Motronic AIT Sensor Modification

[dirtrider]

Afternoon legarem

 

Your 1150 Ma 2.4 system does have a fairly dynamic ignition control system but I would be really surprised if it is pulling any spark advance out at 68°f (20°c).

With you having the IAT disconnected that pretty well locks the spark trim to around 20°c. I just can't see spark advance removal at that low of an intake temp.

 

In the automotive systems I have worked with in the past I don't see much of any spark advance trimmed out at intake temps below the mid 80's°f (26-30°c). The big spark timing reductions come in on turbocharged engines as intake temps can really climb as the boost pressure goes up. There can be some serious spark trim reduction on turbocharged engines at elevated intake temps.

 

I don't have an IAT spark trim chart on the BMW 1150 Ma 2.4 but it would be a real outlier if it pulled spark at only 20°c.

 

I don't know what CCP you are running but you need the correct CCP to get the best spark curve for your engine. I haven't worked much with CCP's on the twin spark but the pink was always best on the 1150 single spark.

 

[roger 04 rt]

Afternoon legarem

 

Your 1150 Ma 2.4 system does have a fairly dynamic ignition control system but I would be really surprised if it is pulling any spark advance out at 68°f (20°c).

With you having the IAT disconnected that pretty well locks the spark trim to around 20°c. I just can't see spark advance removal at that low of an intake temp.

 

'''

 

 

 

Hi DR,

What do you think of the possibility that, with the IAT disconnected, and the Motronic knowing that it must run using the 20C fueling table no matter what the temperature, that the spark would be retarded as a "limp home" condition? This so that if it was cold out (say -20C) (and it knows it has no way to know, there's a mouth full !), with the mixture now 12% leaner than stoic because of the outside air, it would pick a safe timing.

[dirtrider]

Evening Roger

 

Modern ECU's don't use much of a Limp Home like the older units did. No real reason to as they just ignore the errant sensor & use the remaining sensors to go on fueling & sparking. In some cases they might insert a standard default (like the IAT does). We sort of have to assume BMW fuel handling engineers figured the 02 sensor would keep the fueling close even at -20°c with a failed IAT sensor.

 

Put a GS-911 on the the 1150 & it should show around 68°-70° (20°c) with the IAT disconnected. That is what the Motronic sees for temp input. Most cars do the same thing.

 

 

There's a lot we don't know about the Motroic 2.4 but it is based on the automotive version so should follow basic automotive logic. But like anything else until proven you just never know for sure. Common sense logic says no open circuit IAT spark retard but BMW being involved says who knows for sure.

 

 

If BMW assumed a failed IAT sensor required reduced ign timing due to lower temp ambient intake air then why wouldn't they also assume it needed a richer mixture at failed IAT?

 

[roger 04 rt]

Evening Roger

 

Modern ECU's don't use much of a Limp Home like the older units did. No real reason to as they just ignore the errant sensor & use the remaining sensors to go on fueling & sparking. In some cases they might insert a standard default (like the IAT does). We sort of have to assume BMW fuel handling engineers figured the 02 sensor would keep the fueling close even at -20°c with a failed IAT sensor.

 

Put a GS-911 on the the 1150 & it should show around 68°-70° (20°c) with the IAT disconnected. That is what the Motronic sees for temp input. Most cars do the same thing.

 

 

There's a lot we don't know about the Motroic 2.4 but it is based on the automotive version so should follow basic automotive logic. But like anything else until proven you just never know for sure. Common sense logic says no open circuit IAT spark retard but BMW being involved says who knows for sure.

 

 

If BMW assumed a failed IAT sensor required reduced ign timing due to lower temp ambient intake air then why wouldn't they also assume it needed a richer mixture at failed IAT?

 

Good Evening DR,

 

You've hit on a number of points. Good post.

 

--The GS-911 does read back 20C. And the Motronic responds with an error code and the stock 20C fueling pulses, independent of temperature.

 

--The O2 sensor feedback serves an important function in covering the failure of many sensors once the engine is warm. You've made a great case for why a Closed Loop approach to richer mixtures is better than any Open Loop solution. Multiple failure coverage.

 

--They had to peg the fueling to the middle of the range so that temperatures higher and lower would start and warm up, so the O2 sensor could then lock on and ADAPT!

 

I think we are teasing out many of the functions of the Motronic and I see no reason yet to believe that the Motorcyle Motronic is not a close derivative of the Automotive Motronic--we're just missing the Check Engine Light.

 

RB

[legarem]

Hi DR and Roger

 

If IAT disconnected makes the Motronic look like it is 20C, At 20C with a BP or twin IAT in series, the Motronic should react like the temperature is 0C.

 

No IAT at 20C gave me better results than twin IAT in series. I use the pink plug.

 

By the MPG I did, it seems that between 53 and 55 MPG, I consider both twin IAT or no IAT the same for MPG.

 

Roger, i'll look at the voltage tomorrow with the twin IAT in series. The bike is warm and it will give false readings.

 

Going with a richer ratio than I have with the two methods I tried probably means a programmed wideband O2 sensor

[roger 04 rt]

Hi Legarem,

 

The question isn't so much what the Motronic does. I think it is certain, because I've measured it, that the Motronic drops to 20C fueling when the IAT is disconnected.

 

I have also measured that a BP does shift the temperature by 20C based on both the GS-911 report, and the 6% richer mixture as measured by the LC-1's measurement mode.

 

The question on my mind is, why doesn't your bike run better with more fuel, or how is it getting more fuel without an O2 or IAT/BP boost. Fuel pressure is the first thing that comes to mind.

 

Really though, if you want to know what's going on, the best thing to do is get an AFR gauge in the exhaust. Then all the inductive guessing will be over. In the meantime, I'm wondering if your Motronic IAT input resistor is damaged, leading to a wrong voltage from the input resistor/IAT sensor divider ratio. The open circuit voltage is good, but it's worth checking its resistance (nominally about 2.7K ohms, from memory). We know 5V open circuit, you will measure the connected voltage and the resistance at that time/temp and we'll calculate the input resistance. Then that question will be answered.

 

 

[roger 04 rt]

Hi DR and Roger

 

If IAT disconnected makes the Motronic look like it is 20C, At 20C with a BP or twin IAT in series, the Motronic should react like the temperature is 0C.

 

No IAT at 20C gave me better results than twin IAT in series. I use the pink plug.

 

By the MPG I did, it seems that between 53 and 55 MPG, I consider both twin IAT or no IAT the same for MPG.

 

Roger, i'll look at the voltage tomorrow with the twin IAT in series. The bike is warm and it will give false readings.

 

Going with a richer ratio than I have with the two methods I tried probably means a programmed wideband O2 sensor

 

I quickly measured things this morning.

 

Ambient: 21C

 

Motronic Report by GS-911 no Booster: 21C

Motronic Report with Booster: 0C

 

Open Voltage IAT: 4.95V

IAT to Motronic wire no Booster: 2V

IAT to Motronic with Booster: 3.25V

 

Note: Voltages are approximate, only using VOM, not DVM.

[legarem]

My voltages at 17C

 

Open 5 V

Double IAT in series 3,3 V

Single IAT (normal) 2.3 V

 

Taken with DVM

[roger 04 rt]

My voltages at 17C

 

Open 5 V

Double IAT in series 3,3 V

Single IAT (normal) 2.3 V

 

Taken with DVM

 

Nice work. My assumption would be that your IAT input works correctly. That the single IAT delivers normal fueling and that the double adds 6% to the fueling.

 

To go much further, you need to measure exhaust gas AFR or perhaps idle CO to get a handle on where things are.

 

DR mentioned measuring fuel pressure which sounds like a sensible step.

 

Of course you can just ride the bike but the Motronic is now working two sensors light (O2 and IAT) and is likely to produce a rich mixture when it's warm and a lean one when it's cold.

[JamesW]

Temp: 18C

Open: 4.97 VDC

Homemade booster: 3.34 VDC

 

measured with DVM

 

 

[roger 04 rt]

In order to generalize the open loop solution, someone needs to install an LC-1 AFR gauge into the stock O2 sensor so that we can tell what AFR the various configurations produce.

 

If someone had a spare LSU 4.2 Wideband O2, I would match it with my LC-1 and give it a try on an Eastern Massachusetts volunteer R1100 with MA 2.2. Is there anyone who has the sensor and would be willing to give it a try?