1bdbrd

iTrader: (1)

Ok, so reading the thread about MS working with stock harnesses raised a couple questions that I haven't thought about yet.

1. I will be putting a t56 into my car along with the dakota digital box that should fix the speedo problem with the stock ecu. Since the MS doesn't have a VSS input, does this change anything as far as the t56 swap wiring goes? I remember reading some threads saying that the speedo, even in the cars with electric speedos, isn't controlled by the stock ecu. Will the MS install even effect my electric speedometer?

2. Does the MS have knock sensing abilities? Part of that other thread made it seem like without the stock harness I wouldn't be able to have knock sensor setup. Is this true? I have never heard anything about it before so I wouldn't think so?

RBob

iTrader: (1)

The '91 TPI car ECM provides the VSS signal to the speedo and the cruise control. So if you yank the ECM you will lose both of those.

RBob.

Street Lethal

iTrader: (16)

I was under the impression that VSS input was possible with a dual table code and the addition of an expansion file.

http://www.megamanual.com/ms2/knock.htm

1bdbrd

iTrader: (1)

Cruise isn't a worry of mine since it has never worked in the first place. Speedo is obviously something I need though. I remember reading some threads on here that mentioned that the speedo will work on the electric speedometer cars even if the car was shut off. They were saying that with the car shut off, if you rolled it down a hill it would still register speed? I couldn't figure out how they would work without the ecm but figured they knew more than me. Evidently they were wrong?

RBob

iTrader: (1)

As crazy as this sounds, I can believe that it may be true. CMOS is funny like that. You can power up CMOS logic from the voltage on the inputs of gates. With the VSS being a voltage generator (along the lines of the alternator), I'd believe that moving fast enough that the VSS voltage would power up a section of the ECM. Even with the key off.

More interesting is how someone figured this out. I sure as heck wouldn't turn off the ignition while rolling down the road.

Anyway, the VSS feeds into the ECM of your car. Which buffers it and produces the outputs for the speedo & cruise.

Some time soon I'll try the key-off roll to see if the speedo still works. You have peaked my interest in the arcane.

RBob.

1bdbrd

iTrader: (1)

If the speedometer is waiting on a signal from the ecm to show the correct speed, couldn't that be eleviated by using the dakota digital box?

I really wish I could remember what thread I read that in. It came up once in a search I was doing on a t56 swap but can't remember what terms I used to find it. I also think Mr.Dude said it maybe?

I guess I need to figure out what would be the best way to fix this problem. I would really like new gauges since I haven't ever liked the stock Firebird gauges. Thing is, I can't afford that along with the other stuff my car still needs.

I guess I could keep the stock ecm along with the MS to control the speedometer. How many other gauges does the stock ecm control?

RBob

iTrader: (1)

The ECM also controls the fuel pump relay, no other gauges.

For a stock VSS can use a 4-out buffer box. That is what GM did with the TBI cars. If the T56 has a 40-tooth reluctor then I would use a DRAC. That is what GM did for the trucks.

The real item that puzzles me is why would you want to remove the '7730 ECM (running the $8D mask) and replace it? The '7730 is an excellent ECM and the $8D mask is one of the best that GM put together.

Not only is it fully tunable, there is tons of information on the calibration over on the DIY_PROM board. Along with lots of folks to help out.

RBob.

1bdbrd

iTrader: (1)

The biggest reason I want to remove it is because IMO its way to expensive to tune it and way too difficult. I am going to be in it for the same cost or more trying to tune the stock ecm after I buying all the burning stuff and cables and all. On top of that I don't want to burn proms. I would rather tune it on the fly and have the tune "stored" in the flash memory rather than change a prom every time I make a change.

RBob

iTrader: (1)

Well, OK... But I still don't see why downgrading the ECM is a good path. Remember that it is what actually runs the engine. . .

And there are other solutions for the GM ECMs that are flash based. Don't always need to burn chips for it.

RBob.

1bdbrd

iTrader: (1)

Can you explain why you feel that MS would be a downgrade from the stock ecm?

Off the top of my head, the only other ecu I can use that's made by GM is the LS1 setup like some are starting to use. The cost of it makes it a VERY bad idea IMO because of all you have to buy. I would be in it for close to what I have in the car alone. Otherwise I can't think of another computer to run.

RBob

iTrader: (1)

The stock ECM is leaps and bounds above the MS. For a flash based chip replacement check out the Prominator (www.speedtronics.net). For a RAM based emulator check out the Ostrich (www.moates.net).

TunerPro is free (tunerpro.markmansur.com/), and if you go with an Ostrich it is supplied with a license for TunerPro RT. Look around Moate's web site, Craig sells a bunch of nice stuff for tuners.

RBob.

Street Lethal

iTrader: (16)

GM invested a great deal of money into their processors. Even Bruce used to argue all of the time on the Turbo Buick boards the; "show me what a FAST setup can do over what a stock ECM cannot" question, and nobody had an answer for him. Of course, Megasquirt is a little more advanced than the FAST setups in my opinion, but still, the stock ECM can be made into a better processor overall. One main advantage is long term fuel adjustment (BLM). Megasquirt was designed for those who didn't want to spend that much money on systems such as XFI, as well as for those who wanted a quick fix when swapping from carb to fuel injection and needed a processor....

Mark A 91Formula

iTrader: (3)

Megasquirt isn't what it once was, it has evolved greatly over time. I remember on first release watching guys convert lawn mowers to EFI just because they could. I put it out of my mind until I saw what it had evolved into. Current versions run it all now. $8D is great code, untill you start adding blowers and turbo's, then there is $59, same ecu just repin a few things reflash and retune. Then you start thinking wouldn't it be neat if I could control my alky injection. Hmmm low compression high boost overly large injectors. Now how do we fix that? Hotter spark helps, better control over fuel, peak and hold injectors. Sequential injection may not help the top end much, but it improves the low end usually. Distributorless ignition is nice too. 8 independent coils leaves you with all the dwell time you could ever need, a big fat hot spark across the rpm range.

It really comes down to what you want/need, what your future plans may be. Stock system are tried and true, hacked and documented fairly easy to work with with all the available tools. They can go a long way in making obscene power, untill you start changing radically what the overall combo is then you start looking at the losses\benefits of alternate systems. The guys with LS1 PCM's generally love them, cost is a bit of an issue there though. Megasquirt guys tend to be happy as well, once they're running properly. Megasquirt 3 is also just over the horizon. Basically a huge processor upgrade, and MANY new options. If you buy a megasquirt 2 now, you can upgrade to MS3 later if you'll use the new features.

I'm looking at it as an evolutionary step myself. I'm closely watching what is happening with MS3, it looks like it will fit in with what I want to do with my car. Stock has served me well for a long time though.....

Toehead

Megasquirt does long term fuel adjustment of the VE tables based on feedback from the O2 sensor. If you have a wideband, you can have it try to match an AFR table automatically

Street Lethal

iTrader: (16)

Oh no don't get me wrong, Megasquirt can in fact target a predetermined (forced) AFR ratio to whatever it is that you desire, so can Big Stuff 3, but is it stored permanently in the processor itself though, or would you have to reprogram when the batt is disconnected...?

Toehead

You can do it either way.

Option one is the RAM update, lost whenever you cut the power.

Or, you can set it to store it in the ram, and then burn to flash after a certain number of iterations. Once it is burned to the flash memory, it's permanent.

Homer

iTrader: (1)

I read that in closed loop, the stock computer will learn its way back to 14.7. Can you lean that out for fuel economy, or is that the fuel ratio you have to have with a stock computer? Can you run more than one fuel map?

RBob

iTrader: (1)

Your '8746 ECM (among other stock GM ECMs) has a lean cruise mode. When highway driving the ECM will command a leaner AFR for better fuel mileage.

RBob.

Homer

iTrader: (1)

I have a tbi car that I'd like to upgrade. I am looking into water injection, so I'd want something that can have a fuel map with a full tank of water and a different fuel map with an empty tank. I had been thinking of megasquirt, but I've heard that the factory ecm can do so many things that the aftermarket cannot. What are the things I'd be giving up by going with an aftermarket ecu instead of a tpi one?

Toehead

The biggest thing I found was the emission controls. The megasquirt doesn't run the EGR or purge canister (you could get it to do it, but you would need to do some work)