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91 f150 4X4 5.8 won't run
91 f 150 4x4 5.8 won't run. It will run on carb cleaner. This what I have done. Had bad fuel pump changed fuel pump and fuel filter. Has 40 lbs at the fuel rail. Cranking over 40 lbs at rail. Check injector's with noid light every thing good there. Lossen rail and pulled 1 injector to see if fuel was injecting, it's injectiing fuel. Has good compersion 140 to 150 all cyclinders. It will start and run only while the carb cleaner is being shot into intake as soon as you stop the motor stops. I have no idea where to go from here, I thinking maybe the injectors are not injecting at the right time. Any help would be great.
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90%+ of all crank but won't start situations are electrical related, not fuel. Consider replacing the Ignition Control Module (AutoZone Part No. F125, $42.99)--easy job. It may be that the injectors are fine but the ignition is sparking at the wrong time. Hence, it will only run while spraying carburetor cleaner into the intake. Conceptually, the ICM is a large output transistor (switch) controlling current through the primary coil. ICMs replace points and condenser in older vehicles. In the primary coil, current builds to 5 to 12 amps, generating lots of heat (due to inductance). Then, the ECM controls when the ICM "switches off" current to the primary coil, causing amperage to go to zero. When this happens, 12 to 14 volts in the primary coil is "stepped-up" to 30,000 volts in the secondary coil. This process creates a "type" of alternating current required for the coil (step-up transformer) to work. In a properly working ICM, timing is precisely when needed to fire each spark plug. Your ICM may be "firing" at the wrong time, requiring a "cloud" of carburetor cleaner to run at all. I recommend replacing ICMs every 120,000 miles or 10 years, whichever comes first. |
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See if this link helps: https://www.askmehelpdesk.com/cars-t...ml#post2123675 After that, I don't know what else to suggest, except checking the ECM, Engine Coolant Temperature (ECT) Sensor, MAP Sensor, and Oxygen Sensor. Try swaping the ECM out with a known good one, if possible. |
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That's possible. I usually recommend also replacing the coil when the ICM is changed. They can get damaged from a bad ICM. On Hondas, the next step is to replace the distributor housing with a genuine Honda product, since the CKP, CYL, and TDC sensors sometimes get damaged. There might be a similar problem with your distributor. A bad pickup would be very possible. |
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