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Chokes on startup, shudders while driving

Hey, I'm a new owner of an '89 F150. It's a four speed manual trans, 4.9L 6cyl. This is my first truck and I bought a beater in hopes of learning while I fix it up. I have minimal experience (biggest repairs have been replacing disk brakes on a previous car and replacing the EGR valve on this truck), but I want to learn more.

The truck has a bypass switch and the forward fuel tank was removed. Both of these modifications occurred before I owed it. Also, the clutch is a bit grumpy. Sometimes I'm unable to get it into first (I usually "granny start" from second), and every once in a while it doesn't want to go into reverse.

When I bought the truck, it would just choke and cut off after driving for 30 minutes or so. It would restart after cooling down. My mechanic said it was a problem with the fuel pump and replaced it, and that fixed that problem.

After that, the truck began to have trouble starting. I would flip the bypass switch and the engine would rev up, then drop RPM's quickly until choking off within a couple seconds. When I flipped the switch again, it would start up fine. It would run fine after that.

A mechanic recommended having the fuel injectors cleaned. The fixed the problem for about a week, then it started again. A friend of a friend who has a home garage suggested a vacuum leak, and we found a leak in the EGR value, which we replaced.

Replacing the EGR valve fixed the problem again, for a couple days, but it came back. Meanwhile, immediately after the EGR valve was replaced, a new problem started. Periodically while I'm driving (I haven't been able to detect any pattern), the engine will just shudder or choke a bit. It feels like it's threatening to choke, but it never actually does. Once it starts, it typically does this every couple seconds until I shift gears.

I'd really like help in diagnosing what might be causing the choking when it starts and the new shudder when driving. I realize it could be a number of things. I'd like to prioritize things which are least expensive and which would need to be done anyway for routine upkeep. Any ideas?

Thank you!
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Comments

  • edited July 2013
    Have you checked your fuel pressure? You can often rent/borrow a meter from places like Advance Auto.
  • Get a service manual and therein you should find numerous diagnostic tests to perform. Problems with ignition and/or fuel systems cause the ECM to "adjust" other functions such air/fuel mixture or timing when a sensor detects too much air such as a vacuum leak. Without diagnosing properly you can end up swapping out parts which is not a learning process. First do a tune-up; spark plugs and cables, distributor cap and rotor, timing, oil and filter change, air filter, fuel filter (I would clean out fuel lines too.). Install a fresh battery (make sure it is less than 3 months old) Pour injector cleanor in the fuel tank. Visually inspect all wiring and connections. The truck should start in two seconds by simply turning the key after you do these things. If it takes 10 seconds to start (hard starting) then you have problems in your sensors or engine or wiring or injection. Sounds like you need a complete clutch job as well, that will be a learning experience for certain!. Also get a vacuum gauge when you get a fuel pressure gauge (it should be a 2 in 1 item), and a good digital voltmeter as well as a strobe timing light. Always buy good tools. Always!
  • Your truck is in the mid-year range of TFI ignition module Fords. The modules are prone to heat failure at some point and the problem often surfaces in the summertime. Symptoms vary but can very well match what is going on with the truck.

    The module is the little gray rectangular widget on the side of the distributor and testing them is usually a waste of time as short of a complete, total failure they usually test good.

    Do a net search for TFI Settlement and you can read all about those modules. It will be too late to get any reimbursement for repair costs but the info will explain the whys behind the module problems.

    If you change the module you MUST use the special grease that comes with the new module and you will also need a 4MM or 7/32 deep socket or nut driver to access the 2 screws. Hope that helps.
  • Thanks guys! Those are helpful suggestions. I'll get to work and see if I can figure this out...
  • Your truck should have 2 pumps. A low pressure in tank pump feeds a high pressure pump mounted on the frame rail under the cab on the driver's side. Testing the fuel pressure would be a good place to start the diagnosis. And check the clutch reservoir level and watch the firewall at the master cylinder mounting area while someone pumps the clutch pedal. Some Ford pickups of the 80s suffered from the firewall separating.
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