boughtadodge

Anyone know the effects of the over flow valve if it has more or less pressure? I was messing with mine the other day and noticec that when I put air pressure to it it would start to leak air at around 20 pounds so I took the spring out and stretch it now it held to around 40 psi. I took the truck for a drive and did not notice much difference if any. But the next morning it was real hard to start the next morning the same thing so I put a new one in and it starts great like it should. How can this affect the starting?? What does it do does it advance the timming or something to that affect. On my old IDI fords with the standyne pump there was a solonoid on the front of the pump that would drop the fuel pressure in the pump to ease cold starting is this similar to what that does??

robert chilton

The over flow valve is basically a fuel preasure regulator. Preasure is low and you have driving problems. To high can cause IP pump wear.

LanceD

what is it supposed to be and how do you check it?

boughtadodge

why would to high pressure wear the pump? How does this effect the injection? I had a freind that the spring inside his overflow valve was broke in half so we replaced his and it did not run any different even though it had to have less pressure.

kawi600

yeah I second that question.. what is the pressure supposed to be on these? Mine reads 30psi at idle since I installed an overflow valve I got from cummins which didnt look like the original part at all (it had 3 shims inside and the opening was smaller). I figured maybe it was an updated part??

robert chilton

Higher preasures can rupture seals in the injection pump. When I get home I will see if I can find the link for the TSB that goes into problems with the overflow valve. If anyone wants to dig around a little it is for white smoke and low power for a 94 or 95. Fuel preasure should be12-15 PSI at idle with cruise around 30 PSI.

infidel

Normal fuel transfer/lift pump pressure specifications are 17 - 22 psi at idle and of 25 - 35 psi at 2500 rpm (no load). Pressure should never exceed 45 psi.
More pressure can blow out injection pump seals and rupture the fuel filter and hoses.
For that reason my feeling is stretching the spring is a dumb move without a fuel pressure gauge, you could potentially cause over a thousand dollars worth of damage by skimping on a new $35 valve.

To measure FP on a 12 valve you need to buy an expensive special Cummins tool or make one yourself. The special tool is nothing more than a injection pump inlet banjo bolt that has a 1/8" port tapped into the top of it. If you can tap your manifold for a pyro this is a piece of cake. You must also have a restriction in the line to the gauge to prevent pulsations that will destroy the gauge in the short amount of time that you can't read it. Needle valve almost closed or gauge dampener works.

Cummins "special tool"


My special tool

robert chilton

It never stops amazing me how much info that Infidel has hanging around in his head

SHARPMACHINE

I am with you on that, he does'nt joke around or anything, just solid answers EVERY time.

Mcmopar

[/QUOTE=infidel]
For that reason my feeling is stretching the spring is a dumb move without a fuel pressure gauge, you could potentially cause over a thousand dollars worth of damage by skimping on a new $35 valve.

Click for Cummins "special tool"
http://dodgeram.info/tsb/1996/figures/14-07-96-f2.jpg

My special tool
[/QUOTE]

Infidel,

You must be the bargain man My new overflow valve was 60.00 bucks and the solonoid was like 45 compared to your deal of 28. That or I am just unlucky!!

infidel

Cheapest price by far here, and they were only $20 about a year ago.
Inflation I guess

Precision Diesel Injection and Turbo Inc.
Marty Tompkins
888-734-7349
$35 + $7 shipping and handling.

boughtadodge

Yea the $20.00 ones were junk I had three out of five fail. They would shoot out the ball that was in the end. Then Marty replaced them with the newer more exspensive ones and they work great . I put a new one in the truck just stretched the one that was in there to see what upping the pressure a little would do.

Lil Dog

Upping the pressure will advance the timing slightly. If the injector gets to its pop-off pressure sooner because of the higher input pressure to the injector plunger, then you have increased your timing without any movement of the pump gear.

The same problem can happen with lazy injectors. As the pop-off pressure drops on the injector the sooner it injects the fuel....early timing..

I paid top dollar for an OEM O.F. valve a year ago after hearing problems with the cheaper ones. I like to replace parts ONCE...

kawi600

So you check the pressure at idle and at 2500rpm no load. What about if your pressure dips down to 18psi or so with your foot in it? Is that bad?
The cummins OV I got was really expensive and its raised my pressure to 30 at idle and 30 at 2500rpm no load

infidel

It's not bad but I wouldn't want to see it go much lower.
It could be caused by a slight lag caused by dampening the line to the gauge.