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78 bus FI starts well, idle well, stalls as pushing pedal
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hamid
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PostPosted: Mon Feb 12, 2018 7:34 pm    Post subject: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

Hi
I just had my 78 engine rebuilt with original fuel injection system. it has been working great and smooth for the last couple of weeks since I got it back. the other day after driving it the night before with no issues, I started the car and it started fine idling great. as I pulled out of driveway it started to stall but did not die. as I let the gas pedal off, it returns to normal idle. as I push the gas more and more the engine stalls as if it is running out of gas. I know the very basic concept of the FI but no way I can figure this out without help. my house is far from the mechanic. I described the situation he said look for vacuum leak. then start checking the electronic of the system.

as I turn the switch on there is a click. as I start it turn on right away. the AFM or sensor seems to be working correctly on visual inspection. I checked for vacuum leak but all hoses are connected. now what is the next step? I read the pamphlet provided on this site but that is a lot of testing. based on the symptoms what could be the most probable so I look for that? thanks a lot
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williamM
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PostPosted: Mon Feb 12, 2018 7:43 pm    Post subject: Re: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

check the contact below the black cover on the air flow box- It should keep the fuel pump running as the air flow increases.
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Randy in Maine
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PostPosted: Mon Feb 12, 2018 7:52 pm    Post subject: Re: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

Spend a moment to inspect the pins & sockets that connect the wiring harness to the AFM and the ECU box. Make sure one of them is not pushed in and not making a good connection. Not common but it does happen.
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aeromech
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PostPosted: Mon Feb 12, 2018 9:35 pm    Post subject: Re: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

Yeah, what he said. Usually happens when the harness connector is left of the AFM
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BUSBOSS
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PostPosted: Mon Feb 12, 2018 11:54 pm    Post subject: Re: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

Check the vaccum system for cracks. Especially the S boot.
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hamid
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PostPosted: Tue Feb 13, 2018 1:34 pm    Post subject: Re: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

Thank you everyone. I will inspect the AFM pins and try to measure the resistance according to the specifications and report back to you. this is the first time I am going to do this. I will also check for cracks in vacuum system.

if there is faulty wiring or pins on AFM or not functioning what are the options? are these part available to purchase as after market at all? I am in southern California. Thanks
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Randy in Maine
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PostPosted: Tue Feb 13, 2018 2:32 pm    Post subject: Re: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

Just snoop around a little. Take the S boot off and inspect it in the bright california sunshine carefully examining the pleats for any sort of cracks. "Shoe Goo" is an OK temp fix until a new one is found.

I like to remove the plug connections at the AFM and ECU and examine them in a bright light. Clean them up with electrical contact cleaner and make sure the connections are 100%. Needle nose pliers and a pair of tweezers with some sandpaper can help clean up and straighten up connections.

That volt ohm meter may very well pay for itself as you check for continuity and resistance in your wiring harness.
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telford dorr
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PostPosted: Tue Feb 13, 2018 3:18 pm    Post subject: Re: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

The pins are available on-line from DigiKey. They have the correct retaining tang to keep them in the connector housings.

This pic shows the FI connector pins.
Image may have been reduced in size. Click image to view fullscreen.

Close-up of the injector connectors, showing new style release bar.
Image may have been reduced in size. Click image to view fullscreen.

This pic shows the regular 1/4" terminals and the smaller 0.110" terminals. All terminals shown have a retaining tang, for use with housings.
Image may have been reduced in size. Click image to view fullscreen.

All of these terminals need an "F" style crimp tool. The Greenlee / Paladin PA8000 series tool with the 2033 dies is the best (Amazon). A less expensive one is sold by DelCity.net.
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hamid
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PostPosted: Sat Feb 17, 2018 11:58 am    Post subject: Re: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

Hello
thanks for your help. I have been reading teh AFC pamphelt and learning about this.
I used the AFC booklet printed from this site and inspected the E.C.U. point by point. all the pins are good. I cleaned with electrical cleaner. I measured all the resistances they are are normal. I checked the temperature sensor it ok.

I checked the connection on the double relay with light meter, they are correct . I checked for vacuum leak I could not fine one. I checked the injectors connectors they are fine.

I turned on the engine and ran it at high RPM it was great for about 10 second and back to the same problem sounding like fuel hungry or running out of gas. back to the idle works great. I turned it off for about 10 minutes, turned it on again and ran at high RPM again great for 10 seconds and the same problem.

i have checked all the connection to fuel pump and solenoid on the starter.

I have not cheeked the fuel pump pressure or the pressure regulator.

I suspect dragging fuel pump. is that a valid suspicion? I will check the current to the fuel pump according to the pamphelt.

any suggestions, recommendation?
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SGKent Premium Member
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PostPosted: Sat Feb 17, 2018 12:28 pm    Post subject: Re: 78 bus FI starts well, idle well, stalls as pushing pedal Reply with quote

it can be an ignition or fuel problem. There can be problems in the fuel supply including where something in the tank is blocking the flow to the pump. It can be any of many parts of the fuel injection system. It can be the points, dwell, timing or electronic ignition.

There are basic troubleshooting steps but if you don't have the tools and experience it is going to be hard for you to work on it. Were it me, I would start with a fuel pressure test.

Pot where you are in southern California into your avatar or sig line and see if one of our folks like Robbie or Gary are near you.
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