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Old 01-02-2013, 02:55 PM   #1
bdp21xls
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EEC Won't Enable Fuel Pump Relay

Hi guys, I'm new to Broncos, and the forum. I have an 89 5.0L which died on the highway a couple weeks ago. Cranks but no start. Got it towed and have been troubleshooting in my driveway.

I am getting a spark, and with starter fluid sprayed into the intake it'll fire once or twice while cranking but won't start. I've been looking at the fuel system, using many threads on this and other sites to guide my efforts.

I replaced the fuel pump relay because it was badly corroded and looked like a likely culprit. It didn't solve my problem though, and I'm starting to think the problem might be the EEC, and here's why:
-I don't get the expected 1-sec fuel pump prime with key on, or while cranking.
-I've traced this to the tan/LG wire on the fuel pump relay not being grounded by the EEC (pin 22 on the EEC).
-If I ground it myself using the test connection, I can hear the fuel pumps running when I turn the key on, and the fuel rail pressure increases. This means the new FP relay works and that the inertia switch is fine.
-I get good continuity between EEC pin 22 and the T/LG wire at FP relay, as well as EEC pin 8 and the brown wire at the FP relay.
-EEC relay is working and all voltages at the relay are good with key on.
-I think EEC grounds are okay. Pins 49, 20, 40, 60 all have good continuity to ground.

I pulled the EEC and opened it up. No obvious signs of burned or damaged components or broken solder joints, but that doesn't really mean anything.

I'm stumped. As far as I can tell, either the computer is bad or something else is causing the computer to not drive pin 22 to ground to trigger the relay and enable the fuel pumps. Could another sensor or a failed TFI cause this?? Any ideas or suggestions would be much appreciated! Also, I tried starting the Bronco with the self-test connection grounded so I knew the fuel pumps were running, and it still wouldn't start. Seems like if the fuel pump issue is my only problem, it should have started when I did that. Seems incredibly unlikely that the computer would just fry itself driving down the highway, but I can't think of anything else that could be the problem.

It was running fine before this. Just cruising along at 60 and there was a sort of snap noise and the engine died.

Thanks in advance!
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Old 01-02-2013, 05:44 PM   #2
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Have you actually hooked up a 12V test light from the relay hot trigger to the relay ground trigger and watched the light while cycling the key or cranking? Have you checked that the relay hot trigger is actually hot (12V)? What fuel pressure does the pump make? If you heard a snap inside the cab, check the fuses. If you find one burned, try to find out WHY before you stuff another one in just to watch it blow. NEVER put in an oversized fuse (smoke-test). Assuming the EEC is NOT fried, the logic used to turn on the FP relay relies on the PIP signal from the ICM (TFI-IV), so it's possible this is an ignition fault. Follow the procedure in Haynes Ch.5 (usually Sec.5 or 7).

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Old 01-02-2013, 05:59 PM   #3
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Have you actually hooked up a 12V test light from the relay hot trigger to the relay ground trigger and watched the light while cycling the key or cranking? Have you checked that the relay hot trigger is actually hot (12V)? What fuel pressure does the pump make? If you heard a snap inside the cab, check the fuses. If you find one burned, try to find out WHY before you stuff another one in just to watch it blow. NEVER put in an oversized fuse (smoke-test). Assuming the EEC is NOT fried, the logic used to turn on the FP relay relies on the PIP signal from the ICM (TFI-IV), so it's possible this is an ignition fault. Follow the procedure in Haynes Ch.5 (usually Sec.5 or 7).

Click these & read the captions:

. . .
Thanks for the pointers, Steve! I really appreciate it. I had been doing all testing with a Fluke multimeter not a test light, but was pretty sure of the results. This afternoon (before I saw your post), I went to the salvage yard and picked up a $30 EEC. Swapped it out, and she fired right up! Apparently that's the culprit. Maybe the snap I heard was a chip frying in the computer. When the weather improves, I might inspect the wiring more carefully for possible faults that might have shorted the EEC. Thanks again for the help.
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Old 01-02-2013, 06:04 PM   #4
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Old 01-02-2013, 08:20 PM   #5
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Just curious if you remember the yellow check engine light illuminating when you turn the key to ON prior to start?
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Old 01-02-2013, 11:37 PM   #6
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Just curious if you remember the yellow check engine light illuminating when you turn the key to ON prior to start?
No it wasn't. That was another reason I suspected the EEC. Couldn't pull codes and eventually realized the light wasn't illuminating at all.
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Old 01-02-2013, 11:44 PM   #7
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I had exactly the same problem roughly 5000 miles after performing an EFI swap (using an '89 Mustang as a donor) on my '79 Bronco. It turns out that whatever circuit enabled the fuel pump was simply no longer working, fried. I ended up wiring the pump to 12V key-on and haven't had any problems for a few years after that incident. Still able to datalog the EEC and everything else runs fine.
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Old 01-03-2013, 01:35 AM   #8
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No it wasn't. That was another reason I suspected the EEC. Couldn't pull codes and eventually realized the light wasn't illuminating at all.
Yea that seems to be the tell tale sign of a EEC not working. Makes it easy to decide which direction to look, fuel pump or EEC wiring, when presented with a no-start condition like this.
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Old 01-03-2013, 09:35 AM   #9
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I have the exact same problem. Just driving down the street and truck died. It cranks like crazy, but won't start. Cannot hear the fuel pump pressure up. I jumped the fuel pump and it is working fine. No check engine light will come on and I cannot pull codes. I replaced the EEC relay and still nothing. I am guessing based on reading the above that I have an EEC problem.
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Old 01-03-2013, 02:02 PM   #10
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Originally Posted by Kustom64Ford View Post
I have the exact same problem. Just driving down the street and truck died. It cranks like crazy, but won't start. Cannot hear the fuel pump pressure up. I jumped the fuel pump and it is working fine. No check engine light will come on and I cannot pull codes. I replaced the EEC relay and still nothing. I am guessing based on reading the above that I have an EEC problem.
Sounds like it, though you might want to verify good power and grounds to the EEC and EEC relay before you swap the EEC. Mine wouldn't start even with the fuel pumps manually enabled by jumpering, which also indicated there was another issue besides lack of fuel, which ended up being that the entire EEC was dead.
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Old 01-03-2013, 02:13 PM   #11
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Quote:
Originally Posted by Kustom64Ford View Post
I have the exact same problem. Just driving down the street and truck died. It cranks like crazy, but won't start. Cannot hear the fuel pump pressure up. I jumped the fuel pump and it is working fine. No check engine light will come on and I cannot pull codes. I replaced the EEC relay and still nothing. I am guessing based on reading the above that I have an EEC problem.
yo K,
NO CODES Troubleshooting;
by Ryan M (Fireguy50) at http://oldfuelinjection.com/?p=44


NO CODES Troubleshooting Due to Poor Grounds, Corroded Wiring, etc.; read more on how to Ground the STI & Proceed w/ Test; run ground wire from Self-Test Input (STI) to battery ground on a Clean body ground

Source: by Jeremy M (Big '92, jermil01)


Ground Locations; comes from two main sources, one is the body/frame ground (G104) and the other is the small black wire that goes directly to the negative terminal of the battery (G101/102). G104 goes to EEC Pin #20 and the TFI ICM. G101/102 goes to EEC Pin #40 & 60. This a direct ground to the battery (-) post and the connection on the radiator support is frequently the cause of problems. It can also corrode developing a poor connection at the negative battery cable connection at the battery post.
Source: by Seattle FSB (SeattleFSB) at FSB http://fullsizebronco.com/forum/showthread.php?t=206734
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Old 01-03-2013, 04:55 PM   #12
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This a direct ground to the battery (-) post and the connection on the radiator support is frequently the cause of problems. It can also corrode developing a poor connection at the negative battery cable connection at the battery post.
Source: by Seattle FSB (SeattleFSB) at FSB http://fullsizebronco.com/forum/showthread.php?t=206734
After I put in my 460 I missed ONE ground wire, and it would not start. The 2 black wires coming out of the harness are supposed to be connected to the radiator support (you can see the bolt the spade lugs attach to). I only connected one. All grounds for the EEC tested normal with a multimeter, and this stumped me for a week. You can see in the pic how difficult it would be to see one of the wires was not connected.

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Old 01-03-2013, 09:52 PM   #13
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Quote:
Originally Posted by bdp21xls View Post
Sounds like it, though you might want to verify good power and grounds to the EEC and EEC relay before you swap the EEC. Mine wouldn't start even with the fuel pumps manually enabled by jumpering, which also indicated there was another issue besides lack of fuel, which ended up being that the entire EEC was dead.
I did the same thing. I jumped the fuel pump to make sure it was working, which it was. I left the jumper connected and tried to start the truck. No go. I talked to a technician today that is convinced I have a Stator or TFI issue. But I am not convinced. I am not sure that those problems would prevent the check engine light from coming on? He wants me to test the red and green wires at the coil. If the EEC is dead, it wouldn't send power to the coil would it? I guess that is a good test right there?
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Old 01-03-2013, 11:50 PM   #14
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Personally, I don't have the expertise to speak to whether that is an effective test or not. I would just check to see whether you're getting a spark, via whatever method you prefer (pull and ground a spark plug, etc.).

In my case, I was getting a spark, but even with the fuel pump jumpered and running, the truck still wouldn't start with the EEC inoperational. Hope that helps.
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Old 01-04-2013, 07:38 PM   #15
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For future search results...

I had this happen on my 90 Mustang, and it turned out to be a bad EEC. HERE is the test procedure I used. The test procedure is outlined in the 3rd post. It's a lot of reading...
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Old 01-04-2013, 09:45 PM   #16
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That there is some incredibly awesome and helpful information! Thanks for posting that up!
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Old 01-05-2013, 01:59 PM   #17
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Wiring for me is very difficult, so bear with me here. I have power to the coil, injectors, fuel pump relay and EEC relay. It does not seem like I have good power to the inertia switch. The light on my test light is dim. I do not have a volt meter, so I am basing this on the dim light. Should I have power through the inertia switch with the key turned to run? I do not have power going through the switch with the key on run. What does this mean? I appreciate any help. Also, the fuel pump does work when jumped at the tester.
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Old 01-05-2013, 03:09 PM   #18
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I was able to get a voltmeter and I found that I only 5.38V going to the inertia switch and nothing coming out of it.
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Old 01-05-2013, 07:03 PM   #19
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Quote:
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...jumped at the tester.
What EXACTLY does that mean?
Quote:
Originally Posted by Kustom64Ford View Post
I was able to get a voltmeter and I found that I only 5.38V going to the inertia switch...
Then there's a fault between that terminal & the battery.
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Originally Posted by Kustom64Ford View Post
...nothing coming out of it.
Then the inertia switch is either tripped (did you push the button down?) or bad.

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Old 01-05-2013, 08:49 PM   #20
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What is means is that I used the EEC TEST port to jump the fuel pump. I grounded the gray single wire at the test port and the fuel pump started running. The inertia switch was not triggered, but I did trigger it and reset it. I was only getting 5.38 volts into the inertia switch and nothing out of it.
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