Can't get stable Megasquirt idle & backfire (?) at TPS cut (280ZX N/A, fuel only)

[Pepijn]

Hi all,

 

I've been trying to finalize my Megasquirt 2 V3.0 installation for some time now. Everything is wired up, giving good values and cranks within a second. My setup is as follows:

• 280ZX N/A
• Megasquirt 2 V3.0 (fuel only setup)
• 240SX TPS
• AFM removed
• No additional mods
• Ran fine before removing the original ECU

I also have a wideband O2 sensor, but can't attach it near the block since there is no bung and installing a new exhaust system is out of the question since the car resides in an underground garage.

 

The first noticable problem is as follows: rough idling around 850-1000 RPM. The MAP sensor is also very wavy, with a worst-case amplitude of 15+ kPa.

Furthermore, when I push the throttle, it feels like the engine almost stalls, but then the RPM increases. When I release the throttle at 'high' RPM (~3000) I hear some popping, which could be a backfire?

I have searched and searched but couldn't find a clear answer on what is causing these symptons.

 

I hope you have some ideas on where I could look for problems.

 

The log attached shows the last run and the .msq is also included.

CurrentTune.zip

2016-06-25_13.25.26.zip

[Chickenman]

1: Why aren't you asking these questions on the Megasquirt Forums?  They have the most knowledgeable support for their product.

 

2: It is an absolute waste of time to try and tune a new stand alone system without a WB O2 AFR meter hooked up. Push pull or drag your car to a shop and get a bung installed for an AFR Meter. Then install one.  Period. Or spend a ton of money and take it to a Chassis Dyno with a tail pipe O2 sensor and spend hundreds of dollars to have them Tune it. Your choice. 

[Chickenman]

BTW.. I had a quick view at your Log, and basically it doesn't tell us a whole lot. Lots of extra fields that are superfluous, but the two most important, AFR and Spark advance are not logged.

 

1: Is the engine completely stock other than 240sx TPS and AFM removal?  That means stock cam, stock compression and stock injectors. If so, you best bet may be to go to Megasquirt forums and download a working .MSQ for a stock 280Z. Note you must tell us of any engine modifications as they all affect VE, which changes the tune.

 

2: You're only controlling fuel with the Megasquirt. Is there a particular reason for that? Are you running the stock mechanical and vacuum advance distributor. If so, then please tell us the static timing and what the total mechanical advance is. 10 degrees static timing at 700 rpm and 32 degrees total mechanical all in by 3,200 is a good starting point ( Vacuum advance disconnected and minimum 95 RON fuel )  

 

3: If you are using a crank fire or some other form of Programmable ignition timing, then why aren't you running a Spark Map Table?

 

4: Your logs have way too many  fields selected for dialing in a basic setup. KISS principle. For initial idle and a basic " Drive it to the Dyno " setup all you need to log is RPM, AFR ( essential!!! ), Spark Advance ( real time ) TPS, CTS and MAP. If you're running a mechanical Dizzy you obviously don't need Spark advance. Don't clutter your logs with useless info.

 

5: Go out and buy this Book: It is THE best resource for understanding standalone EFI systems. Written so the DIY tuner can understand it. Matt Cramer ( Megasquirt Developer ) and Jerry Hoffmann co-wrote the book. You can get it from Amazon Worldwide, but here is the Canadian link:

 

https://www.amazon.ca/Performance-Fuel-Injection-Systems-HP1557/dp/1557885575

Edited June 25, 2016 by Chickenman

[seattlejester]

First off, good for you for including those files.

 

Off the bat the hesitation is probably caused by an accel enrichment being off. Make sure to set it to TPS 100% bias and setup using the included TPS dot graph. It is one of the things people forget to set the most when switching to a TPS.

 

15 kpa fluctuation is fairly small, that is like less then a pound of difference.

 

Unless you have it controlling idle via an IACV, then megasquirt really doesn't have too much control idle. Complaining about that would be moot.  

 

Depending on how you have your ignition setup that isn't very odd. L28's do backfire at least when mine was carb'd it did.

[skirkland1980]

You can tune your idle without a wideband afr gauge. It sounds like it may be lean. Pull a few spark plugs and see if it looks rich. If not add fuel on the fuel table. If the engine likes the added fuel your vacuum should increase (go down one the map). Also make sure fuel supply is sufficient. I actually should have mentioned that first.

[seattlejester]

You are going to have to be familiar with reading spark plugs, and know how to burn and clean them between readings. Not an easy skill. I would say to just  install the wide band AFR gauge. It will answer sooooooo many questions you may have down the road. 

 

All you need is a drill bit and a clamp on o2 bung if you have to install it yourself. Any competent exhaust shop should also be able to install an o2 bung in a few minutes. Just drill the hole, debur, weld bung over it, screw in o2 sensor then route into cabin. 

[Chickenman]

Another reason why OP should install his WB gauge ASAP. Most modern AFR gauges have auxiliary WB and NB outputs. So the gauge  itself can be used as a WB controller.

 

The MS2 V3.0 has WB input that can be integrated with a WB gauge such as Innovate or AEM. It has the ability to self tune to Target AFR maps. That makes tuning sooooooo much easier and faster.  And you can Data log everything. Have an annoying stumble when you " tip in" at cruise or pull away at a Stop . The ability to Data Log with a WB gauge will instantly tell you if you're going Rich or Lean.... and by how much.

 

I've tuned cars for over 35 years with no WB or even NB gauges, as I'm sure other " Old Timers " here have done. . And I've done it very successfully. But with today's technology, I would never waste my time tuning without a WB . I'd never waste my time trying to dial in a stand alone unit with out using it's WB " Self Learning " features. Spend a little extra time and effort right now hooking up that WB Gauge and integrating it with your MegaSquirt,  and you will save time and grief 10 fold down the road.