In times past I've purchased the sub $15 ELM327 BT adapter clones manufactured by the ChiComs for use with the TorquePro Android App. I believe I've been through about 4 of them so far, counting the one I immediately shipped back to Amazon b/c it wouldn't pair/connect with any phone/car combination I tried. I leave it plugged into the XJ6 for clearing the sporadically recurrent secondary air injection fault and for recording data from my morning commute as the whim strikes me. Normally, after some months of service, some of the data values get screwy (-40 Xmsn oil temp, for instance) and I'll order a replacement. Most recently, my latest clone developed a short and blew the Data Link Connector (DLC) fuse as reported elsewhere here in the forum.


So I reassessed and sprung for a higher-order device this time: IIRC, it is one of the models the TorquePro developer recommends. Additionally, I downloaded the included OBDWiz software to my Windows 8.1 tablet. After installation, I noted that TorquePro will still cut the fuel pump off on my diesel Excursion despite that I installed a "plug-in" that addresses "certain late 90's/early 2000's F-150 ECU's that would errantly shut the engine down. So it performed as did the clones on the Exc. I tried the OBDWiz and it was interesting and different from the TorquePro but still, recorded/displayed data start-up to shut-down as it should.


However, once I moved the adapter to the XJ, I noticed several parameters "frozen" a few minutes after commencement. A more studied view determined that "everything" coming from the ECU was frozen but GPS, barometer, and all phone-supplied data continued to update. When I tried the OBDWiz, it first presented me with a choice of ECU's to poll, one with 29 PID's and another with 9 available PIDs. I chose the 29. Hooked up and recorded the stuff you'd expect and after some minutes, reported a "communication failure" and asked if I'd like to reconnect. I should mention, with the frozen data on TorquePro, if I exited the APP and restarted it, I'd get new, fresh updated data for a few seconds before it would lock up again. But if I checked adapter status while it was frozen, it reported everything was fine and on the up-and-up! OBDWiz didn't play that game, but kept disconnecting every so many minutes or seconds, but when it was connected, everything was sweet. Trying to connect to the other module with 9 PIDS, just made the screen flash once and return me to the choice of two ECU's to connect to. Dashed any hope that I might somehow get Chassis codes or something out of it.


Anyway, this is new and peculiar behavior and I'm stumped as to whether something has gone dodgy in the OBDII interface in the car? Or if it is a peculiarity of the Scantool adapter? (I haven't yet tried it with the S-type.)


Next item that may or may not be related....as I'm shopping for tires, currently, I'm faced with the dilemma that although the 225-60X16 (26.6" dia) Michelin Primacy's have certainly served me well, currently hosting 78K mi. against a warranty of 60K, and Lincoln's head can still be buried in the tread, I fancy replacing them with Mich's new Premier A/S. However, that is not offered in the 225-60, but rather 215-60X16 (26.1" dia)or 225-65X16 (27.4" dia). I prefer the smaller vs. the larger but thought I'd see where my speedo was running vs. GPS accuracy to see if I was already on one side or the other of the nominal as-delivered spec. My recollection from former times when I recorded and analyzed my commuting data was that the ECU was reporting about 2.5 MPH less than the GPS at steady-state 70 mph. With my limited looks given my new OBDII adapter arrangement that still seems to be the case, with a lesser differential at lesser speeds as would be expected.


Now the puzzler: The speedometer needle tracks nearly spot-on to the GPS display. Everywhere, always. (Excepting and accounting that the GPS jumps around a bit on accel/decal and with curves and corners) But...but...I thought speed reported by the ECU was what the speedometer needle was supposed to be displaying? No? Separate sensing and computing systems? They are surely different values for the same parameter on my car. It would be believable that the 225-60 Pirelli's fitted at the factory were a close match in dia. to the 225-60 Mich's....so agreement with the GPS is to be expected...but why then is the ECU reporting a slower speed?


Jumping on to the next topic; tires....the 215-60X16's are offered in load index 95. Not a problem for me...I noted Doug's considerations in the tramlining thread regarding fitment of Load index 96 and by the same reasoning I see no problem; (but Jeffrey@Discount Tire certainly does! "I can't sell you that tire..") The tires are rated at 1,521 lbs each which would work out to 3,042 per axle or 6,084 lbs per car. The door placard puts max gross takeoff weight well below that, as well as considerable margins being available at each axle:





Now I realize this is a long and rambling post with, let's be honest, no particular point....but if you've slogged through til the bitter end with me....I'd be genuinely interested in your opinion as to the source of my intermittent data connection? my disparity between speedometer on the IP and ECU speed? and/or if I'm a devious and dangerous scofflaw for hankering to fit load range 95 tires with a paltry capacity of 6K+ pounds to my 5K lb car.....

 

It's a bit too late to ponder the bulk of your post. For now I'll stick with the load rating bit. Much easier

It's all a matter of 'margins' of safety.

The constant in the load rating system is that the rating is always taken at 35 psi for all passenger car tires. If you carry less pressure (intentionally or otherwise) the load capacity drops. And so does the margin of safety. Car builders and tire sellers like bigger margins, especially when it doesn't cost them anything to create them and insist on them....as, after all, 'tis you and I that must pay for higher tire ratings, not them.

Anyhow.....

It's easy to see how load capacity *could* get uncomfortably small if a person dropped down a 2 or 3 notches AND also ran the tires at the 'comfort' settings as shown in the manuals. What it is....26 psi or something like that?

As enthusiasts we're too well informed to let anything like that happen. Right ? keep the tires pumped up and you'll be fine.

The tire store guy is covering his butt. Can't blame him. Everyone wants to sue the other guy nowadays.


Cheers
DD

 

Thanks Doug, but the troublesome bit for me is that the specs from the Michelin site, Discount Tire, and Tire Rack all claim 1521@44 psi. So planning to run them at 35-36 gives me a bit of pause.....


Brought the tablet on this morning's commute and have confirmed the "communications failures" with OBDWIZ are several (but variable) minutes apart (2-10) whereas the freezes with TorquePro are on the order of seconds after comms are established (2-15 perhaps)

 

Certainly worth checking and verifying....but where are you seeing that?

For the Michelin, for example, I see max load of 1521 pounds and I see a max allowable pressure of 44 psi. I'm not seeing where the load rating is taken at 44psi inflation.

maybe I'm looking in a different place?

Cheers
DD

 

I think further research spurred by your comments has resolved it. The source was the table on Michelin's site where a column was headed "Max load" or some such and the cell entry was 1521lbs@44psi. Found all max loads rated at 35 or 36 psi depending on convention and so it is 1521lbs at 35 psi...but also 1521 at 36, 37, ....44psi.

Also found a load/inflation table and worked out for max wt conditions, I'd need to have 29psi in the fronts and 32 in the rears, as a minimum. ...but I'd normally be running 35....so academic...I think I'll pursue the 215-60X16 solution further once the alignment issues are sorted

 

Jaguar's repair manual for 95-97 X300 (Avialable in the download section) indicates TPI listed for JAGUAR RECOMMENDED tire fitments; ALL OTHERS S/B 44 PSI per their specs.