Howell TBI issue on Jeep

Four-Runner

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Joined
May 15, 2015
Location
Durham
I have a 89 Wrangler with a 258 with Howell TBI fuel injection conversion (installed for several years). It has been cutting off going down the road recently... when I try to restart it the fuel pump is not running when I turn the key, after sitting for some time it will restart and run down the road for a bit before cutting off again.

I checked the fuel pump fuses in the harness, and checked that I'm getting battery power to the relay with the key in position 2 & 3. I replaced the fuel pump relay and that was not the issue, seems like the ECU may not be sending power to the signal terminal of the relay or maybe a wiring or grounding issue?

I'm getting beyond my abilities, any thoughts?

May be time for some help... any recommendations for a shop that is familiar working with Howell/older GM TBI setups?

Appreciate the help.
 
Check all ground wires. Betcha that will fix it. Ask me how i know.
;)
 
Four-Runner said:
How many grounds wires are there?

I assumed the fuel pump relay and ECU had a common ground
Click to expand...

The ECU needs a really good clean ground, but the fuel pump relay coil is driven with a 12v signal and can be grounded anywhere. I don't know about that particular ECU, but many ECUs use a low side driver to switch the relay coil, so the ECU completes the ground and the other side of the relay is connected to 12v whenever the ignition is on. You can switch either side of the coil, it doesn't matter and one way or the other is usually a matter of convenience and what's driving the coil. Low side drivers are cheaper and have lower internal resistance, so they're used in ECUs and things like that very often where you're driving a power device with a processor of some sort.
 
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On my Howell, I had fuel pump issues and their ground to the pump ran all the way from the pump back up to the engine compartment. I added in a solid ground to the frame at the pump and it solved that issue.
 
In case it helps someone in the future, my issue wound up being a loose connection at the distributor. Hitting a bump in the road would cause the ECM to lose the tach signal and thus injector pulse and fuel pump run signal.

Lots of head scratching for what ended up being an easy fix.
 
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