Lots of carbon coming from a 4AG

[phrostbyte]

Hey peeps,
After trying every method I know of to try to fix the 4AGE in my cousin's AE86...

When we got the engine, it was running like absolute shit. I worked my wonders and it's now an engine that pushes pretty fkn nicely. But there is still one problem. We are getting a hell of alot of carbon out of the exhaust when it's either under lots of load or when the revs are high enough when not under load.

I've tried changing injectors, got a cam breather filter, cleaned out the intake manifold, etc etc. Our last thought was that it was possibly a blown HG between cylinders and oil routes. Compression check brought up 185, 190, 180, 185, which as you all know, is fairly nice compression for a stock 88kW Bigport 4AGE.

Any thoughts people?

Cheers,
Kev.

[Nim]

It's definatly notun-burnt fuel? Perhaps it's running rich up high?

Chuck it on a Dyno and get A/F ratios, unless you've already eliminated this.

[phrostbyte]

The exhaust definately does smell like its running rich.. But the coil is a brand new Bosch MEC-717, brand new NGK Iridium plugs, brand new Top Gun 8.8MM Pro series racing leads... Definately not an ignition problem. And we have tried stock old model bigport spray injectors and late model bigport squirt injectors, no difference made. The pump is a JDM AE86 in-tank fuel pump.



Edit: the question is WHY it's running rich... (We've tried 3 different model 4AG ECU's by the way)

Kev.

[BradW]

Cold start injector leaking.

[slide86]

excessive fuel pressure in the rail. ie pressure regulator is always shut providing max pressure to the rail all the time.

does it have flap typre AFM. My GZE had the same problem when the spring in the AFM was slack causing the flap to move to easily and provide incorrect signal. black smoke would come spewing out the rear under acceleration.
minor adjustment of the spring made it better but not perfect....

[RWDboy]

Yeah excessive carbon could be just a result of rich mixture.

It may not even smell like it's 'running rich' (ie it may not smell like fuel) because complete combustion is still occuring - that is to say, the mixture is still getting fully burnt (or as close as cars tend to get anyway) but the resulting by-product mixture is different

You will always get Carbon, Carbon Oxides (gases), hydrocarbons and nitric emissions. What will give you more carbon emissions (black crud) is when the mixture is very rich, and still burning properly. A good idea would be to check the EGO sensor, AFM, cold start injector, fuel pressure etc and make sure they are still operating ok.

Definitely sounds more like a fuel issue than an ignition issue.

[Biggo]

I wonder if it keeps this up will it stuff the cat?

[RWDboy]

Well sorta and sorta not... as long as unburnt fuel isn't getting to the cat then it won't be excessively bad. But carbon coating the thing can't be good either.

[phrostbyte]

Lol if it had a cat, i can guarantee it would be absolutely screwed by now . We havent bought a proper exhaust for the thing yet, it's using parts of a 1.5" 4AC exhaust with a cannon on the back at this stage.

Gave the cold start injector thing a shot, only thing that did was made it a bit harder to start hahah. Will try swapping the fuel pressure regulator tomorrow.

Thanks,
Kev.

[ira11y]

Also make sure all the vacume lines are in good condition, especially to the MAP sensor. It could also be a MAP sensor on the way out, if you have a spare swap it over and see what happens.

Remeber that the old ecu maps for the bigport generally ran fairly rich anyway and will usually blow a small amount of fuel/blackish smoke on hard acceleration and at high rpm when the fuel air mix is pretty high on the map point.

[30psi 4agte]

What spark plug gap are you running?. Sounds like it could be breaking down under load / high rpm. This doesn't mean it may necessarily miss, but may not be providing a clean / full burn and the excess carbon is being noticed out the back.
Spark plug gap should be 0.8mm.
Q/ What spark plug gap do you run?
This may not be the cause of your problem but definately give it a go as I have seen this happen before.

[phrostbyte]

Plug gap is 1.1MM as specified by Toyota. More powerful coil than usual too, and massive spark plug cables, we actually tested with a pin in the spark cable to a ground point, the spark managed to jump a huge 11cm to ground when not compressed, so I don't see any problems with a 1.1MM gap under compression. I personally run 1.1MM gap plugs on my 4AGE with no carbon or misfire problems...

MAP sensor is fine, I was actually running it on my 4AGE for a while, no problems there. We have tried two different model bigport ECUs aswell, no difference.

It is a pickle, no doubt about it

Kev.

[30psi 4agte]

I thought you may say that. I knew you had 8.8mm leads and decent coil but please give it a try!!!!
like i said it may not be the cause of your prob BUT i have had it happen even with a decent coil!!. For the 10 min it takes to do just give it a go it will eliminate another possible cause for your problem.
Then send me a pm and tell me that you bloody told me it wasnt it if it doesnt work ( Ha Ha)
All the best m8

[RWDboy]

Not getting a clean full-burn usually results in fuel coming through the exhaust, not carbon.

[30psi 4agte]

TRUE. I think it is still likely to be burning the fuel in the cumbustion process but most likely not all of it(hence the excess carbon of a uncompleted burn). Like i said im prob wrong and it may not be his prob but i have seen this before and it may well be worth a shot!