I got my new overflow valve from Piers and checked the spring height before installing. It measures .440. I have read that the height should be .550. The truck runs good with the new valve but I'm wondering how long the new OFV may last? Didn't really want to stretch the spring on a new valve.

 

Are they the same brand? I would suffice to say they aren't. And if it is working properly I would go with it. Also the springs when colapsed can be resprung but won't hold long anyways. Goodluck,,Rick

 

O/F valve spring should be .5 inch.

 

I personally feel it very foolish to stretch the spring without a fuel pressure gauge.
Odds are you can create way to much pressure and blow out injection pump seals or crack the filter and lines.
I've seen the lift pump put out in excess of 100 psi.

 

I have a brand new lift pump and OF valve. My fuel pressure is 22 at idle but it pulls down to around 17 (maybe even 15) under heavy throttle. Any suggestions why this might be?
Thanks,
-john

 

I'm in the same boat as you basically. I haven't bought a lift pump yet but I'm thinking about it. I installed my fuel pressure gauge and found that I was at 20 PSI, now that I've installed a new OFV I'm up to about 25-28 PSI idling and can pull it down to about 20 PSI under load. The truck runs fine but am somewhat concerned after learning what some of the other trucks are running for fuel pressure. I ordered a fuel strainer kit from Cummins this morning after finding the part numbers off of Infidels old post, didn't want to take it apart until I have new seals. I don't think it is dirty but it is a cheap try. Also priced a lift pump from them for kicks and was quoted $178. I think I'll go with Infidels advise again on the pump if the screen doesn't help.
With the P7100 being cooled and lubed by engine oil, can low fuel pressure destroy it?

 

No, low FP won't hurt a P7100. In fact, your more apt to hurt it running with high pressure. And, besides, your FP is fine with the new OF valve. I'd be happy if mine was 20 PSI under load. From what I've been told 20 under load is just fine (22 @ idle, 25-30 @ 2500 RPM unloaded I think are the #s in the shop manual).
-john

 

The first place I always start in this situation is to check the accuracy of the gauge with another one. Just a few seconds of pulsation with an undampened line can damage a gauge or sender.
Second place to look is at the filters including the one in the tank.
Also check for a kinked hose behind the engine and at the tank.