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Altitude compensation

553 views 9 replies 3 participants last post by  Steve_B 
#1 ·
I've got to thinking about this issue, but can't turn up anything in my reading.

I live at 1,300m here in Kampala. My S600 seems to be running a bit rich (based on smelling the exhaust).

The Bosch systems on my Jag V12 and my Porsche 928 have air pressure sensors to help compensate for higher altitude driving.

I can't seem to find anything similar on the S600.

So is the compensation for altitude done strictly by the Lambda feedback based on the oxygen sensors?

This leads to another question of the compensation map built into the LH computers, that I'm posting separately.

Cheers
 
#7 · (Edited)
The Bosch systems on my Jag V12 and my Porsche 928 have air pressure sensors to help compensate for higher altitude driving.

I can't seem to find anything similar on the S600.
I will have to chime in here and say that this is likely incorrect.

1. Jaguar uses Lucas ECU for fueling, not BOSCH
2. Jaguar XJS uses MAP sensor (manifold pressure = vacuum)
3. Barometric sensor is not found anywhere on the XJS platform except for the last two years of production (when they used the 4-speed GM 4L80e transmission) and the barometric sensor corrects the shift points. Nothing to do with fuel.

I am not familiar with the Porsche 928. Your M120 engine uses the same engine management systems as mine. As already said within this thread, there is a vacuum input to the EZL modules. Almost impossible though that the perceived richness is due to that. My understanding is that MAFs and coolant temperature will have a way more important effect. MAP signal is more critical for the ignition timing, but I could be wrong.

Steve
 
#8 ·
Steve,

Checking my notes: My facelift (1992) does use a Lucas, but its a Bosch licensed unit (Digital-P 26CU). As it uses Lambda feedback, it is very similar to the LH 2.2 (same era). The injectors are Bosch.

This unit also incorporates altitude correction, where the MAP sensor is built into the ECU. That's why there is a vacuum line running from the engine compartment to the boot-mounted ECU (who ever thought running a soft vacuum line under the entire chassis should be shot!). Even the FPR is vacuum regulated, just like the system in the S600, so that the pressure changes based on the engine load.



Cheers
 
#10 · (Edited)
Steve,

Checking my notes: My facelift (1992) does use a Lucas, but its a Bosch licensed unit (Digital-P 26CU). As it uses Lambda feedback, it is very similar to the LH 2.2 (same era). The injectors are Bosch.

This unit also incorporates altitude correction, where the MAP sensor is built into the ECU. That's why there is a vacuum line running from the engine compartment to the boot-mounted ECU (who ever thought running a soft vacuum line under the entire chassis should be shot!). Even the FPR is vacuum regulated, just like the system in the S600, so that the pressure changes based on the engine load.

Cheers
This discussion does not belong here (wrong forum :))), but since it is already ongoing, I will add a few more lines:

1. The EFI system in question has its roots in the Bosch D Jetronic system, true. But it is not BOSCH, and at least in the States, CANNOT be serviced by any shop specializing in European makes. Just try it!
2. O2-sensors for fueling (unheated and later on heated) has been state-of-the-art technology since the late 70s.
3. The Lucas ECU uses MAP, but no MAF. The drop in manifold absolute pressure is the only feedback (in conjunction with the throttle position sensor voltage and air/coolant temperature) the fueling computer uses. Above 2000 rpms or so, O2-sensor feedback is irrelevant. Guys that run these beats on the German autobahns report fuel economy (an oxymoron, apparently) in the single digits (mpg that is)....
4. The ECU is in the boot because that is perhaps the only dry place in the car.
5. The vacuum line from the engine to the boot is steel (!). There are rubber hoses at the ends only.
6. TPS (throttle position sensor) wiring is NOT shielded or coax.

Bottom line. As any V12 (double-six) from this era, the system is quirky. However, the computer-savvy Jag owners have one huge advantage on their side - MEGASQUIRT.

I have seen one. And coupled to a manual transmission....the combination is TOTALLY AMAZING!!! Can be done for less than $10K. And then moving the needle on the speedo past the 160 mph mark is as easy as 1-2-3-...
I am still drooling.

This, with a M120 is a six-figure project.

Best regards,
Steve

PS Please not that MAP is not for altitude compensation only. The MY '94 and '95 have separate barometric sensor that alters shift points (electronic transmissions)
 
#9 ·
Oh another feat of British engineering:

The signal cable from the throttle position sensor is a very small (22ga) coax. It too runs unprotected under the chassis from the engine bay to the boot. As if the TPS is not already starting life from a handicap by being Lucas...
 
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