N1XRR

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/stock-fc-timing-what-required-451013/

It comes down to this: For the time being I will be running fuel-only Megasquirt. I need to know what is absolutely nessessary for the stock computer to create spark.

13B_boost

I think I know what you want to do. But let me suggest that you run that setup with a distributor to minimize the complications with getting it to run.
Megasquirt = injection
Distributor = ignition
Could'nt be any simpler.

muythaibxr

Megasquirt with msns-extra DOES do rotary ignition now. I spent a week or two writing/testing the code to make it work reliably on an oscilloscope. I'll be testing in tofuball's car in a week or 2.

Ken

N1XRR

I know and that is AWSOME!

The one thing the distributor setup doesn't have is boost retard. Plus, the stock timing is actually working right now. I really need to know, besides the CAS and the pressure sensor, what else do I need to make spark with the stock computer?

muythaibxr

a dual lm1815 vr sensor conditioner and a few pull-up resistors installed properly on the megasquirt.

The pressure sensor that's built into the megasquirt's good to about 20 psi of boost... so you don't need another one unless you're going higher than that.

renns

nixr,

Please clarify what you are trying to do... Are you trying to keep the stock ecu for spark control, or are you trying to modify your MS box to provide spark control?

muythaibxr

oops, I misunderstood your question.

You're trying to get the stock computer to do ignition? My question is "why?" Why let the stock computer do ignition when the megasquirt can do it?

The answer to the question I THINK you're asking is "search the forum." There are some people who kept the stock computer for ignition in the past (before the MS had the wheel decoder and the rotary ignition code)... and I'm pretty sure I saw a post or two about that.

I think it was something along the lines of "you can disconnect everything except power, ground, and ignition-related wires, and still get proper spark advance," but you should search to confirm.

N1XRR

Well, my LM1815's will be arriving later this week. I ordered 10....if I can get one running, I'll build 4 more for the other RX7's I'm getting ready to Megasquirt...nevermind that I got them for $1.90 each....yay for discounts because of volume @ work!

As the car sits, the stock timing works. I want to eliminate as many problems as possible when first trying to get this car to run. Then I will rip the rest of the harness out and put the spark stuff on.

How about some eye candy? Here's the engine bay:

Rex4Life

N1XRR,

I can offer some info to help out on your questions, although it looks like your almost ready to go with full MS ignition.

I will probably take a similar route for my MS install: start with fuel only, then move on to ignition--better to fight one demon instead of two. Then once you have fuel working good, move over to ignition.

I can't tell exactly by the pic but it looks like your car is an S4 since I see only one TPS.

Seems the easiest way would be to connect up what you need for MS fuel and disconnect the injector wires from the ECU. This means you will need the coolant and TB temp sensors for the MS. Put in a resistor for the coolant sensor on the stock ECU side to trick out the computer into thinking it is running at normal temp. Also put in the full range TPS like renns mentioned. And yea hook up the rest of the MS stuff per instructions.

Running this way you can be assured you will have good timing. I believe the timing is dependent upon: CAS, AFM, water temp, boost pressure, TPS. How much each sensor impacts the timing is unknown (except for CAS), and I'm not sure what part of the AFM is used (temp, airflow, both). You can safely transition the O2 sensor over to the MS also.

I'm basing this on a chart for input/output device chart for the S5 ECU (pgs. F2-74, 75). Don't know exactly if the S4 is the same but my guess is that there will be alot of similarities. You may be able to get away with just CAS, and boost sensor for the stock ECU--but I don't know that for sure--I'm not willing to bet my engine on it.

Seems like this method will safely get you through a few weeks till your full up on MS ignition. Hopefully I won't be too far behind you.

Scott

BTW: Nice looking engine bay!

N1XRR

Thanks Scott, thats the kind of answer I was looking for.

Seeing as I've looked all over and I keep getting conflicting information, I will strip the electronics down to just CAS and boost sensor and see if I get spark from there.

The throttle body on that car is a S4....but I have a fully modified S5 throttle body sitting right next to me hooked up to my Megasquirt "test bench". I won't be able to try this setup out until Saturday....so, we'll see if it works as planned.

Rex4Life

Ok if you go with the "stripped down" setup, I'd recommend keeping off the boost--especially if this is temporary. There is no sense ruining your engine due to messed up timing.

Renns has already said you can run this way but I'm not sure his was a turbo . Also note his proceedure was a little more involved (see his post in your other thread). NA's can get away with alot more than the turbo.

Scott

renns

n1xrr,

I described exactly what I did, and supplied pics in your other thread. This worked perfectly for a year and a half. My install was n/a, so there were no boost complications. As far as the impact of each sensor on the oem ignition control, without detailed testing you'll never know. There is lots of conflicting info on this forum in that regard. I did test briefly with the afm disconnected, and I noticed no change in ignition timing. That said, I set up another local guy with my old piggybacked MS system, and he had timing issues after removal of the afm. Perhaps after some period of time without a valid afm signal it drops to limp home mode?

To be safe in a turbo application, leave all the sensors intact, and just splice the injector wires. To be really conservative, disconnect the wastegate actuator from the wastegate itself, and wire the gate in the open position. If the gate is sized properly it'll keep you out of boost (below 2psi at least).