Motor Runs Rough w/ new install............HELP

idaho_88

New Member
Dec 1, 2005
15
0
0
Boise,Idaho
Heres the dilemma,
I have my 88' mustang at a local motorsports shop. The tech installed a 331 motor w/ trickflow top end kit(Track Heat, Stage 2 cam). Also things to factor are a 70mm Accufab TB, 80mm PMAS meter, 30lb injectors, new IAC, and a kirban FPR.

Well going to pick it up tonight and the a/f ratio is at like 14.5- 15.5 at idle. Car idles at 1100 and stutters a lil bit. Fuel pressure is at 35 psi. Well on the dyno it of course leans out at around 4000 rpms.

So we set the fuel pressure to 42-45 psi and it smells really rich and won't idle worth a damn. A/F ratio is alot better at 11.8-12.5 at idle. We are stumped on how to get the car to idle correctly and not lean out while driving.

1. How do I get the car to idle with the proper fuel pressure/a-f ratio?

2. Will the car always lean out at higher rpms with out a programmble tuner?

Thanks for the help, I appreciate it.
 
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Fuel pressure should run 38-40 PSI at idle with the vacuum line disconnected from the regulator & capped.

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

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See http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see http://www.midwayautosupply.com/detailedproductdescription.asp?3829 – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $35.

Wal-Mart may now have the LCD display scanner for less than $35
 
I called the shop and he says he can't get the fuel pressure to drop below 35 w/ vaccum hooked up. He said if he disconnects the vac line and caps it off it runs so rich he can't keep it idling. Timing is set at 15*, could the brand new FPR from Kirban be the problem?