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View Full Version : Misfire, runs way lean



HwyStar
01-31-2014, 12:54 AM
If I had time, I would chase it down, but I had to sleep. I was about to go try out the new tune Dave sent me today, and the car acted like it was only running on a couple cylinders and it AFR was showing pegged 22.3. No code came up that was related to it. The tach jumped around a bit, which makes me think the ignition control module might be bad. But, if that were true, wouldnt it run rich? I visually checked the crank sensor, and didnt see any damage. Chased wires from front to back by the fuel tank. Didnt find anything obviously wrong. I tried the two icm I had were beat up and were bad, so I couldnt check that. I will put the scope on the cmp and ckp tomorrow, and that will narrow things down. Just pissed that I didnt get to do wanted I wanted to. Any insight what it might be so I can narrow my search?

XR7 Dave
01-31-2014, 09:54 AM
Perform a full tune write while it is doing that. Sometimes the write is incomplete when written with the engine off. Seems to be random in my experience. Make sure that the status doesn't show any write errors.

S_Mazza
01-31-2014, 11:59 AM
If I had time, I would chase it down, but I had to sleep. I was about to go try out the new tune Dave sent me today, and the car acted like it was only running on a couple cylinders and it AFR was showing pegged 22.3. No code came up that was related to it. The tach jumped around a bit, which makes me think the ignition control module might be bad. But, if that were true, wouldnt it run rich?

Don't forget that the car is not equipped with fuel sensors. It only has O2 sensors. When the cylinder doesn't fire properly, there is leftover fuel in the exhaust, but there is leftover oxygen too because it didn't burn up with the fuel. The O2 sensor sees the oxygen and reports a lean condition. It has no idea whether any fuel is there or not.

HwyStar
01-31-2014, 12:49 PM
You know, that does explain a lot about o2 readings. And, turns out, I did have the engine secured, ignition off. Thats probly what it is. Thanks!

Silenced
01-31-2014, 04:16 PM
Don't forget that the car is not equipped with fuel sensors. It only has O2 sensors. When the cylinder doesn't fire properly, there is leftover fuel in the exhaust, but there is leftover oxygen too because it didn't burn up with the fuel. The O2 sensor sees the oxygen and reports a lean condition. It has no idea whether any fuel is there or not.

Very eloquently explained. +1 for you.

HwyStar
01-31-2014, 11:25 PM
Did as you said. I re-wrote the tune, and amazingly the car straightened out. I got pissed for no reason at all. This is one of those times where its nice to have some experience on hand.

Went out and did a couple of full power runs in 3rd with datalogs and man, this car feels great! AFR started off at 12.5 and ended off at 11.5. Thats a lot closer. Thanks Dave!

HwyStar
01-31-2014, 11:29 PM
By the way, what do you think of timing when I initially go to WOT? Does it seem like timing is low? Like the car is going safe due to something its seeing?