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Old 10-22-2019, 12:04 PM   #20
DieselSJ
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Join Date: Jun 2016
Location: Phoenix, AZ
Posts: 574
Re: 87 GMC Sierra R3500 7.4L TBI vacuum diagram

Code 24 is speed sensor malfunction. The sensor is built into the speedometer. You should be able to see (or feel) the wires coming off the back of the speedometer and make sure it is plugged in. If sensor is bad, then you have to replace the speedo.

Code 44 is lean. I chased lean codes for a while on mine. I had bad wiring to the O2 sensor, bad fuel pumps, plugged filter.

Watched the video with your injectors and they should not be going on and off like that - you want a continual steady spray. I'd probably start with replacing the electrical connectors on the tops because those look bad. There are also small filters on the injectors themselves. Get a rebuild kit and pull the injectors out of the pods and replace those screens. I can't tell if the injector just isn't firing or if you are getting air in your fuel. Use a stethoscope to listen to the injectors and listen for consistent clicking - if it still clicks when you have no fuel spraying then problem is with supply. If it stops clicking intermittently then you have an injector or wiring issue.
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87 R30 CC Dually, TBI 454, NV4500, zero rust barn find
87 Jeep Grand Wagoneer, 6.5 turbodiesel, 700R4
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