Mike(j9fd3s) and I have been talking about this all day....

How does the stock ecu adjust the timing when you make fuel corrections with the s-afc? Since the igintion is based on rpms and load, and the s-afc manipulates the MAF(load), which would make the ecu think the maf is +- close or open. Then the ecu would change the timing, thinking its under +- load. So whats the deal? Either n/a or t2 ecu....

Another Question, If you turboed and n/a motor, could you use the stock n/a ecu with a piggy back? Just change the pressure(map) sensor? Or would u need the t2 ecu? and is the n/a ecu's map just a piece of the t2s map? ( -15 to 0 pressure)?...

The reason are one, we love talking about this all day,we been yappin about igintion split too , and I might be turboing and n/a in the future, on a budget until he has enough funds to do it right(standalone ems and rebuilt t2 motor).. so in the meantime we would be boosting an n/a motor, and using a piggy back, most likley the popular s-afc.

 

yeah if you have big negative corrections it should advance the timing too, food for thought

mike

 

......

 

I am not certain exactly how the S-AFC effects timing. HOWEVER, it is my GUESS that the ECU sets timing according to TPS value and boost/pressure sensor reading. I would imagine that AFM (the RX-7 does NOT have a MAF) reading has very little to do with timing.

I did. I have the stock ECU running 4 550CCs with an S-AFC.

If you change the NA boost sensor to the TII pressure sensor, you will need the TII ECU. They sensors have different ranges. You coulld, however, keep the NA boost sensor, but also install the TII pressure sensor and use it on the S-AFC in place of the TPS. That way you have boost referenced fuel control, not throttle referenced. If you are doing this, I would suggest just going with an aftermarket pressure/boost sensor as it will have a standard 0-5V output the S-AFC is expecting.

 

I have done some limited testing of 2nd gen ignition timing, and have found no signs of timing changes with AFM movement.

My testing was performed at idle, by simply swinging the door of the afm to the fully open position and watching the timing light. No change in ignition timing was noted. This test was repeated with the OEM map sensor hose disconnected (and vacuum leak plugged), with the same results.

I'm running the Megasquirt standalone ecu, and am still using the stock ecu to control ignition. I would like to repeat the above tests at elevated engine speeds as well, but need a couple more hands! My gut feel is that afm sensor data is used to calculate injector duty cycle only, and the map sensor is the basis for ignition timing.

Perhaps someone else has a more definitive answer? No use repeating tests if the answer is out there...

Roger.


[QUOTE]Originally posted by 1Revvin7

How does the stock ecu adjust the timing when you make fuel corrections with the s-afc? Since the igintion is based on rpms and load, and the s-afc manipulates the MAF(load), which would make the ecu think the maf is +- close or open. Then the ecu would change the timing, thinking its under +- load. So whats the deal? Either n/a or t2 ecu....

 

Thxs for the replies guys. Interesting... Renns if you ever do get the results let everyone know.

 

Will do... If you've got some specific rpm/map points of interest, send them to me.

Given that I am running a standalone fuel controller on an otherwise stock vehicle (strange, I admit), it's a good opportunity to test the oem system. With an extra set of hands I can hold the engine at a specific rpm, apply vacuum (or pressure) to the oem map sensor, swing the afm door, and read ignition timing. If I do a more detailed test I'll try to mark out the pulley in 5 degree increments or so.

Just thinking... If the function of the stock 2nd gen ecu was better understood, it could be used as a retrofit to 1st gen cars as a distributorless igntion controller. T2 ecus could be used to provide DIS and boost retard for those turbo 1st gen cars running standalone fuel controllers. Hmmm....

 

hmm well i know someone who has tested stock ecu's and the afm and boost sensor effect the fuel (www.16paws.com), we know its not the tps though the s4 doesnt have a full range one

mike

 

kaboom^^^^^

 

If the AFM acutally has a say in how the ECU sets the ignition timing and your SAFC manipulates that data, I would guess that richening a range with the SAFC would bring a small retardation of timing, assuming the ECU retards timing under increased load. However, if the ECU sets timing based on the MAP sensor, nevermind.

 

Sure afm will affect fuel delivery. That is it's reason for being. No data on ignition timing though? I'm new to the 2nd gen scene, and find it surprising that someone hasn't figured this out yet...

Above is true until the user swaps in larger injectors, and uses the safc to correct fuel mapping. Negative corrections could potentially result in timing advance, as Mike said earlier in this thread.

Roger.

 

I was in the process of putting a second gen ECU and cas in a 82RX at one time. I got the car running but noticed it seemed doggy. I got a timing lite out and rev'd the engine. The timing did not advance. So I added the tps of the 82 to the ECU and then the timing advanced and the car ran a lot better.. So....I'm not saying the tps does all the timing, just some of it anyway. At least at the beginning of acceleration.

 

yah, it seems like it would be a smart thing to check for

mike

 

That's strange, because I am running with the TPS removed in my 2nd gen, and have verified timing does advance with rpm increase. I have a full-span TPS installed that is used as an input to the Megasquirt controller only. Did you have the oem map sensor connected? If not, perhaps the ecu falls back to tps if map sensor data is absent?

 

No, never got to rig the pressure/boost sensor up. A salvage 87tuboii car came into my life and the project got dropped. 82 finally got sold off a couple of weeks ago. Toooooo many cars. Spend your whole life just getting inspections, plates etc for 'em.

 

Hmmmmm well looks like we got the respones from the handful of guys who actually know **** around here. Guess this is done then, no one knows. Well If my friend ever gets his car, I will find out. Thxs for the replies guys.

 

I gave you the answer. The AFM reading does not effect timing. It is based upon manifold vacuum and throttle position.

 

Now Aaron... Your previous comments shown below hardly sounded like the definitive on the subject. It's those words like 'GUESS' and 'imagine' that may cause some skepticism on the part of the reader.

I've got the FSM for my old '79 in front of me, and it shows nice graphs of timing change with rpm (centrifugal advance), and timing change with manifold pressure (vacuum advance). Switching to distributorless ignition in 1986, it would seem obvious that the oem would at least duplicate the previous system. That would give two primary inputs to the ignition timing equation: map, and rpm. Now why tps is needed is beyond me, as map would seem to be a valid load indicator.

This subject is of interest to me, as I'll be experimenting with MegaJolt, the ignition controller companion to my Megasquirt efi controller soon. Having access to REAL DATA from the oem setup would be helpful. I have enough spare bits laying about that I could cobble up a system in my basement and do some detailed testing. Heck, it's too cold to do much outside anyways.

Roger