NO PC - Mega Squirt/Mega Tune, never ending issues Options

[Scott S]

Hi All -
Does anyne have a megasquirt/megatune FI set up that actually works... at altitude?

My brother has been building a big bodied audi S-4 for thre years. As of today the car has less than 1000 miles on it over that time. The car is blisteringly fast - it dynos between 550 and 600hp at the crank. However the megatune management system is so unreliable/unstable that the car will run great for an hour, then start doing things like randomly shut itself down, or drop a cylinder for no reason. The guy who is the go to guy back east actually reccommended that he set his idle to 1500+ rpm's to keep the car from stalling when the AC is turned on. Other than that, the usual response is just to wait for the next upgrade. The mechainic who is doing the build is fantastic and just as pissed as any one over the issue.

The lower elevation guys have no issues, it only seems to be affecting those at higher altitudes. Its like they never tested the system anywhere above sea level.

There have been a few threads on the MS system on our board, but even after searching, I could not find where anyone was ever beyond the point of "well, there are some issues, but I will work them out later". Just curious if anyone has actually successfully installed a fully operational system.

Thanks - sorry for the book...
Scott S

[Scott S]

Here is what he just sent me:

I appreciate it, but my issue is the interface with OEM electrics and devices, so they most likely will not have similar experiences as it's S car specific. This is MS on steroids, albeit wimpy ones. we are fighting consistency in the ECU talking to the OEM bits, and certain bits falling off the radar unexplainably and then popping back up. The signals get lost, so it's a combo of the system and almost 20 year old wiring. ground placements seem to make a huge difference, etc. My injectors were not being talked to correctly, due to an impedance issue so the pulse width was all over the board. It's fussy, I don't like fussy.
FYI, ECU is in the car - probably two feet from the coil packs

[JamesM]

Here is what he just sent me:

I appreciate it, but my issue is the interface with OEM electrics and devices, so they most likely will not have similar experiences as it's S car specific. This is MS on steroids, albeit wimpy ones. we are fighting consistency in the ECU talking to the OEM bits, and certain bits falling off the radar unexplainably and then popping back up. The signals get lost, so it's a combo of the system and almost 20 year old wiring. ground placements seem to make a huge difference, etc. My injectors were not being talked to correctly, due to an impedance issue so the pulse width was all over the board. It's fussy, I don't like fussy.
FYI, ECU is in the car - probably two feet from the coil packs

True, any Megasquirt install is going to be car specific and also specific to the particular way it was installed in that car, however there are only so many things you can do with Megasquirt and so many different ways you can set it up, so there are some problems that are seen somewhat more universally that someone new to Megasquirt might not expect. People with Megasquirt experience could still probably help you track down the problem faster.

Data logs can be very helpful.

The info I have so far is still a little sketchy as far as helping me figure out if it is one central issue causing the problems or multiple little issues.

Improper resistance with your injector circuits could be causing things to overheat which could cause other problems, which was the first thing I suspected when you mentioned it was time related, however if you are seeing pulse widths jump around in mega tune there is a good chance it would be related to something else as Megasquirt does not take any sort of feedback from the injector circuit. Sensor readings cutting in and out could cause pulse widths to jump around as the ECU is trying to adjust for what it sees as changing conditions, but what is causing the sensors to cut out? Could be bad wiring, interference, bad sensors, or if they are all cutting at the same time maybe processor resets? Tach spikes will also cause pulse width to jump around.

Without looking at data logs and knowing more about the setup though we are just guessing.