Lambda Goes Lean on a Twinspark with Emerald ECU - Alfa Romeo Bulletin Board & Forums

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post #1 of 7 (permalink) Old 03-02-2017, 11:32 AM Thread Starter
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Lambda Goes Lean on a Twinspark with Emerald ECU

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I've been running my Twinspark on an aftermarket ECU for a while. It's an Emerald K3. I have Spica Throttle bodies and no AFM or MAF. Using MAP, but currently I am not doing anything with the signal. I have a Wideband 02 sensor with a PLX controller to do adaptive (learning) mapping. So currently the car is mapped with RPM and TPS.

Every week for that last few, I've been reading the adaptive corrections and writing them to the fuel map. That's going OK. There are a few edits as I go through different driving conditions.

Last week I experienced a bit of stumbling at low throttle positions. RPM between 2500 and 3500. Sort of like when cruzing, easy on the pedal. I opened up the live screen on the laptop and when this occurs, the Lambda reading goes full lean. This week when cold it is very bad, but settles into only stumbling a little when fully hot.

Did a search here and online and found many people who have seen this say the sensor goes bad this way. Especially with the type of sensor that I have. It's the LSU 4.2 variety which is prior to the 4.9 which is longer lasting and more reliable. I got a new one. This did not change the stumble.

To verify, I turned off the adaptive mapping and the closed loop mode and am just running on my fuel map, open loop. The 02 reading should not affect the running of the car. It still stumbles.

Others have also mentioned air leaks. Exhaust leaks would affect the 02 reading, but not the running of the engine if the 02 is disabled, as I have it. Intake leaks would affect the running if the intake air were metered with an AFM or MAF since the ECU would have a false reading. I don't have metered intake air. I think air leaks is not my issue. Is my thinking sound here?

I am left with thinking that one or more injectors is not squirting. What do you think of my conclusion?

If that is the case, are there any suggestions on how to determine this? I have a fuel pressure gauge near the FPR and the fuel pump is a loud one. The fuel pump sound is constant when the stumbling happens and the guage reads fine 41-44 PSI all the time.


It could either be a fauly injector or an intermittant signal to the injector. Does a fauly injector behave this way? I don't know injectors all that well.

I am doing batch fire, so there is only one wire from the ECU firing all injectors. I did it this way because I am using the stock harness and the Bosch ECU fires them this way. The Emerald folks suggested that I use separate wires, but said one driver could handle the load of 4 injectors with no problem.

Is there a way to measure the signal to the injectors while the engine is running to associate the dropout to the injector signal?

Hoping this is common enough to have some simple solutions.

Thanks,

Stefano
Concord, CA
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post #2 of 7 (permalink) Old 03-09-2017, 02:30 PM Thread Starter
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I have some more info. I think it has something to do with my Throttle Sensor.

When the car is off, with the ECU on, I look at my live screen and move the throttle and I can see the % value rise perfectly. It can go from 0 too 100% and stay at any value if I hold the throttle there. So I can hold the throttle at 50% and the throttle % value on the live screen shows 50. Perfect.

When the car is running, it doesn't do that. When I move the throttle fast, the live screen will register it increasing in % to 15 or 20, but it drops down to 1%, 2% even 0%. Even when the throttle is depressed in the realm of 20-30%. Looking at the injection table while the engine is running confirms this. The live cell is jumping around at the first two rows relating to the first two TPS values, even though the rpm is in the 2500 to 3500 range. First Pic is the injection screen showing the zone the cells jump around when the throttle should be about 20%.

Rev-ing it works briefly and the live screen % value increases, but always drops back down to nothing.

I wiggled the connector while it was reading low and throttle depressed and no change. The connector is factory crimped. It seems tight. If it was crimping related, it would have to be at my ECU connector crimp, but that is inside the cabin and don't know how the running of the car would affect that. It's protected from heat and vibrations.

All I am left to assume is that the TPS is faulty when the car is running. Vibrations, maybe? I hope that this kind of failure is common and can get some confirmation. It is pretty accessible and I can replace it. I guess I will proceed with that right now. I don't think they are too pricey. My TPS is the style of Pic 2.
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Stefano
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Last edited by iachella; 03-09-2017 at 03:21 PM. Reason: spelling
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post #3 of 7 (permalink) Old 03-11-2017, 06:07 PM Thread Starter
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Does anyone have any experience with erratic TPS signals?

I have improved things. But hoping for some expert knowledge.

I replaced the TPS with another that is I think higher quality. The jumpy signal is still there, but not as bad. It seems to drop to zero less often and for shorter periods of time, so I think the ECU is not reacting to it in time. I have also read that grounding some sensors to the engine can introduce interference. The stock wiring harness of the TS has all the grounds on the valve cover. I removed them and bound them all together and connected a thick wire to the chassis. There also is an offset value to the TPS signal that can be set in the Emerald software. I chose a value that corresponds to just depressing the throttle a tad. The combination of these things makes the car drive fine, but I can still see the TPS signal jumping up and down a few cells when holding the throttle steady.

The MegaSquirt software has a signal smoothing feature that would come in quite handy at this time. I have read on those boards that people have had this issue and solved it with this smoothing function. I will see if the Emerald folks know of this problem and have a solution.

I am wondering if a Bosch style TPS is more robust. The end plate on my Spica Throttles was drilled to accept this GM style of TPS, so it may not be that easy to just change it. Maybe there is a version of the GM style one that is more robust?

Any knowledge out there?

Stefano
Concord, CA
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post #4 of 7 (permalink) Old 03-12-2017, 07:34 AM
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Stefano,

The first thing I would suspect here is grounds. I know there is a lot of stuff written up on that for the MegaSquirt. My guess is that you've got a lot of noise on yours when the car is running which could cause problems like you are seeing. If you do some searching around on that you should find some things to look at.

Here some basic info for the MS that I used:

https://www.diyautotune.com/support/tech/other/grounds/

Wiring and Sensors

Kevin

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post #5 of 7 (permalink) Old 03-13-2017, 11:49 AM Thread Starter
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I removed the grounds from the valve cover. It improved (but I have a new TPS, too), but has not completely gotten rid of the fluctuations.

I am wondering if other grounds should be isolated from the TPS ground.

Stefano
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post #6 of 7 (permalink) Old 03-19-2017, 08:31 AM Thread Starter
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It does turn out to be the grounds.

The TS wire harness has all the grounds bound together in 4 ring bundles and then bolted to the valve cover. Two of them feed back through the harness to the ECU connector. The Emerald ECU has two ground pins labeled ECU ground and Sensor grounds. I used both pins with both the ground wires, so I had separate wires going all the way to the ring bundles.

The Emerald folks do not recommend that they be tied together, but I did not pay attention to that because the wiring harness was a factory piece and so I assumed that the Bosch people knew what they were doing. It has to be better than doing it yourself, right?

For whatever reason, no. But, since I had run both grounds, it was fairly easy to isolate the two and ground the ECU to the chassis and bundle the others and keep them off of the chassis or engine. The TPS signal is rock steady now. Maybe some other sensors will have a cleaner signal now too.

I just need to clean things up a bit. It doesn't look nice with 6 or 7 ground wire rings with a nut and bolt through them hanging out in mid air.

Other aftermarket ECUs are probably similar. I just wonder how Bosch could get away with it without problems.
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Stefano
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post #7 of 7 (permalink) Old 03-19-2017, 09:02 AM
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Good question. The Megasquirt also says to isolate ECU and sensor grounds.

Kevin

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