Carbed 3F decel / emission control computer testing (re. after-fire) (1 Viewer)

[Cruisunder]

Old topic but today’s testing may add some new data for posterity. She has the occasional afterfire at downhill deceleration that i don’t want to result in a destroyed exhaust so started investigating. It’s reproduceable going downhill at 80-90 kph trying to brake by engine. Vac at that point around 25” Hg.

As Toyo designed the ecc to manage this exact problem, I wanted to test it. Found the ecc behind the kick panel at the passenger side (LHS, Australian cruiser).

Inspected solder joints and didn’t find any of the reported cracking.

This ecc has a 5 pin connector and is wired as beliw (25 is ecc, 26 is vac switch and 27 is 2-wire fuel cut solenoid):

The vacuum switch was grounded with engine off, and I was curious at what vacuum the switch would open and break the connection with ground. I fabbed a little rig with a sturdy syringe and suspended weights off it to create a controlled vacuum on tge switch:

Appears the switch opens at around 16” Hg. That means that when driving normally with a vacuum of 19-20” the vacuum switch is open which the ecc sees as the engine not being under load.

I then connected the fuel cut solenoid to 12V so it would provide fuel for idle, and then connected a multimeter to the ground wire from the ecc to the solenoid. From idle up to almost 2,000 rpm the ecc provided ground to the solenoid. and at 2,000 rpm the ecc disconnected from ground to close the solenoid and idle fuel circuit.

Posting Gregory’s manual for testing the decel system for info:

So the entire system functioned exactly how it should, cutting fuel not needed during deceleration.

Still have an occasional afterfire event …

With the ecc system ruled out, wgat else can I look at?

Hope this test serves someone else, thanks guys!

 

[Spike Strip]

That Emissions Computer thing is way different than the USA version, to control the ICS.

If you're getting exhaust backfire it's only because too much unburned fuel is going down the exhaust and igniting, so it's most likely a carburetor issue, but could also be fouled plugs or bad ignition wires, meaning a cylinder isn't firing sending the fuel downstream ...

Nice pix, thank you! I've never seen the 3F version of that.

 

[OSS]

Advance your timing and see if that helps. As @Spike Strip stated - unburned fuel is ending up in the exhaust

 

[Spike Strip]

@Cruisunder

Is there such a thing as a 3F Emission Manual (or similar from Toyota), or only in the Gregory's Manual ?

Or is it correct to think there are not many emission controls on the 3F engine to warrant a Factory manual?

The decel circuit might be described in the 1981-1990 60-series Chassis Manual, but it's not in the one available in the US. Was there a specific manual for the 3F carb'd FJ62 in Aus ?

And is the same ECC you're using?

Cheers !

 

[Cruisunder]

@Cruisunder

Is there such a thing as a 3F Emission Manual (or similar from Toyota), or only in the Gregory's Manual ?

Or is it correct to think there are not many emission controls on the 3F engine to warrant a Factory manual?

The decel circuit might be described in the 1981-1990 60-series Chassis Manual, but it's not in the one available in the US. Was there a specific manual for the 3F carb'd FJ62 in Aus ?

And is the same ECC you're using?

Cheers !


View attachment 2970741

Yeah that's the one I have.

I'll look at the FSMs tonight.

 

[Cruisunder]

Didn’t find anything emission control related in my FSM which is US/Canada.

The way it functions and the values triggering the fuel cut solenoid to close seem very similar that for the 2F, below:

Would love to have a non-US 3F manual, but Gregory’s is pretty good too!

 

[Cruisunder]

Advance your timing and see if that helps. As @Spike Strip stated - unburned fuel is ending up in the exhaust

@OSS what step-change advance would you say to note a change? She’s currently sitting at 7-9 deg BTDC.

 

[OSS]

Advance it a bit then test drive. Keep doing that incrementally until you hear it ping.
Back off (retard) about 2° from where you heard it ping and see how the engine runs/power/torque by the seat of your pants and ears. See if the afterburning diminished.
Some of the fuel entering the cylinders isn’t getting fully burned and is exiting into the exhaust.

No guarantee that advancing the timing will eliminate the after burning, but it can’t hurt to try.

There’s more going on with your engine than an inop deceleration fuel cut system
When I purposely disconnected my vacuum switch on my 2F to disable deceleration fuel cut, the exhaust only slightly burbles/gurgles when engine braking down a long hill. Definitely not troublesome or harmful - and barely noticeable.

 

[Spike Strip]

Yes, @Cruisunder , ICS seems to function identically to the 2F, though with fewer emission circuits or inputs for the ECC. When people desmog here, on a 2F, the ECC is usually removed or disconnected, and almost every ECC I've come across has failed by now, anyway. That decel fuel cut feature on the Aisan carbs is a nice thing to have, so I was just wondering if there were a simpler way to make it functional without the USA-version ECC.

Thanks very much for posting.

 

[ToyotaMatt]

@Engineer8000

this is Russ's Specialty ...............

 

[Engineer8000]

The 3f computer could be made to work at the correct rpm for the 2f application. Could one of you with a 89550-60180 post some clear pictures of the component side of the circuit board and tell me the transistor and IC numbers. The 81+ 2f computers are not that complicated. I have all the replacement parts to make them work.

 

[Cruisunder]

Advance it a bit then test drive. Keep doing that incrementally until you hear it ping.
Back off (retard) about 2° from where you heard it ping and see how the engine runs/power/torque by the seat of your pants and ears. See if the afterburning diminished.
Some of the fuel entering the cylinders isn’t getting fully burned and is exiting into the exhaust.

No guarantee that advancing the timing will eliminate the after burning, but it can’t hurt to try.

There’s more going on with your engine than an inop deceleration fuel cut system
When I purposely disconnected my vacuum switch on my 2F to disable deceleration fuel cut, the exhaust only slightly burbles/gurgles when engine braking down a long hill. Definitely not troublesome or harmful - and barely noticeable.

The decel circuit was tested and works as it is supposed to, ruling out the slow / idle circuit as the culprit for excess fuel going to the exhaust. So what “more going on” could cause this to happen? Carb overhauled 2 yrs ago, vacuum leak tested, new spark plugs / points / dizzy cap & rotor, valve clearances & timing set to specs.

 

[Cruisunder]

The 3f computer could be made to work at the correct rpm for the 2f application. Could one of you with a 89550-60180 post some clear pictures of the component side of the circuit board and tell me the transistor and IC numbers. The 81+ 2f computers are not that complicated. I have all the replacement parts to make them work.

 

[Cruisunder]

 

[Engineer8000]

@Cruisunder Thanks for the great pictures. Can you tell me any of the markings on the seven circled components, thank you.

 

[Cruisunder]

@Cruisunder Thanks for the great pictures. Can you tell me any of the markings on the seven circled components, thank you.

I'll need a microscope for that
Will try

 

[Engineer8000]

My guesses based on similar Fujitsu Ten circuits:

1 .33 (334), .47 (474) or .68 (684) or maybe 473?
2 2sd571 (or just D571)
3 23c945 (or just c945)
4 104, 25v
5 6.8 or 9.1
6 MB4206
7 6.8 or 9.1

 

[Cruisunder]

1 - invisible
2 - D57.. and 1.. underneath
3 - C945 and K78A underneath
4 - 25V and 4732 underneath
5 - 9.. I think
6 - MB4206
7 - 6.. I think

 

[Cruisunder]

Before giving the suggested timing advance increase a go, I decided to pull the dizzy (19100-61160) and check it over as a matter of eliminating possibilities. Found it to be pretty gunked up, to the extent that when extending the governor springs by pushing the weights out, the springs wouldn’t return them.

Cleaned it all out and seems to move freely now. Will put back and start testing timing curves tomorrow I hope. Does anyone know if the small spring looks like it’s designed that way with the play it has around the post?

Btw, stop pin bushing stiil seemed ok.