I added a fuel pressure guage today with the help of advice from DTR members. At idle I have 20 psi at about 1600 rpm it raises to 25 psi and then starts slowly cycling from 25 to 20 psi? Could this be overflow valve, it has about 50,000 miles on it. The transfer pump has about 100,000 miles on it. Any ideas?

 

Pinch closed the rubber return line that passes behind the fuel filter with pliers, engine running.
If the pressure shoots way up your lift pump is fine, OF valve is the problem.

 

I pinched closed that line this afternoon and pressure went to about 40psi and held steady, if reved over idle it would climb further. I will get a new overflow valve for it. Thanks

 

You could open you OFV up, take a BIC pen spring, cut it to the same length as the one in there already. Run both springs. Cheaper than buying a new OFV.

 

If it opens up.
It's been years since OF valves with the removable tops were available.
If the OF valve has ever been replaced it's very likely it won't open up.

 

The reason I put in the pressure guage was this truck when at opperating temp. Will often crank over extra times before starting, once started will idle about 200 rpm below normal. It will then run for about 20 seconds and then start to die with the injection pump knocking/tapping until it stalls, after stalling sometimes the injection pump will make a knocking/tapping noise one final time. I have observed this happen with the pressure guage showing 20psi. I have cleaned the pre filter, adjusted/verified operation of the shut down solenoid, throttle linkage,and fuel lines.


Also when this happens if reved up about 2000 rpm it will kind of miss and then run ok with no smoke and some times just stall out. always having fuel pressure and no smoke. once comes out of it runs perfect?

Please help!!!!!!!!

 

I put up with the same thing intermitintly for at least five years.
In fact it was the reason I also installed a fuel pressure gauge.
Sorry to break the news but this is a common '94-'95 injection pump problem due to the delivery valve cylinders warping and causing them to stick.
Only solution is to buy a rebuilt injection pump.

 

Thanks for the reply Infidel. I was afraid the pump was going out. This truck has 383,000 + miles on original engine. Engine is good otherwise, should I be leary of spending the money on a new pump? I am afraid of the engine having a major break down shortly after spending the money for the pump. Do you think it would run like this without getting worse?


Thanks again for the info.

 

I've got a 215 P pump with 110k miles available. came off of a 98 12v. in excellent condition, has never been opened.

please PM if interested....

 

As it got worse mine would finally just stall out, especially on long drives or hot days. Think that heat made the warpage worse.
Happened more often with less than half a tank of fuel because of higher fuel temperature.
Usually after 10-15 minutes it would start up again, sometimes run great for hours, other times just a few miles.
And of course it almost always would die where there was no place to pull over.

I got my rebuilt here US Diesel for about $1,100 with a one year warranty.
I went for a 215 pump since it was the same price.
I see all kinds of better deals but these guys are local for me and have an excellent reputation.

Good idea to get the injectors tested while the pump is out since you have so many miles.