Engine/Transmission (1998.5 - 2002) Fuel pressure fluctuates - SPA gauge

[BT]

I installed an SPA fuel pressure gauge last summer. The sender is connected to the schraeder valve on the VP44 using Geno's schraeder valve hose. The gauge worked great and pressures were very consistent, usually 13. 7 psi at idle and down to 9. 5 psi when under load.



A few weeks ago the fuel pressure readings started fluctuating all over the place - driving down the highway at 65 the gauge would read 19. 7, then 7. 5, then 12, 13. 5, for example, all in a matter of a second. It never settles down and reads a consistent pressure like it used to. At idle it still fluctuates but in the 15 to 12 psi range. I made sure the quick-electrical connect on the SPA sender was fine and the ground wire is fine.



I will change the fuel filter this weekend but changed it within the last 7,000 miles, so I don't think this will solve the problem. I don't think it is air in the fuel pressure sender line either, because I haven't touched it and there are no visible leaks.



I'm wondering if the lift pump is going bad. Does the pressure output from the pump start to fluctuate before it fails? It seems odd it would spike with high pressures if it was failing. Anybody have this problem before or any ideas?

 

[Bigsaint]

BT... tough call as it could be either the sender for the gauge or the pump. I'm guessing sender though because those are pretty big swings. The FP does fluctuate under throttle and while at idle with a dying pump to a certain extent, but your readings sound a bit extreme to me while under throttle.



Best bet is to get/make a simple mechanical FP gauge and hook it up to rule out the sender IMHO.



What display rate to you have your SPA set at ? I had to bump mine up to a refresh every 2 seconds to keep it stabil with the PE pumps.



I have had my SPA sender mounted at the bottom of the fuel filter for several years now ( without a snubber) and so far so good. I do believe that a few members here have had failed SPA senders though, so it's a good chance that is it.



If you were not getting the ultra high readings, just sporadic low readings, I'd say no doubt the pump is going.



Forgot to add...



When you checked the SPA plug wires, did you take the plug apart ? If you never have, that would be my first thing to check. The connections are not making contact by much, even when properly inserted into the plug.



Scott W.

 

[jbone]

BT, What Big Saint said---I just went thru this with my Westach and after changing out the lift pump--found problem to be the same--seams there was a batch of bad senders--still waiting for my replacement--almost feel unprotected without my gauge... R, JB

 

[MD500E]

Mine craped out over a year ago. I would see 5, then 22, then 11, then 19, and so on. I plumbed in a temporary mechanical gauge into the cab to make sure it was a bad SPA reading and not the fuel pump. Well, a year later the SPA gauge still reads all over the place and i still have the mechanical one plumbed into the cab. Also the sender on my trans temp which just so happens to also be a SPA, just started doing the same thing the other week

 

[Bigsaint]

I might be dating myself here a bit... does Briar Hopper still offer his test gauge kits ??? BT would be a good canidate for one if he was not so inclined to build his own.