WARNING! Faulty Fuel Pump Relay Can Cause Fire!

[porwolf]

I had a common problem with my "79SC lately: The fuel pump was always running. I is supposed to run only when the ignition switch is in the "Start" position, or when the engine is running. My fuel pump was running when I turned the ignition switch on to the "Run" postion before the engine turned over. Here on Pelican I read that if the fuel pump is running without the engine running the cylinders can easily be flooded. Not good! It could also cause an engine fire! The possible cause could be a disconnected or mal functioning Air Flow Sensor, AFS,. So I took out my Ohm meter and checked the terminal 85 at the fuel relay socket: I had continuity to ground there with engine off. So, the AFS was OK. I looked at the schematic of the fuel relay circuit trying to find out what could cause the fuel pump running withpout the engine running. It became clear that if the fuel pump relay did not do it's job of connecting terminal 30 to terminal 87 when the ignition switch is in the "Run" position the fuel pump will always run because it gets it's juice from terminal 87a. So I checked the continuity of my fuel relay between terminals 85 and 86, the ones that power the relay coil. Result: Open circuit! Aha, that is my problem! The relay does not switch! The realy I used was a URO relay, only about 1 year old! I still had my original Wehrle realy. I tested the continuity between terminals 85 and 86, and sure enough the meter showed 65 Ohms.
Then I put my Wherle relay into the socket and sure enough the fuel pump did not run with the engine off! I also noticed when I put the relay into the socket with the ignition switch in the "Run" position the relay clicked noticibly. That should be a goo way to test a fuel pump realy. My URO realy did not click!

Lesson learned: Just because the engine can be started and the engine is running does not mean that the fuel pum relay does it's job to keep the fuel pump fvrom running when it should not. And also: Beware of URO realys!

I made myself a diagram of the fuel realy and pump circuit that may be helpful for other Pelicans:

I edited the graphic to change the fuel pump fuse No. from 18 to 16. See the new graphic in my post below.

[kerthunk]

The URO relays are rubbish. I've seen many of them literally fall apart, some with a year or less of usage.

[KNS]

There have been so many problems with URO parts everyone here should anything with the name on it.

[boyt911sc]

Originally Posted by porwolf

I had a common problem with my "79SC lately: The fuel pump was always running. I is supposed to run only when the ignition switch is in the "Start" position, or when the engine is running. My fuel pump was running when I turned the ignition switch on to the "Run" postion before the engine turned over. Here on Pelican I read that if the fuel pump is running without the engine running the cylinders can easily be flooded. Not good! It could also cause an engine fire! The possible cause could be a disconnected or mal functioning Air Flow Sensor, AFS,. So I took out my Ohm meter and checked the terminal 85 at the fuel relay socket: I had continuity to ground there with engine off. So, the AFS was OK. I looked at the schematic of the fuel relay circuit trying to find out what could cause the fuel pump running withpout the engine running. It became clear that if the fuel pump relay did not do it's job of connecting terminal 30 to terminal 87 when the ignition switch is in the "Run" position the fuel pump will always run because it gets it's juice from terminal 87a. So I checked the continuity of my fuel relay between terminals 85 and 86, the ones that power the relay coil. Result: Open circuit! Aha, that is my problem! The relay does not switch! The realy I used was a URO relay, only about 1 year old! I still had my original Wehrle realy. I tested the continuity between terminals 85 and 86, and sure enough the meter showed 65 Ohms.
Then I put my Wherle relay into the socket and sure enough the fuel pump did not run with the engine off! I also noticed when I put the relay into the socket with the ignition switch in the "Run" position the relay clicked noticibly. That should be a goo way to test a fuel pump realy. My URO realy did not click!

Lesson learned: Just because the engine can be started and the engine is running does not mean that the fuel pum relay does it's job to keep the fuel pump fvrom running when it should not. And also: Beware of URO realys!

I made myself a diagram of the fuel realy and pump circuit that may be helpful for other Pelicans:

porwolf,

Nice write up and illustrations. If I may add something to your post, fuse #16 not #18 is the right number (typo). Refer to the high lighted section of your post: You could run the FP all day long and there would be no fuel going into the cylinders except:
1). You lift the FD plunger to deliver fuel to the injectors.
2). You have leaking injector/s to cause flooding.

Otherwise the the fuel delivered by the FP would be recycled back to the gas tank. FP running when the ignition switch @ ON position is typical or normal condition in the early CIS engines ('73.5- '75). As you have demonstrated, the three (3) most common culprits of prematurely running FP for '76-'83 SC's are:
1). A defective FP relay with a bad coil.
2). A defective AF switch.
3). Terminal #85 has no ground contact.

The fact that your FP was running with the ignition SW @ ON was a clear indicator of abnormality in the system. Good you decided to investigate the root cause of the anomaly. Good discovery.

Tony

[porwolf]

Thank you, boyt911sc, for the corrections. You are right the fuel pump fuse should be No. 16 instead of No. 18. I corrected my graphic accordingly. I also understand that as long as the FD plunger stays closed there should be no fuel going into the cylinders if the fuel injectors are not faulty. But it should be safer if the fuel pump is not running and pressurizing the system unnecessarily.

Any way I did correct my my graphic, here it is: