stutter and miss unless fuel pump is jumpered

jd20phill

Member
Jun 2, 2005
104
0
16
36
Little Rock, Arkansas, United States
Sorry, this is going to be a bit long, cliffs at the bottom. I've been searching around the forums for numerous days on supramania for an awser to this problem, but have yet to find one. I have a 1990 Supra Stock Turbo 5 speed that keeps sputtering when i accelerate and misses occasionally at idle. It runs extremely rough when cold and hesitates and stumbles when warm. The car is not showing any codes. It all started when i came home from college after the car had not been driven daily for a few months (my dad started it up about once a week) and the tempatures dropped below 20 degrees.

I figured it was a fuel pump issue, since everything else I tested was working, so I jumpered the fuel pump from the diagnostics box to make it run at 12v (or is it 11v) at all times... the stuttering and idling problem went away and it drove like a dream. I figured it was the relay, but couldn't find the procedure in the tsrm (at least in the EFI Fuel section) to check the fuel pump relay, so i replaced it with an extra one i had lying around; but the problem still persists. Anyone ever have a similar problem or a solution that does not involve running the fuel pump at 12 volts all the time?

Cliffs:Car stutters and misses unless fuel pump is jumpered from diagnostics box...no codes.
 
Last edited:

Adjuster

Supramania Contributor
Stock pump? It was designed to have variable voltage supplied to it.

Replacement pump from someone like Walbro or Holley? They generally like a full voltage diet.

So easy to do this.

Get short wire. I've found solid wire works best. About 12ga house wire..

Cut a piece 2" long.
Strip both ends back 1/4" each.
With a smooth face hammer, and a vice or anvil, gently hammer the 1/4" bare copper wire ends flat into a spade type connection. (Not too thin, not too thick. Look at the blades on the plug your going to "replicate" and match that size and thickness. You will need to possibly trim the wire some with side cutters or dikes.)

Ok, loop the wire into a "U" shape with both flat spades pointing at the top of the "U".

Now, on the right fender apron/strut tower, you will notice a silver box deal with cooling fins on it. This has two wires and a plug sticking out of it.

Un plug the wires. Notice the size of those spades in the plug? That is the size you need to copy with your "U" of wire..

Ok, now plug in the U to the plug/wires that goes into the harness. (Leave the silver thing unplugged to anything, and you can even remove it if you like a save .0000lbs of weight from your Supra... LOL) You can secure the "U" of wire with electrical tape if your worried about it. Mine is custom short, and covered in tape, so you can't see the wire anymore, and can barely see the plug actually. ;)

Congratulations! You have now jumpered the fuel pump to full voltage all the time. Whatever voltage your car is putting out, will go to the pump with no changes from the silver box anymore. :)

This is a good/required mod for anyone who's running the Walbro pump.

:) Good luck.
 

jd20phill

Member
Jun 2, 2005
104
0
16
36
Little Rock, Arkansas, United States
Thanks, one quick question before i do this though. I have the stock pump that is most likely a lot more than two years old (how long i've owned the car). Wouldn't running the stock fuel pump at full voltage shorten its lifespan considerably or would it be alright to do so?