95 F150 Intermittent Fuel Pump
03-14-2016, 05:32 PM
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95 F150 Intermittent Fuel Pump
I am new to this site, so thanks in advance for any help I can get. Also, I am not a highly skilled mechanic, but do have basic skills.
Truck: 1995 F150, 4.9L inline 6 cyl, 2WD, Automatic transmission, standard cab. This is not my everyday driver, so it isn't driven every day.
Symptom: Normally, when turning the key to the ON position, just before the START position, I can hear the fuel pump engage (a low whining noise). However, it will randomly not engage, therefore not starting. if I wait for about 30 minutes, it will start. It starts 100% of the time if it has been sitting for a long time (ie - overnight, or at one location for a couple of hours...). It also does not happen every time I drive it. There is no pattern. I can run to the store 5 minutes down the road and it might happen. Or, I can drive it for an hour and it might happen. Or, not. It is so random, that I have not been able to establish a pattern at all (engine hot, cold, warm....).
Troubleshooting that I have done (some were due anyway):
1. Replaced fuel filter.
2. Installed new fuel pump (done by a reputable mechanic shop).
3. Swapped the fuel pump relay with the horn relay to rule it out.
4. Installed new fuses and/or swapped out with another same size fuse.
5. Checked the inertia switch and it was never tripped. Went ahead and manually tripped and reset it anyway just to make sure.
6. Installed new battery and new batter cable connectors.
7. Verified that the spark plugs are getting fire.
I have gotten more serious about solving it lately, so I have performed another troubleshooting that I will describe here:
When it would not engage a couple weeks ago, I crawled underneath and saw the connecting plug where the wires from the fuel pump plug into the wiring harness. It is located directly over the rear axle. I wiggled it, got back in and it started. It happened again a few days later and I did the same thing and it started. Thought I had it solved. This weekend, I stripped the wires before and after the connector and spliced wires to bypass the plug. Unplugged the connector just to make sure I wired it right and it started and ran just fine. Plugged the connector back in and drove to town. It wouldn't start when I got back in at the store. Unplugged the connector and it started. Drove to next store and it would not start when I got back in. Plugged the connector back in and it still would not start. HOWEVER, for some unknown reason, I set the parking brake and it started immediately. I remembered that I did the same thing at the previous store. So, either I got lucky and just happened to wiggle the right wire and the parking brake has nothing to do with it or there is some sort of wire (ground...) that is tied in or nearby the parking brake.
The parking brake theory does not make sense to me, but I am willing to try most anything at this point. Does anyone know if there is anything associated with the parking brake that would affect the connection?
Truck: 1995 F150, 4.9L inline 6 cyl, 2WD, Automatic transmission, standard cab. This is not my everyday driver, so it isn't driven every day.
Symptom: Normally, when turning the key to the ON position, just before the START position, I can hear the fuel pump engage (a low whining noise). However, it will randomly not engage, therefore not starting. if I wait for about 30 minutes, it will start. It starts 100% of the time if it has been sitting for a long time (ie - overnight, or at one location for a couple of hours...). It also does not happen every time I drive it. There is no pattern. I can run to the store 5 minutes down the road and it might happen. Or, I can drive it for an hour and it might happen. Or, not. It is so random, that I have not been able to establish a pattern at all (engine hot, cold, warm....).
Troubleshooting that I have done (some were due anyway):
1. Replaced fuel filter.
2. Installed new fuel pump (done by a reputable mechanic shop).
3. Swapped the fuel pump relay with the horn relay to rule it out.
4. Installed new fuses and/or swapped out with another same size fuse.
5. Checked the inertia switch and it was never tripped. Went ahead and manually tripped and reset it anyway just to make sure.
6. Installed new battery and new batter cable connectors.
7. Verified that the spark plugs are getting fire.
I have gotten more serious about solving it lately, so I have performed another troubleshooting that I will describe here:
When it would not engage a couple weeks ago, I crawled underneath and saw the connecting plug where the wires from the fuel pump plug into the wiring harness. It is located directly over the rear axle. I wiggled it, got back in and it started. It happened again a few days later and I did the same thing and it started. Thought I had it solved. This weekend, I stripped the wires before and after the connector and spliced wires to bypass the plug. Unplugged the connector just to make sure I wired it right and it started and ran just fine. Plugged the connector back in and drove to town. It wouldn't start when I got back in at the store. Unplugged the connector and it started. Drove to next store and it would not start when I got back in. Plugged the connector back in and it still would not start. HOWEVER, for some unknown reason, I set the parking brake and it started immediately. I remembered that I did the same thing at the previous store. So, either I got lucky and just happened to wiggle the right wire and the parking brake has nothing to do with it or there is some sort of wire (ground...) that is tied in or nearby the parking brake.
The parking brake theory does not make sense to me, but I am willing to try most anything at this point. Does anyone know if there is anything associated with the parking brake that would affect the connection?
03-14-2016, 06:29 PM
#2
Well, your engine control module is right on the other side of that big aluminum block that the parking brake lever bolts to (ECM controls the power to the fuel pump relay).
There's also a ground behind there too.
I would suggest that you take your test light and check where power is at your Fuel pump relay when it's working good and then test the same thing when it isn't - to see if it's an ecm issue.
That relay basically plugs into wires which can be accessed from underneath (un clip everything and turn it over). Sometimes you can get corrosion there.
Could also be an issue with your harness going back to the pump - I'm just thinking that unplugging or plugging in the bypassed plug might just be jiggling the harness at the weak spot you can't see ?
A test light and something to lie on would be good for the next time it happens - leave your kick panel off.
When it happens, start testing where power is getting to and where it's not.
I believe the circuit will be ECM - relay_ inertia- dash switch (dual tank)- pump.
Bear in mind that you only get power for 2 seconds to the pump after you cycle the key - unless the ecm gets a signal from the engine that it is running. So you would need a helper.
That's all the ideas I've got at this point.
There's also a ground behind there too.
I would suggest that you take your test light and check where power is at your Fuel pump relay when it's working good and then test the same thing when it isn't - to see if it's an ecm issue.
That relay basically plugs into wires which can be accessed from underneath (un clip everything and turn it over). Sometimes you can get corrosion there.
Could also be an issue with your harness going back to the pump - I'm just thinking that unplugging or plugging in the bypassed plug might just be jiggling the harness at the weak spot you can't see ?
A test light and something to lie on would be good for the next time it happens - leave your kick panel off.
When it happens, start testing where power is getting to and where it's not.
I believe the circuit will be ECM - relay_ inertia- dash switch (dual tank)- pump.
Bear in mind that you only get power for 2 seconds to the pump after you cycle the key - unless the ecm gets a signal from the engine that it is running. So you would need a helper.
That's all the ideas I've got at this point.
05-26-2016, 05:56 PM
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Update. Have not yet solved the problem. Thought it was the PCM and mechanic put a new one on it. But, it still happened after the new one was on. He has determined that when the fuel pump does not engage, the fuel injectors are also not getting fire. I have an appointment to take it to the local Ford dealer to see if they can find out what might be causing it. In the meantime, I wondered if anyone has any ideas that I could check for something that tells both the fuel pump to engage and injectors to open at the same time?
Thanks.
Thanks.
05-26-2016, 08:14 PM
#5
The injectors don't get a signal unless the engine is turning, just to clarify.
The pump should do a 2 second (roughly) prime every time you turn the key off and back on.
If the pump doesn't prime every time you turn the key off and back on, then the pump circuit (or the pump itself - I know it's new, but..) is faulty.
Going back to the test light and following the circuit in the first post I sent is probably your best bet at finding the break in the circuit.
I have seen where the connectors under the relay were bad and caused a similar problem, but I don't see how setting the parking brake could affect that. Maybe setting the P/brake is just a coincidence ?
The pump should do a 2 second (roughly) prime every time you turn the key off and back on.
If the pump doesn't prime every time you turn the key off and back on, then the pump circuit (or the pump itself - I know it's new, but..) is faulty.
Going back to the test light and following the circuit in the first post I sent is probably your best bet at finding the break in the circuit.
I have seen where the connectors under the relay were bad and caused a similar problem, but I don't see how setting the parking brake could affect that. Maybe setting the P/brake is just a coincidence ?
06-08-2016, 08:22 AM
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Resolved! Follow Up
Local Ford dealer mechanic noticed an after market device mounted on the firewall that was in the mix of the electronics. I had noticed it before, but it had "Ford" on the label, so I thought it was OEM. It turned out to be a device that allowed the truck to run on propane. And it had it's own wiring harness that was spliced into the factory harness in multiple places. The mechanic showed me how to tell the difference between the after market harness and factory and I spend a couple hours getting rid of it and re-splicing the factory wires that they cut. Starts every time and runs fine. I have not seen any other evidence of propane equipment on the truck. The truck was a surplus service vehicle from an HVAC company, so there are various places where you can see that they mounted tool boxes, etc..., so some screw holes here and there did not stand out to me as something unusual.
As a side note, I called the number on the device (Dual Curve is the model) and that company is out of business and the device is not longer made. But at least someone answered the phone and gave me the number for an outfit in Minnesota that retrofits vehicles to run on propane (CNG) and they said that the truck was probably running on propane at one time and they stripped everything off except the device and wiring harness. Thought I would post a follow up in case it helps someone else. Thanks for the help and suggestions. I now know more about propane wiring harnesses than I ever wanted to. This thing nearly drove me nuts.
As a side note, I called the number on the device (Dual Curve is the model) and that company is out of business and the device is not longer made. But at least someone answered the phone and gave me the number for an outfit in Minnesota that retrofits vehicles to run on propane (CNG) and they said that the truck was probably running on propane at one time and they stripped everything off except the device and wiring harness. Thought I would post a follow up in case it helps someone else. Thanks for the help and suggestions. I now know more about propane wiring harnesses than I ever wanted to. This thing nearly drove me nuts.
