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Tech Area => General Buick Tech => Topic started by: richmobj on April 16 2013, 06:21:34 AM

Title: Cross counts on scanmaster with O2 sensor unplugged
Post by: richmobj on April 16 2013, 06:21:34 AM

I have a fresh rebuild on my engine, 42 lb injectors, TT chip, hot wire kit, MAF translator, 43 psi fuel pressure line off at idle.  When I start my car it smokes and runs very rough for a short period of time, stinks of fuel, then it stalls out.  I figured that the problem was caused by a leak in my drivers side header (smoke poors out of the previously welded crack) which was making the O2 sensor tell the ECM to dump in more fuel.  I ordered a set of new headers (TA performance) to correct the problem. 

In the mean time, to verify my diagnosis, my buddy told me to reset the ECM and then unplug the O2 sensor and start the car to see if the car runs a little better since it should go into open loop on a cold start.  I did this and the car still ran rough which  tells me that I have another problem besides the leak in my header.  While performing this test, the thing that surprised me is that the "CC" section on the Scanmaster kept counting up with the O2 sensor completely unplugged.  Is this normal? 

Title: Re: Cross counts on scanmaster with O2 sensor unplugged
Post by: motorhead on April 16 2013, 10:08:11 AM

$5 says the cam sensor is out of spec.

Title: Re: Cross counts on scanmaster with O2 sensor unplugged
Post by: richmobj on April 16 2013, 10:13:49 AM

What's the cam sensor have to do with Cross Counts showing up with no O2 input?  The Cam sensor is new, installed at 25 degrees after TDC with window opening 180 degrees from the notch for the cap.

Title: Re: Cross counts on scanmaster with O2 sensor unplugged
Post by: earlbrown on April 16 2013, 12:33:30 PM

Did you run the 'unplug the O2' test with fuel fouled plugs?   As far as the CCs going up, that's just crazy. just one more reason the scanmaster can't be trusted as a troubleshootin g tool.


Don't forget the basics when troubleshootin g.  You could end up waaaaaaaaaaaaa y down the wrong path.

Title: Re: Cross counts on scanmaster with O2 sensor unplugged
Post by: motorhead on April 16 2013, 01:06:45 PM

Quote from: richmobj on April 16 2013, 10:13:49 AM

What's the cam sensor have to do with Cross Counts showing up with no O2 input?  The Cam sensor is new, installed at 25 degrees after TDC with window opening 180 degrees from the notch for the cap.

Because it is probably 180* out despite what you think.

http://www.gnttype.org/techarea/ecmsensors/camsensor_FAQ.html (http://www.gnttype.org/techarea/ecmsensors/camsensor_FAQ.html)

8.

This brings up some more points. (Might as well be thorough) What happens if you set the cam sensor 180 degrees out? For ignition, nothing. The plug that was supposed to be on compression will now be on exhaust, and vice versa. The car doesn't care! Ignition will be perfect. Fueling, on the other hand, is a different story. More on that later.

11.

So, I hope everyone's convinced that adjusting the cam sensor has absolutely no effect on ignition timing, but can only cause a no-start or tremendous backfire & stalling if running.  A stretched/slipped timing chain therefore also has no effect on ignition timing.

12.

HOWEVER, adjusting the cam sensor has a tremendous effect on FUELING, as the SFI syncs off the cam too. I don't know much (yet) about the fueling specs, but it apparently has a much narrower window than ignition in order to sync to the wrong cylinder. This is why if you have the cam 180 deg out the car will run terribly because the fueling is all messed up. Basically it'll be in a SFI mode where fuel is puddling for 1 rev before being sucked in.

Title: Re: Cross counts on scanmaster with O2 sensor unplugged
Post by: richmobj on April 16 2013, 03:47:45 PM

Okay, I'll go check the cam sensor again.

Title: Re: Cross counts on scanmaster with O2 sensor unplugged
Post by: richmobj on April 16 2013, 05:52:41 PM

Okay, you were probably right.  I'm going to change out the plugs and wires though before I fire it up to be sure.  Thanks for the advice.