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[4g67] combustion failure while cruising
http://www.4g61t.org/forum/viewtopic.php?f=6&t=39144		 Page 1 of 1
Author:  vicore [ Wed Sep 24, 2014 3:02 am ]
Post subject:  [4g67] combustion failure while cruising
Since a couple of weeks a got the problem that the combustion stops for some seconds.

I do not call it ignition failure because my wideband is reading 17+ in that case until the engine runs normal again. If there would be only a failure in ignition the wideband should read fat mixture not lean as mentioned, right?

Before and after that behaviour everything runs fine. Lambda is jumping up and down - everthing alright.

Most of the time, that failure ends automatically within 1 or 2 seconds, if not it helps to push the pedal to the metal. It even occurs with MAF is disconnected and the ecu runs in limp mode.

Currently there is the C53 ECU in the car but it's the same with my evo8 ecu. I dont have another spare ecu to test, just a 2g N/A ecu - how far are the differences between evo8 and 2g FL?

Temp sensors look fine so far and no code saved in the ecu :(

Hope you have some more ideas - thanx
Author:  Flying Eagle [ Wed Sep 24, 2014 6:26 am ]
Post subject:  Re: [4g67] combustion failure while cruising
Unburned fuel/air, means just that, you now have extra air passing by the sensor when you have a misfire.

ECU/wideband see's lean, and ECU will try to richen the mixture.
Author:  Flying Eagle [ Wed Sep 24, 2014 6:32 am ]
Post subject:  Re: [4g67] combustion failure while cruising
Just for shoots and giggles, humor me and check the (PTU) power transistor unit connector terminals/pins.

Should be right beside the factory spark plug wires as they run down the back of the head, connector is right there, just below that.

A faulty ECU could be ruled out, because it happens with another known good unit.

I would start to look at what causes the spark to fail to all cylinders, like a heat related connection issue.

Also, check the connections at the coil pack setup. Bit of a pain to get in there, I know.
Author:  vicore [ Wed Sep 24, 2014 6:44 am ]
Post subject:  Re: [4g67] combustion failure while cruising
Douh, you are absolutely right! Lean could be a result of a missing spark - thanks for pushing me that direction and straighten that out! I'll check the ignition-system.

It is not strongly temp-related. It happens sometimes with a cold engine as well, for example while leaving a parking lot.
Author:  Flying Eagle [ Thu Sep 25, 2014 7:27 pm ]
Post subject:  Re: [4g67] combustion failure while cruising
How are the wires in the jackets just behind the Coolant Temp Sensor on top of the thermostat housing?

I can see them making an intermittent connection inside the jacket. This is a very common spot for the wires to break. This could be giving a signal like -40 C due to infinite OHMs.
Author:  vicore [ Thu Oct 09, 2014 4:11 am ]
Post subject:  Re: [4g67] combustion failure while cruising
Transistor, Coils, Cables and Plugs are new/changed meanwhile. Problem still occurs. When I had the malfunction in idle I pulled;pushed;moved;bended all the cables in the engine bay without changing anything. Unplugged the coolant temp sensor (signal jumped to -59°C) but the behaviour didn't change. No matter which ignition cable I pulled the engine died. Currently testing with another (told good) ecu but it is exactly the same!

here a link to some logs:
http://www.file-upload.net/gal-108150/yytgv4/1.html

the time at the end of the file name indicates the "beginning" of the malfunction. sometimes timing goes badly wrong - don't know why. In the file with ..._499s.csv the timing starts to behave strange beginning at ~160s.... Fuel is still coming. InjPulseWidth is increasing, I think due to Lambda-regulation since the lambda detects more O2 and interpretes the mixture as lean and tries to compensate that....
Author:  vicore [ Fri Oct 24, 2014 3:08 am ]
Post subject:  Re: [4g67] combustion failure while cruising
Meanwhile:
CAS, MAF and another ECU been tested... no change

Yesterday after starting the engine went fine for a minute... then it started again :(

Here's a video of it:
https://www.youtube.com/watch?v=7sR4KMPpQ6w
Author:  Flying Eagle [ Fri Oct 24, 2014 8:11 pm ]
Post subject:  Re: [4g67] combustion failure while cruising
Have you run the engine with the ISC (Idle Speed Controller) unplugged?

If the resistance intermittently changed, it could cause a very unstable idle but you could still have power with the throttle open.

Does the problem only occur at idle?

Erratic idling will cause timing compensation and related lean issues.

I would disconnect the ISC when you have an idle around 900 RPM and see what happens, and try driving around.
Author:  vicore [ Sun Oct 26, 2014 12:57 pm ]
Post subject:  Re: [4g67] combustion failure while cruising
Nope its rare occurring while idling. More often it happens between 1900 and 2500 rpm. I'll try your ISC-test when it occurs next time in idle, maybe I have more than only one problem :(

But thanx for sharing your ideas ;)
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