I finished my install of my new Isspro EV2 fuel pressure gauge today and after startup and idling for a bit the pressure stays steady at 42psi. I haven’t checked it driving but revving to 2000 RPM showed no change in fuel pressure. I ordered a new filter from Riffraff today even though it’s not due yet normally. I also have parts on the way to do the hutch mod in another couple of weeks. Anything else I should be looking at?
Todd

 

Do you have any other ISSPRO gauges like a boost gauge?

If so what happens when you plug the harness from the FP gauge into the boost gauge and vice versa?

Does the gauge drop to zero when the truck is turned off and then do a full range sweep when turned on?

Does your truck seem to struggle with fuel supply if you are ignoring what the gauge says?

Did you install the FP sensor in the pre or post filter port?

Does the gauge fluctuate at all when driving, even one PSI?

Did you use a snubber or 90 degree bend for the sensor?

Does the PSI drop a bit after turning the truck on (not starting) and letting the fuel pump shut off?

 

Do you have any other ISSPRO gauges like a boost gauge?
I do but they are Isspro EV1 gauges that I’ve had for 13 years now so the plugs aren’t compatible.

If so what happens when you plug the harness from the FP gauge into the boost gauge and vice versa?

Does the gauge drop to zero when the truck is turned off and then do a full range sweep when turned on?
When I turn the truck off the gauge stays at 28, and does not not do full sweep when turned on. Warning light comes on, needle drops to 0, then needle kind of ticks up to around 32. Just checked it again and pressure wouldnt go above 32 do I have a bad gauge?

Does your truck seem to struggle with fuel supply if you are ignoring what the gauge says?
Truck runs fine and is peppy when I get on it. Just installed the gauge cause I wanted one and wanted to see what pressure was before I did the hutch mod.

Did you install the FP sensor in the pre or post filter port?
Pretty sure it’s post filter port. It’s the same port you used on yours.

Does the gauge fluctuate at all when driving, even one PSI?
None.

Did you use a snubber or 90 degree bend for the sensor?
I used the snubber and the sensor is strait off of that. I ordered a 45* flow through NPT fitting but it’s not here yet.

Does the PSI drop a bit after turning the truck on (not starting) and letting the fuel pump shut off?
With key on, engine off the gauge slowly “ticks” down to 0. It is not a smooth sweep like my other Isspro’s.

 

The ticking down is OK, mine does a similar thing when going down from 65 PSI after the pump turns off.

I "think" you have a bad sensor, but that is hard to say without verifying the gauge is not faulty. I would suggest calling ISSPRO tech support and discussing it with them. When I had a faulty FP sensor, they sent a replacement with the snubber at no cost to me. They were very helpful and got things sorted very quickly and to my satisfaction.

I was able to verify the sensor was faulty by plugging the sensor into the boost gauge harness. The FP reading went from normal to around 75 PSI, then when throttle was applied it would go up to about 90 PSI.

I had the micro processor go bad in my EGT gauge a few years ago and they replaced that at no cost to me as well. The EGT gauge would not move at all and was stuck at 350 unless power was shut off. This is why I suspect the FP sensor and not the gauge. Be sure they know you drive a 7.3L diesel.

I might be wrong about the full sweep motion, I haven't started my truck in 3 months and might be thinking about one of my other vehicles.

 

Thanks. I’ll give them a call tomorrow and post back the result.

 

I would rig up a cheapo fuel pressure test kit and get a second opinion. Even if you just test it at idle with the kit you will be able to confirm your isspro pressure sender is either good or faulty. Should hold around 60-65 psi at idle and light cruising. Will dip a little if you wail on it into the mid-high 50's. If the isspro pressure sensor tests good there will be some fuel system troubleshooting needed, but I would start there.

 

I respectfully disagree...

A well functioning fuel pump on stock injectors should not go that low. My FP never goes below 60 PSI, even on a spirited run to the top of 3rd or 4th gear pushing north of 35 PSI boost near 3000 RPM.

I cannot remember what the low safe point/threshold for FP is, but I want to say it is 48-50... He stated his truck runs fine and is "peppy". I would not describe a truck with a failing fuel pump as peppy.

The call to ISSPRO is cheaper than cheapo, it is free. They will help troubleshoot their product and make it right when the faulty part is identified.

I highly doubt the FP is really in the low 40's when idling or bringing the RPM up to 2000. That is not a true under load test in my opinion. Although, I am wrong just about every day, so there is that...

 

Could be.

Been there.

 

Todd, any updates on your FP gauge/sensor?

 

Sorry for the delay. I got ahold of tech support today and then talked to the engineer at Isspro. He had me check the voltage between pins 5 & 6 on the back of the gauge and the voltage showed 1.93 which correlates to 36 psi. He said that meant the gauge was working correctly and didn’t feel the sender was the issue either. He told me about his OBS 7.3 that has run on the drag strip with as low as 20 psi. He did offer that I could send in the sender and they could bench test it to ensure it was working properly.

My fuel filter should be here tomorrow and I’m going to see if that makes any difference. I had to run to the base today but got the 45* adapter installed beforehand. The gauge seems to have settled on 36psi at idle and drops to 30 to 31 at about 2k RPM. If the fuel filter doesn’t make any change I’ll send in the sender to have it checked out. Should be doing the SSJ/Racor Hutch mod in mid-May.

 

Todd, no need to apologize, life gets in the way at times when we are playing with our trucks.

If the filter does not fix the issue, use the SkySkiJason method of testing for actual fuel pressure like Brandonpdx suggested.

I believe SSJ said a 5/16" hose and a 100 psi mechanical gauge with a barb connected to it off the bowl drain valve stem would do the trick. You could hook up the mechanical gauge, start the truck and check the mechanical gauge pressure versus the ISSPRO electronic gauge pressure and move forward from there.

If it truly is in the 30's, you will need to find the cause of the low pressure.

If you need, I can find the exact parts SSJ called for, just let me know.

 

That would be awesome if you have the parts list handy. You said he hooked into the bowl drain valve stem? I didn’t realize there was a valve stem somewhere in there. I thought the only drain was the yellow swivel handle.

 

Yes, the yellow handle. Clamp a piece of 5/16” fuel hose to the valve outlet )instead of the rubber hose/steel line that is there now. Any cheap 100psi pressure gauge from hardware store will work for a short test. 6-7 ft of hose is enough to get to the mirror or behind the windshield wiper do you can see it while driving.

There is no significant loss of power until below 20psi of fuel pressure. You’ll start to notice below 35psi on a long, hard pull. My cut-off is 40psi. When I can’t maintain that pulling a grade - it’s time to change the filter.

The in-tank and pre-pump mods are needed no matter what. I have installed lots of fuel pressure gauges and found low fuel pressure on trucks that ‘run fine’. Used to always be the in-tank filters, but as these trucks get older, I rebuild more and more FPR’s.

 

He has mentioned it a few times and below is only one example.

https://www.ford-trucks.com/forums/1...l#post19167148

You and I are talking about the same drain on the back of the fuel bowl, the one with the yellow swivel handle. Remove the semi-rigid rubber drain hose and attach the 5/16" hose and gauge.

This will give you a way to check the fuel pressure via a mechanical and electronic gauge. If in fact your fuel pressure is in the 30's, it should be resolved sooner rather than later.

If the mechanical gauge shows ~62 psi, then you can call ISSPRO back and ask for a replacement sensor based on your findings.

EDIT: It appears Jason and I were responding at the same time...

 

Got the new fuel filter in today and now at idle the gauge is at 42psi. I’m gonna get the parts for the mechanical gauge in a couple days and check that. After the hutch mod my next mod is probably the RiffRaff FPR upgrade. When I get the mechanical gauge I think I’m gonna attach it where the Isspro sender is for uniformity. I figure I’ll check it with and without the snubber. The Isspro engineer said the snubber smooths out the pulsations.