UPDATEDHowell TBI owners!!!,problem solved. - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 09-02-2002, 04:16 PM Thread Starter
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UPDATEDHowell TBI owners!!!,problem solved.

Let me first state that I haven't begun troubleshooting this problem yet.

I drove my Scrambler for over an hour last night at slow/stop speeds while spotlighting deer. The Jeep ran fine and never sputtered. This morning I tried to start it up, and there is no fuel output from the injectors on the TBI. I can hear the fuel pump cycling when the key is turned but nothing is happening at the TBI. Any suggestions on where to start? First, I am going to pull the fuel line and verify that fuel is leaving the outlet on the pump from ther I am not sure what to check.

Thanks,
Tom
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post #2 of (permalink) Old 09-02-2002, 08:22 PM Thread Starter
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Re: First problem w/Howell TBI, No Fuel at injectors..

BTT
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post #3 of (permalink) Old 09-02-2002, 08:25 PM
 
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Re: First problem w/Howell TBI, No Fuel at injectors..

Can you put a test light across the wires to the injectors to see if they are getting power? Either there's no fuel pressure (and I see you are working on that) or the injectors are not opening due to either a problem with the ecu or wiring. I imagine the ecu needs 12 volt power and some input from the ignition to sense the engine turning over. The other sensors will just effect how well it runs,and would not likely prevent the injectors from squirting. Make sure it's generating a spark as you turn it over, else I imagine the ecu doesnt' know the motor is turning over and needing fuel.
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post #4 of (permalink) Old 09-02-2002, 09:10 PM
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Re: First problem w/Howell TBI, No Fuel at injectors..

TimnMB has some valid points.

Pull the computer codes.

Because the fuel pump is cycling doesn't mean it is outputing. Pull the fuel input to the TBI and see if you've got gas circulating from the pump to the inlet to the TBI.

Then, if you've got fuel you have to check that the ignition system is working. It's the ignition that sends the signal to the computer, which in turn pulses the injector.

If you've got spark, then check the wiring to the computer to see if the pulse is getting to the computer. If it is, then the computer is the likely culprit.
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post #5 of (permalink) Old 09-03-2002, 12:22 AM
 
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Re: First problem w/Howell TBI, No Fuel at injectors..

You can also try removing your battery cable over night. This will allow the computer to default to the original program. You may have triggered a flooded condition somehow which will turn off the fuel pump. You may get a short run out of your pump when you first turn on your key but it will be too short to supply enough fuel to run the engine.
You can also run a hot wire to your fuel pump to see if it is working properly. Disconnect the fuel outlet line and run it into a gas can to catch the fuel.
We had a guy loose his fuel suction tube in his gas tank up in the Rubicon a few weeks ago and it also did the same thing as you describe.
Like Leve said, check your trigger wire. This wire should be connected to the coil and gives the computer the pulse necessary to fire the injectors.
Can you hear the injectors firing?
Good luck.
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post #6 of (permalink) Old 09-03-2002, 08:40 PM Thread Starter
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Re: First problem w/Howell TBI, No Fuel at injectors..

Here are the results of my initial diagnostics.

1. No codes stored in ECM
2. Fuel pump is operational
3. Test light reads positive at injector terminals
4. No Spark during cranking

With my limited knowledge of the Howell TBI's interaction with the Motorcraft ignition, I don't understand why there isn't any fuel even though there is no spark. I do understand that my ignition module probably bit the dust and needs to be replaced. I will replace it and hopefully everything will be okay with the Howell system. Most engine problems are related to no spark, or no fuel. I am slightly perplexed that the Howell(or Chevy) system complicates diagnosis by eliminating fuel, when there is no spark. Anyone else care to verify my initial diagnosis.

Thanks,
Tom
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post #7 of (permalink) Old 09-03-2002, 09:21 PM
 
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Re: First problem w/Howell TBI, No Fuel at injectors..

I don't know a darn thing about the Howell kit, so I'm just venturing an (un)educated guess...

If the Howell injectors are triggered by the pulses from the distributor pickup, then no pulse = no spray.
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post #8 of (permalink) Old 09-04-2002, 08:54 AM
 
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Re: First problem w/Howell TBI, No Fuel at injectors..

The fuel injection system you have works on what is known as Speed Density. Speed is determined by rpms as sensed from the ignition module pulses to the coil, and density from the MAP (manifold air) pressure sensor in the intake manifold (or on the ecu). That calculation plus sensor inputs, calculates the amount of fuel required by the engine. The ecu won't deliver fuel to an idle engine. Unless the ignition system works and delivers pulses to the ecu, its "internal tachometer" reads zero, and delivers no fuel. The pulses that open the injectors are timed to the ignition pulse, their duration is determined by the ecu's speed density calculation. So as said earlier, no spark equals no squirt.
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post #9 of (permalink) Old 09-04-2002, 09:17 AM
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Re: First problem w/Howell TBI, No Fuel at injectors..

Tom, if this were a "modern" EFI system you'd be really lost, as they use crankshaft postion and camshaft position sensors to monitor where the engin's at. The GM TBI is pretty crude by today's standards and doesn't do anything like that. All it does is take the pulse fromt he ignition module and use it to trigger the ECM. So what you have to do is trouble shoot the ignitions system.

Of course it's likely a module problem... but that's where you start.

Once you do get it back up and running a fun thing to do is to set the engine to about 12*BTDC on cylinder 1 and then turn the ignition to "RUN and slowly, by hand, crank the engine past the about 8* firing point. You'll actually hear the TBI's pulse as they get the pulse from the ECM, which got it from the ignition module. Then you'll hear the fuel pump cycle because the regulator noted a drop in fule line pressure to the TBI input. It really is fun and helps you to learn how the sytem should work. Then you'll know more when it doesn't work.

So, in short... it's not a Howell failure.
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post #10 of (permalink) Old 09-04-2002, 12:46 PM
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Re: First problem w/Howell TBI, No Fuel at injectors..

Howell uses all stock interchangeable GM parts if I remember correctly. I think you could get a junkyard computer and swap it in from a late 80's car or truck with the same number of cylinders. Also-check your ground wires and ignition on switches. Lots of howell usesrs have an external switch for the computer that needs to get turned on. The ignition system is also another place to start looking as mentioned above. ~TIM~
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