isn't working.

I'd say this applies to all other 82-83 6.2's with the secondary fuel filter at the back of the intake. I know yours if aftermarket Racor, but you may have it plumbed in a way to check.

J

[raunch]

Thanks for the testing tips. I've been away since last Thursday....two in my family are confirmed swine flu. They are getting better and we are all well.

Anyway, last Thursday night I just went ahead and replaced the lift pump. The pump was not expensive, but being my first one, the job was fairly difficult. I also replaced the fuel cap, and the rpm isssue at cruising speed no longer occurs. There are some other symptoms that are likely air related, but with the family sick and other projects to work on, I took the truck into the shop for further diagnosis. If they find anything interesting, I'll be sure to post it.
Thanks again.

[raunch]

No notable news from the shop. They just did some thourough checking of things and all is well--no air in the system or other gremlins. However, before it went in, I did find another split return line. Same place as before on the drivers side end plug near the firewall. I think I've got some low-quality hose. Possibly that split was letting some air in.

So far so good. Running real smooth and starts great--other than a little bit of blubbering on the colder starts.