91 hatch idle troubles

[Jared Hess]

I have a 91 hatch with a 306 x cam, pro comp 190 heads, rockers, speed pro pistons, cobra intake, 24lb injectors, cobra ecu, street fire ignition just to name some of the mods. My problem is right now im not running o2 sensors and since the first start up it won't idle right it will bounce around a little when first started then idle ok for 5 to 10 mins then slowly lose rpms till it dies. The car screams when you take it for a ride I havent been able to run the o2s do to my current h pipe but fixing that soon. Any advice would be highly appreciated.

 

[Jared Hess]

This setup is all new for this motor including being efi so i wasn't sure if the ecu needed the o2s to learn all this stuff since its never seen it before or i have other issues. I've only put about 5 to 10 miles right around my house on it.

 

[jka]

The problem is not have the sensors hooked up ..running the o2 sensors really should help clear up your idle and make the ecu happy.

 

[jrichker]

Fix ALL your sensor problems first BEFORE doing anything else.

See the "Surging Idle Checklist” for help with all your idle/stall problems. You can guess at the problem and throw parts at it, or you can use the checklist to help you find the problem quickly and inexpensively. The checklist is right here in the Stangnet 5.0 Tech forum and you don’t have navigate to some other unknown web site. It‘s free and doesn’t cost anything: at last count there were more than 103,000 visits and still climbing

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

 

[Jared Hess]

Thanks for the info i'm hoping the o2s fix it but some of the people around my area swear u can run ur car without them i just figured yea u can but for one it will be in open loop and two my setup hasn't been seen by this ecu so it needs all the sensors and help it can get to figure it out right. If it doesn't work tho i will be sure to use that checklist.

 

[madspeed]

run them o2's!!!

 

[Jared Hess]

getting a new x pipe with bungs friday hopefully get it on and hooked up after christmas

 

[madspeed]

youre on the right track

 

[jrichker]

Thanks for the info i'm hoping the o2s fix it but some of the people around my area swear u can run ur car without them i just figured yea u can but for one it will be in open loop and two my setup hasn't been seen by this ecu so it needs all the sensors and help it can get to figure it out right. If it doesn't work tho i will be sure to use that checklist.

I have spend 45+ years fixing cars and 20+ years fixing 5.0 EFI Mustangs. I will tell you based on experience, do it right and fix all the sensor & wiring problems.

5.0 EFI Mustangs have a "Limp mode" that they will switch to when critical sensors aren't working. It operates on fixed computer paramters to protect the engine from damage with reduced HP and economy. Since 86-88 Mustangs don't have a working Check Engine light, you can be in Limp Mode and not know it. The car will still run, but not as good as it will when all the sensors are working correctly.

 

[JasinC19]

Hi I have an off road BBK H Pipe left over from my build that was on the car for like 2 days. I will sell them to you. Send me a PM if you are interested.

Jason