My fuel pressure always sets at 11PSI at idle. I got to wondering how accurate the gauge was. I hooked up a calibrated gauge under the hood (NIST traceable) and low and behold, it read 14 PSI at idle. The gauge is a DiPricol 0-30 PSI fuel pressure gauge. That makes it off by 10%! Now, I'm wondering if my pyro is off too! If it's off 10% then my engine has been too hot! I emailed the place I purchased it but havn't heard back yet. The sad part about all this is when I purchased the gauges, I asked if there was a guaranteed calibration and was told no. I bought them anyway.

 

I assume you have an electrical FP gauge. The sender is probably shot, I went though three senders before giving up and going with a mechanical gauge. Senders just don't hold up to the vibration and fuel pressure pulsations of a diesel. A couple of the senders failed in much the same way you describe, they only read zero and the pressure the gauge saw most often (in the normal range) with no in-between. Gave a false sense of security.

 

Nope.. It's mechanical.

 

Well then there is only one thing that can be broken, the gauge itself. Most times when a mechanical gauge is bad it's obvious, the needle doesn't return to zero.

 

I also have a variance in my FP between my gauge and direct hookup under the hood. I have a mechanical autometer with the diaphram isolator. However, it's due to the position of the isolator in relationship to the guage itself. Autometer suggests that the isolator be level with the guage. Well, that just wasn't possible. The gauge reads 1 lb less than an under the hood reading. As long as I know that I don't have a problem.

Ben

 

Bill: Mine returns to zero ok. Diesel Power Products says they'll replace whatever is bad. It could be the isolator.

Ben: I can't figure out why the isolator and the gauge would have to be level with each other. That's a weird one.

 

Rattle,

I'm not sure. From the pump to the diaphram is fuel and then from diaphram to guage it's antifreeze. The amount of resistance pushing the anifreeze is greater uphill than level?????????? I honestly don't know. That's what Autometer's intructions said. All I know is that it's 1 pound less across the board. That works for me. Way better than the autometer electric piece of junk that was in there before. The sender died within 20 miles of installing it.

Ben

 

Loose the isolater and run the line straight to the gauge. The gauge may be just fine. Remember it only indicates what it's being told...... the isolater may be lieing to it.

 

I've got a mechanical ISSPRO with no isolator in my truck. Thing is rock solid at 20 psi (19 at WOT. I have a PE pump). No leaks at all. No rattle. And since I don't have an isolator, I know that if something does start acting funny, it's either the gauge or the pump. Nothing else there could be.

 

big blue
How did you hook up your guage with no isolator? What kind of line? Do you have any diesel fumes in the truck? I guess i am worried about the interior smelling like diesel all the time. My isolator reads incorrectly by a long shot and am starting to get pi@$ed off. I was thinking of just runing it straight to the guage with no isolator or putting it outside infront of my winshield on the outside of my truck.

Chris

 

Merrick sent me a pre made line. It is a hydraulic line with a -4 AN 90* on one end and a straight -4AN on the other. It's about 6-7 feet long. It's kind of a PIA to route, but not to bad. You just got to really think about it. There is no diesel smell in my cab and no leaks.

 

Chris, since everything is already hooked up just trade the isolator for a coupling. I would try to blow the antifreeze out first. If it didn't leak antifreeze in the cab it won't leak diesel.

 

Who made your isolator and who did you get it from? Diesel Power Products says there are some that are defective that they sold. They're replacing mine free of charge.

 

I got mine thru BRC diesel which is a friend of mine. He is replacing it with a diaphram soon or maybe we will do what infidel said.

Should we get all the anti-freeze out. I imagine we should but just asking. Then just bleed the line with diesel i guess? Does the diesel gel up in winter because it is pretty much in the air or does it not affect it?

Chris

 

The antifreeze will eventually make it's way back into your fuel system. Don't really know how bad it would be but don't think it would be good. Just pucker up and blow it out while the line is disconnected.
Montana gets a bit colder than KY, never had a problem with the FP gauge not working in the cold. Could be that it does gel but doesn't effect the gauge. Even when gelled diesel is still somewhat fluid, it just won't go though a filter.