1986 B2 2.9L - Fuel pump relay wiring issue

[Jbrownjr]

She was running rough a few months ago after leaving the mechanic shop. We'd already replaced every solenoid and relay that he thought might be the issue and recommended a new main wiring harness.
We found a good donor (86 B2 2.9L Automatic 4x4...for our B2 2.9L Manual 4x4). Now she won't start. Cranks, but:

• She won't fire
• Fuel pumps won't turn on

Focusing on the Fuel Pump relay connector, we get 12v on the yellow wire, but 0v on the red wire when turning the key on/start.
I tried grounding the Fuel Pump slot on the ODB-1 connector, but no change.
Jumping between the yellow and Orange/Lt Blu the high-pressure pump runs. Seemed like a bad Fuel pump relay. We replaced that...no pump action when turning the key.
Seems the EEC ought to ground pin #22 to close the circuit for a few seconds when the key is on/start, but it doesn't.
Testing the Tan/Lt green wire we found it's grounded all-the-time. (Confirmed that the ODB-1 Fuel Pump slot is, of course, also already grounded even though it shouldn't be?) it should only be grounded for a few seconds WHEN the key is turned?
Testing for a grounded out wire between the fuel pump relay connector and the EEC (Tan/Lt green wire), I tested for continuity. No shorts.
We happened to have a 2nd EEC, so I swapped them out. No change.

Either I'm misunderstanding the expected behavior, or I'm just stumped on where to look next.
Any ideas?

 

[Tiha]

The red and the Yellow should have power with the Key on.

The red line gets it power from the EEC Relay.

The EEC relay should have power on the yellow wire all the time.

So move over and check the eec relay. Maybe that is bad.

 

[L\Bronco]

I agree with Tiha. Check for 12v at the red wire on one of the injectors, that will tell you if the EEC power relay is on (Key on)
If not, make sure that the blk\LT grn wire at the EEC power relay (BROWN) is grounded. It should be a fairly big wire right at the batt neg cable. If memory serves me, its a plastic single pin inline connector pretty close to the batt with the BLK\GRN wire running through it, they used to corrode inside and the EEC system can't power up.
Hope that helps
Cheers

 

[Motech]

Both relays function the same as a switch that connects battery voltage to components by grounding an ignition powered coil. Two key differences:

1. EEC Power Relay receives its ignition feed directly from ignition switch, and is permanently grounded at battery negative
2. Fuel Pump Relay receives its ignition feed from EEC Power Relay, and is grounded by PCM.

I agree that you need to take a look at the EEC relay. If you find with key on that you have power at three terminals, go look at the ground pigtail off your battery negative terminal. That is the most troublesome circuit on these B2 models as it is the direct ground for both the EEC Power Relay and the PCM itself at pin 60.

 

[David D]

I fought a similar problem with an 87 B2 after trying everyone's suggestions with no luck I finally located the problem. It was corroded connectors on the rollover switch that is under the carpet on the passenger side footwell.

 

[Jbrownjr]

Spot on!
I wasn't getting any juice on the yellow wire. I noticed in the drawing that wire essentially connects to the starter relay.
When we replaced the wiring harness someone ("I") connected the eyelet connector to a ground ***** rather than the starter relay. (The ground fender ground close by has an eyelet that is just about the same size. )
With that yellow wire on the starter relay the fuel pump is audible again. Thank you!

She cranks, and with a shot of starter fluid in the intake, she occasionally fires, but won't start yet.
I put a timing light on one of the spark wires and cranked, but no blink (no spark).
Next step is checking the ignition coil.
We also replaced the distributor assembly (replaced with a new one) a few weeks ago. There is a possibility that went in a tooth or two off...so it could just be timing at this point.

 

[Groovtubin]

She was running rough a few months ago after leaving the mechanic shop. We'd already replaced every solenoid and relay that he thought might be the issue and recommended a new main wiring harness.
We found a good donor (86 B2 2.9L Automatic 4x4...for our B2 2.9L Manual 4x4). Now she won't start. Cranks, but:

• She won't fire
• Fuel pumps won't turn on

Focusing on the Fuel Pump relay connector, we get 12v on the yellow wire, but 0v on the red wire when turning the key on/start.
I tried grounding the Fuel Pump slot on the ODB-1 connector, but no change.
Jumping between the yellow and Orange/Lt Blu the high-pressure pump runs. Seemed like a bad Fuel pump relay. We replaced that...no pump action when turning the key.
Seems the EEC ought to ground pin #22 to close the circuit for a few seconds when the key is on/start, but it doesn't.
Testing the Tan/Lt green wire we found it's grounded all-the-time. (Confirmed that the ODB-1 Fuel Pump slot is, of course, also already grounded even though it shouldn't be?) it should only be grounded for a few seconds WHEN the key is turned?
Testing for a grounded out wire between the fuel pump relay connector and the EEC (Tan/Lt green wire), I tested for continuity. No shorts.
We happened to have a 2nd EEC, so I swapped them out. No change.

Either I'm misunderstanding the expected behavior, or I'm just stumped on where to look next.
Any ideas?

Ive had SAME ISSUE, pull the steering column plastic off, there is a CONTACTOR ASSY made of METAL, the rivets break, i had ta RE-secure w/ZIP TIES, has worked 12 years + like that HTHS!

 

[Jbrownjr]

Spot on!
I wasn't getting any juice on the yellow wire. I noticed in the drawing that wire essentially connects to the starter relay.
When we replaced the wiring harness someone ("I") connected the eyelet connector to a ground ***** rather than the starter relay. (The ground fender ground close by has an eyelet that is just about the same size. )
With that yellow wire on the starter relay the fuel pump is audible again. Thank you!

She cranks, and with a shot of starter fluid in the intake, she occasionally fires, but won't start yet.
I put a timing light on one of the spark wires and cranked, but no blink (no spark).
Next step is checking the ignition coil.
We also replaced the distributor assembly (replaced with a new one) a few weeks ago. There is a possibility that went in a tooth or two off...so it could just be timing at this point.

And the plot thickens...She runs...barely.

Timing is confirmed (10 degrees BTC). Given a little feathering on the gas pedal, we can get her to idle. It's a bit rough, but at that point we figured we'd take her for a spin.
As soon as you give her gas, she stumbles really bad. I can limp along in first gear about 5-10mph, but nothing more.
Tried pulling codes (KOEO), but got the ole "1-1" ('Everything's fine here')
Fuel pressure at KO was down around 20psi after sitting overnight and just turning the key to "on", but after a few cycles it climbs to 35psi. Running (with persuasion that pressure remains pretty constant, sometimes up to 38psi.
Now that it would idle for 3-5 minutes, I figured I'd pull codes (KOER). I started seeing numbers flash by ('Morse code') but without a partner at the time, I couldn't remember them. When I did get a partner with a pen/paper...I couldn't get any blinks at all. (Sigh...)
Reverting to pulling codes KOEO, I finally got a few clues!

85 "Canister purge circuit failure"

I suspected wiring on this one (since we recently replaced the main harness), but wasn't able to locate the solenoid. I found the canister, and started tracing the small plastic hose. One lands on the underside of the throttle assembly, so I traced the other...

I have to share a bit of context before continuing. (This will be entertaining) A month or so ago we were at this point and gave it to a local mechanic. He diagnosed everything he could (we had already replaced many solenoids, regulators, coils, etc.), so he checked the main gears. (Remove front engine cover, replaced gaskets and appropriate parts that tend to wear) It hadn't jumped gears. "Not that". He suggested the wiring harness, suspecting bad wires somewhere. (We had already spliced a number of bad wires, temporarily bypassed fusible links, etc.) Driving home that evening, I was following my son who's driving the B2 about 10 miles toward home. A few miles from home we got separated AFTER I had noticed some backfiring (heard and saw small 'explosions' coming from the exhaust system). I figured I'd meet him at home, but before he showed up he called me from around the corner. "The Bronco caught fire, I called 911" Sure enough, I met him at a gas station parking lot with the fire department drenching the underside. A few rubber exhaust hangers had completely melted. I have to say it's a miracle there wasn't a bigger explosion with the fuel lines nearby and the gas tank so close. We let it sit overnight, then the next day it started up (running rough still) and made it home. Now back to the story...

Tracing that evap line toward the gas tank, I followed it past the fuel filter, and then it stopped. Melted! Could that have something to do with "85"?

I'm attaching a picture of the evap canister, red arrow is the 'compromised' evap line.
3rd picture is where the break occurred. (Anyone know what that electrical connector is for? Seems to pass through the floorboard under the driver's seat)
2nd picture is the far end of the evap line. (I'm guessing that plastic tube should sit within that rubber hose? Seems like a pretty loose fit to me)


32 "EGR position sensor below closed limit"

The EGR valve was one of the many parts we had replaced within the past year. Assuming it's good, but I'll mechanically test that tomorrow after work.
Meanwhile, I found a very helpful article on testing the EVP sensor (https://www.fullsizebronco.com/threads/egr-valve-position-evp-sensor-testing-replacement.218407/) but there's nothing like that on/near my EGR valve. The vacuum line runs to passenger fender wall, to this solenoid I haven't identified yet. (Pic #4) Any thoughts on how to troubleshoot "32"?

 

[Tiha]

Is the 86 one of those years with 2 fuel pumps? One in the tank and one on the rail?

I see that goofy canister on the frame in your pic. Made me think of that.

If that is the case you probably need to flow test the fuel system. Those two pump systems had a problem where as it would build enough pressure but not enough flow.

So after the high pressure pump you pull the fuel line and put it in a pop bottle. Jumper the fuel pump relay and time how long it takes to fill the bottle.

Would have to do some digging but I think it is about an ounce a second should be the flow.
It is usually obvious. It is usually way over or way under.

 

[L\Bronco]

Is the 86 one of those years with 2 fuel pumps? One in the tank and one on the rail?

I see that goofy canister on the frame in your pic. Made me think of that.

If that is the case you probably need to flow test the fuel system. Those two pump systems had a problem where as it would build enough pressure but not enough flow.

So after the high pressure pump you pull the fuel line and put it in a pop bottle. Jumper the fuel pump relay and time how long it takes to fill the bottle.

Would have to do some digging but I think it is about an ounce a second should be the flow.
It is usually obvious. It is usually way over or way under.

Tiha is right on the money. When the in tank pump fails, they would often make static pressure, but couldn't keep up running.
The flow spec is 1 quart in 30 seconds. we would run them for 15 and look for a pint. (They would normally produce higher than spec.
Another check you could do is watch the fuel pressure at the rail while it's running poorly with the vacuum hose removed from the regulator, it should be steady at the same value it was during KOEO (35-40psi). If it drops while the symptom is there, it indicates a fuel volume issue.
If you fail the volume tests, check the filter in the cannister in pict 3. (they didn't always use a filter in there, sometimes its just a standpipe. But its often overlooked)
Good luck.
Cheers

 

[Jbrownjr]

Update:

Pressure remained between 35-40psi after removing the FPR vacuum hose.
Just to further validate, pulled a fuel line and ran it for 15 seconds. 14oz. (A few oz short of a full pint.) Close enough I assume?

At that point I was going to pull codes (KOER), but it wouldn't start.
Checking the EEC relay - passed.
Fuel pump relay - failed. Following the test outlined HERE. Tan/lg wire is grounded. (I assume that's bad)
With a test-light on the + terminal and the other end on Tan/lg I get 12 volts. Removed the computer and it's no longer grounded, so the EEC is grounding it.
Since I keep reading '...ground the Tan/lg circuit...' to test the fuel pump, I'm assuming it's not supposed to be grounded all the time?

We do happen to have another computer (from a donor), but the same result; so I need validation on whether Tan/lg ought to be grounded 'full-time'?

 

[L\Bronco]

Hey JBrownjr
According to the wiring diagram you posted earlier, the tan\lt grn should be the control wire the PCM uses to activate the FP relay. It should only be grounded for 2-3 sec on initial key on, then grounded once the PCM sees a viable PIP signal from the ign system. If it is grounded all of the time, both fuel pumps should run as long as the key is on. (Is this the case?)

2 questions, what type of test light are you using? (LED or old school filament type?)
And was the relay plugged in or disconnected when you tested between B+ and tan\lt grn?

 

[Jbrownjr]

Thanks for confirming...I thought the behavior was suspicious.

Test light is 'old school', just a bulb. (I do have a digital voltmeter, if that helps?)
Relay was unplugged when I ran the last test. It stayed grounded until we disconnected the computer. This, I assume, confirms there's no short in the wiring itself. (Between FP relay and the computer). Fuel pumps don't run all-the-time, only when I short/jump the FP circuits.

Sure seems like the computer is grounding that circuit when it shouldn't, so a defective/fried computer? (It's under warranty...but we've already warrantied it once. I'd just like another level of confidence before going back to O'Reilly's for another.)

 

[L\Bronco]

Thanks for confirming...I thought the behavior was suspicious.

Test light is 'old school', just a bulb. (I do have a digital voltmeter, if that helps?)
Relay was unplugged when I ran the last test. It stayed grounded until we disconnected the computer. This, I assume, confirms there's no short in the wiring itself. (Between FP relay and the computer). Fuel pumps don't run all-the-time, only when I short/jump the FP circuits.

Sure seems like the computer is grounding that circuit when it shouldn't, so a defective/fried computer? (It's under warranty...but we've already warrantied it once. I'd just like another level of confidence before going back to O'Reilly's for another.)

The test light is good here. It doesnt make sense to me that the wire is grounded all of the time without the pumps running. Normally the PCM grounds the wire to activate the relay, to, in turn, activate the pumps. If the wire is always grounded, the pumps should be on as soon as the key is on.
The fuel pump relay should be the green one and the eec power relay should be brown, (On that older stuff)
Looking at your diagram, The pinout for the fuel pump relay should be as follows:
Pin 85-red 12V with key on
Pin 86 Tan\lt grn grounded by PCM (2sec at key on, then continuous while there is a valid pip signal.
Pin 30 Yel hot at all times
Pin 87-orange\ lt blue power to pumps, should be hot when the relay clicks.

Maybe verify all 4 wires with the relay plugged in and key on. Also verify all of the wire colors.
Something is amiss here for sure.
Hope that helps
Good luck

 

[Jbrownjr]

Back for another round...

I need to correct my last report. with the Fuel pump relay connected Tan/lt grn (Pin 86) is getting a continuous 12v.
I grounded this wire (from the self-test connector), and with the key on the pumps run.

Maybe related...until the last round of testing, I could get it to start and idle for a while. Something changed while performing these tests, and now it just cranks, never even tries to start. Having confirmed fuel pressure just recently, I tested the ignition coil (with a spare spark plug) and got a nice orange spark (just over an inch long). Spark wires, rotor assembly (cap, Pick-up coil, TFI) were all replaced within the past month or so. I need a 2nd set of hands to test spark at each plug/wire, but clearly that was working just a few weeks ago. Now I'm wondering if I fried something along the way.

Also to add...with the Tan/lt grn circuit grounded (pumps running) I tried cranking, but no love.

We've been struggling with getting this thing to run for so long, and every so often we get these setbacks. Really frustrating.
This time...as long as y'all will keep providing guidance, I'll stay with it.

Next idea to try?

 

[Tiha]

Verifying spark is pretty simple, Take the intake loose, shoot some starting fluid in. Crank. See what happens.

If it is getting spark it should run or try for a second.

This is fuel injected right?

Could be a cam or crank sensor. ECT can really mess with them. But crank sensor usually fires the injectors.

So make sure you got spark. If you do, then put a gauge on and make sure fuel pressure is in spec.
After that we need to verify the injectors are firing.

 

[Jbrownjr]

Of course!
Starter fluid into the intake DOES result in at least some firing. Hardly enough to turn over on it's own, but definitely responding!

2.9 EFI, yes.

I checked fuel pressure at the rail a few weeks ago. It took a few key cycles to get up to ~35psi, but it held. I need to get a battery charged for another vehicle at the parts store where I 'rent' the fuel gauge later today. I'll check again. I noticed they also rent noid lights...we never did use that test before we replaced all of the injectors last summer. (Parts guy had no idea how to use them, so I held off until I could research that.

I'll report back fuel pressure soon.

 

[Tiha]

If you push in the schrader valve it should squirt pretty high not just dribble out

Even with low pressure it should try to start.

You can use a test light on the injectors but it doesn't light very bright. You really only need to verify one, if one is working they all should be.

 

[Jbrownjr]

Did I mention we've been at this for more than a year?
Did I mention on more than one occasion we end up following the same (basic) troubleshooting steps because the same symptoms appear?
Feels like a game of whack-a-mole...and after a while it's no longer fun. (Keep your sense of humor Jack )

I did mention that 2 weeks ago fuel pressure was between 35-40psi, right?
Fuel pressure: 0 psi just now.

I have to ground the Tan/lg wire at the diag connector, so that when the key is on the pump runs. (We'll fix that after it starts)
Yes, I hear the High-pressure and low-pressure pumps running.
Yes, I confirmed the pressure gauge is working on one of the tire's Schrader valves.
Yes, fresh gas was added a few weeks ago, so the tank isn't dry either. (still some stale fuel? Yes)
This is actually good news!

Since we've been here before, I'll go back to basic troubleshooting by removing sections of the fuel line between the tank and fuel rail.
(Fuel filter? clogged line? FPR?)

I also borrowed a noid light set, so I can test the FI 'the right way'.

Progress!

 

[L\Bronco]

Pull the line off before the high pressure pump and make sure the low pressure in tank pump is pumping, (it should move 1 pint in about 15 sec.) When they fail, you get many of the conditions you have described. I think there are other issues, but stat with getting fuel pressure while the pumps are on. Then...
Good luck