TPS Connector and Injector connectors off mk1a please

[Evo4Jon]

I Hadn't noticed that lnk before !... So in fact the actual load is 2.07ohms per ecu channel if we treat the load on 10 and the load on 20 as 2 x 4.15 Ohm resistors in parallel and the injectors all fire together.

I have concluded that the injectors are Peak and Hold type based on the low resistance rating but I am struggling to see how the engine can run if the injectors are not fired in 2 batches ? Can you shed any light on this ? is it down to the width of the pulse ?

I have a feel that my Greddy ecu aint gonna be happy with this ! - even with the extra resistance I will be adding to the resistor box to increase impedance

[Sillyhatday]

The injectors all do fire at the same time, the 4AGE engine in general used MPFI (multi point fuel injection) as opposed to the more modern SPFI (sequential port fuel injection). The ECU only has one output for the fuel injectors, in the form of a single transistor. (There's two inputs to the ECU, but are linked internally) According to the internet, Japan had grouped injection in some cars. Which may lead to explain why the injectors are wired in two groups, so they could be easily wired together or split for other markets.

Effectively, the fuel air mixture sits about on top of the valves until they open and they are fired once per 360 degrees of crank rotation. Yes its crude, and sounds stupid, which is why with technology we have made systems to fire injectors separately. Benefiting in fuel economy and performance etc.

Remember these were released in 1984 and the car development started in the 1970s. Using early 80s tech they made a pretty good ECU. The ignition timing is done off a '3D' map. I barely understand it myself and I wont go into a much bigger tangent.

There is a LOT of information on the internet about the 4AGE ECU for both the MR2 and the AE86. Depending on how tech savvy you are it's worth reading. There's a bunch of people who have reverse engineered the hardware and software. I understand the hardware talk but the detailed software talk baffles me.

Have a look for a PDF online called lifting the lid on the mk1 mr2 ecu. It explains much better than I can

[jimi]

I'd forgotten about the articles by Jeremy Ross on the MK1 ECU I have a copy on my web storage, you can download it from here http://myweb.tiscali.co.uk/jlawson4/...k1_MR2_ECU.pdf

[Sillyhatday]

I'd forgotten about the articles by Jeremy Ross on the MK1 ECU I have a copy on my web storage, you can download it from here http://myweb.tiscali.co.uk/jlawson4/...k1_MR2_ECU.pdf

Haha, I did wonder. I found it really interesting

[Evo4Jon]

Thanks for the input ! ...Hmmm Looking at the Jeremy Ross article, it's looking more and more unlikely that by simply increasing the value of Solenoid resistor to give a higher impedance will work overall. It may stop the Emanage from blowing output transistors but I think the extra resistance will stop the Toyota ECU from working at all. I have just opened a 17070 ecu and Both #10 and #20 are indeed soldered to the same copper strip on the board and they both share 2 hefty transistors. They are not independent of one another. I never realised how amazing Honda 1992 ECU's were when I used to socket them, tune with a rom-emulator and create myself an eeprom - until now ! Toyota engineers were all over the place !

[jimi]

Forgot to say, I had a look at a copy of the MR2 electrical manual (dated November 1984) that I have and it shows the injectors (with no solenoid resistor) connected the same way as the later ones ie in pairs connected to 10 and 20 with a link between them.

[Evo4Jon]

Brilliant ! very useful thanks

The injectors were 13.5 ohms back then but that still means that the ECU saw only 3.375 Ohms if they were all connected in parallel. how very odd. I have been reading up on the differences of impedance and how it affects current flow etc. But 2.07 ohms vs 3.37 ohms is not what I was expecting at all !

Any chance you could screen print and upload the schematic please of the (17030) 1984 wiring?

[jimi]

Any chance you could screen print and upload the schematic please of the (17030) 1984 wiring?

I have it scanned, I'll put this link up for a couple of days, you can use it to download a copy of the manual, let me know when you have it so I can take the link down.
http://myweb.tiscali.co.uk/jlawson2/UK%20MK1%20Electrical.pdf

[Evo4Jon]

OK I have downloaded it ! Thanks Jimi !!

Yes the ECU sees 3.4 Ohms in that diagram with the 4 13.5ohms injectors in parrallel... The later models (mk1b) only 2.07 Ohms

if we take 14v as alternator voltage (max) current flowing through circuit in a mk1a is 14 / 3.4 = 4.11 amps
IN a Mk1b the current flowing is 6.76 amps

Peak and hold type injectors will see these current values as a spike and then the current will drop to a lower value once the injector is open. After market ECU's maybe dont have enough of a load to read what the injector is doing during the hold phase ?

[Evo4Jon]

Jimi, Do you have enough information to check which TPS is partnered with which ECU ?

My car is a 1989 mk1b with 89661-17140 ecu. I am curious to try the 89661-17070 on my car with the correct TPS.

When I connected the 070 ecu during testing for my fuel tank rust problems I preferred the TVIS coming in at a lower RPM, but I noticed that the AF ratio was more extreme than it should have been. It went from very lean to very rich and during part throttle was all over the place. I concluded that maybe it was due to different injectors (and it may be too), but have since learned that the TPS's are different for for the early, mid and late cars. The way the AF's were rising and falling in an extreme manner was definitely in reaction to the movement of the TPS. I am just keen to experiment.