Megasquirt and Rough Idle??

[Kingsstar]

I just bought a 92 Talon Tsi and its idleing rough. It idles between 900-1050, but its never constant, what could cause this. When i start it up it doesnt want to stay running untill the engine warms up. I have to give it a little gas to help it idle.

Thanks

 

[mobythevan]

The ASE (after start enrichment) needs to be adjusted to fix the problem with starting it cold and it dieing all the time. You need to make ASE longer and up the percentage (longer, like 20 seconds).

As for idle being inconsistent, what size injectors is it running? and check to see if EGO correction is active while it is idling, that will cause it to fluctuate.

 

[Kingsstar]

Ok, so i checked the ASE and it was running in cycles so i switched it to sec, but whats an ideal setting? It has 850cc injectors and the EGO is at 100.

 

[mobythevan]

With 850cc injectors you are going to need to set all the values in the VE table the same around idle(500-1200rpm and 20-40map approximately), otherwise it is going to fluctuate a lot with that big of injector. At idle you basically don't want the injector pulse width changing. I am running 850cc injectors on mine and that is what I did to fix choppy idle.

The ASE is just something you have to play with everytime you do a cold start. Try a length of 20 seconds and then everyday at cold start try upping the percentage 5% and see if you start affecting it. It takes a while because it is hard to get back to a cold start condition.

I am assuming that you are running a version of the MSnS_Extra code so that you have more options for ASE. You may also want to upgrade to 029 type code to have the latest cold start options available. One of the big problems is that the older codes would always do ASE, so once it was set up good and you stopped to fill up gas, then it would be very rich for 20 seconds, but I believe the newer codes actually look at coolant temp and skip ASE when warm.

If you get stuck I can send you my msq file for MSnS_Extra024s13 code, but I haven't worked on cold starting with this car yet becuase I am changing throttle body first. But it might help you with the VE table around idle to see what I did???

 

[GVR4592]

Does MS have a warm-up enrichment based on coolant temperature as well?

 

[mobythevan]

Does MS have a warm-up enrichment based on coolant temperature as well?

It does, but the options are not very good in some of the early codes. It is best to run 029 version of the code to have all the features available for warm up enrichment. That allows steady erichment for some time then decaying, or decaying over entire time, etc

Also looks at coolant temp to see if erichment is needed at all, where some early codes always used enrichment, ignoring coolant.

I had the cold start working very well on my Datsun with L28et using only a bosch air regulator, the bi-metal type that run coolant through the sensor. I haven't had much time to play with it on my Talon, and I don't want to until I swap throttle bodies and remove the ISC completely, since megasquirt can't control it anyway.

 

[GVR4592]

Just trying to clarify this. You can add enrichment based on coolant temperature over a selected period of time, but you can't add enrichment based solely on coolant temperature?

 

[mobythevan]

you can have both

the enrichment over time from startup is the after start enrichment (ASE), user specifies the amount of time, percentages and decay method over the time

there is also enrichment just from coolant temp and that is just called warmup enrichment in megasquirt. This has a table for the various temps that you setup, temps and percentages.

I might have been confusing the issue, when I said the enrichment ignored coolant reading in earlier codes I meant ASE only.

 

[GVR4592]

OK I see what you're saying. That's pretty much how AEM works.

With AEM as soon as the engine exceeds minimum cranking speed it uses the "Start Extra" table to add enrichment. It add's the specified amount of fuel based on coolant temperature, it also uses the "Start Extra Decay" table to specify a specific amount of time for "Start Extra" to add enrichment also based on coolant temperature. When that time exceeds, it then switches to the "Warmup Enrichment" table. The whole point is to add some additional fuel after startup to stabilize the idle until the "Warmup Enrichment" table can take over.

Usually we leave the "Start Extra" alone until we optimize "Warmup Enrichment" and the main fuel table. A lot of the idle issues caused by AEM are due to a lack of resolution in the main fuel table in the idle area's, we usually change it a bit. After that it usually idles pretty well. Can you change the resolution of the numbers in the main fuel table with MS?

 

[mobythevan]

I am not sure if this answers your question, but meqasquirt can only adjust the injector pulse width by a resolution of .1 milliseconds, this becomes a problem with injectors that are large like the 850cc. This is where I ran into trouble because at idle a change of .1 ms to PW is too much of a fuel change at idle, either way too rich or way too lean. That is where the high resolution version of the code can be used to allow I believe .001 millisecond adjustments. But that code at least in MSnS_Extra format is not used by very many people and is really new, so I haven't tried it.

Just by smoothing my main fuel table so that the ECU isn't trying to adjust fuel during idle I was able to get a nice idle that is a little rich, around 12:1 with 850 injectors and not running high resolution code.

The operation of ASE and warmup is basically the same in the MSnS_Extra029 code. That "start extra" type enrichment keeping you running while the pistons quickly raise in temperature and idle becomes easier to control.

 

[GVR4592]

AEM uses the main fuel table and a modifier called Microsect/Bit. If the Microsec bit is too high, a small change in the main fuel table can swing the A/F by a lot, causing an unstable idle. You can change Microsec/Bit to gain more resolution. So basically even if you change the a cell in the main fuel table by .1 milliseconds, the change isn't equal to .1 milliseconds because of the modifier. If MS had something like that you could change it and gain more resolution at idle and A/F tuning would be a lot easier.

Before I knew about this I couldn't get a stable idle any leaner than 13:1, now I have a very stable idle at 14.5:1

 

[Kingsstar]

Yea, if you wouldnt mind sending that file i would really appreciate it.
Thanks

 

[mobythevan]

Yep, that is the problem, MS doesn't have a way to modify that resolution unless you go to high resolution code.

Kingsstar, I'll have to get my file downloaded off the laptop so I can email it to you, I'll write myself a note and hopefully remember.

NOTE: you will have to make sure you install the correct MegaTune and the correct MSnS_Extra.ini file for megatune so you can open the file and look at my settings. If you don't know how to do that yet check out the megasquirt forum www.msefi.com to learn more.