Boost Control Issue - need direction on next step


Active Member
Well leave it up to me to cost myself unnecessary money and headaches.

My fuel gauge is off so I had a 300 mile round trip planned so with my great intelligence and inquiring mind I said I’ll take 10 gallons of E85 with me and run the car til it runs out so I’ll know exactly where Empy is on the gauge. Well I Know exactly but it cost me greatly to find out. At half way between E and 1/4 tank it’s completely empty.

I knew that it was getting close just from using an average of 12 mpg from previous test and 17 gal tank so I got off the interstate and was going to just add the fuel well when I got off the interstate it died at the light about 200 yards from a safe place to refuel, so I just refueled right there at the light.

I know get to the point.

Heres where the fun begins. The car would not start only crank, so I assume that I blew the fuse from excessive cranking. All fuses are good. All us this is in the middle lane of the off ramp.
Checked the edash and zero fuel pressure. Ok I figured that I ruined the pump by running it in a dry tank. Then I remembered that I have dual pumps and the second one is activated by the Hobbs at 10psi so I bypass the Hobbs switch look at the edash and see 38 psi. I proceed to cranking the car and it starts so I drive over to right lane all while telling my wife how smart that I am for being able to figure this out and before I can finish pumping myself up the car dies and I coast into the gas stations parking lot. Zero psi on edash.
Fuses are still good
I understand what happened to the primary pump but what do you fellas think happened to the second pump. It shouldn’t have been hot because it only comes on at 10psi and wasn’t being used. I wouldn’t think that first pump got so hot that it could have damaged the second pump.

needless to say a 46 mile tow and at minimum to new pumps just to say that I know for a fact that with exactly 17 gallons of E85 with E content of 74 driving an average of 75 miles per hour on a 86 degree day on 275/60R 15 Mickey Thompson tires with 24 psi of air in them and one pissed of 148 lb wife in the passenger seat that my car is completely empty at 238 miles and the gauge exactly half way between E and 1/4 tank.

I hope that this helps someone so you won’t have to perform your own experiment.

thanks for your attention.
you say you have edash so assume XFI is your ecu , why wouldnt you swicth over to 93 for a long haul trip , easy enough to add a second tune for 93 with less timing , leaner AF , and less boost to the ecu and use the edash to switch
Also shouldn’t the flex fuel sensor sensor just calibrate the tune also.
I drive my car at 300 least miles every weekend if the weather allows it and always just keep around 10 gallons with me Incase I get away from a E85 station but I have never needed to use them in that situation. I’m always near E85 stations. I was just trying to know exactly where the needle was when the car was absolutely empty.
Well I found out the hard way.
I just don’t understand why the second pump stopped
Do you have the Racetronix harness? You can switch which pump you want as the primary. I rotate them so each pump is getting used regularly. I assume your pumps are E85 compatible?
Yes the pumps are E85 pumps
No I don’t have the racetronix harness. I’ve been wanting to for a while but something always comes up. This setup has worked flawlessly for years, my curiosity just got the best of me this time.

it would nice just swap it around, I never thought of it that way, I guess I’ll just have to stay over 10 psi of boost more often. Lol

Do you have the part # for that racetronix setup
The fuel itself is cooling the pump as it is submerged and the fuel is going through it. As you are driving the level and amount of fuel is becoming less and less. This results in hotter fuel and hotter pump(s). When you went to the second pump with very little fuel, it was already hot as it is hanging right next to the first pump that overheated and it over heated too.
I like to keep at least half a tank of fuel in all my vehicles with an intank pump. If you are steadily running low on fuel that pump is taking a beating. Especially on long trips as it is circulating fuel and heating it up.
Are these pumps in a factory fuel tank with the dog dish bowl inside?

Check the fuel socks on the pumps too, easy way to overheat is have a clogged or collapsed sock.
I dropped the tank and the primary pump is burnt. It has physical damage.
The secondary pump works. I did find the hot wire fuse holder melted. It was not melted initially when I swapped over to the second pump. 100% sure. The damage came when I ran the 2nd pump direct. That explains why the second pump stopped working but what caused it to melt the fuse holder I don’t know. My setup was rigged from the jump so I’m going to do it right this time with a plug and play setup. I’m considering going this route

Please pm if you guys have any recommendations.

I have verified that the grey wire at the factory harness in the rear activates the pump for a few seconds but while I had my engine out I did a major engine bay clean up and I can’t find the factory grey fuel pump test wire for anything.
Do you guys know where would be a convenient place to tap into this wire underneath the car or under the dash or anywhere. I would like to have it available for test purposes in the future.
I’ve torn into my harness as far as I’m willing to in the engine bay.

Do you guys know where would be a convenient place to tap into this wire underneath the car or under the dash or anywhere. I would like to have it available for test purposes in the future.
I’ve torn into my harness as far as I’m willing to in the engine bay.


The gray wire on the four-wire plug of the fuel pump control module (by the MAP sensor)
That's a very nice set up. The wiring is all heavy duty and matched to the draw of the pumps. With the Racetronix harness, there is a tap for power indicator lights. You can wire up lights to that show when the pump(s) are on.
Switch to DW300 pumps (note pump polarity during install) and beef up the grounding by running a 10 gauge ground wire from the battery ground to the rear of the car. Connect the 10 gauge ground wire to the racetronix ground bundle back there.
Wire it so the second pump is activated by the XFI for more precise control.