Doug_TX

Here's my current setup:
2002 HO 6 speed using a Quadzilla Commander to monitor Fuel Pressure (FP). I've cut loose from the stock Lift Pump (LP) and bypassed it using a Holley Blue on the frame rail just forward of the tank. The Blue is powered by a relay mounted on the firewall and triggered off the original LP cable. No performance modules or upgraded injectors. The Commander FP kit was one that Q'zilla had switched to the lower pressure sending units that they tested to ensure it would work with the lower FP as seen on the Dodge Cummins applications.

The issue:
On startup and idle the FP is good and consistent. Showing about 12 - 13 psi at idle. At WOT it doesn't drop much (usually to about 10). But the problem is that from time to time I'm seeing random pressure dropoffs. Sometimes as low as 2 or 3 psi. Then it will jump around and go back to somewhere between 10 and 13. I've bypassed the relay, swapped the relay, all to no effect. I replaced the 'overflow valve' (DC calls it the 'return flow check valve'). To date the best success I had was when I removed a shim (behind the RV spring in the Blue) and lowered the pressure. It seemed to stay betwen 10 and 13. So I 'stretched' the spring a bit more and now I'm back to where I was before.

Needless to say, this is totally driving me insane. I added the Commander to let me know about the health of the fuel system and so far I've done nothing but pull my (limited) hair out. Anyone have any good suggestions on what my problem may be? And if you want to say "Replace the Holley with a FA$$, please don't as I'm unable to dump that much for that right now. Can anyone help me figure out why my FP readings are going insane like this? It's mostly random but I don't get the drops when I'm fairly heavy on the throttle. I tend to see it more when I'm in a constant cruise with light throttle (but that's when the demands on the fuel delivery are light).

Anyone?

D2 Cat

Is your FP gauge mechancial or electrical?

I had similar trouble with an elec. gauge. It started on an evening before I was going on a 700 mile trip. I didn't think it was the LP 'cause it was near new. I had the Valcan big line kit installed. I didn't have time to tinker much.

I removed the sending unit (for the elec. gauge) from the line and connected a 1 1/2" mech. gauge. I had some insulation like used for wrapping AC tubing. I cut off a piece about 2" long and inserted the gauge in it and left it just sticking out of my hood. It showed nearly 14 PSI on the entire trip! I'd double check the gauge esp. if it's electrical.

Doug_TX

No. But the truck is stock with no performance mods.

Doug_TX

It's electrical. With the Q'zilla Commander. But Q'zilla claims the senders are all tested and no failure history.

PaulDaisy

I have seen more than one report that Quad Comm fuel pressure sender is not working very well for people. Double check this issue with a mechanical gauge, that would be my suggestion. Then if it is indeed the sender, I think Quadzilla will replace it for free (I recall someone reporting that here, do a search for Quadzilla Fuel Pressure).
-P