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

My MS would reset itself when it got power surges because of EMI. Did he build his own board, or buy a pre-fab? Did be build his own wiring harness?

I have ran multiple and different MS systems in one form or another for years.

I am not as high as you in terms of elevation but SLC is definatly above sea level. Max ambient air pressure i see here is about 85kpa. With my megasquirted 914 I have not yet encountered any issues that stem from running at high altitude that i am aware of. Last autocross i took it to was up at alta ski resort ~8200ft elevation and i did not seem to have any problems running up there as well, other then the problems you would expect when trying to autocross a 914 at 8000+ ft elevation after a 4000ft climb anyways.

I suspect your problem might not be entierly altitude related.

What hardware version and code version are you running and what are the details of your setup? are you controling ignition as well as fuel?

And whats the deal with setting the idle to 1500+? is this due to a lack of an idle control valve?

I need more information here to get an idea of whats going on.

Do you have any datalogs when the problem is occuring?

When you say you drop a cylinder is that just for a single ignition event or does it continue to miss?

If you are having processor resets I would suspect some sort of interference or bad hardware. The resets themselves can cause all sort of other issues when running as during initial boot up the MS takes a pressure reading to use for altitude compensation. If a reset occurs and the processor takes its altitude compensentation reading while the engine is spinning it is going to get an incorrect measurement and from that point on everything will be fuched up.

one more thought... I just reread your post and saw that it runs fine for an hour before it starts acting up which gives me a couple more questions...

what are the details on your injector setup, low or high imp injectors? resistor pack? PWM?
and
where do you have your ECU mounted?

Both McMark and James have asked where it's mounted...if it's near the coils it will do weird shit to the ECU.
I run SDS and it has no altitude issues, many aircraft with that system, in fact one of the testbeds is the owners plane and they are located at an airport.

I ran mine all summer last year with no problems.

I just emailed him for detailed specs on his set up.

I do know that the mechanic is very very knowlegeable, and was not only factory trained, but spent many years as a mechanic for the factory rally teams over seas. Hopefully Jeff (my bro) will send over some pics too - the fab work is pretty impressive.

Thanks for the replies - I figured this board would have some folks in the know...

Just got back from Tahoe going over donner summit >7000 ft. Ran like a champ with no hickups.

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

2' still might be too close, also look for proximity to other devices like the alternator and solenoids.

Also 2' from the coil packs...is it in the engine bay? They don't like moisture. In an front engine car the ECU should be under the dash.

Hi Mark -
I will pass that along. The ECU is in the stock location (well, at least close to the stock location) in the interior of the car.

Thanks!!

Scott,
I have no MS experience but I do have "big bodied Audi S-4" experience, if you mean 1992-94 S4s (95 S6 is same car different name). I have a 93. These are the 5cyl 20valve turbo cars.
These cars have problems with the ignition coils and the ignition modules that drive the coils. Mine, it takes a while before the coil (1 of 5) starts dropping out and I am not sure which one it is. Since they are hard wired to the harness and all 5 are mounted on a cover over the spark plugs you can't just unplug 1 and plug in a new 1 to test. I tested the ignition modules by swapping them into my A6, 1 at a time. S4s use 2 of the A6 modules.

There is a tuner shop in Davis CA that knows these cars very well, www.2Bennett.com. They have always been helpful and friendly to me.

Most of the Audi tuners seem to modify the programming in the OE ECU, it does require a different MAP sensor in the ECU to go up much in boost. I think Audi used a separate Baro pressure sensor for altitude comp from the sensor in the ECU. I was reading where MS used the same sensor for both and just use the initial value (before start up) for altitude comp.

I hope he can get the issues worked out soon, my S4 is fast (for a 4 door lux sedan) at the stock 230HP I can only imagine what 500-600 would be like.

Jim

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.

Hi Jim -
Yep, I am with you. On this particular car, all of that has been removed from the top of the motor and is relocated on a bracket well away from the motor. I *think* he is using high output GM coils.
I am a fan of the car, but know very little about the technology behind it. I know the car no longer runs a mass airflow unit, the intake is a 100% custom unit built by the shop (I think it was need to alleviate turbo pulsing) the intercooler is simply massive (some in the audi circles were a bit bummed that the bumper had to be cut -I guess they are hard to come by) - the list goes on and on.

The brakes and susension are simply awsome - camber plates, Cayenne fron calipers and I think boxter fronts are used on the rear. Again, I am just not in that world at all - but after riding in the car (even when it was at lesser HP) I can see how people get hooked. Last summer we pulled away from a z06 like it was nothing. All sorts of cool noises from that car too (lots of "psst's"). Just trying to help him out if I can.
Last night he wanted to part it out and then have the body shells of both cars crushed over a webcam feed to what ever forum he is involved with (he has another shell that he wants to build into a track only car). Pulled out my best big brother "now, now, now, lets step back a minute and think this through".