I"ve been converting my 88" 535i come a track vehicle for the critical year. I just obtained all the switches and also the grasp kill switch collection up. Currently I don"t hear the fuel pump start as soon as the ignition switch is flipped. Ns have linked the start and run wires come a solitary switch so the I can flip one switch to turn everything on and then I have a push button for the starter signal. All of that functioned like a champ before, yet now i don"t acquire anything native the fuel pump. I checked the voltage going to the key relay and also that was fine. The just thing that was odd come me was the the middle 87 pen was reading 0.6 volts v the relay out. Relocating on come the fuel pump relay, I obtain 12 volts coming into the relay"s signal line and to the entry line. It looks choose the ECU is not connecting the relay signal line to ground. The ECU was taken the end for some welding and it did finish up v a welding magnet attached come it in ~ one suggest Is is possible that the ECU got toasted by the magnet? everything worked good with the exact same wiring before. The only addition is the death switch and I can"t think of any kind of reason that it could reason this kind of issue. The basic solution can be to just put a switch inside for the fuel pump. Might I damage anything by having the pump on every the time? as I recognize it the pump always runs at a set speed and the regulator is responsible for adjusting the pressure. That to me means that to run it off of a move shouldn"t really be one issue. I carry out see the safety worry of gaining into one accident and also having the pump running full bore dumping fuel top top my burning corpse. Doesn"t sound wonderful.If the solution is just getting an additional ECU and giving the a whirl climate I have the right to make the happen. I"d at least like to see if the thing cranks effectively with the pump relay bypassed. Does that sound prefer an okay idea?Any tips are significantly appreciated!!Thanks
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-Dave
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proto17Posts: 159Joined: Jul 06, 2015 8:57 AMLocation: Maryland

Re: Permanently Bypass Fuel Pump Relay?

Postby proto17 » Nov 25, 2016 11:30 PM


Oh, and I"ve read that the ECU has a transistor inside the handles ground connection the fuel pump. Anyone had actually success instead of / resoldering the thing? any kind of chance the could aid me now? If the magnet caused issues then it"s likely that the ECU"s memory is hosed and nothing will job-related correctly =\
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proto17Posts: 159Joined: Jul 06, 2015 8:57 AMLocation: Maryland

Re: Permanently Bypass Fuel Pump Relay?

Postby proto17 » Nov 25, 2016 11:33 PM


Just remembered, the automobile did start and also run till it ran the end of fuel, so the ECU shouldn"t be entirely borked.

You are watching: How to bypass fuel pump relay


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Mike W.Posts: 25256Joined: Feb 12, 2006 1:00 PMLocation: Covid 19 Life during Wartime

Re: Permanently Bypass Fuel Pump Relay?

Postby Mike W. » Nov 25, 2016 11:44 PM


The transistor provides ground to the relay, no the pump. For testing, sure, bypass it. However it was set up no to rotate on v the ignition for a reason, a great one, if one the you will hopefully never care about. Execute not leave it bypassed, that"s no smart. I have not heard of any type of need come reflow the fuel pump relay transistor, so never ever heard of anyone act it. It have to crank just fine v the ECU disconnected, you can pull it out of the car and also it need to crank just fine. The won"t fire or run of course, yet it is in now method connected come the starter circuit.

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dsmithPosts: 2346Joined: jan 20, 2012 1:52 AMLocation: Charleston, SC

Re: Permanently Bypass Fuel Pump Relay?

Postby dsmith » Nov 26, 2016 9:24 AM


If the worked and also now doesn"t, i would gain it to run again an initial before editing circuits. You have the right to use a committed fuel pump switch, yet it shouldn"t it is in necessary and should still it is in fused and relayed. I had actually a race automobile with that collection up and also was a pain. Though, dedicated circuits can make for simpler diagnosing in a race car. Simply to confirm, every power should be cut with the kill switch. It should be in line with the battery and also ignition.Keep preventive ECU"s and also an extra death switch. They execute fail.
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proto17Posts: 159Joined: Jul 06, 2015 8:57 AMLocation: Maryland

Re: Permanently Bypass Fuel Pump Relay?

Postby proto17 » Nov 26, 2016 2:20 PM


I left things alone last night and also then this morning simply bypassed the ECU for grounding and also went right to the an unfavorable terminal top top the battery. That acquired the pump running with the ignition on and also not on anytime that the kill switch was on. Safety occasionally
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Sadly, the vehicle simply would certainly not crank up. Engine would revolve over and it would certainly sound prefer it was going to concerned life and also then nothing. The fuel pump was definitely running the totality time. I then tried providing it a small gas while beginning and it pertained to life, yet it sound horrific. Misfiring like mad, smoking, simply nasty. Go this sound prefer a toasted ECU? i did carry out a dual check of all the ECU grounds and also everything was great there. It was a check after thinking more about the ECU no grounding the fuel pump relay. Perhaps one of the ECU grounds acquired hosed in the wiring. Yet nope, all grounds space good. Additionally verified the the connection from the ECU harness to the fuel pump relay was good. I also checked for spark and also there certainly was spark.I"ll start trying to find a new ECU anyway just in case.Oh, and I did make certain to wire points up so that the battery and alternator room disconnected by the death switch. I acquired this one https://www.pegasusautoracing.com/produ ... AgCq8P8HAQ and also the plan was to crank the automobile up and also test that out thanks all!
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