Fuel Pump Keeps Going in Run Position
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Fuel Pump Keeps Going in Run Position
I'm having an intermittent problem with a fuel pump that doesn't shut off when I turn the ignition switch to RUN. Whenever this happens, the engine won't start, either. Twice, after this happened, I've removed the negative battery cable overnight, and the problem disappeared.
I might mention that the vehicle has been sitting in essentially the same spot during this intermittent situation. I moved it a few feet once. It was after doing some skid plate adjustment and testing of the fuel level sensor that the problem began.
At this point, I think my problem boils down to a simple question:
If the ignition switch is in the "RUN" position, then what determines when the pump stops priming?
Is it a preprogrammed, automatic timing cycle within the computer (EEC)? Or does the computer look for some outside sensor reading, such as fuel line pressure, before turning off the fuel pump relay? Or maybe something else causes the pump to stop at the end of the "RUN" cycle?
If I could figure this out, then I might be able to solve the intermittent problem.
The truck is a 1990 Bronco 4WD, automatic 5.8 liter , 351 W, Eddie Bauer
,
Tuned
Joined: Apr 2006
Posts: 410
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From: West Virginia
With the ignition switch on, the EEC power relay is turned on. The EEC provides power to the PCM ( powertrain control module). The PCM closes the fuel pump relay for 1 second. If it does not see 120 rpm or more it will shut off the fuel pump relay.
It sounds like you might have a fuel pump relay sticking.
It sounds like you might have a fuel pump relay sticking.
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I'll Check the Relay, but . . .
Okay. I think I found out how to check the relay for sticking next time it happens. I'll see if that's the problem Thanks for the tip.
So if the PCM is working well enough to kick on the fuel pump relay, it should be able to kick it off, too. Which would mean my PCM is probably okay, right?
Would the fuel pump being stuck ON also keep the engine from starting? Because that's what's happening in my situation.
So if the PCM is working well enough to kick on the fuel pump relay, it should be able to kick it off, too. Which would mean my PCM is probably okay, right?
Would the fuel pump being stuck ON also keep the engine from starting? Because that's what's happening in my situation.
Tuned
Joined: Apr 2006
Posts: 410
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From: West Virginia
Would the fuel pump being stuck ON also keep the engine from starting? Because that's what's happening in my situation.
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Buck,
Next time the pump stays on in the run position, I'm going to test the activation coil to see if it's getting an on or off signal. Then I'll know if it's the relay sticking, or instead the pcm/sensor. From there I can look to the next step. In the meantime I'm going to try and get a fuel pump relay.
The question remains though; shouldn't the engine still start, even if the fuel pump is stuck on? If so, wouldn't that indicate a different failure? I read somewhere else that it should start anyway. But who knows!?
It's around 2 A.M. here, so I'm going to bed. I'll check for any follow-ups tommorow morning.
Thanks again.
Next time the pump stays on in the run position, I'm going to test the activation coil to see if it's getting an on or off signal. Then I'll know if it's the relay sticking, or instead the pcm/sensor. From there I can look to the next step. In the meantime I'm going to try and get a fuel pump relay.
The question remains though; shouldn't the engine still start, even if the fuel pump is stuck on? If so, wouldn't that indicate a different failure? I read somewhere else that it should start anyway. But who knows!?
It's around 2 A.M. here, so I'm going to bed. I'll check for any follow-ups tommorow morning.
Thanks again.
Last edited by seedpress; Aug 24, 2010 at 10:40 PM. Reason: spelling
Tuned
Joined: Apr 2006
Posts: 410
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From: West Virginia
If it is just a stuck relay then I would say that the engine should start. But when you said it would not start, that is what got me wondering if the PCM is keeping the relay on indication another problem.
Next time it does it, after you check the relay feed, see if you have spark. Easy check, pull plug wire and see if it sparks close to a ground.
Also need to see the engine is getting gas, are the injectors firing. Another easy check, spray a little starting fluid in the throttle and see if it wants to turn over.
It's a little after 4am here and I'm going to bed too. I will not be on again until Wed morning when I get home from work. Hopefully someone else will chime in here with some other ideas as well.
Next time it does it, after you check the relay feed, see if you have spark. Easy check, pull plug wire and see if it sparks close to a ground.
Also need to see the engine is getting gas, are the injectors firing. Another easy check, spray a little starting fluid in the throttle and see if it wants to turn over.
It's a little after 4am here and I'm going to bed too. I will not be on again until Wed morning when I get home from work. Hopefully someone else will chime in here with some other ideas as well.
The Southernmost Mod
Joined: Dec 2004
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From: Caracas, Venezuela
Exactly my thoughts, the relay seems to be getting stuck, it's a <$10 part.
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Elder User
Joined: Feb 2007
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From: Chicagoland
If it is just a stuck relay then I would say that the engine should start. But when you said it would not start, that is what got me wondering if the PCM is keeping the relay on indication another problem.
Next time it does it, after you check the relay feed, see if you have spark. Easy check, pull plug wire and see if it sparks close to a ground.
Also need to see the engine is getting gas, are the injectors firing. Another easy check, spray a little starting fluid in the throttle and see if it wants to turn over.
It's a little after 4am here and I'm going to bed too. I will not be on again until Wed morning when I get home from work. Hopefully someone else will chime in here with some other ideas as well.
Next time it does it, after you check the relay feed, see if you have spark. Easy check, pull plug wire and see if it sparks close to a ground.
Also need to see the engine is getting gas, are the injectors firing. Another easy check, spray a little starting fluid in the throttle and see if it wants to turn over.
It's a little after 4am here and I'm going to bed too. I will not be on again until Wed morning when I get home from work. Hopefully someone else will chime in here with some other ideas as well.
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Well the intermittent situation continues:
The truck was starting again, and then I disconnected the battery overnight. Today, once again, with the ignition in the RUN positionthe fuel pump wouldn't shut off.
So I set out to do some tests. I pulled the relay. it wasn't stuck closed. I put it back in. The problem persisted. I rigged up a test to see if the fuel pump coil was getting the 1 -2 sec turn on pulse from the ECC, or a latched condition instead. But then suddenly the problem went away. Since then the truck has been sitting for hours and the intermittent problem hasn't returned.
So this is sort of thing that has been going on for days. Now I'm waiting for the fuel pump to stay on again to test for the 1 - 2 sec pulse from the EEC before buying a replacement one. I'll check for spark then, too. With such an intermittent problem, the truck is not going out on the road. Tomorrow, however, the relay will be replaced and the truck driven around the property to see what happens.
Pulled the codes, but before warming up the engine. I got 47 (twice -- one after the other) and then 22.
The truck was starting again, and then I disconnected the battery overnight. Today, once again, with the ignition in the RUN positionthe fuel pump wouldn't shut off.
So I set out to do some tests. I pulled the relay. it wasn't stuck closed. I put it back in. The problem persisted. I rigged up a test to see if the fuel pump coil was getting the 1 -2 sec turn on pulse from the ECC, or a latched condition instead. But then suddenly the problem went away. Since then the truck has been sitting for hours and the intermittent problem hasn't returned.
So this is sort of thing that has been going on for days. Now I'm waiting for the fuel pump to stay on again to test for the 1 - 2 sec pulse from the EEC before buying a replacement one. I'll check for spark then, too. With such an intermittent problem, the truck is not going out on the road. Tomorrow, however, the relay will be replaced and the truck driven around the property to see what happens.
Try to pull the trouble codes
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A Follow-Up
First, thanks for all the help offered. You guys are great!
I've arrived at a temporary solution:
After testing the "run" system, it turned out that the relay itself was not sticking. The problem was the EEC itself, which was was signaling the pump to run continuously. This was an intermittent problem, so it was difficult to pin down for a while.
I finally pulled the computer and, sure enough, two of the electrolytic capacitors had leaked. Not only were they shot, but the leaked electrolyte had begun corroding some pins on one of the semiconductors. The computer board is covered with a conformal coating to protect it against moisture and contamination, but the electrolyte had also seeped under or through that coating and discolored the board in places.
First I cut out all three of the electrolytic capacitors, although only two of the three had leaked. Then I tried to clean the spilled electrolyte. To remove the corrosive electrolyte I had to strip off the conformal coating where I saw board discoloration. I tried to clean the affected areas with rubbing alcohol, dilute acetone (used for finger nail polish remover), and WD-40. Also, one logic IC (integrated circuit) had three pins that were corroded by the electrolyte. I tried as best as I could to clean them mechanically.
The two leaking capacitors were 47uF 16V, and the third a 10uF 63 volt. I didn't have these values on hand, but coincidentally I had just bought a hundred 22uFs with a 63V working voltage. So by paralleling two of the 22s I was able to get 44uFs, and in series I got an 11 uf. Electrolytic caps have a wide tolerance range anyway, so I hoped that would be good enough. The one problem was all the original caps were 105 C temperature, whereas my replacements are only 85 C. But my computer is behind the driver's kick panel, instead of in the engine compartment. So, I am hoping it will work, at least for a while.
It was a pain to replace the caps! First, I found it difficult to solder the new, "paralleled" capacitors to the printed circuit board. Then, I wasn't sure how many layers the board had -- it's easy to overheat and ruin underlying layers. Finally, some of the copper pads to which the new caps were being soldered were also very close to fine-pitched copper traces. My finished "repair" is a real mess! But it seems to be working.
After all this, the pump is no longer latching up in the run position, and the engine starts. The Bronco hasn't been driven on the road yet. So, I guess I'll see how that goes soon. I am planning to get a replacement computer pretty soon, because I don't trust the old one, especially with my "iffy" repairs.
I'm not proud of my fix-it project, therefore I'll leave the finished product to your imagination; however, if you ever look inside your own EEC, you might want to know what leaking caps look like, so here's the “before” picture of my leaking caps:
I've arrived at a temporary solution:
After testing the "run" system, it turned out that the relay itself was not sticking. The problem was the EEC itself, which was was signaling the pump to run continuously. This was an intermittent problem, so it was difficult to pin down for a while.
I finally pulled the computer and, sure enough, two of the electrolytic capacitors had leaked. Not only were they shot, but the leaked electrolyte had begun corroding some pins on one of the semiconductors. The computer board is covered with a conformal coating to protect it against moisture and contamination, but the electrolyte had also seeped under or through that coating and discolored the board in places.
First I cut out all three of the electrolytic capacitors, although only two of the three had leaked. Then I tried to clean the spilled electrolyte. To remove the corrosive electrolyte I had to strip off the conformal coating where I saw board discoloration. I tried to clean the affected areas with rubbing alcohol, dilute acetone (used for finger nail polish remover), and WD-40. Also, one logic IC (integrated circuit) had three pins that were corroded by the electrolyte. I tried as best as I could to clean them mechanically.
The two leaking capacitors were 47uF 16V, and the third a 10uF 63 volt. I didn't have these values on hand, but coincidentally I had just bought a hundred 22uFs with a 63V working voltage. So by paralleling two of the 22s I was able to get 44uFs, and in series I got an 11 uf. Electrolytic caps have a wide tolerance range anyway, so I hoped that would be good enough. The one problem was all the original caps were 105 C temperature, whereas my replacements are only 85 C. But my computer is behind the driver's kick panel, instead of in the engine compartment. So, I am hoping it will work, at least for a while.
It was a pain to replace the caps! First, I found it difficult to solder the new, "paralleled" capacitors to the printed circuit board. Then, I wasn't sure how many layers the board had -- it's easy to overheat and ruin underlying layers. Finally, some of the copper pads to which the new caps were being soldered were also very close to fine-pitched copper traces. My finished "repair" is a real mess! But it seems to be working.
After all this, the pump is no longer latching up in the run position, and the engine starts. The Bronco hasn't been driven on the road yet. So, I guess I'll see how that goes soon. I am planning to get a replacement computer pretty soon, because I don't trust the old one, especially with my "iffy" repairs.
I'm not proud of my fix-it project, therefore I'll leave the finished product to your imagination; however, if you ever look inside your own EEC, you might want to know what leaking caps look like, so here's the “before” picture of my leaking caps:
Junior User
Joined: Apr 2010
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hey seedpress
what would cause the caps to blow cause i was having the same problems as you and its the same thing and before i get another computer i want to know what caused it so it doesn't happen again and i might do the same thing you did for a week or so intill i get paid here is my post and computer
https://www.ford-trucks.com/forums/9...college-5.html
what would cause the caps to blow cause i was having the same problems as you and its the same thing and before i get another computer i want to know what caused it so it doesn't happen again and i might do the same thing you did for a week or so intill i get paid here is my post and computer
https://www.ford-trucks.com/forums/9...college-5.html
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hey seedpress
what would cause the caps to blow cause i was having the same problems as you and its the same thing and before i get another computer i want to know what caused it so it doesn't happen again and i might do the same thing you did for a week or so intill i get paid here is my post and computer
https://www.ford-trucks.com/forums/9...college-5.html
what would cause the caps to blow cause i was having the same problems as you and its the same thing and before i get another computer i want to know what caused it so it doesn't happen again and i might do the same thing you did for a week or so intill i get paid here is my post and computer
https://www.ford-trucks.com/forums/9...college-5.html
Before you pop in a new computer, you need to make sure that something outside the computer didn't fry it. Otherwise your replacement unit will suffer the same fate. Good luck with that! I wish I had some advise about pinning down the problem, but I don't.
Before you buy a replacement, check out my discussion threads on replacement computers:
https://www.ford-trucks.com/forums/9...computers.html
and here:
FullSizeBronco.com - 78 - 96 Ford Bronco offroad club, forums, tech, installs
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