Cant keep her running
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Junior User
Joined: Apr 2015
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Cant keep her running
Ok ladies and gents I've had a similar problem previously which was thought to be fixed. I have 1990 crew cab long bed with a 460. It will start and run perfectly fine then after about 20 mins of driving, it will shut down and will not start again till it's cooled down for at least 30 mins. I recently replaced the rear tank pump as well as the pip sensor on the distributor, but it feels as thought the truck is becoming increasingly difficult and wanting to run less. I checked fuel pressure on the rail and it was strong but it would drop off after a few moments then immediately return. Any information will help.
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Junior User
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Ok so today poked around and replaced the fuel pump relay under the hood, ran the same. So then I moved to the rollover switch inside the cab on the firewall the button is depressed not loose either, so I don't imagine it shaking to shut me down im lost from here though. Any suggestions?
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Since it happens on both tanks that would imply the Fuel Pump relay may be dropping out or the coil, contacts may be bad. You can swap it with the horn relay to test.
You could jumper Pin 2 & 6 on the Data link so the fuel pump stays engaged whenever the key is in the Run/Start position. Verify power is getting to the pump when the pressure drops to 10.
You could jumper Pin 2 & 6 on the Data link so the fuel pump stays engaged whenever the key is in the Run/Start position. Verify power is getting to the pump when the pressure drops to 10.
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Junior User
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I had replaced the fuel pump relay with a new one and it had no effect. How might the coil adjust my fuel pressure?. Would the jumper just be for temp fix or is this something I could rely on for a while?
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Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
The coil does not adjust your fuel pressure.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Does the fuel pressure still drop? The jumper eliminates the computer dropping the fuel pump relay.
In a nutshell the PIP provides the trigger to the computer for the ignition (spark) and it tells the computer the engine is running so it will keep the fuel pump relay energized. You are running in a closed loop. So in theory if the PIP was dropping out, yes you stated you replaced the PIP sensor (on it? it's inside), but in this scenario the short amount of missing PIP signal may be triggering the computer to de-energize the fuel pump relay (i.e. fuel pressure drops). So the jumper eliminates the computer.
Since you state the problem persists you still have to determine if the proper timed spark is dropping and verify the pressure is staying where it should be.
In the mean time it might be a good idea to run the KOEO tests and stored code display. Since you may have multiple issues let's see what the computer thinks.
In a nutshell the PIP provides the trigger to the computer for the ignition (spark) and it tells the computer the engine is running so it will keep the fuel pump relay energized. You are running in a closed loop. So in theory if the PIP was dropping out, yes you stated you replaced the PIP sensor (on it? it's inside), but in this scenario the short amount of missing PIP signal may be triggering the computer to de-energize the fuel pump relay (i.e. fuel pressure drops). So the jumper eliminates the computer.
Since you state the problem persists you still have to determine if the proper timed spark is dropping and verify the pressure is staying where it should be.
In the mean time it might be a good idea to run the KOEO tests and stored code display. Since you may have multiple issues let's see what the computer thinks.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Warm up the truck, then do this: How to run a self test
As stated in the write-up there are two portions to the tests. The first part are the actual Key On Engine Off (KOEO) tests. If any of the tests fail you will get a flash out of the code(s). There is a "separator" flash then the flash out of any stored codes is displayed. It is important to note when the codes were display because many times the code definition changes based on whether it was displayed in the KOEO tests, CM (stored codes), or the Key On Engine Running (KOER) tests. No need to run the KOER until any KOEO and/or CM codes are corrected.
If you do not like counting flashes consider purchasing a code reader such as the Equus/Innova 3145.
The same site with the test procedure also has the code definitions. Your truck should display two digit codes.....
As stated in the write-up there are two portions to the tests. The first part are the actual Key On Engine Off (KOEO) tests. If any of the tests fail you will get a flash out of the code(s). There is a "separator" flash then the flash out of any stored codes is displayed. It is important to note when the codes were display because many times the code definition changes based on whether it was displayed in the KOEO tests, CM (stored codes), or the Key On Engine Running (KOER) tests. No need to run the KOER until any KOEO and/or CM codes are corrected.
If you do not like counting flashes consider purchasing a code reader such as the Equus/Innova 3145.
The same site with the test procedure also has the code definitions. Your truck should display two digit codes.....
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
At idle with the vacuum line attached to the fuel pressure regulator should be between 30 to 35 PSI. Remove the vacuum line the pressure should go to 40-45 PSI.
As load increases, and vacuum decreases, the fuel pressure increases. At no time with the engine running should you see pressure go below the ~30 PSI value.
As load increases, and vacuum decreases, the fuel pressure increases. At no time with the engine running should you see pressure go below the ~30 PSI value.