External fuel pump
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Senior User
Joined: Apr 2012
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Hate to tell you, the fuel pump issues are back. It hasn't rained yet, but is extremely humid.
Have a Dr. appointment to get to. Be back in a couple hours. Time for more diagnostics.
Have a Dr. appointment to get to. Be back in a couple hours. Time for more diagnostics.
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
On those wet days when the fuel pump is constantly running I assume there is no moisture getting near the ECM? I'm not aware that the fuel pump is driven by any sensors. I think it's just a simple timer.
With that said, when I recently replaced my ECM the very first time I went to start the truck the fuel pump was on for much longer than usual. I was concerned there was an issue, but so far I haven't been able to repeat it.
You have only one fuel tank, right?
With that said, when I recently replaced my ECM the very first time I went to start the truck the fuel pump was on for much longer than usual. I was concerned there was an issue, but so far I haven't been able to repeat it.
You have only one fuel tank, right?
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
You installed a new Fuel Pump Relay?
Computer turns the Fuel pump relay on. So if the pump stays on, the computer is telling it to. (unless you have some strange short at your relay socket) Why on a humid/rainy day indicates the computer is affected by the humidity?
So, tell me again, why did you replace your very original computer?
Did you have these two issues with your original computer? Pump? Codes?
Last edited by vjsimone; Jul 17, 2016 at 12:28 PM. Reason: Modify text
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
I’m not surprised.
You installed a new Fuel Pump Relay?
Computer turns the Fuel pump relay on. So if the pump stays on, the computer is telling it to. (unless you have some strange short at your relay socket) Why on a humid/rainy day indicates the computer is affected by the humidity.
So, tell me again, why did you replace your very original computer?
Did you have these two issues with your original computer? Pump? Codes?
You installed a new Fuel Pump Relay?
Computer turns the Fuel pump relay on. So if the pump stays on, the computer is telling it to. (unless you have some strange short at your relay socket) Why on a humid/rainy day indicates the computer is affected by the humidity.
So, tell me again, why did you replace your very original computer?
Did you have these two issues with your original computer? Pump? Codes?
Take a closer look at your Build Date....?
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
I’m not surprised.
You installed a new Fuel Pump Relay?
Computer turns the Fuel pump relay on. So if the pump stays on, the computer is telling it to. (unless you have some strange short at your relay socket) Why on a humid/rainy day indicates the computer is affected by the humidity.
So, tell me again, why did you replace your very original computer?
Did you have these two issues with your original computer? Pump? Codes?
You installed a new Fuel Pump Relay?
Computer turns the Fuel pump relay on. So if the pump stays on, the computer is telling it to. (unless you have some strange short at your relay socket) Why on a humid/rainy day indicates the computer is affected by the humidity.
So, tell me again, why did you replace your very original computer?
Did you have these two issues with your original computer? Pump? Codes?
Instead of replacing the computer again I would look for something strange on the inputs to it and also try to figure out why it doesn't give codes. Are those two problems one and the same?
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
My, admittedly ancient, memory tells me that he had exactly the same symptoms with the original computer - long running pump and no codes. So, why the search for another computer? It would be hard to expect two very complex devices like the computer to fail in exactly the same way.
Instead of replacing the computer again I would look for something strange on the inputs to it and also try to figure out why it doesn't give codes. Are those two problems one and the same?
Instead of replacing the computer again I would look for something strange on the inputs to it and also try to figure out why it doesn't give codes. Are those two problems one and the same?
He should look closer at the Pump Relay socket wiring? Other than that, run the heater in the cab to dry up the humidity? Engine warms up the Engine compartment. He stated that on a rainy day, after the engine is warm he does not have the pump issue.
Most of the outputs come from a driver/transistor, they are not easy to get to. I am guessing the Fuel Pump Relay is operated by one of these devices, I’m sure I have seen moisture related issues in electronics in my past. The computers are not sealed.
Agree, I cannot imaging two replacement computers having a moisture problem at all.
Need to find the part where his issues were the same with his original computer, man, 11 pages now…….
Last edited by vjsimone; Jul 15, 2016 at 09:26 AM. Reason: Modify text
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
I believe the two computers he has are new/rebuilt, these two replaced his original computer. He just ordered his 4th computer.
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FTE Legend
Joined: Jul 2010
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From: Northeast, OK
The EVTM's don't show alternate wiring depending on computer versions. So any computer should give codes - assuming that the 85's gave codes. In other words, since I doubt two computers failed in exactly the same way, I think he has a problem with either sensors or, most likely, wiring that is preventing the computer from giving codes. And, it is likely that the same problem is causing the poor running when wet.
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Thread Starter
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Senior User
Joined: Apr 2012
Posts: 452
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If it's wiring, it'll be like navigating a jungle for me, but I am game to try.
The EVTM's don't show alternate wiring depending on computer versions. So any computer should give codes - assuming that the 85's gave codes. In other words, since I doubt two computers failed in exactly the same way, I think he has a problem with either sensors or, most likely, wiring that is preventing the computer from giving codes. And, it is likely that the same problem is causing the poor running when wet.
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
I don’t believe these two new computers have failed. I’m thinking more like his replacements have been the wrong versions. Now that he thinks his build code may be 1/86, he would most likely have a later version computer. Are the issues related? Hard to know, I will guess not, but I’m wrong 3 times a day.
He should look closer at the Pump Relay socket wiring? Other than that, run the heater in the cab to dry up the humidity? Engine warms up the Engine compartment. He stated that on a rainy day, after the engine is warm he does not have the pump issue.
Most of the outputs come from a driver/transistor, they are not easy to get to. I am guessing the Fuel Pump Relay is operated by one of these devices, I’m sure I have seen moisture related issues in electronics in my past. The computers are not sealed.
Agree, I cannot imaging two replacement computers having a moisture problem at all.
Need to find the part where his issues were the same with his original computer, man, 11 pages now…….
He should look closer at the Pump Relay socket wiring? Other than that, run the heater in the cab to dry up the humidity? Engine warms up the Engine compartment. He stated that on a rainy day, after the engine is warm he does not have the pump issue.
Most of the outputs come from a driver/transistor, they are not easy to get to. I am guessing the Fuel Pump Relay is operated by one of these devices, I’m sure I have seen moisture related issues in electronics in my past. The computers are not sealed.
Agree, I cannot imaging two replacement computers having a moisture problem at all.
Need to find the part where his issues were the same with his original computer, man, 11 pages now…….
"Someone told me it was bad. Now that I understand more, I don't think it was bad at all."
"Yes, I was able to get the codes with the old ECM. Not with the new one."
This last quote is key to me - wrong replacement version.
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Senior User
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Good memory, Vincent!
"I replaced the ECM when I rebuilt the engine. I'm not certain they gave me the correct one. Having to replace it again irks me, but I want to be certain they give me the correct ECM this time around. How can I be certain?"
"Someone told me it was bad. Now that I understand more, I don't think it was bad at all."
"Yes, I was able to get the codes with the old ECM. Not with the new one."
This last quote is key to me - wrong replacement version.
"Someone told me it was bad. Now that I understand more, I don't think it was bad at all."
"Yes, I was able to get the codes with the old ECM. Not with the new one."
This last quote is key to me - wrong replacement version.
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
Vin# 2FTDF15N3FCB28096
Cargo Master
Joined: Jun 2013
Posts: 3,176
Likes: 15
From: Somewhere n North America
The EVTM's don't show alternate wiring depending on computer versions. So any computer should give codes - assuming that the 85's gave codes. In other words, since I doubt two computers failed in exactly the same way, I think he has a problem with either sensors or, most likely, wiring that is preventing the computer from giving codes. And, it is likely that the same problem is causing the poor running when wet.
Others have stated, and from what I have read, there were a lot of programming changes to these computers by the 86 model year. Could these programing changes effect the newer version computers enough to effect the self-test if installed in an older vehicle? I know nothing about backward/forward compatibility of these computers?
I hear you on the wiring. Well if he rang the wires out correctly, he measures no shorts in the test connector wires and measures no opens in the test connector wires. The wires seem to be oriented to the right pin/connectors. I’m ruling out self-test wiring, but he needs to do some wiggle testing on his cable bundles.
That Fuel Pump Self-Test wire could be suspect. But not sure how that would be related to Self-Test.