PDA

View Full Version : engine dies when ideling down



94MustangSC
08-25-2008, 11:12 PM
So I got my engine back together after a complete rebuild. It was making a few funny noises, so I spent my evening tracking them down to a small vacuum leak and the couplers on my FMIC sucking shut. So I got those problems fixed to find that now the engine idles a bit too slow and rough, but much quieter. If I give it some throttle, as it idles back down it will stall and quit. After that happened a few times, I would start it and it would immediately quit. It still runs, but will hesitate if I give it some throttle. It only started this after I fixed the leaks. Any idea's?

dwayne
08-25-2008, 11:37 PM
still sounds like you have a vac leak.

94MustangSC
08-25-2008, 11:50 PM
That's kinda what I was thinking, it was just too dark to look anymore. Any idea's on how to track it down? I use clamps on all the vacuum hoses, plug all the open ports, and made sure to check everything twice. Is there any sure fire way to find it?

dwayne
08-26-2008, 12:22 AM
crank it up let idle use carb cleaner,spray around until engine revs up,you shpuld find the vac leak,

94MustangSC
08-26-2008, 01:07 AM
I tried that first thing. I sprayed every connection pretty thoroughly with no results.

dwayne
08-26-2008, 01:15 AM
ok,now are you sure you got all the air out of the fuel rail.

BirdofPrey97
08-26-2008, 09:03 AM
Tried the carb cleaner trick and it did not work for me, but the leak was still where my IC connection was. Tore it down 1 piece at a time and put back together to see where the issue was so that next time it was apart I would know where the issues were in the past.

rzimmerl
08-26-2008, 09:19 AM
What throttle body are you running? If your running an after market throttle body, sounds like you need to adjust the throttle screw and bypass screw.

94MustangSC
08-26-2008, 10:13 AM
I'm sure there is no air in the fuel rail. The funny thing is that it ran fine when I first started it up and for a good 30 minutes until I fixed the one vacuum leak I could find.

94MustangSC
08-26-2008, 10:15 AM
It's a mustang throttle body. I don't think it's a compatability issue. I've had the car dyno tuned twice with this setup, with no problems.

BirdofPrey97
08-26-2008, 11:15 AM
It's a vac leak, guessing from the info given. Fun parts of the SC world. Welcome!

94MustangSC
08-26-2008, 03:34 PM
So I talked to a guy who teaches this stuff for a living. I had the car tuned previously with the silicone couplers running to my FMIC sucking themselves shut whenever the car was in vacuum. I also put a new cam in since the last tune. His thoughts are that now I have stopped the couplers from sucking shut, in combination with the new cam, the engine is not getting enough air to match the fuel delivery at idle. The engine was intially tuned with a small amount of air coming in at idle. Now it is getting much more air, more easily. So the IAC, or the throttle body set screw need to be adjusted to make up for the difference in airflow at idle, and in vacuum. Any thoughts on this info? Any ideas on adjusting the IAC?

Mike8675309
08-26-2008, 09:32 PM
So I talked to a guy who teaches this stuff for a living. I had the car tuned previously with the silicone couplers running to my FMIC sucking themselves shut whenever the car was in vacuum. I also put a new cam in since the last tune. His thoughts are that now I have stopped the couplers from sucking shut, in combination with the new cam, the engine is not getting enough air to match the fuel delivery at idle. The engine was intially tuned with a small amount of air coming in at idle. Now it is getting much more air, more easily. So the IAC, or the throttle body set screw need to be adjusted to make up for the difference in airflow at idle, and in vacuum. Any thoughts on this info? Any ideas on adjusting the IAC?

Does your throttle body have a bypass screw? This will typically be located close to the idle air control motor. If so, use that for your adjustments. Otherwise you have to use the throttle stops. Disconnect the IAC connector and make sure the throttle stop allows the throttle plate to close all the way. Open the bypass screw and start the motor. Slowly close the bypass screw until the engine idle starts to drop, slowing down until right where the engine wants to die. Shut the car off and hook the iac back up. Unhook the battery and sit for 20 minutes to clear any adaptive memory. Hook the battery back up and start the car. The EEC will re-learn idle.

See if it works better like that. With the EEC-IV and the Idle Air control, when the Throttle body is set so the EEC-IV has a range of control, the engine shouldn't die unless there is a problem with a vac leak or idle air control motor. That is assuming you don't have fuel trims set so different that the EEC-IV can't trim out enough fuel to maintain idle.