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Discussion Starter #1
I just finished installing an efi system in my 73 Bronco. I went to start it up and it started but it wouldn't idle correctly. It would only idle at 2300 to 2800 rpm. I played around with the idle air bypass sensor. I even changed it for another one that I had in the shop. No change. Then I changed my throttle body. I had a modified TB on that I bored out and made a new flapper for so I thought maybe that’s the problem. I changed it back to a stock TB. This helped. Now it wants to idle, but now it idles very rough if it idles at all. I then pulled the plug on the distributor that allows me to set the timing this helped, but it still surges while trying to idle. I have not run a diagnostics test.
The other twist is that the motor it is on is a stroked 393 with a lightning lower intake Gt-40 upper 24# injectors 70 mm mass air calibrated to the injectors.
The computer is stock to 91 Gt A9L.
Is this my biggest problem?

Thanks for any help.
 

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There's no reason a stocker A9L or A9P shouldn't run a 393. You might not get a perfect tune, but it should run it fine.

What happens if you pull the plug on the IAC (throttle bypass)?
What are you using for a harness? Salvage a stocker? Not necessarily a problem, just trying to get some details.

I want to take a glance at something on my stock TB before I start throwing too many things out. My Mustang usually runs so well I rarely have to screw with it, so I probably haven't been near the TB in a couple of years aside from pulling the intake elbow so I could clean the filter.

We're getting ready to do a frankenstein EFI swap on an 85 F-250. Mostly done sorting through the harnesses, and waiting for my roommate to get the rest of the parts together and the time. Will be an 85 351W running on an A9L or A9P, with a combination of 92 Bronco and 93 (if I remember right) 5.0 Thunderbird harnesses. We're using the Bronc engine bay harness for most of the sensors, with the Tbird engine harness (injectors), pinned to the Stang pattern.

Yeah, we're nuts. So I know where you're coming from. :D
 

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Discussion Starter #4
Its stock mass air off a cobra.
I reworked the harness and checked all the sensors they all get power and they are all new.
I have been messing with timing but thats not the problem.

I have no Idea. All I know is that I am leaving to go wheeling in colorado saturday so I hope i get it figured out ASAP!!!
I hate bringing and knowing that I have to work on it.
 

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broncodude_73 said:
I have not run a diagnostics test.
You'll be much closer to knowing where the problem is once you do this.

broncodude_73 said:
The other twist is that the motor it is on is a stroked 393 with a lightning lower intake Gt-40 upper 24# injectors 70 mm mass air calibrated to the injectors.
The computer is stock to 91 Gt A9L.
Is this my biggest problem?
I'm thinking you're on the right track here. You're confusing the A9L a 'lil bit it sounds like with the 393 cubic inches and the 70mm MAF.

If you haven't already found this place, try www.fordfuelinjection.com. You can get an excellent understanding of how the system works.
 

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wetnsloppy4x said:
...If you haven't already found this place, try www.fordfuelinjection.com. You can get an excellent understanding of how the system works.
Ryan, the fella who runs the site, is also a Bronco driver. He frequents a couple of Bronco boards under the name Fireguy50. I don't know offhand if he's on here or not.

The A9L/A9P should run a 393 (I've seen 'em run much stranger than that), but I believe the Cobra meter uses a special calibration that only works right with the Cobra computer. You should need either a MAF calibrated for the 24lb-ers with a normal (non-Cobra) comp, or a Cobra comp rather than the A9x. Don't take my word for it, and check with Fireguy before you spend your money.
 

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It's been awhile since my Mustang days, is your tps properly set? I can't remember what the voltage should read with the sensor in the correct position, but you aren't going to get it to idle well without the proper setting.
 

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Traveller said:
It's been awhile since my Mustang days, is your tps properly set? I can't remember what the voltage should read with the sensor in the correct position, but you aren't going to get it to idle well without the proper setting.
Less that 1 volt. (.96 or so)
 
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