Engine runs weired......Please Help

[xtreme02stang]

I just got done doing a V8 swap in my 93 4cy. Its a new 306 with a single turbo, Im running 42lbs injectors with a 75mm Pro-M Blow through mass air meter, I also have a msd 6btm, I am running a stock cam, 92 or 93 harness and stock computer.

Ok now to the problem. I started the car for the first time the other day after completing the swap. The car started up on the first try, and ran fine all the way up the 180deg, and held steady, But shortly after it reached its running temp it went from running smooth to developing, what seems like a miss fire, the engine shakes, it does not clean up when I rev it, and has a poping noise exiting the open down pipe(sounds like a small back fire). But here is the weired part, while its running bad if you shut the car off and then start it again, it goes back to running smooth again, but after a few minets it instantaniously reverts back to what seems like a miss fire. Mind you this is not while driving the car, it is just idleing in the driveway. Any help would be greatly appreciated, thaks in advace. (Hopefully)

 

[BK_CAULEY]

start by pulling the codes as it can be a host of problems. then let us know what you get. and we can work from there.

Updated 21-Sep-2007 to update diagnostic connector diagrams

Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of a systematic process that checks and eliminates possible causes. This idle problem checklist will use the same troubleshooting strategy and methodology.

By the term surging idle, I mean an idle that wanders up and down more that 100 RPM, or an idle that starts low and goes high and stays there.

The obvious first step is to dump the codes and see what the computer says is wrong…

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.

See http://www.troublecodes.net/Ford/

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.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

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.​

 

[Vipersix]

Sounds to me like it's getting too hot. Definitely pull the codes and see what the computer thinks.

 

[BlownFiveLiter]

So it's running ok, as long as you remain in open loop? It sounds like you're possibly in need of a tune at this point, should everything check out ok, as far as pulling codes goes. Once you go into closed loop, it's taking readings from the O2 sensors and MAF and making corrections based on what it senses the air/fuel ratio to be. When you shut it off and restart it, you'll be in open loop for a short period of time, so that's why it goes back to running good again.

Edited to add: What do you have your base timing and fuel pressure set to currently? Those are two more factors that may play a role in how your car is running. Are you making boost when your car starts to run rough? Did you remember to close the gap up on the plugs to around .035, so you don't blow out the spark?