2nd Gen Non-Engine/Transmission Serious Fuel Pressure Fluctuations, help?

[CYauch]

Short story: got the chrome fuel filter cap from Geno's, along with a 30psi West gauge from them also, with the sending unit. And, got everything else from them to hook it all up. Mounted the sending unit to the top of the fuel filter cap, grouned it to the body, made the other connections, and feed off a fuse holder that doesn't have a fuse, and is +13v hot when the key is turned on (hooked in on the side panel of the driver side dash when the driver's door is opened). Its securely mounted there so I'm confident that that isn't the issue. At first start, pressure reads arouns 12 psi or so at idle, moves up to around 14 or so after a min or two. At WOT, will drop down to 10 - 11psi (normal, I think). This is what is killing me, for no rhyme or reason, in the extreme heat, cold, rain or shine, the damn gauge starts going all over the place. At idle, pressure will go to 4psi, at WOT, its sits at 0. Then for no reason at all, it will climb to 8 or so, then drop again when I come to a stop. From a dead stop, I can accelerate the **** out of the truck, and the pressure will sit about 6, jump to 15 or so, then hover around 12 like normal. A few good hard accel's like that, and it will act normal for a while, then repeat its self all over again. On other days, the damn thing performs perfectly, sometimes even going a week or two without a hiccup.



Now, some maintenace and parts replacement history. The reason why I got the gauges was because I got some watered down fuel from the local Truck stop (Cone). Cost me a new Lift Pump, Injector pump, fuel system cleaning, dropped and cleaned tank. Fuel filter gets changed every 2 or 3 oil changes. This particular problem has been happening from day one that I have owned this gauge & filter cap setup. What are the odds of the sender being screwed up from day one? I did ohm checks on it, was within specs. Or is it possible that on this chrome fuel filter cap that Geno sells, and mounting the sending unit on the top of it, that just a spec of sit might be getting trapped between the sending unit sensor and the actual fuel itself? I feel confident that my pressure is ok because the engine 'sounds normal' when acceleration, idling, etc. I get my normal puff of black smoke when i romp it, to. Interstate driving is ok, and responds very well if I want to pass some slow arse in . 2 secs.



I'm at a loss, and hope that someone can point me in the direction to isolate the problem to either something electrical, the sending unit, or maybe the gauge itself. I can post pics if needed that show the electrical connections and how everything is mounted.





O, and sorry, not so short of a story

 

[rweis]

Air in the sensor line? Run truck, loosen sensor line until fuel comes out of loosened joint, tighten joint.



Bob Weis

 

[klaybus]

Lp

Get a mechanical guage & verify pressures. You should also add a snubber line between the fuel filter canister & the sending unit. (Rubber Hose) Worked good for me.



Good luck,

Clay

 

[rweis]

On the snubber line, use RUBBER not braided stainless like I did. Stainless braided line looks neat, but is not flexable enough. I did braided stainless on a couple of gauges and had to replace the sensors and the line with more flexable rubber.



Bob Weis

 

[nps]

Westech FP gauges seem to be sensitive to ground loops. Did you ground the sender and the gauge to the exact same ground point? If not, make sure you have a straight wire from the sender to a ground point, and a straight wire from the gauge to the same ground point.



Many have reported fluctuations on readings when turning on lights, AC, etc. when a ground loop is present.

 

[CYauch]

Air in the sensor line? Run truck, loosen sensor line until fuel comes out of loosened joint, tighten joint.



Bob Weis

The sending unit is mounted directly on top of the fuel filter cover. The pic here is kind of grainy, but I can post the full pic (this is an expanded thumbnail) when I get home for more clarity.



As you can see, I do not have a hose to the sending unit, and since I am in my office, i can't verify that both the gauge and sending unit are grounded at the same point. However, I seem to recall that the ground wire from the gauge is supposed to run back to the sending unit, then a wire from one of the terminals on the sending unit is grounded to the truck itself (in this case, I believe I grouded it to the firewall, but will check when i leave the office this afternoon).



As for a mechanical gauge, any recomendations? Or should I just go get one from the local autoparts store?



And while I am a former electrican by trade (programmer now), I wondered about maybe getting some EMI from the wiring harness that runs long the firewall, at the top and between the engine and master cylinder? The attached picture somewhat shows the harness.



I guess I will mess around with the wiring this weekend. The fluctuations do not seem to be associated with the lights turned on, the wipers, etc. but this is not to say that it could be a contrbuting factor, but I can't pinpoint cause of possible other issues that may be contrbuting? I'll also post more detailed pics the wiring to and from the gauge when I get home.



Thanks for those who have helped to far.



Here's the link to the filer cover and sending unit