Paging Ray O

Its that time again Ray, another of those general but somewhat specific questions that calls upon your knowledge of all things T.

The '91 Alltrac ignitor - intelligent or dumb? I'm using the Megasquirt to fire it with ~3ms dwell but its not happy and rev limits at 5.5Krpm.

Having read through the 2nd gen to 3rd gen conversions people have done, when they try to use a gen3 ECU and gen2 ignitor (mine) they have the same problem as me and require the gen 3 ignitor. This smacks of the signal from the ECU being "different" in some respect. I dont have a 205 ECU available to scope out. The only thing i can see, other than voltage of IGT signal, is the pulsewidth.

Any ideas?

Reply to
Coyoteboy
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Gee whiz! Cant you ever ask a question I know the answer to?

From reading the circuit descriptions in the '93 Previa manual and the '97 Avalon manual, I cannot discern which generation the igniters are, although the '93 manual does not describe the IGF (ignition confirmation) signal but the '97 does. The '93 just says "check for voltage," while the '97 specifies

5 volts at idle. There is no pulse width specification for the '93 while the '97 just shows an oscilloscope depiction of a square wave with 5 V potential and a pulse width that looks like somewhere between 3 and 5 ms. The other difference is that the '97 has a distributor-less ignition and so its igniter produces IGT-1, IGT-2, and IGT-3 for the 3 coils, while the '93 only had 1 IGT signal.

Bottom line, my guess is that the difference in igniters would have to do with the capacity to deal with different pulse widths or somehow react quickly to the next signal at higher RPM.

I have not studied how the rev limiter works, but I had assumed that the ECU limited revs based on a signal from the tachometer. Are you getting an actual fuel cut at high RPM or does the engine just not go any higher? If the engine is actually cutting fuel, look at the tach signal. If it just won't go any higher, it sounds like an igniter swap is in order.

Good luck!

Reply to
Ray O

"Ray O" proclaimed to alt.autos.toyota ...

I like to keep you on your toes :) My local toyota dealer flatly refuses to give me ANY information, and wont even give me part numbers for reference or accept part numbers when ordering parts. They flatly refused to give me ANYTHING without a license plate number for my car, even when I offered my VIN number, then when i gave them it they said "oh we dont have that one on database, its too old, can we have your VIN?"! They just dont like dealing with older cars it seems.

So it sounds like the '97 is a "dumb" ignitor with the dwell controlled by the ecu, whereas the '93 is a smart one? The one I have has a single IGT and an IGF. As far as I know it works on a

5v "square wave" of sorts, but I have no details on exactly the formation of it. It runs beautifully
Reply to
Coyoteboy

Toyota's general rule of thumb is that they will NOT give you information to help you 'modify' your car, nor will they support you if you have modified your car.

But your local dealer, while he has to follow these rules, certainly should be willing to sell you parts you specify, and is usually more than happy when you supply the part numbers. Maybe things are different there, but here, walk in with a part number and they order it, no problem. Of course, if YOU screw up, you're stuck; 15% 'restocking fee', and NO refund on electrical parts once it goes out the front door! (They try to press the No Refund for electricals, but if you get it, look at it and say, "That ain't it!" they will usually take it back with the 15%)

Go to a different dealer. Or, if you're lucky like me, make friends with one of the techs. One of our local guys, "Supraman" knows the MA70 inside out, upside down and backwards, and tells me what to order in order to get better / more durable or higher perfomance parts.

Good Luck!

Reply to
Hachiroku

A major limitation in my background and experience is that my job was only to make cars conform to factory specifications, so I did very little fiddlinng around.

As a side story, the son of a very high ranking company execcutive went to school in the town near where our office was located, so the office supplied him with an employee lease Supra. Employees are not supposed to modify their lease cars and are supposed to return them in good condition, other than normal wear and tear. The employee's son spent lots of money installing turbos on his Supras (under the employee lease at that time, you get a new car every year), and when the cars were turned in, the service traininer and field technical specialist had to spend days looking for and un-doing all of the modifications, but not before test-drivinng the cars for a few days first ;-)

I really don't know the difference between a smart and a dumb igniter.

The only reason I can think of would be due to a change in suppliers or for emissions.

That sounds like a methodical approach. Now I'm curious as to whether the actual dwell is controlled by the ECU or by the igniter, with the ECU just supplying a timing or trigger pulse. If that is the case, then a shorter ECU dwell should fix the problem.

Reply to
Ray O

"Ray O" proclaimed to alt.autos.toyota ...

I dropped the dwell to 1ms (starting and running dwell) and it made a hint of difference, but only in that it made the rev limit barrier more variable than it was before - anything between 5K and 6K. Very confused. Will keep at it and I'm sure I'll figure it out eventually!

Wish someone gave me a supra in any condition (modified or not!) for work - I get a nice smile and then asked to justify why I want a parking permit!

Reply to
Coyoteboy

Hachiroku ???? proclaimed to alt.autos.toyota ...

Theres only 3 local dealers, all of which are "unhelpful". All of which require 2 day special order for anything from a piece of plastic trim to a bog standard bolt. None of whome allow you into the back to see the guys who do the work, you just get to speak to a man with an EPC and order forms or the pretty lady on the front desk.

That said, when we had a recall on the landcruiser they were very helpful and went above and beyond the call.

Reply to
Coyoteboy

"Ray O" proclaimed to alt.autos.toyota ...

Just FYI:

I swapped the standard ECU and dizzy back in and took the old 'scope to the IGT pin - I get 4.8ms 5v-5.5v pulses at idle, and 0.9ms at 5500 - that works out at a fixed % dwell of about 7.5% (which seems a little low but so be it, it works fine on the Toyota ECU).

So its a dumb ignitor.

Cheers! James

Reply to
Coyoteboy

Thanks for the update, although to be honest, I don't know that I'll ever need that info again! ;-)

Reply to
Ray O

"Ray O" proclaimed to alt.autos.toyota ...

You can never have enough information :)

Reply to
Coyoteboy

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