The GM Tech 2 is a military grade custom hand-held computer designed to enable the GM shop technician the insights and capabilities to diagnose and maintain their charges. GM has now replaced this system with a computer based MDI system. However, for vehicles like my 2007 Cadillac XLR or 2008 Cadillac STS-V, the Tech 2 can be a key diagnostic and repair tool.
As an experiment, I ordered a Tech 2 on AliExpress.com from NO.1 Auto Diagnostic Tool Store. I selected this source based on the AliExpress reputation level and number of reports.
I ordered the device on Sunday, and it arrived in Texas to my door on Wednesday — with free shipping and very good DHL service from Hong Kong to Texas!
After some initial user error, I was able to plug Tab A into Slot A and Tab B into Slot B and etc. With the Tech 2 properly connected I was able to read from and interact with my 2007 Cadillac XLR. I still have a lot to learn about the Tech 2 but for plug it in and see it work tonight was a success.
I will update this article as I use the No 1 Auto Diagnostic Tool Store Tech 2 a bit more, and will mention in future articles when it is in use. I paid for the item with my own funds, and no one sponsored this article.
Noting that in Tune 2 the 5500+ RPM response in baseline was better, I adjusted the PE table for Tune 3 to return to 1.176 from 5500 RPM+, (12.5:1) and kept 1.148 below that point (12.8:1). So from start, Tune3 basically ONLY has this change from stock.
The intake air was 6F hotter now at 88F, and I adjusted Virtual Dyno 12 lbs for 2 gals missing fuel. The red line was from Tune2 this morning, and the blue line is from Tune3 later in the morning. The engine coolant was now at 203F, and we are getting IAT retard where earlier we were actually getting IAT advance.
Calculated hp peak 310.7 hp at 6688 rpm, peak torque 305 at 3328 rpm.
I think we see that, assuming they are equivalent below 5500 RPM, tune3 in blue has a better trend from 5500 rpm up than tune2 in red. The difference is however subtle.
First, I wanted to adjust the tune to recognize that we have E10, or gas with up to 10% ethanol. This gas has a lower stoichemic makeup, and an ideal ratio is 14.2:1 air:fuel instead of non-alcoholic gas at 14.7:1 air:fuel. The Cadillac factory tune assumes 14.7:1 fuel. I set the tune to 14.4:1 since we have an uncertain mix of alcohol in the fuel.
Second & Third, in our Texas heat the Cadillac is just on the border of heat retard from engine coolant temperature and intake air temp. I addressed each of those to move the ‘border” a few degrees higher and get that retard out. We’ll look for any sense of knock or knock retard on these runs just to be careful.
The two test runs with those changes appear to have lost 8 hp and 5 lb ft of torque. Not what I hoped. In this graph the red/blue runs are from earlier today, the green/yellow runs are from after the tuning changes.
The stoichemic setting change had the effect of moving the XLR 0.3 richer on in AFR, which is not what it appears to want. The other changes allow it run a bit more timing. My sense is we need to keep the AFR, but I am uncertain if the Wideband O2 sensors in the XLR are auto-magically compensating for fuel quality and driving to lambda for the current fuel, then reporting that as 14.7 AFR?
The calculated hp before/after is not as dramatic as the Virtual Dyno.
For the next tune I plan to replace Stoich at 14.7, and move PE from 1.176 to 1.148 (12.8:1). This will have the net effect of going the other way from baseline — taking the overall fueling 0.3 AFR leaner than factory tune from 12.5:1 to 12.8:1 in AFR terms.