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Old 08-08-2018, 01:49 PM   #1
Join Date: Oct 2003
Posts: 3,257
Default 1990 LX fuel pump

1990 LX, Ex-DPS car
180k-ish miles
A9L computer
100% stock other than exhaust

This started a while back, so I don't remember precisely what all occurred, but here is the gist:
Previously had a starter and the solenoid on the driver's fender well go out, swapped both. Then, the car would only run if you held the key in the START position as the car was running and give it a little extra gas. I replaced the ignition switch with a Motorcraft unit. Fuel pump wouldn't come on, so I replaced the relay under the seat to no avail.

Fast forward to yesterday. Car has been sitting. Put a fresh battery in the car, it will still crank very strong, but no fuel pump whine. Tested the fuel pump relay and the replacement relay I bought, both test good on a 12V source. Checked the inertia switch for power, but didn't get any. Checked the injectors for power, none. Attempted to ground out the test port under the hood to make the fuel pump run, but it didn't work. Took my new relay and swapped it for the original ECM relay (which also tested good) behind the glove box, and even swapped in the A9L out of my convertible that runs and drives great. No dice.

Pulled the FP relay out and jumpered the 2 pins and the fuel pump came on. I had already looked for blown fusible links, so I searched harder but now I'm leaning toward the ignition switch being faulty. I read some threads on here and one stated that the ignition switch could be in the wrong orientation. Not sure how that's possible, and the car DOES crank when the key is turned all the way forward to the START position. The fuel pump doesn't come on, however, and when the relay is jumpered it won't stay running when the key is released.

What do I test next? Thanks in advance.
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Old 08-08-2018, 02:41 PM   #2
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Join Date: Aug 2001
Location: Well, it's one louder, isn't it?
Posts: 11,838

The inertia switch should have 12V when the ignition switch is in the run/start position. Ensure the blue 20G fuse link coming off of the starter relay is not cleared. It seems you have 12v to power the pump (orange/light-blue wire), but you are missing the 12v signal to pull in the relay (Red/Black wire). The ECU applies a ground signal at the relay coil (tan/light green) to run the fuel pump. A few seconds when the key is in the run position and then constantly once the engine is running until the key is turned to the off position.
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Old 08-08-2018, 08:21 PM   #3
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Join Date: Jan 2014
Posts: 313

If it started after swapping the solenoid then I would suggest checking the wiring of the solenoid. You have a 12v crank only signal that runs to the solenoid. Thatís where I would start.
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Old 08-08-2018, 08:48 PM   #4
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Join Date: Apr 2005
Location: seagoville
Posts: 5,081

Maybe bad a9l. I have a spare if you need to test out if your close by

2003 f250
1990 mustang gt stock 68k miles
1990 mustang gt 347 t56
1994 peterbilt 377 dump truck 450hp cat
1997 freightliner 500hp detriot[/FONT]
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Old 08-09-2018, 01:11 PM   #5
Join Date: Mar 2007
Location: Anna
Posts: 941
Default Pump

I had a similar prob w/ my 92. I was the connection at the plug behind
the kick panel down by the drivers left foot.

IIRC green/tan,. I just spliced around the plug.
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Old 08-09-2018, 04:43 PM   #6
Join Date: Oct 2003
Posts: 3,257

Ok, so this is going to be very anti-climactic. Previously, I took my car in to get an inspection and the damn starter started hanging up in the bay and it kept cranking while the engine was running. They got it to finally break loose and one of the guys told me that it was hanging up because it was wired wrong. The guy said he "fixed the wiring" on the solenoid/starter relay. I argued with them and told them the car was just fine until the starter decided to hang up.

I towed the car home and checked the solenoid, and it was fried. Bought a new one and swapped it in. I was careful to put all the wiring back exactly as I found it, only connecting one post at a time. Then, the car wouldn't start and so I thought I fried something related to the fuel pump.

After cutting wiring looms apart and probing, swapping the fuel pump relay, swapping the EEC, swapping the EEC relay, etc., it turns out the guy at the inspection place/shop must have put the damn blue wire on the wrong post when he "fixed" the wiring. Fuel pump was only getting power while cranking the engine. That's why it wanted to start, but would die as you let off of the key.

I'm mad at myself that I didn't catch it, but this is the exact reason that I didn't want some random person "fixing" my wiring. Thanks for all the help and resources!
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