My Kiwi3 OBDII device arrived today, and I have had an early go with it,
Initially I tried two free apps on my iPhone - Auto Doctor and the kiwi app. The AutoDoctor was very stable whereas the kiwi app kept dropping out and giving no data even through the device said it was connected. I therefore bought the ‘pro’ version of AutoDoctor as it should give me more info. One review said it is the app that works best with Apple devices..

I have discovered my rev counter over-reads by at least 100 rpm, up to 150rpm at some points (this is all below 3000rpm - haven’t looked at high revs yet).

Ambient air temp was 26’C when I was driving around. When warmed up, air intake temp, which I assume is beyond the inter cooler, was 20’-30’C above ambient, but most of the time around 25’C above ambient. When the throttle was fully opened, IAT initially would actually drop a few degrees (presumably the increase in cool air before the supercharger gets hotter), then come up again to about 25’C above ambient. When throttle fully backed off, temp actually rose to about 60’C (34’C above ambient), presumably because the supercharger is hot and there is minimal airflow.
I did 3 hard runs under full throttle on a short stretch of road a mile long, and the temp was pretty stable. I presume this reflects the fact the car had a new Bosch IC water pump a year ago. My air box and filter are standard, std Eaton M90, new Bosch water pump, but Powerhouse 110% lower drive pulley.

Tonight I have finally worked out how to get MAF readings, so will see what my max is tomorrow if I get a chance.
Also when I get to go for a long drive, I will see if the temp rises.

 

Today I played with Auto Doctor Pro app a bit more.
I have attached some graphs of real-time MAF and revs, excuse kid-crayon annotation, but it was the best I could do on the side of the road before I forgot which was which.

firstly, % throttle opening - I can barely get this value over 50 % even under full throttle. I think there is some incompatibility between the early Jag OBDII software and the readings I am getting. I am fairly certain my throttle is wide open, given the power I’m getting

Secondly, MAF readings - these are in g/sec, and I think there is a magnitude of 100 needed. I can get up to 2.2 g/sec under full throttle, as seen on the graphs. The max flow for an XJR MAF meter is 1022kg/hr (divided by 3600 secs/hr) = 284g/sec. I think I’m getting up to about 220 g/sec, but I would be interested in Andy’s interpretation of this.
I have a Powerhouse 10% overdriven supercharger pulley, yet seemingly I cannot max out my MAF meter, assuming my assumptions above are correct. This might improve if I had a set of decent extractors..

Thirdly, there is some real rubbish, eg: fuel consumption 0.1L/100km. However the engine temp is interesting, mostly around 93’C, but sneaking up to 100’C after a hard run up a hill. This pushes the dash temp gauge well past “N”, which it never normally does when the OBD device is not connected, and I wonder if the OBD device somehow makes the dash temp gauge read more accurately instead of being a ‘dummy gauge’ as many people say it is.. I will remove the OBD Kiwi3 device in the next day or two and see if the car’s temp gauge reverts to its old behavior.
I did some full-throttle runs with
1. Paper filter and box together, as standard,
2. Box and snorkel together, but paper filter removed
3. Paper filter only, lid and snorkel removed,
4. No filter and no lid.

The graphs are below (note the MAF is always the lower line but they’re not all the same color)
If you look at the MAF reading at, say, 5000rpm, it is almost exactly the same regardless of filter or lid, which leads me to think there is not much restriction in the paper filter and snorkel/box. However I didn’t go back to my old K&N pod, because the relays are now in the way of that set-up. Also, this isn’t ‘cold air’ induction, especially since it was 26’C when I was doing these runs.

 

I tried to edit and add to the above post, but it seems I can’t edit 24 hrs later.

One other interpretation of my max airflow readings is that I have the conversion factor wrong and I am actually maxing the MAF put on each graph. I am assuming 2.2g/sec needs to be multiplied x100 to give 220g/sec, given that the known max for an XJR MAF is 284 g/s

In next day or two I will swap in a brand-new XJR MAF that came in the post today from Worldcarparts, and see what numbers that gives. I bought a new one a month ago, which seemingly is faulty as the car wouldn’t idle, but kept stalling. They have kindly replaced it.

I am hoping Andy will confirm there is a conversion factor required from the mid-90s Jag OBDII outputs and the modern OBD readers and software.

 

 

My XJS and both my XJ6s needed the throttle cable adjusted to allow full opening of the throttle plate. Actually on mine the cable was also in the wrong hole in the bracket that holds the adjuster. There are two holes in the bracket one has M and the other has A molded into it. All of mine had the cable in M (for manual) instead of A (for automatic). I don't know if there is a difference in cable pull with the different hole positions.

 

Thanks Scotlad

I searched X300 cables and found this useful old thread.... https://www.jaguarforums.com/forum/x...e-cable-48809/

Prior to slightly tightening the cable, I removed the stopper under the accelerator, not realizing it is probably a kick down switch (which doesn’t matter as my car is converted to manual), but by unwinding it I’ve ripped the wires out... I wasn’t expecting a switch as my base-model 3.2 has mechanical kick down .

Anyway, the pedal goes a bit further to the floor, and the max throttle opening has gone from 51% to about 57-58%, which has improved my 80-120km/h acceleration time in 3rd gear by 1/2 to 1 sec, from about 5 to 4-4.5 secs. And MAF max is up from 1.8g/s to 2.0 g/s(probably multiply 100x). I can push the pedal past the floor stud, but all I get is a pulley squeal, possibly supercharger but don’t know..

 

You should also try and verify by observation (of the butterfly) if the throttle is actually opening only 50-60%. The figures you are seeing is an interpretation of the signal provided by the TPS. If the TPS is faulty or not correctly adjusted then you could see a low %age even if the throttle is actually fully open.

 

I think I will get my mechanic to check it next time it’s in. The car is pretty quick, and I think it is probably fully opening but the data doesn’t match. Because it’s XJR I can’t easily see the throttle, and I don’t have a hoist. But it goes faster than I’d expect if only getting 55-60% of full throttle opening.

 

Turns out the bare bit of cable at the throttle body end is frayed and bunches up when the gas pedal is pushed, then jams and blocks full opening.
The cable part number seems to be unobtanium, so my mechanic is going to make a new one using the old cable ends (?lugs -forgotten the proper word ). Hopefully that is the solution...

 

If you visit a aircraft hanger you might find someone to swedge on a new terminal on a new cable . I found mine frayed as well some months ago . You would have to remove it at the gas pedal and slide it out of the housing . The MAF rate above 225 g/sec seems about right as I calculated it at isobaric conditions somewhere above there at around 270 for 6000 RPM ( on a piece of paper somewhere ) . The intake gas is at a vacuum so it would be less then my calculation . There is a " saturation ' point on the curve in the sensor voltage vs. Maf values that limits the meter from reading accurately on the high end . From my understanding the reason for the different MAF meter for the S/C engine . If you see 5 g/sec at idle ( after the multiplication factor ) you should be interpreting the data correctly all the way through the throttle range .

Have you seen your STFT ( 0.0 ) as the ECU calculation and final regulation result and the physical angle of the butterfly at the 50 % or so ELM327 reading ?

 

Thanks Lady Penelope - I haven’t looked at all the fuel trims
I did email Andy, and he confirms the air intake temp sensor is after the intercooler, just prior to the air entering the cylinder head, in fact between the runners to cylinders 2 and 3.
He also confirmed the MAF numbers need multiplying by 100 to get g/sec. it actually measures 1/10th of kg/sec.

 

I got the Buzzbomb back from Mark my mechanic. He has made a new throttle cable as the old one was frayed and jamming. A new one is seemingly unavailable.
On a quick trip around the block tonight, max throttle opening was up from 56% to 95%, and max MAF reading from 200 to 265 g/sec.
What a difference. It is a different car. I haven’t been out on the open road, but I will have a go tomorrow, see what my 80-120km/h time is now. It was about 4-4.5 secs in 3rd gear before. I would expect it to be quicker - maybe 3.5secs.

As an aside, in my ongoing quest for MAF meters, I found a used genuine LNA1620AA for XJR on UK ebay for 50 quids and snapped it up. They don’t seem to come up very often. Once that arrives I will compare its max airflow with my existing genuine and new generic MAFs. I think my new Worldcarparts one reads about 10% lower than my genuine old one. I will post the results.

 

Good find on the reason for the butterfly not going fully open and getting a 30 % increase on MAF . I thought my theoretical flow rate calculation at speed was off , but it matches pretty close . My ELM327 lost it's key so I'm out of business on that as well as the downpipe removed for a crack . Still waiting on my retirement check .