Jackal air pressure sensor

[Rich A]

My Jackal has a low speed misfire and sometimes stumbles a bit at low speeds. I set the valves and TPS, and I checked the wires/caps and the exhaust for leaks.

Here's what I'm wondering. I'm in Santa Fe, NM (elevation 2190 m). The barometric pressure (BP) reading from Guzzidiag shows around 800. I'm assuming the units are hPa (mBar). But the actual BP today is 30.2 in Hg which is 1023 hPA, so there seems to be a big difference. Could that be causing the miss, and if so, is there a fix? (I can't find an air pressure sensor in the Jackal wiring diagram!)

Tnx--Rich A

[bigbikerrick]

Hey Rich, you are  at just a bit higher  elevation than me. I dont believe there is an air pressure sensor on these bikes. What did you set the TPS voltage at? I had to play around with mine to get it to not have a miss/stumble at around 2500-2800 rpms, then mess with the air screws to get the idle correct. They are a bit finicky. I remember having to re tune mine about 3 times to get it right. I dont have Guzzi diag, I just used a multimeter , and have 2 permanent leads where I hook it up for the TPS reading.
Rick.

[Kiwi Dave]

According to the workshop manual, the air pressure sensor is included in the ECU (see item 59 of the workshop manual page 5 of the Electrical System.

http://www.thisoldtractor.com/mg_manuals/workshop_manual_california_en_de_ne.pdf

[pehayes]

I think you have the 15M computer and that the pressure sensor is inside that box.  I have 98EV which uses P8 computer.  The wire plan for the 98EV is always a problem.  Some parts are correct for P8 computer and other parts are correct for 15M computer.  Carl Allison's  98EV plan shows that item #59 is a pressure sensor and inside a 15M computer.


98EV erroneous
http://www.thisoldtractor.com/guzzi007/schematics/1998_EV.gif

2000 Jackal
http://www.thisoldtractor.com/guzzi007/schematics/2000_Jackal.gif
Shows the sensor inside the computer.

Patrick Hayes
Fremont CA

[Wayne Orwig]

Yes, the Jackal has the 15M. The sensor is inside the ECU box. If you look on the box there is a round plastic 'knob'. That is the vent to allow air in and out of the ECU to get to the sensor.

The air pressure sensor is going to just tweak the mixture. GuzziDiag allows you to tweak the mixture (though mainly affecting idle). If you adjust the mixture, does that help?

[Rich A]

I set the TPS @ 14x mV closed and 52x mV @ idle. The bike seems to run better with the CO trim way up (+80), and that seems to make some sense. I would think that if the ECU is using 800 as the BP, that would equate to less (20%?) air and 02, so it would meter less fuel, leading to a lean condition. I don't mind a work around, but I'd like to understand what's going on.

I've turned the air bleed out 1-1/2 turns and that seemed to have no effect, and I turned them back to all the way in. Opening them would lean the mixture even more, right?

Rich

[bigbikerrick]

Yes ,Rich , I believe turning the idle air screws out lets more air in and thus leans the mixture. I had no idea there was a barometric pressure sensor inside the ecu. Learn something new every day! My 03 Aluminum( hydro) has the 15 ecu, in the left side cover. A couple of years ago, I replaced my TPS with a HD unit, and now have the stock one back in, as there was nothing wrong with it. I originally thought it had a "dead spot", but it did not.   
 It ran pretty good with the HD TPS, but MPG dropped by 4-5 miles, so thats what prompted me to go back to the other TPS.
Good luck with it,
Rick.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

[Kev m]

The barometric pressure (BP) reading from Guzzidiag shows around 800. I'm assuming the units are hPa (mBar). But the actual BP today is 30.2 in Hg which is 1023 hPA, so there seems to be a big difference.

A couple of thoughts on this thread.

* Are you sure GD reads hPa (mBar) and not some other unit of pressure measurement. kPa would be too high, but 800 mm Hg would = 31.5 in hg. which would suggest the sensor is working properly.

* If the reading IS low, is it possible the passageway is restricted and can be cleaned at all?

* Air pressure IS not an insignificant input for the mapping of a Speed/Density EFI system, I'd call it a major factor.

* Air bleed screws - the primary purpose of the air bleed screws on this system are to set balance at idle. They are used to bypass a microscopic amount of air for fine adjustment (the coarse adjustment made by the linkage and the positioning of the throttle plates). Although I guess you guys are right in theory that they can lean out the mixture ever so slightly, I don't think that's going to have a significant effect on overall mapping or performance, even at idle. It should really be just an RCH in mixture input.

[Rich A]

A couple of thoughts on this thread.

* Are you sure GD reads hPa (mBar) and not some other unit of pressure measurement. kPa would be too high, but 800 mm Hg would = 31.5 in hg. which would suggest the sensor is working properly.

I bet you're right, i.e., that the BP units are mm of Hg (or Torr).  I still don't know why I have to set the CO trim so high.

Rich

[rocker59]

What clearance did you use on the valves?

.10mm intake and .15mm exhaust may help, if you've got them set tighter.

[Rich A]

What clearance did you use on the valves?

.10mm intake and .15mm exhaust may help, if you've got them set tighter.

I set them a little tighter 0.076 and 0.127, which I think is between the US and world specs.

Rich

[antmanbee]

I bet you're right, i.e., that the BP units are mm of Hg (or Torr).  I still don't know why I have to set the CO trim so high.

Rich

You have the TPS set too low fully closed, which will lean out your fueling. Set your TPS fully closed at 157mv. Then readjust the CO trim.

[rocker59]

I set them a little tighter 0.076 and 0.127, which I think is between the US and world specs.

Rich

I recommend loosening them up.  I've seen world spec clearances get rid of the stumble on several bikes.

.10mm intake and .15mm exhaust is the minimum I would set them.

 

[Rich A]

Thanks for the advice everyone.

Rich A

[rtbickel]

 One of these days I am going to have to drag myself into the 21st century and get the equipment and figure out how to do this kind of stuff since the nearest dealer is now 200 miles away.

[Rich A]

One of these days I am going to have to drag myself into the 21st century and get the equipment and figure out how to do this kind of stuff since the nearest dealer is now 200 miles away.

What's amazing to me is that it is possible to do this at all (basically for free), thanks to the efforts of a few generous and knowledgeable people. Many thanks to them.

Rich A

[Meinolf]

Hi,

wow, a wealth of misinformation (and some getting it right). Rich is using one of my BINs, so some clarification seems indicated.

Pressure sensor
is soldered onto the PCB inside the 15M/RC next to the plug. There's no passageway for the air to the sensor, the ECU box is not sealed. The sensor occasionally dies, use Guzzidiag to check if
a) the shown pressure in mBar/HPa is close to the actual one or
b) does the shown pressure vary in line with the actual pressure.
if neither is true, a (dirt cheap) replacement sensor can be soldered onto the PCB. Some experience in using a soldering gun  is recommended.

Air pressure is one of several factors used to calculated air mass. The original MG (and Ducati and other manufacturers of that time) BIN use faulty correction tables for air pressure and air temperature correction. I'm using correct(ed) trim tables in my BINs.

TPS base line setting
is 157mV!!! The value in the service manual is wrong!!! Someone at Guzzi or Marelli didn't divide and round the result correctly. Getting the 157mV with a completely closed throttle is the major contributor to matching throttle opening in degrees to the voltage coming from the TPS. It's not so important at larger TPS openings but very important at the low load points.

Bypass valves and CO trim
are heritage tools (pre-GuzziDiag time) for sync'ing the cylinders and setting the idle speed. My BINs are designed for totally closed bypass screws and CO trim set to 0. Why? Because totally closed is easier to duplicate than one and xxx turns of two screws with tips fitting into a receptacle inside the throttle body. How would you know who last applied which torque to these tiny screws and their seat and deformed them?

Idle sync and idle rpm setting
are best done with both throttle stop screws. NOT with bypass screws. Get a beer, take some time and take a close look at the throttle opening mechanism and the involved bearings. Idle settings is pressure oriented versus the draw effect when opening the throttle.

Valve play
with the original camshaft should be at least 0.22mm for intake and exhaust. The ramp up part of the original camshaft is infinitely long, the factory recommended settings lead to a valve opening of ~0.1mm for more than 100° crankshaft rotation. Save the indicated mean pressure and give the valves more time to conduct heat to the valve seats. 0.25 to 0.30mm are the valve play values you should use.

Cheers
Meinolf