Troubleshooting
Fleet Mechanic
Joined: May 2005
Posts: 1,575
Likes: 11
From: Puyallup, WA
89's were the last year of a low pressure fuel pump in the tank and a high pressure pump on the frame rail. It was also the last year of the frame rail mounted reservoir, and in that it has the valving for fuel return to the individual tanks (if equipped with 2) and a filter in it.
You will need to troubleshoot the low pressure pump as well as the high pressure pump. Both are required for the fuel system to provide fuel to the truck. The fuel selector valve, if the truck has more than one fuel tank provides the pathway for power to be routed to the low pressure pump in the specified tank
The high pressure pump is run by the ecm / relay.
There is also a roll over switch that can be triggered by a collision that shuts off power to the system.
Do not confuse the system you have with a 1990 and later system, they are plumbed completely different, and do not use any low pressure pumps - so when getting troubleshooting tips, they need to related to 1989 and earlier (mid year 1985)
You will need to troubleshoot the low pressure pump as well as the high pressure pump. Both are required for the fuel system to provide fuel to the truck. The fuel selector valve, if the truck has more than one fuel tank provides the pathway for power to be routed to the low pressure pump in the specified tank
The high pressure pump is run by the ecm / relay.
There is also a roll over switch that can be triggered by a collision that shuts off power to the system.
Do not confuse the system you have with a 1990 and later system, they are plumbed completely different, and do not use any low pressure pumps - so when getting troubleshooting tips, they need to related to 1989 and earlier (mid year 1985)
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New User
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More about collision
Sadly to say my father last year while plowing hit an ice berm that bent the plow and frame. Where is that turn off valve when a collision takes place?
Last edited by ShakeyJC; Oct 1, 2017 at 09:48 AM. Reason: Typo
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Do you have one tank or two. If two, are you not getting fuel from either tank? My '89 had sat for almost a decade before I bought it. The selector valve was stuck only allowing access to the front tank which unfortunately left me stranded in the side of the highway. I didn't know know that until I ran the front tank down, went to switch to the rear tank and nothing happened. I didn't know it hadn't switched sources since it showed the level in the rear tank as full.
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Tanks
Geez. How fast was he going?
Do you have one tank or two. If two, are you not getting fuel from either tank? My '89 had sat for almost a decade before I bought it. The selector valve was stuck only allowing access to the front tank which unfortunately left me stranded in the side of the highway. I didn't know know that until I ran the front tank down, went to switch to the rear tank and nothing happened. I didn't know it hadn't switched sources since it showed the level in the rear tank as full.
Do you have one tank or two. If two, are you not getting fuel from either tank? My '89 had sat for almost a decade before I bought it. The selector valve was stuck only allowing access to the front tank which unfortunately left me stranded in the side of the highway. I didn't know know that until I ran the front tank down, went to switch to the rear tank and nothing happened. I didn't know it hadn't switched sources since it showed the level in the rear tank as full.
Last edited by ShakeyJC; Oct 1, 2017 at 03:06 PM. Reason: Spelling
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Joined: Sep 2017
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Fuel pump
It was turning on before but sounded weak, so I changed the pump and replaced the filter so now it pumps past the filter, where as the old pump was not. You can prime it, turning on and off the ignition but the engine only stays on momentarily.
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