need help???
Thread Starter
Staging Lane
Joined: Oct 2002
Posts: 79
Likes: 0
From: los angeles
need help??? My engine is misfiring after about 5 minutes of being on. I will star the engine and it will idle fine but as soon as it worms up it starts shacking to the point that it turns off. I thought it was a reducer leaking air but I went to the muffler shop and got it fixed, but it still doing the same thing. Spark plugs are new wires look good also. I will try and get some codes out of it to see what’s going on. Any ideas what might be going on here? 
Thread Starter
Staging Lane
Joined: Oct 2002
Posts: 79
Likes: 0
From: los angeles
The exhaust does not get smokey. How can I check for vacum leaks. I still havent gotten a hold of the diagnostics tool. Also my 02 sensors are about 1" or 2 from the end of the open exhaust. could this be a problem 
Joined: Nov 2001
Posts: 1,707
Likes: 33
From: Anderson, Indiana
Absolutely that will cause problems!
When your engine goes closed loop, the reversion pulses are pulling outside air back over the O2 sensors. The PCM sees that air and thinks the engine is running lean; it compensates by adding more fuel. Regardless of how much fuel it adds it can't get the O2's reading correctly. It reality it doesn't need any extra fuel at all, so the engine is running terrible now.
There's nothing wrong with running the engine a little with open exhaust, but just unplug the O2 sensors so that the PCM can't go closed loop. Then, as long as the engine is mechanically ok it will sit and run fine. Then when you get the exhaust hooked up, plug the sensors back in.
When your engine goes closed loop, the reversion pulses are pulling outside air back over the O2 sensors. The PCM sees that air and thinks the engine is running lean; it compensates by adding more fuel. Regardless of how much fuel it adds it can't get the O2's reading correctly. It reality it doesn't need any extra fuel at all, so the engine is running terrible now.
There's nothing wrong with running the engine a little with open exhaust, but just unplug the O2 sensors so that the PCM can't go closed loop. Then, as long as the engine is mechanically ok it will sit and run fine. Then when you get the exhaust hooked up, plug the sensors back in.
__________________
91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
