Hooking up GSL-SE vac. advance to stock ECU (Carb / standalone setup)
 

Hey all - I'm studying up on the GSL-SE vacuum advance system, trying to get it all dialed in for the Standalone Fuel Computer swap coming up.

I've currently got the vacuum advance dashpots hooked up to straight up to manifold pressure. It has made a HUGE improvement on driveability and regained a lot of low end power (previous owner did not have them hooked up). The car no longer surges when cruising and also no longer smells like half-burnt fuel!

Anyways. The factory system is hooked up to a check valve, which is controlled via the ECU. Page 4b-20 of the Factory Training manual gives the conditions under which the check valve passes manifold pressure through to the vac advance:

http://www.jimrothe.com/mazda/84_tra...raining_4b.pdf


Operation after engine warm up

• VC at and above DC2 line
• VC cut at and below DC2 line
• When there is sudden acceleration from a position at or above TV02, VC is cut for 3 seconds (to prevent "Knocking") *TVO change rate 20% or more/0.13 sec
• Reference - VC Vacuum from intake manifold to vacuum advance diaphragm

https://www.rx7club.com/attachment.p...1&d=1364918865


When Radiator coolant temperature is 15*C or higher and engine coolant temperature is 50*C or lower.

• During 1100-3600 rpm for 120 seconds after engine is started, VC is cut, and exhaust gas temperature becomes high to warm up the catalytic converter quickly

https://www.rx7club.com/attachment.p...1&d=1364918865

Basically, I'd like to have the stock system working at full potential, and am trying to decipher where the ECU will be getting all of its signals from so I can try hooking it back up via check valve / ecu rather than just straight manifold pressure.

Here it comes down to a matter of deciphering those charts. What's DC2? How about TVO / TVO1 / TVO2? Perhaps chart is drawn from signals from the O2 sensor?

Coolant temperature seems straightforward - just off the coolant temp sensor.

The only other thing I can think of is perhaps the ECU might be in limp-mode, which may affect the vacuum advance. However i haven't come across anywhere in the FSM that talks about limp mode for the GSL-SE.

i was just looking at that. the problem with the haltech is that it actually cannot duplicate the factory strategies, even the platinum stuff can't do it.

the good news is that the second one, where the vacuum advances are cut for 120 seconds after a hot start, is so the cat lights off faster. if you have no cat, its not needed.

the TVO numbers are Throttle Valve Opening, its kind of related to the DC lines, which are like load lines. basically the ECU has "zones", and the GSL-SE uses the DC lines to mark the zones, for instance anything less load than DC1 is considered deceleration... the later cars have something similar, but they use numbers that aren't as oddball.

so the first thing where VC is cut for three seconds is done with the two VC solenoids, and i'm really not sure how you'd do this with the haltech either.

the stock GSL-SE ecu has no limp home modes, BUT it doesn't have default values either, so for instance if you unplug the water temp sensor, the GSL-SE ecu will just think its -20C and inject fuel for -20C.

So it sounds like the TVO values would be determined via Throtle Position Sensor, correct?

I'm wondering if its possible to splice into these sensors' lines to send data to both the stock ECU, aftermarket gauges, and the Haltech at the same time? Or do they need to be run straight from terminated sensor back to the ECU thats in charge?

Interesting note on the Haltech ignition mappings!!! That corroborates what Robert and I were talking about - He has dyno tested both, stock distributor w/ old school vac & mech advance, as well as standalone fuel/ign. The standalone had maybe 3-5 more HP. I believe this was on a 200-250hp engine build (not sure of this car - I think it was on his 13b bridgeport racecar)

I'm wondering if those variables are really that significant - as you mentioned the 2nd cut is simply to warm up the cats. Although I dont have any now, my galactivated hippie self wants to throw in a couple of cats down the road. But even as such, its called warming your car up - and I do it every time before I drive. I dont just jump on the road and mash it in, i let it idle for a minute and then take it easy until I see a temp reading on the dash gauge. I think this is due to being so accustomed to turbo cars (no boost till warm kiddos!!!) but so far this approach has done me well.

Currently (13b 6 port Street port, Dellorto 48dhla) I've got the vacs hooked up to straight manifold pressure, run exclusively at the whim of engine pressure. From what I understand the difference compared to ECU/solenoid vac will be mainly under deceleration and idle, where that check valve would be returning the vacs to atmospheric pressure.

So far its running amazingly well. Decel and idle are waaay more smooth (than no vac advance hooked up at all, as PO had it), and the exhaust gasses are way cleaner. I'm wondering if this setup may work just as well with the injection - maybe more backfiring on decel?

The thing that really makes me want to get the factory system hooked up is the rapid accel cut to prevent detonation. Once I get the EFI system hooked up I plan on pushing the ignition to its advanced limits to try to maximize the street port, high flow exhaust, and 4 fuel injectors / CAI. This seems like the most practical advance adjustment of all of them.

i would think TVO would have to be done with the TPS, although where the breakpoints are is a bit esoteric, or even random.

some sensors you can splice, and i think the TPS is one of em, the temp senders you can, because they are based on resistance and not voltage.

with the distributor (or stock ecu), sometimes you have to sacrifice a little power here and there to get it right at peak, with a full ecu, in theory you don't, so its been my experience with full ecu cars that the peak power is really close (1-2hp), but you gain around the peak (5-10).

the carbs can be setup to run surprisingly well, i've got a Weber on my P port, and its actually really tame.

i haven't maxed out the timing yet, or actually i've done enough experimenting to learn that the thing actually wants a timing curve, and that i think i could do it with a distributor, but it needs a different curve than stock for sure

Clarification - temp senders you CAN? or canT? more wire = resistance

i think no, you either need a separate sensor, or maybe you could add a resistor? there is probably some way to do it