Using 7m ecu for spark only -no AFM

[andrew_mx83]

backstory:

cressida was switched to straight LPG, ecu was left to control spark with no AFM. everything worked fine except that is ran a VERY basic timing map which seemed to do nothing other than increase with revs.

obviously the computer SHOULD BE pulling timing out under load.

that motor shit a big end bearing last year -one possible cause could be running 40+ deg of timing at high revs not being reduced under full load. not good for bottom end bearings at all.

i have a permanent solution for the new motor i am building (5m dizzy + aftermarket ignition) but i have the motor out of the daily in the car at the moment and cant easily get the 5m dizzy in it. i also dont want to blow this one up!




sooo, temporarily i would like to use the ECU to control spark, without an AFM but still have some load correction on the timing -doesnt have to be perfect.


if the AFM gives a 0-5v signal depending on load (airflow), what would stop me rigging up a potentiometer on the throttle, going between 0 and 5v from idle to WOT. i understand this isnt the perfect solution but i am not interested in fuel metering, just to have SOME load correction on the timing curve. basically timing should decrease depending on throttle position.



thoughts?

[woggin]

why dont u just change the ignition to vacuum advance? I dont think the computer would like that much but it would solve the problem of just cranking in more timing!

[Supra967]

5V at idle and 0V at WOT (just either side of both) if its a GE AFM. Don't think it would work very well, you can have full throttle and bugger all air flow. What's wrong with with placing the AFM inline somewhere to meter air?

[andrew_mx83]

its crap lol!

i had it in when first went to gas.... you would not believe the difference taking it out made, even with a shitty timing map it picked up shitloads of power and economy

plus there really isnt anywhere to mount it with a holley 650 which is going on shortly. i think it is more important to get the timing better now im going back to petrol


im not fussed if its not spot on 100% of the time.... not like its metering fuel or anything. as long as it isnt running 50deg of advance at 6000rpm WOT ill be happy.

question is, will it even do that or just throw everything up the shit?



and woggin i do have a vac advance dizzy for the new motor, but it has to be mounted in the block instead of the head and i dont want to fuck with this motor too much. i want to be able to put it back in the daily STILL RUNNING and stock

[auto351]

The way I see it the Engine RPM will set the proportional timing, which will advance with engine speed & the air flow meter will be used to calculate the effective vacuum for timing correction high vacuum = advance in timing.

The 3 Engine V Air Flow conditions

1) At Idle or backing off the throttle.
The Engine speed faster than the AFM (Idle 5v) position there are higher vacuum level

2) Engine running at constant speed
The Engine speed matches the AFM (cruise) position then there would be medium vacuum levels

3) Heavy load and or under acceleration
The Engine speed slower than the AFM (WOT 0v) position there would be a low vacuum level


So by using the throttle position to drive what was the AFM reading,
If you open the throttle from a standing start the timing will be retarded due to condition 3 above and as the engine speed increase the match the substituted air flow signal the timing will advance, similar to the factory setup but in this case would retard the timing more that a proper AFM setup

If you have no AFM signal then condition 1 above would apply giving extra advance...

You would need to measure the voltage on the input of the AFM to see if its 5V or 0V when not connected.

It could even work by having the WOT voltage set permanently


EDIT:
What have you done with the ping sensors

[thechuckster]

either re-fit the AFM or put in the dizzi and igniter from a 5ME - you need to retard timing based on MAP - the 7MGE ECU does that by determining load from the TPS, AFM & RPM, the earlier ECUs do no timing control at all as they have a vacuum advance pot.

Using the TPS as a load signal generator will be counter-intuitive/productive in many circumstances

[andrew_mx83]

It could even work by having the WOT voltage set permanently


EDIT:
What have you done with the ping sensors

the other option, if this all goes belly-up is to plug the AFM in, but not in the air path and wedge the flap open with a screw-driver -ecu always sees full noise so wont let to timing get too far out of hand.

knock sensor still plugged in, this is currently the only thing i can see that will retard my timing. however with 130RON i dont think it will ping in a hurry....

either re-fit the AFM or put in the dizzi and igniter from a 5ME - you need to retard timing based on MAP - the 7MGE ECU does that by determining load from the TPS, AFM & RPM, the earlier ECUs do no timing control at all as they have a vacuum advance pot.

Using the TPS as a load signal generator will be counter-intuitive/productive in many circumstances

nowhere to put AFM on top of a holley
nowhere to put 5m dizzy in a 7m, unless i take the crankcase ventilator off, change oil pump shaft and a few other little things. this will all be done on the new motor, but dont want to screw with this one too much.




i guess all i can do is give it a try.... wont really be able to see how much timing it got under load tho, bit hard to hold the timing light while driving lol

[thechuckster]

just pull the guts out of a 5ME dizzi and insert into 7M dizzi - i should have been more explicit about that.

running without any vacuum a advance/retard means the moment you floor your freshly rebuilt engine at low-to-mid-range revs, your timing will be way out (advanced) and put the motor in a position likely to lead to detonation.

If you run with the AFM stuck full open, it'll be at max advance for each rev range.

If you get the timing running sensibly, you 'll get more power across the rev range and also more reliable response.

Given that you broke the last motor with too much timing advance, am just concerned that you seem intent on repeating the episode?