ok heres the deal--bought the truck bout a year ago..previous ower said it got around 18mpg on open hwy and for the most part around town also.(I couldnt get that out of it, evevn cruising down the interstate at say 65mpg I was only getting 16mpg at the absolute max) ok i had it for less than a month before i put a holley blue and an EZ on it. No change in mileage(most of my driving is around town anyway). In march i put a raptor 100 on it(including big line from tank to filter) because my blue puked out--no change in mileage. Couple months later changed the APPS and torque converter--No change. Then here lately my fuel psi has been fluctuating very strangely. The raptor has been set to 15psi at idle and wouldnt drop below 10 psi under heavy throttle since i have put it on, but now sometimes it will idle around 12 or 13 sometimes 14 and drop pretty duractically. sometimes it will drop to 6 or 7 and yesterday i noticed it getting down to 3 and 4. And then the next day it may be idling at 16 and not drop below 9. Installed a hot comp last week...also thought I might get better mileage with it on setting 3 or round about--no luck. The comp box has nothing to do with the fluctuating psi because it was doing it before the install. I have changed fuel filters, sending units for gauge, the overflow valve, all in hopes to fix the problem--but no luck. Have developed a slight leak in the fuel heater temperature sensor on my filter housing...dont know if there is an oring in it to change on not...checked with dealer n they said I would have to buy the whole housing and I defiantly dont want to do that because of the price tag attached to it. So I did what anybody else would do put some RVT on it and it has almost stopped it..need one more application. But anyways, could that maybe be my problem that it might be sucking air through there or do I really need a big line kit from filter to VP? Sending unit possibly bad again? Got a blockage somewhere? I would say no to any of these questions, unless maybe it is the air getting in there. Thanks in advance guys.

 

There is a thread about the wif sensor, common found o-rings inside. Do a search.

Don't know what to say about the raptor mine has been rock solid steady except when grid heaters are on then psi will drop. It could just be a minor elec. connection problem. Could be a gauge problem.

I was always 12mpg or better when I checked so I quit. It doesn't really matter to me.

 

Mine gets ~16 mpg all around but overhead shows ~ 12 mpg around town. Stock tires so Ohead is reasonably accurate.

 

The Raptor does have a screen on the input side of the pump. If that gets clogged your fuel pressure will suffer. Also the spring can wear as well, try cleaning the screen first, and if it still is fluctuating crank it up a hair by the adjustment and you may find it will steady itself out again.

 

i get 18 or 19 in my 99

 

Automatic?

 

You need to check that you are getting 12 volts at the connector to your lift pump. while checking it you need to pull-push and wiggle the connector to find bad or broken connection. I dealt with this problem on my 99 and found a broken ground right next to the connector.

Disconect connector to lift pump and place volt meter on connector, have someone bump the starter but dont start the vehicle this will send voltage to
the lift-pump for 30 secomds.


Mike

 

wouldnt it sound different if this was happening?? pump sounds just like it always has...today im going to put a dial gauge directly at the pump and check it.

 

You would think... I spent alot of time trying to figure mine out, even put a new lift pump on it and I thought I had it fixed, two days later it started all over again. All I can say is at idle it seem to work fine and bump testing the lift pump the pump sounded the same. When I tested the connection with a meter I was getting a fluctuation from 4 to 12 volts and when I manipulated the wires I could get it to 0 volts and the pump would make no noise.

After replacing the bad connection my fuel pressure has been great.

Let us know what the problem ended up being.

Mike

 

checked the strainer on the raptor...just as clean as can be, checked the voltage..its throwing 12v. I turned the pump up a little bit the other day just in case it might have something in the line it would blow it out..no luck. But its dropping from bout 17.5 down to 6 with the comp turned all the way up and from 17.5 to 11 with it turned off. in the mean time i put my an inline dial gauge in between the 44 and my sending unit just to double check me electric gauge..i got the same reading so that rules out it being the gauge.

 

Were the two in-tank filter screens removed when the new pumps were put on?

 

no.. you guys recon it could be the overflow letting too much return to the tank...overtflow was replaced bout 3 months ago. i wouldnt think it would be bad.

 

With the aftermarket raptor I really suggest putting in a draw straw. I had similar issues before my draw straw and after the draw straw my issues went away. got mine at Vulcan performance

 

i second that, had the same problem, first i pitched the screen on the bottom of module, i ran 2 fuel pumps at that time, then FASS and straw, problem gone for ever. i also had a bad gauge that cost me a ton.

for a temporary repair i would take the fuel cap off and blow shop air in the suction fuel line before the pump.

you can make you own draw straw if you can find bulkhead fittings and can thread tubing.

 

OK , this happens to me too especially at his time of year. I get a little moisture built up in my fuel tank through the summer. It sinks to the bottom of the tank. There it causes a problem when the weather turns cold. Might be some alge or crud in there too, all floating at the bottom of the tank. It gets thicker in the cold weather. So, it gets hard for my pump to pull fuel through the screen on the stock OEM fuel pickup. I had this happen when I refuled and picked up some water one time in Northern Utah in the winter. I have found two ways to fix it, one easy and one way harder, but more fun if you like working on your truck. The easy way is to add fuel treatment to get rid of the water. The big 18 wheelers do it and the stuff is for sale in the truck stops in gallon jugs. The fun way to fix it , if you have the time and you like to work on your truck, is to put a draw straw into your tank with out any screen on the end of it. And put it right on the bottom. It will pick up the crud and water and your filter can take it out. Just make sure you have good filtering because it will pick it up! Fuel treatment fixed mine more than once.