relying on gauges - really really long story - venting

[Guest MistressMotorsports]

When I had the race motor rebuilt last month, I decided to install a $650 EGT monitoring system that has one thermocouple for each exhaust port and a digital display for the cockpit. You can even set high/low alarms so that the display turns red if you go outside set parameters. Pretty slick idea. I decided to use the system to get a little finer tuning on the Webers. So, I put my base jetting in and check all the temps. At idle 4 are ok, one is a little hot, one cold. So, I stagger jet the idles thinking I maybe didn't synch the carbs well enough, and that I'll tune again at the track. Then I go up to Willow Springs where I can get some long top gear runs to tune the WOTs. Same thing, 4 holes are dead nuts, one is hot, one is cold, same bad holes as before. Lots of phone calls, questions, found that the sensors came with calibration certs, etc. I was pretty sure L28s never needed wild stagger jetting (like from 150 to 190 mains in differnt holes to get the temps to even out.) This really starts to bother me, I'm looking for vacuum leaks on the lean cylinder, tearing into the carb on the rich one, re-measuring jets, etc. Can't find anything, even the plugs look like they should when I lean them out or fatten them up. I go home pissed. So, the next weekend I decide, just for the hell of it to swap sensors between cylinders. Turns out the two sensors that read rich or lean ALWAYS read rich or lean regardless of what hole they were plugged into. So, now it's obvious that the motor/jetting/plugs were right and the sensors were wrong. I have the guys at House of Cobras (my engine shop) get all over the sensor guy. Sensor guy comes over acting all kinds of "you guys are idiots, these sensors are never wrong," and we proceed to show him that the abnormal readings follow the sensors. A light bulb goes on over his head. He's now worried that he made 300 sensors from a potentially bad batch of wire. So, all I want is a couple of known good sensors to replace the 2 bad ones. He goes away, I'm expecting to get a call that the sensors are in. The call I actually get is that he now thinks the sensors are fine, the digital display must be f****d, and he wants to see it. So now I have to get the damn display out of the car and get it to him, even though I'm really sure it can't be the display since we already tried plugging the sensors into different ports on the display head. Jeez. Guess I'll let him figure this out himself. When he finally gets it, I'm sure I'll get a good system, but the next race is less than 3 weeks away, so he better get on it soon.

 

So, just a warning, be sure to make sure your gauges are correct before making changes to your car. Fortunately, I never went lean enough to hurt anything, but I could have if I only paid attention to the gauge.

 

Sorry for the rant.

 

Mike

[DavyZ]

No, don't worry about ranting...this is a common complaint abut guages or sensors being incorrect in their readings, just like my spelling BTW

 

Pete and others have suggested always testing them first before fitting them to the car. I know Autometers are not the best, but that's what I'll put in the car anyway!!!!!!!!!

 

Davy

[Chaparral2f]

It seem like there are a lot of people like the guy who made the sensors who seem to think that the everybody is out of step but them. H:ope he gets his sh// together in time for you to go racing.

[Tim240z]

I too am very disappointed in the accuracy of gauges. I have all autometer ultralite gauges and you would think that they would at least be close?! I checked my temp gauge against the PCM (LT1 hooked up to my laptop and running freescan). That damn Autometer was at least 15-20 degrees high!!! (assuming that my PCM and its sender is accurate). Well, this jives with what Pete found with his thermometer test.

Tim