Fuel pump always running! 91
09-04-10, 04:41 PM
#1
Lead Lap
Thread Starter
Fuel pump always running! 91
So as some may know I have been dealing with and trying to fix this issue for over a month now. So far I have replaced the Fuel Pump, resistor, and relay and still no dice....
Does anyone else have any ideas??
Also does anyone know where the fuel pump ecu is at one this car I found one on ebay but is listed as 92-94 so i just wana know if a 91 has the same one.
Does anyone else have any ideas??
Also does anyone know where the fuel pump ecu is at one this car I found one on ebay but is listed as 92-94 so i just wana know if a 91 has the same one.
Last edited by hobojoe; 09-04-10 at 07:55 PM.
09-04-10, 09:33 PM
#2
The pump pressurizes when the key is at ACC also?
The thought I have is that something in the ignition switch is translating to the pump/ECU that the key is at the ON position. If relay and other wiring is stock, could be the ECU as suspected.
Easiest is to call your parts guy and have him cross reference whether the '91 is the same part # as the '92 ECU.
The thought I have is that something in the ignition switch is translating to the pump/ECU that the key is at the ON position. If relay and other wiring is stock, could be the ECU as suspected.
Easiest is to call your parts guy and have him cross reference whether the '91 is the same part # as the '92 ECU.
09-04-10, 09:40 PM
#3
Lead Lap
Thread Starter
^^ Yea just found out the 92 and older doesn't have a fuel pump ecu so if the ecu is bad its the main ecu Lovely!
The pump runs 24/7 key in or out doesn't matter. I am going to try and check the EFI relay using the jumper tomo....
Any other research help is greatly appreciated I've been searching for hours now, and seem to be the only one where the pump doesn't shut off rather than doesnt start haha.
The pump runs 24/7 key in or out doesn't matter. I am going to try and check the EFI relay using the jumper tomo....
Any other research help is greatly appreciated I've been searching for hours now, and seem to be the only one where the pump doesn't shut off rather than doesnt start haha.
09-05-10, 09:30 PM
#5
This leaves me 
as to the cause.
Time to start poking with the continuity tester and see why the pump line is staying hot/on. The relay is the correct part # and is wired right? Beyond that I haven't heard if anything in the trunk harness could cause this.
How is the wiring harness to the fuel pump? That line drops down from the rear shelf behind the seat.
as to the cause. Time to start poking with the continuity tester and see why the pump line is staying hot/on. The relay is the correct part # and is wired right? Beyond that I haven't heard if anything in the trunk harness could cause this.
How is the wiring harness to the fuel pump? That line drops down from the rear shelf behind the seat.
09-06-10, 11:02 AM
#6
Lead Lap
Thread Starter
Ill take a look since i still have the whole rear seat out from changing the pump. I also figured I would check the EFI relay, and if I cant find anythere there then its time to tear into the dash to get to the ECU and Circuit Opening Relay.
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09-06-10, 12:54 PM
#8
+1.
I haven't had the ignition switch in this LS out so this is conjecture: if it is built similar to the door key cylinder, I can see why there is a short. The housing that contains the electronic contacts is in nylon and after being turned manually with the key, metallic particles had embedded/smeared into the nylon so it would be close enough to cause arcing. If in this case it is sufficient, it could carry enough current to fool the EFI system into thinking it is <on>.
All else being ok in the wiring looms, I first suspect the ignition switch contacts.
I haven't had the ignition switch in this LS out so this is conjecture: if it is built similar to the door key cylinder, I can see why there is a short. The housing that contains the electronic contacts is in nylon and after being turned manually with the key, metallic particles had embedded/smeared into the nylon so it would be close enough to cause arcing. If in this case it is sufficient, it could carry enough current to fool the EFI system into thinking it is <on>.
All else being ok in the wiring looms, I first suspect the ignition switch contacts.
09-07-10, 06:19 AM
#9
fuel pump is controlled by the ecu, not the ignition switch. the ecu grounds the relay which turns the pump on. same as most toyotas. your relay could be stuck closed. pull the efi relay and check to see if any of the pins in the socket have continuity to gnd. if the pin going to the ecu has continuity to gnd when the key is out, the transistor for the fuel pump circuit is fried.
if this is the case, instead of replacing the ecu, you could remove the wire that is supplying the +12v to the relay coil circuit and replace it with an ignition switched source, then the pump will only run when the key is on. however, as cheap as 90-92 ecu's are, itd be best to just replace it.
if this is the case, instead of replacing the ecu, you could remove the wire that is supplying the +12v to the relay coil circuit and replace it with an ignition switched source, then the pump will only run when the key is on. however, as cheap as 90-92 ecu's are, itd be best to just replace it.
09-07-10, 02:57 PM
#10
Lead Lap
Thread Starter
Thanks all, I have to say I just got Volume 1 of the service manual and after reading through all the EFI section both the switch and ECU are suspect as well as the circuit closed relay. So tomorrow once im free im going to be digging into all the parts with my meter and hopefully I can find the cause.
09-08-10, 04:36 PM
#11
Lead Lap
Thread Starter
Well folks I really feel like a DUMB @#$ writing this but I found my problem. I was installing my new hood struts just 15 min ago and decided to look at my front tires since there new to see how they were looking.....
Well in doing this I looked up and yea.....my whole wiring harness moreso the one on the fuel pump relay side but still both are torn there is no insulation left on the a few of the wires at all. So looks like tomorrow I get to go do some rewiring becuase new harness = $3,800.
Well in doing this I looked up and yea.....my whole wiring harness moreso the one on the fuel pump relay side but still both are torn there is no insulation left on the a few of the wires at all. So looks like tomorrow I get to go do some rewiring becuase new harness = $3,800.
Last edited by hobojoe; 09-08-10 at 05:02 PM.
