Engine/Transmission (1998.5 - 2002) Inconsistant fuelpressure

[SMolteberg]

I have seen a lot of different fuelpressures lately. Since I bought the truck a year ago I put in a new LP right after I installed my gauge. It have read about 15psi at idle and around 13psi at WOT. Sometimes this winter it would read a littel lower sometimes (10psi) It was in a cold period and, and next time it started it was back to 15psi again. A few weeks ago the fuel pressure started to drop on me. Every time I started the truck I would see a different reading on the gauge. It never dropped when I was driving, and I also didn't see any lower PSI during WOT. One day I could see 8psi the other 11psi. One day on my way home from work I saw 1psi.



Next morning I put in a new fuelfilter, still 1psi at idle. I got a good dieselflow when I bled the air after the filterchange. I then got out my spare LP even I thought it was a bit early for the old one to lay off (8000 miles). I fired it up again and still 1psi at idle! I had to leave for work and on my way I could see it was slowly climbing to 4psi. (I have seen this happen earlier also) On my way home again it read 5psi at idle and slowly climbing to 7psi.



I have kind of ruled out low pressure and more suspected my gauge for bad numbers. It's a mechanical Diprocol from Geno's with an isolator. Any others had any problem with them? Since I'm in Norway it's not so easy to get hold of a other instrument to doublecheck my readings. I talked with our Volvo mechanic at work and I could borrow his instruments, but he didn't have any connections that would fit my schrader-valve, it seems that that valve are a US standard and not much used here in Europe



Any experienced the same situation here? Would be happy for any help

 

[Gary - K7GLD]

I put in half a tank of fuel a week ago for a 300 mile trip we were making - and not too far down the road, my usually steady PSI started fluttering and dropped down to the 10 PSI the pusher pump supplies.



My PSI never did return to normal except when the truck was first started - it would get up to 20 PSI, and then quickly drop back to about 10 PSI. A few days ago, I took off the LP, and installed what was actually my original LP that I had traded several years back as part of some related testing.



That pump behaved exactly like the first one! And it was thoroughly checked and tested for proper operation on my work bench - as was the one I just removed - both work perfectly - except when installed on the truck!



I think local fuel supplies have changed - and foaming/viscosity are enough different to cause fuel foaming and cavitation inside the LP under operating conditions.



I didn't feel like messing with the situation - or hoping for another tank of fuel to somehow magically correct the situation, so I have eliminated the stock LP, and installed another Carter 4600 pusher pump down on the frame rail near the other I have been using since the truck was new.



I now again have stable PSI - at 15 PSI idling speed - neither of the 2 Carter 4600's generate enough PSI or fuel turbulence by themselves to create foaming or cavitation.



Now all I have to worry about, is whether they can also provide enough flow to keep up with my various power mods!



Again, at least in my case, I suspect formulation of local fuel supply is the culprit - we DID make the switch from Winter to Summer fuel at about the same time - and with other fuel changes on the near horizon, I suspect other changes went into the mix at the same time.

 

[BT]

Sounds like you have air building up in your fuel pressure sender line. I had the same problem and installed a 3-way valve to bleed off the air in the fuel pressure sender line periodically when the gauge starts giving erratic readings. Works great. See previous thread:



https://www.turbodieselregister.com/forums/showthread.php?t=102481

 

[Gary - K7GLD]

Sounds like you have air building up in your fuel pressure sender line. I had the same problem and installed a 3-way valve to bleed off the air in the fuel pressure sender line periodically when the gauge starts giving erratic readings. Works great. See previous thread:



https://www.turbodieselregister.com/forums/showthread.php?t=102481

In my case, I verified PSI with an outboard mechanical gauge...

 

[SMolteberg]

Sounds like you have air building up in your fuel pressure sender line. I had the same problem and installed a 3-way valve to bleed off the air in the fuel pressure sender line periodically when the gauge starts giving erratic readings. Works great. See previous thread:



https://www.turbodieselregister.com/forums/showthread.php?t=102481

Thanks BT! I also have the same Geno's rubber hose from the schrader valve on th VP44 to my isolator. I think it might be a bleeder-screw on the diesel side of the isolator.

I have also thought about air, but couldn't figure out how it could sneek into the system without any other problems. Will bleed it first thing tomorrow!



PS. Bought the truck myself in Seattle and shipped it off to Norway, I'm in Seattle usually twice a year visiting friends.

 

[BT]

I think there is a lot of air in the fuel when pumped (when i fill my tank, it takes a long time to allow the foam to slowly dissipate until the diesel can be seen in the filler neck), and enough stays in the fuel as it is drawn from the tank. A little bit comes out of solution and finds its way into the fuel sender line through the schraeder connection. Eventually it builds up and as it compresses with pressure surges in the fuel system, you see erratic high and low pressure readings at the gauge.

 

[SMolteberg]

I got it fixed! It was air that had sneaked into the isolator on the antifreeze side. If this comes back I might go for a steel line with a valve and dump the isolator. I spent a few hours troubleshooting this and swapped a perfectly good LP. I ordered a test gauge with a long hose from Rip at Source Automotive just to rule out the fuelsystem itself. After I hooked it up it climbed right up to 15psi. My salute to Rip that managed to ship the gauge to me overseas in only four days. That man deserves a reward of some sort

With the money spent on just to monitor the fuelpressure at this point I'm not so far away the cost of a new VP-44 (if it ever goes out) :-/