Off the road.... again! Fuel pump issue

Just got the car back on the road for about a week and a half after dealing with a starter issue (thanks again TMC for the help on that one). Went for a drive last night and the car died... felt like it ran out of gas...

Now I've had this problem before, less than two years ago when my original 86 fuel pump died on the 401. Turn the key, no fuel pump priming sound...

Same thing now, turn key no fuel pump priming sound, car turns over but won't start (no gas going to the motor). But my fuel pump is less than two years old, installed by DaSilva Racing. BBK fuel pump...

Prior to me having it towed from Toronto to Pickering anyone have other suggestions as to what I should check in the event it's not the fuel pump?

Thanks

don't quote me but I think there is a relay switch behind pass.kick panel that might be the problem

Relay location

86-'91 = under driver seat
'92-'93 = inner fender, under MAF meter

Also check to be sure it didn't trip the collision switch in the trunk.

I checked my voltage at the harness on the back side of the fuel tank with the key in the on position and I'm getting fluctuating voltage from 9.7 and down... no idea if this is right or not...

Will check collision switch as well...

Thanks

Quote:

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Originally Posted by 86 t-tops

I checked my voltage at the harness on the back side of the fuel tank with the key in the on position and I'm getting fluctuating voltage from 9.7 and down...

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What is the voltage at the relay socket?

Even at 9.7 volts, the pump should still do something.

Amperage/current is another thing...

if the pump has been receiving low voltage (measure voltage with it running, between its ground and power input) chances are good it is hurting the electric motor parts and making it hot from the resistance - it will attempt to draw higher current; much like an amplifier that gets hot when the voltage is too low.

First thing is to ensure the pump is getting decent power - then if it doesn't work; means you gotta get it pulled out.

I will test voltage at the relay...

Thanks

Ok... had my car towed to DaSilva so that they could take a look at what I thought was a fuel pump issue. They tested the fuel pump... it's working but not priming when you try and start the car... they found a burnt wire coming off the starter solenoid which tells the computer to turn on and make things happen... they installed a fusible link where the burnt wire was and things didn't work out...

Joe was very helpful and suggested that I replace the main engine wiring harness instead of trying to track down what looks to be a short in the harness... he indicated that I would need a harness from an 86 GT, since that is what my car is, as the 87 and 88 speed density harnesses won't work.

Has anyone ever dealt with a similar issue and were you limited to the same year harness as your car? I'm sure Joe is right but if I could use a harness from 86 to 88 it would make my search for a decent one that much easier....

Pretty sure the initial prime is a function of the TFI. Do you have a spare TFI to test? It's a helluva lot easier to replace the TFI than an entire harness.
Incidentally, did Joe identify the burnt wire? I presume it is a brown fusible link that leads to the yellow wire for both the pump and EEC. Trouble for me was that the brown wire doesn't appear on a wiring schematic aside from an eyelet to the starter solenoid.

Looks to be a blown fusible link on what looks to be a black wire with a yellow stripe... they tried another fusible link and it started to smoke... looks to be a short somewhere in the harness... I'm pretty sure that it's this black/yellow stripe wire that turns the EEC on...

The brown fusible link that leads to the yellow wire is fine.

Just talked to Mustang Specialteaz and they also stated that it's a one year harness as well... but don't have one in stock, will keep an eye out for one.

I don't have an extra TFI...

Pretty sure I fried that same wire when it grounded to the chassis! I kept part of it because the fusible link remained intact while the rest of it went up in a cloud of smoke! But I thought my Bk/Y wire was for the alt... different year, different engine, YMMV.

So I have the main wiring harness disconnected inside the engine bay. On the inside I have the computer harness disconnected and one brown plug just above the computer disconnected as well... however, there is a small group of wires the looks to run across the interior dash back over to somewhere on the drivers side. I'm assuming this group of wires runs to the fuel relay under the driver's seat.

Anyone have any tricks to disconnecting and fishing this wire out without removing my dash, driver's seat, and carpet? I would like to avoid cutting any wires....


If not I'm very tempted to cut these wires and then splice them back to together with a replacement harness or my harness if I can repair it.
Thanks

Quote:

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Originally Posted by toofast306

Pretty sure the initial prime is a function of the TFI

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Initial prime is a function of the ECM.

Subsequent pump activity is triggered via the PIP.

So my journy continues... I know very little about electrical (can install a car stereo but that's about it) but I've looked at several electrical diagrams for 86 mustangs and the wire I'm dealing with is 100% the EEC power on lead from the starter solenoid (Black with an Orange stripe).

I had replaced a section of this wire last summer as it had become brittle and broke... thus not telling the computer to turn on. In hindsight it may have been a fusible link that I replaced with just a regular wire. The burnt wire that Joe, from DaSilva, found was the wire I had added last summer. I'm surprized it lasted this long...

To try and find the fault/short I unpluged and unraveled the main wiring harness back to the firewall in the engine bay. I pulled the black and orange wire from all others and found no damage or burn marks... my hope for an easy fix is now gone.

My understanding is that this wire goes to pin #1 on the EEC. However, I was wondering if it first gose to EEC relay located next to the EEC behind the passanger side kickpanel and then to the EEC. When starting the car the key is turned and the ignition switch tells the EEC rely to close and power is then fed to the EEC from the black and orange wire from the solenoid... or am I way off the mark?

The reason I'm asking is that I think Joe noted some smoke coming from the dash when they tried another fusible link on the black and orange wire that attaches to the starter solenoid (sent an email to Joe to confirm). Could this be from a another fusible link blowing that runs from the ignition switch to the EEC rely? I swear I saw such a wire when looking at the 86 wiring diagrams.

The Black/Orange feeds the Keep Alive memory of the ECM, the ECM relay and the Fuel Pump relay.

slope could re wire the space shuttle...seen it wit me own 2 peeperz

Ok... that helps and make sense based on what I did tonight...

1. connected a fuse holder to the black and orange wire and hooked it back up to the starter solenoid (this was the burnt wire Joe found while the car was at DaSilva racing). I figured if it is bad the fuse will blow... it didn't (15 amp fuse used).

2. Unplugged the EEC Relay and checked if I'm getting 12 volts at the plug from the black and orange wire, I am.

3. Unplugged the main computer harness, left the EEC Relay unplugged, and checked if I was getting 12 volts at pin 1, I am. This makes sense as I believe this is the Keep Alive power to the EEC feed. So the keep alive power looks to be good at the EEC harness.

4. Checked the Red/Light Green wire at the EEC relay plug for 12 volts when the keys are in start position, I am. This means that the ignition feed to the EEC relay is being provided power.

5. Plugged the EEC relay in and checked if I'm getting any power at pin 37 on the main computer harness, fed by a red wire from the EEC relay plug, as this should occur when the key is in the start position based on the wiring diagrams I've reviewed. Nothing! No power at this pin... this red wire also splits off and feeds the inertia switch, then the fuel pump.

So... based on this I would say that my EEC relay has gone bad as it's not closing the circuit to power the fuel pump... thoughts? Comments? This is just based on me testing voltage at the key points based on the wiring diagrams...

Not sure why the EEC relay would go bad or how this caused the fusible link (and my repair wire) to burn up at the point were the black and orange wire connect to the starter solenoid.

I think my next move is to order a new EEC relay... I'm assuming you can as I've never looked for this part...

Based on this schematic, I'd say you're right on the money.
https://www.google.ca/search?q=86+mu...l%3B1213%3B973
Can you bench test the EEC relay to be sure?
Also note that ignition switches were/are problematic.

Picked up another EEC power relay today... pluged it in and turned the key... inline fuse I installed on the black/orange wire coming from the starter solenoid blew. Installed my old EEC power relay, replaced the blown fuse, and turned the key... fuse did not blow. I believe this is telling me that the replacement EEC power relay works while my old one doesn't... and that I continue to have a short to find... only triggered when the EEC power relay switches over...

Was trying to trace the short with a tool I have, sends a low voltage through the shorted wire so that it can be traced, and I think it burnt out the replacement relay... prior to burning out the black orange wire did show as a short on my tool... perhaps right where it passes through the fire wall... beyond this I'm running out of ideas... don't think I'm driving anywere soon...

I'd pop open the case of the ECM if you don't find a short on any circuit that carries VPWR:

ISC
EVR
CANP
TAB/TAD
A/C WOT cutoff relay
Fuel pump relay
Injectors + harness

So I took a break, had a beer, and went back out to the garage. Started to re-test all the voltages I had already tested... noted in previous posts...

I was testing pin 37 on the EEC harness, expecting to get nothing as before, and I got 12 volts!

Plugged the harness into the EEC and turned the key... car started! I have no idea why...

The replacement EEC relay, which I thought I burnt out durning testing, was in and the inline fuse I installed on the black and orange wire near the starter solenoid had a 10 amp fuse in it. I have unravelled the wiring harness to hunt for damage and moved it around... perhaps that eliminated the short but not the best solution.

No confidence in driving the car... time to get CAA...

Well you are on the right track....

Oh... one question... how warm should the EEC power relay get when the car is running, if at all?

I should also add that I broke the tabs off of one side of the salt and pepper shaker connections (behind the upper intake). Is this going to be a major issue?

Quote:

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Originally Posted by 86 t-tops

I should also add that I broke the tabs off of one side of the salt and pepper shaker connections (behind the upper intake). Is this going to be a major issue?

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LOL, no. It's rare to find a Fox that has them still intact.

A zip-tie around each pair will keep them together if it will worry you.

+1 on the above.

Had the same thought when I bought some tonight.

So I took the car out for a quick drive and it died again after about 5 minutes of driving... fuse on the black/orange wire from the starter solenoid blew (used a fuse instead of a fusible link)... tried a new fuse and it blew again...

I let the car run for 20 minutes the other day... no problems... perhaps it's something that occurs while the car is driving that causes a short...

I'm at a loss... next step is to try and push the car into my garage as it's currently sitting on my drive way...

That would drive me over the t-top , sucks .
I'm not doing much better alt every three months over here .