Sudden change with start up fuel pressure

[JeepBuilder]

I noticed a fuel pressure change that happened overnight. I have only owned the truck for a couple months and I am still learning what is normal for this rig. It is a 2001 DRW 3500 24 valve with a 5 speed. It has the 95 GPH FASS adjustable fuel pump located under the bed. Till a couple days ago start up consisted of the 2 second pump cycle that would put my fuel pressure at about 12-15 PSI. Waiting for the wait to start light to go out, fuel pressure would drop pretty fast to 5 PSI or less till I got to cranking. On start up fuel pressure would quickly settle to 14-16 PSI and has been very steady even with a heavy throttle. So no real concerns with pressure under way even now. Two mornings ago I hit the key and the fuel pump came on and it barely made 5 PSI. Curious I cycled it again and it made 8-10 PSI. Start up the pressure raised to the expected 14-15 PSI, but it took about 5 seconds instead of a rapid 1-2 second rise it had been known for. I changed the fuel filter today and no real change worth a mention. I read the FASS instructions on their website, I then read the entire section on the VP44 and related fuel components on the factory manual, and browsed a half dozen threads on several forums. I am stumped so far. I was going to order a new overflow valve and see if is was sticking or causing this. My fuel pressure gauge is a new ISSPRO mechanical gauge I put in right after buying the truck and finding a grossly inaccurate westach electric unit. I installed the ISSPRO with a correct snubber and I believe it is accurate. I also found a filter between the tank and FASS pump this evening. I will change it tomorrow however I have never seen a filter do what I am seeing happen just overnight. The truck currently runs good and has no starting issues.

So the main concern here is the sudden increased time it takes to make pressure on the gauge on the two second (more like 3 second) pump run during wait to start. And the slower rise to running pressure.
Could my overflow valve be stuck open? Why the sudden change in pressure build up?
When the truck is shut off, should the fuel pressure hold the 10 PSI the overflow valve shuts at? Or is it normal for fuel pressure to drop to zero 5-7 seconds after shut down?

I have most all the bugs worked out. I appreciate the help here on this forum. I am way closer to mechanical victory because of it.

 

[petersonj]

I have an older FASS frame mounted pump, but it is not adjustable. I have read many posts regarding problems with pressure settings on the adjustable FASS pumps, but I have no personal experience. You could have a problem with the FASS pump.

Another cause to consider is that you may be losing your prime when the engine is shut off for awhile. If that is occurring, then air would be entering the fuel system. When the lift pump is energized on the next start up, the lift pump will start flowing fuel normally, but the air would begin to compress causing the pump to build pressure at a slower than normal rate. That could match your symptoms.

Does the problem only occur only when the truck has been setting awhile? After the engine has been running for a few minutes and is turned off and then restarted, does the problem still occur? If it doesn't occur, then I would suspect that air is entering the fuel system while the engine is shutdown for a period of time.

- John

 

[DavidC]

I do not know if it is still the same. I have read of people removing the adjustable part which essentially was a plastic ball and spring and finding a groove cut in the ball allowing more fuel to return to the tank.

 

[JeepBuilder]

I will have to see what happens after a short drive. Near as I could tell it made a little more pressure after a restart with a brief wait between. And I suppose if air was entering it would have to be between the tank and pump on the suction side. Anything downstream of the pump would be pressure and it should leak more so. It seems an air leak would also be damp and I will have to look for that. I have a long day on the road and I will have to take a look later. I wonder if a call to FASS would be worth the time.
It is sure acting like an air cushion is there.... Or just draining back. I will have to think on it today while driving. Thanks for the reply.

 

[JeepBuilder]

I do not know if it is still the same. I have read of people removing the adjustable part which essentially was a plastic ball and spring and finding a groove cut in the ball allowing more fuel to return to the tank.

That might be worth a look. I can tell the pump has some age on it from the outer appearance. This was an overnight change though.

 

[DavidC]

That might be worth a look. I can tell the pump has some age on it from the outer appearance. This was an overnight change though.

The only thing I can think of is that it depends on how the ball seats/restricts the bypass of fuel. That may vary at different times.

 

[BigPapa]

Is your gauge electric or mechanical? If it's mechanical, does it have an isolator?

-Scott

 

[JeepBuilder]

The gauge is a new mechanical Isspro with the included isolater from Geno's. It is about two months old. I have some new details. After a lot of driving yesterday and some time to think on this issue, I decided to verify the gauge first. And I was processing the air in the system possibilities. I don't think I am getting air in the system. I am thinking out loud here, but if I were getting air in from a cracked line, loose fitting, etc it would seem that the injection pump would be ingesting some of that air and making the motor run bad. Plus there is no wet spots from a leak. I am pretty sure diesel would find its way through a void and make a damp spot Pre or post pump. So when I got home I separated the rubber line off the fuel side of the snubber or isolator. I hooked up a gauge I had without bleeding. Turning the key for the 2 plus second run made immediate fuel pressure. Sitting all day first, no islolator or pillar gauge in the loop. A very quick rise like I was used to seeing.
This pic is the second run inside the cab and not the first run on the injection pump line. Same reading both places with a fast and normal rise in pressure.

#ad


Inside the isolater fuel side the diaphragm looks odd. The dome of the diaphragm looks to be off to one side. I hooked the rubber fuel line back up to the islolater and this is where something did not seem right. I disconnected the ISSPRO gauge and there was a vacuum on the 1/8 line filled with antifreeze. It pulled in air about 4 inches down that was a bear to get out. Using a flat tipped hypodermic needle I use for filling paint in emblems, I was able to get the air out and fill it with more coolant. I attached the gauge in the picture above and again the pic shows the reading from the second short run. There were small clear blobs in the line that look like possible fuel or some type of growth.

I took the gauge inside and hooked it up to a brand new 3M spray gun regulator. The gauge reflected what I gave it till I hit the upper max readings. It had some variance but it did not concern me since the lower readings were spot on and that is where my system works.

#ad


I reinstalled the gauge on the line making sure to have antifreeze wicking out the connection while tightening. I bumped the starter for a 25 second pump run and bled the air from the isolator bleed port. I turned the key and no reading on the ISSPRO gauge????? This was a bit confusing since the gauge tested good in the shop. I put my little gauge back on and it and it read fine with a normal quick rise in pressure first try. OK now I am puzzled and decide to go mow the property before dark and feed a few mosquito's.
Before I went in for the night I hit the key again. Normal quick rise on the shop gauge.
Fast forward to this morning. I went out and hit the key and everything is normal with the first try making a quick 14 PSI. Second try 15 plus.
So I am wondering why the vacuum on the line from the isolater to the ISSPRO gauge? Did my fuel system make a vacuum? I have determined so far it is a gauge or isolator issue and not the pump or line leaks. I can hear the pump working under load moving fluid right of the bat. I need to tinker with it some more, but this is what I found so far. I am thinking about calling Geno's and see if they will sell me a new isolater only without everything else.

 

[BigPapa]

You could call Geno's, but I've had excellent results dealing directly with Isspro. Describe to them what's happening and the testing you've done and I bet they'll know whats up.

Isspro: 800-888-8065

-Scott

 

[JeepBuilder]

I too have had really good experiences with Isspro. They made me a custom pyrometer with an OD green bezel for an old duece and a half I used to own. I had not thought to call them. That is a great idea. Thank you Scott! And I did speak to Geno's today. I explained what I had found and done, that I was not sure if the isolator was the culprit or not. But that it looked odd regarding the diaphragm being off center looking in the fuel side and the clumps of what looked like bio growth in the line. I asked about buying a isolator without everything else and they wanted to send one no charge. Every time I have talked to them, they prove to be outstanding. If it is not the isolator I will get back with them and be sure it is paid for. The one thing so far that I keep coming back to, is the vacuum in the gauge side when I loosened the fitting. The antifreeze quickly receded at least 4 plus inches towards the isolator. I have been thinking about what could cause that all day. I have not taken the truck anywhere yet. I did hit the key passing by twice today. It made quick pressure to 15 PSI on the shop gauge both times. Nothing like a little mystery....

 

[JeepBuilder]

I wanted to put a final conclusion post on this thread. It was the new Isspro fuel pressure gauge. Before I nailed what was wrong I had contacted Geno's and we talked about what it was doing. They sent me a new isolator right away with a call tag for the old one. I put it on and same darn thing. My shop gauge worked fine, the Isspro was now not even bumping the needle on the truck, but made pressure on the bench with air. So I contacted Isspro and they sent me a new gauge also right away and oddly it was sluggish on the first activation. Second hit with the IGN key it was just fine. Fast 15 PSI in the two second run and a solid 14-15 while driving. This new gauge reads 1 PSI higher than the first one. It is also much more responsive to throttle use. I called Genos and paid for the second isolator as I wanted to keep it. I hope there are no more issues to head scratch on. I have been driving it for a week now and all seems to be fine. I want to offer a kudos to both Genos and Isspro for the help and replacement parts they wasted no time getting to me. Both companies are outstanding and I wish others would follow suit. The continuous repairs are over. Tomorrows wrench time will be putting a hammerhead bumper on with a Warn 12K winch and a couple LED lights. To many deer and moose on the roads to not do this...
Thanks for all the help.