EFI stalls when put in gear

[MY 4 BY]

I just completed an EFI install using mostly Ford parts. GT40 upper and lower intakes,new 91-95 Mustang wire harness and computer etc. Pretty happy with it so far but it has some problems. When I put it in gear it wants to stall. (auto trans.) I know it's going to do it, so I can goose the throttle to compensate, but I shouldn't have to do that. I set the voltage on the TPS to .94 VDC but that didn't make any difference. It has a surge at idle too. I checked for codes and it shows only "soft" codes related to missing emissions equipment that I'm not running. Any ideas?
Thanks

 

[welndmn]

I would check the IAC first.
Also peak around for a vaccum leak.

 

[Viperwolf1]

Timing? Fuel pressure? Vac leaks?

 

[MY 4 BY]

I'll check for vacuum leaks today, but how do I test the IAC? Timing is set at 12*. Don't have a fuel pressure gauge.

 

[BUCKNBRONK]

Check ur IAC. Its either installed wrong or defective.

 

[Viperwolf1]

I'll check for vacuum leaks today, but how do I test the IAC? Timing is set at 12*. Don't have a fuel pressure gauge.

IAC is a computer controlled vac leak. If you unplug it the engine should almost die. Might be a good idea to clean the carbon out of it and check the condition of the gasket.

 

[MY 4 BY]

I unplugged the IAC with the engine idling and there was no change in RPM. I removed the IAC and noted that the gasket is in good condition and that there is no way to install it wrong--it has two ports and no connecting passages. I applied battery voltage to the IAC and confirmed that the valve/plunger was moving, and tested it for resistance - it measured 10 ohms -7 to13 ohms is acceptable per the Charles Probst book. I cleaned the inside of the IAC with starting fluid, reinstalled it, but no help. I'm going to do the vacuum leak test next using propane.

 

[anoblefox]

when the timing was set did you have the spout connector disconnected?

 

[Viperwolf1]

I unplugged the IAC with the engine idling and there was no change in RPM. I removed the IAC and noted that the gasket is in good condition and that there is no way to install it wrong--it has two ports and no connecting passages. I applied battery voltage to the IAC and confirmed that the valve/plunger was moving, and tested it for resistance - it measured 10 ohms -7 to13 ohms is acceptable per the Charles Probst book. I cleaned the inside of the IAC with starting fluid, reinstalled it, but no help. I'm going to do the vacuum leak test next using propane.

You're on the right track. Sounds like the computer has the IAC completely closed to try to lower the idle speed and the vac leak is keeping it high. Don't forget to check the PCV valve.

 

[Ourobos]

94/95 Mustang uses an electronic transmission, could be looking for the transmission, which harness did you use in particular, and what ECU?

 

[MY 4 BY]

94/95 Mustang uses an electronic transmission, could be looking for the transmission, which harness did you use in particular, and what ECU?

I used the Ford Motorsports wire harness, with a used A9L computer.

 

[MY 4 BY]

You're on the right track. Sounds like the computer has the IAC completely closed to try to lower the idle speed and the vac leak is keeping it high. Don't forget to check the PCV valve.

I used acetylene instead of propane (had more of it ;D) but I'm convinced that there are no vac. leaks. I checked REAL good around the PCV area. Any other ideas? I appreciate the help.

 

[MY 4 BY]

when the timing was set did you have the spout connector disconnected?

Yup, I had it disconnected, and thanks for thinking of that.

 

[73azbronco]

First, does your IAC move at idle in park? Are you sure it works right?

Next, If the IAC is not moving when gear shiter is moved from N/P to D/R, the computer is not seeing the tranny, or is not working. Assuming the iAC is good, which may be a bad assumption OBTW, I'd focus on inputs to the computer specifically the tranny inputs, play with those and see if the IAC output changes at idle. If not, your computer may be badish.

 

[Ourobos]

^ A9L doesn't 'look' for a transmission.. It's not electronic

 

[MY 4 BY]

First, does your IAC move at idle in park? Are you sure it works right?

Next, If the IAC is not moving when gear shiter is moved from N/P to D/R, the computer is not seeing the tranny, or is not working. Assuming the iAC is good, which may be a bad assumption OBTW, I'd focus on inputs to the computer specifically the tranny inputs, play with those and see if the IAC output changes at idle. If not, your computer may be badish.

The IAC is a enclosed component...how can I tell if it's moving?;D And inputs to the computer from the trans?...it's a C4..not electronically controled.

 

[doghows72]

VSS signal to the computer? Mine did that and I found I needed the VSS. It's worked fine since putting it in.

 

[MY 4 BY]

VSS signal to the computer? Mine did that and I found I needed the VSS. It's worked fine since putting it in.

Good suggestion and thanks for making it, but this Ford Motorsports M-12071-A50 wire harness doesn't have the option.

 

[welndmn]

Do you have a different throttle body?
Have you tried to set base idle?

http://sbftech.com/index.php/topic,1031.0.html

 

[MY 4 BY]

Do you have a different throttle body?
Have you tried to set base idle?

http://sbftech.com/index.php/topic,1031.0.html

I have a Mustang throttle body, 1991 I think. I set the TPS voltage previously.