Having a hard time getting acurate a/f readings. The tail pipe readings show 15-17/1 from idle to redline. Is this just a bad place to get a reading. I know the best place would be after the turbo and before the muffler, but no room. I have a bung at the Y pipe just before it goes into the turbo, but don't know if that's accurate.
The motor has 1300 mi since complete rebuilt. The dyno runs are showing 11-12/1 range. After the motor was installed it went back to get rechecked. The exhaust pipe is dark brown to black which would indicate a richer reading.
It goes back to the shop in a few weeks to get checked, but was wondering if there is anything else to check.
I tried the LM1 on two other n/a cars and it reads fine.
thanks,
Harold
'79 930/DP935 3.5 twin plug.
http://www.dp935registry.com/

 

Harold, were the dyno runs on an engine dyno or chassis dyno. If chassis, did they insert the probe in the exhaust tip or did they use the bung at the Y? wb sensors accuracy will be effected by the pressure at the Y location as well as possible overheating of the sensor housing. Also, I'm not sure if you have any catalytic converter installed? If not, my first thoughts would be that your not probing deep enough from the exhaust tip and are getting some reversion, or you have some air leaking in from exhaust joints(both problems I had when I first installed my LM1) or more seriously that your lean readings are correct. My o2 sensor is currently mounted about 10 inches from the tip with a fabspeed single out exhaust and I'm getting good readings. If your using innovates clamp on probe, I'd be suspicious of it.

 

Engine dyno. If you look at the shot you can see a sensor at the right end of the muffler. I tried the LM1 sensor there and at the end with the bracket and got the same readings.

 

Harold, I'm not familiar with the construction of that muffler so bear this in mind. The fabspeed I use is similar in appearance, but if I installed my sensor in that location it would be in the batting material and not in the direct flow of exhaust gas. In fact at that 180 end, my exhaust tubing has no perforations in it, so measurement there would be awful. Are you familiar with the internal construction? The sensor should be directly in the flow. That being said, it is very common for conditions to be very different between the engine dyno and in car as many variables have changed. I would for now be concerned that the lean #'s are correct and not run/test the car on boost until you are sure. The results even briefly could be catastrophic. Talk first to your mechanic and get a chassis dyno done but approach load with a close eye on a/f. Could be as simple as the wur boost line or low fuel pressure.

 

I pulled the end plug out and put I light in there. No batting, 2 chamber, and it's a straight shot out the exhaust pipe. After the motor was installed the shop checked all the settings. It was also smogged a month later. I won't be drivng the car until it goes to the shop. I'll be adding an a/f gauge after this gets sorted out.