EEC relay electrical issue

codeJunkie · Nov 7, 2018

Hope I'm posting this in the right section...I have been chasing an electrical gremlin for a few weeks on my 88 2.9L 4x4 Ranger that I'm hoping to get some insight on. The issue is the engine will crank but not turn over, fuel pumps are not priming and no spark. Fuel pump relay doesn't switch on.

I have tested that the EEC has good ground connections, the EEC relay connector has a good ground and is receiving 12v at the high and low voltage terminals when ignition is on. However, the output terminal is only giving 2.5v when ignition is on. If I bypass the EEC relay with a jumper wire the fuel pump relay clicks on and the truck will start and run perfectly fine.

I replaced the EEC relay twice, the EEC connector pigtail, ignition switch and lock cylinder and cleaned up all ground connections. I have tested with a known good EEC and still the EEC relay only puts out 2.5v.

I'm to the point where I'm thinking about bypassing the EEC relay altogether and throwing in a switch to toggle the EEC and fuel pump relay on and off, lol.

Any thoughts of where else I should be looking?

adsm08 · Nov 7, 2018

When you jumpered it and everything worked, did you jump it from the correct pin of the relay, or did you just pick one of the hot ones and go?

Uncle Gump · Nov 7, 2018

adsm08 said:
When you jumpered it and everything worked, did you jump it from the correct pin of the relay, or did you just pick one of the hot ones and go?

That is the million dollar question...

Sounds to me like a voltage drop on the input side of the EEC relay circuit.

adsm08 · Nov 7, 2018

Uncle Gump said:
That is the million dollar question...

Sounds to me like a voltage drop on the input side of the EEC relay circuit.

That's what I am thinking too. IIRC the two wires in question splice off from common switched source very close to that relay. If the splice is failing one side may be loosing power while the other isn't. I have had it happen at least once on one of my own 1st gens.

Uncle Gump · Nov 7, 2018

I just looked at a schematic the other day that was posted on a thread here in rusty's weird 2.9 issue.

If I remember... the EEC relay was powered from a fusible link. I have seen where the connection between the fusible wire and copper wire corrodes and would cause this exact condition.... dropping voltage at the poor the connection.

codeJunkie · Nov 7, 2018

So going by the picture attached I put a jumper wire between 3 and 4.

1 is where I am testing ground.
2 is getting 12v with ignition on
4 is getting constant 12v

codeJunkie · Nov 7, 2018

Uncle Gump said:
I just looked at a schematic the other day that was posted on a thread here in rusty's weird 2.9 issue.

If I remember... the EEC relay was powered from a fusible link. I have seen where the connection between the fusible wire and copper wire corrodes and would cause this exact condition.... dropping voltage at the poor the connection.

Thanks for that info...I'll check the fusible links next.

kimcrwbr1 · Nov 7, 2018

Have you checked the fuse and connector at the fuse block? The ecm and fuel pump relays should have full time power with the ignition switch off. Sounds like there is resistance in the power feed somewhere possible corroded wire under the insulation. Turn the ignition on and feel the wires or connectors for heat resistance equals heat!

Uncle Gump · Nov 7, 2018

You need to check the secondary input side of the relay dynamically (EEC relay active). Pin 4 if your description is correct.

If it's 12V static test and falls to 2.5V dynamically... you're dropping voltage before any work is getting done.

codeJunkie · Nov 7, 2018

With EEC relay plugged in and ignition on, pin 4 has 12v, pin 2 has 12v, pin 3 has 2.5v. I am grounding my test lead to both the engine block and directly to the battery ground, same result either way.

Uncle Gump · Nov 7, 2018

Lets back up a second... because it appears you are dropping 9.5V across the switch side of the relay.

Remove the relay... you should have on that connector... 1 pin hot at all times... 1 pin a constant ground... 1 pin switched 12V from the ignition... and 1 pin with nothing. If you jump the hot at all times to the pin with nothing... you have bypassed the relay at the relay connector. Does the truck start and operate correctly?

codeJunkie · Nov 7, 2018

That is correct. If I jumper pins 4 and 3 the truck starts and runs.

The way I understand the relay, pin 1 is ground, pin 2 is voltage from ignition switch, pin 3 is the switched output, pin 4 is voltage from battery.

So pin 2 should only get 12v when ignition is switched on, which is true. Pin 4 should have 12v at all times, which is true. Pin 3 should have 12v when voltage is applied to Pin 2, which is not true. I tested the ground, Pin 1, with a test light, but maybe that could be an issue still? I'm thinking not if I'm getting 12v on the other 2 pins.

kimcrwbr1 · Nov 7, 2018

The eec relay provides power to the computer and power to the fuel pump coil. The computer provides the switched ground to the fuel pump coil. The power distribution box has two 30a fuses one for the computer and one for the fuel pump. If you jump from the battery pos at the eec relay to ignition switch at the eec relay and everything works then your problem is in the ignition switch circuit.

codeJunkie · Nov 8, 2018

kimcrwbr1 said:
The eec relay provides power to the computer and power to the fuel pump coil. The computer provides the switched ground to the fuel pump coil. The power distribution box has two 30a fuses one for the computer and one for the fuel pump. If you jump from the battery pos at the eec relay to ignition switch at the eec relay and everything works then your problem is in the ignition switch circuit.

This is kind of where I was thinking the issue is when I was probing the EEC and fuel pump relays as a first step in diagnosing this mess. After replacing the EEC relay the first time, I traced what I think are all of the grounds in the ignition switch circuit to insure continuity. The lock cylinder was loose, which is why I replaced that along with the ignition switch. All fuses look good. I'll take a closer look at that part of the equation, though.

Uncle Gump · Nov 8, 2018

I think your understanding of the relay is correct. They're really pretty simple.

If you can jump pin 4 to 3 and everything works... It blows my theory of resistance in the secondary hot at all times circuit. If I had your testing results... 100% of the time I would grab a new relay and the vehicle would be motoring down the road (with the exception of yours). Because your test results indicate there is some high resistance in the secondary (switched) side of the relay.

Since you have swapped in a known good relay... I would ensure the connections on pin 3 and 4 grip the relay terminals tight... then it's time to move to the primary side of the relay. Why... because it's the only thing left and maybe there is some resistance in the switched ignition and/or ground side of the coil in the relay that weakens the coil and isn't allowing the switched contacts to "slam" closed... creating the high resistance in the secondary side contacts that is confirmed there.

Put the test light back in your tool box and do the remainder of your testing with a DMM. Test lights will fool you into thinking all is good when in fact they may still illuminate with resistance in the circuits you are testing. Test the ground circuit with an ohm meter to ground... relay removed. should be 0 resistance. Then check the ignition circuit dynamically (relay active) with a volt meter.

kimcrwbr1 had great suggestions also... jump in battery for the switched ignition... also try jumping in ground for the ground side.

EEC relay electrical issue

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