Fuel mixture

"Nobby" wrote in message news:NxI_g.33059$ snipped-for-privacy@newsfe4-gui.ntli.net... How do you turn the mixture up on a 1990 Celica

Basically it's pinging and quite flat on performance since I have put a cold air intake and a straight through performance exhaust system on. I have turned the timing back 3 degrees to try and stop the pinging but according to a emissions test it is showing around 0.4% and it has 200215 miles on the clock and sounds like new with no smoke or rattle/rumble what's so ever.

The engine is a G3SE engine, although the top of my engine seems to be very hard to find anywhere in the UK, due to the plenum chamber and intake which is built all over the top of the rocker cover unlike all other G3SE engines including Jap spec designs. All the top parts are nearly all squared of and almost hiding the plugs from view and the only thing that seems to be adjustable is a spade ended screw on the top of the throttle valve block that the air intake ducting attaches to. Does this screw adjust the air, to increase/decrease the mixture?

The engine is a G3SE engine, although the top of my engine seems to be very hard to find anywhere in the UK, due to the plenum chamber and intake which is built all over the top of the rocker cover unlike all other G3SE engines including Jap spec designs. All the top parts are nearly all squared of and almost hiding the plugs from view and the only thing that seems to be adjustable is a spade ended screw on the top of the throttle valve block that the air intake ducting attaches to. Does this screw adjust the air, to increase/decrease the mixture?

Counter clockwise, same as the 1989 ;)

mike hunt

Nobby

The mix on a 3sge can be adjusted in many ways. but first I would put a higher grade of fuel in it to stop the pinging as the 3sge heads are very very prone to cracking when the motor pings.

The idle mix screw is hidden under a plug on the outlet side of the airflow meter if you have one. it adjusts the amount of air bypassing the flap inside. screw it out to allow more air past and lean out the mix. You can also pop open the top of the airlow meter and loosen or tighten the clock spring that profides resistance for the flap. this will affect the amount of fuel and the amount of timing the motor gets. If you have a map senser I would look for a vacuum leak in the system, this is proberbly causing the pinging and flat running.

You could also get a variable pot and wire inline with the water temp sensor to change the mix that way, kind of running with the choke on.

Or finally you could bite the bullit and get a interceptor compunter such as a unichip installed, this is the most expensive but will yead the best results and should you make any more mods such as using a 5s crank to stroke it you can account for them as well.

The engine is a G3SE engine, although the top of my engine seems to be very hard to find anywhere in the UK, due to the plenum chamber and intake which is built all over the top of the rocker cover unlike all other G3SE engines including Jap spec designs. All the top parts are nearly all squared of and almost hiding the plugs from view and the only thing that seems to be adjustable is a spade ended screw on the top of the throttle valve block that the air intake ducting attaches to. Does this screw adjust the air, to increase/decrease the mixture?

No air flo meter on this particular engine, in fact when I took it for the MOT we had trouble, finding the engine spec was defiantly not the type for the type of car I have, In fact nothing on the data base at the ministry of transport. The car has only one previous owner, with every piece of document and receipt he had from new stamped at a Toyota dealer, even the DVLA came up with the engine design, spec and block number from the day it was registered. STRANGE!!!!

I found a Pic of the type of 3SGE you have and I think the screw you are talking about on the throttle body is the idle speed adjustment screw. This type of manifold appears to STD on the 3sge after the TVIS was dropped. you can see it in the celica MR2 and caldina. When they dropped the TVIS they also dropped the airflow meter. Get the MOT guy to check again as I would people in britian with that motor on the web so the data must be somewhere.

I would look to see if any vacuum lines got knocked off when they put the cold air intake on. does the car run rough at idle? it could be that with a free flowing exhaust and modified air intake you changed the amount of "fresh air" the car get compared to the old system. resulting in more oxygen getting in and it therefore needing more fuel. did you get new extractors for the motor? it could have killed the O2 sensor when it was burning off.

also how did you change the timing. to do it properly the car needs to be warmed up, and have the t and e1 terminals of the diagnosstic connertor bridged to hold the motor on the base timing so you can adjust the dissy correctly.

I did the timing with the engine at normal running temp with the terminals on the diagnostic adapter bridged and at the speed a Haynes manual said turned to 15 degrees.

The original ducting off the valve block has only a ambient air temperature sensor which I have tested, and reads the correct value in omes, and is now fitted lower where the air comes in. I understood that the colder the air the denser the air, there for more fuel is needed to richen the mix, also the sensor tells the ECU the air need richening as if it were a cold day or started from cold.

One thing that did puzzle me was that the timing advanced very quick and not progressive through the rev range, kind of all or nothing if you no what I mean. So if I were to rev it gradually the timing would be about where it should be, but suddenly jump to its limit.

I've messed with cars for years but not as complex as this and can't remember a dizy that act's this way. The only parts on the dizy are the wires and pick up coil with no other parts to wear out, so I can only assume the ECU does all the calculations with the various info from different sensors, but all the readings from the diagnostic plug read within there limits...

I think it was "Nobby" who stated:

F i n d

y o u r

l i n e

w r a p

a n d

F I X

i t !

Y o u r

p o s t s

a r e

H A R D

t o

r e a d ! ! ! ! ! !

15 degrees base timing is way to much for these engines on normal fuel (91 RON), 10 is normally what you need to set. You can get away with 12 degrees if you use a 98 RON fuel which will give you a bit more power. There could be a chance it was accadently altered when the cold air was fitted.

The timing will advance very quickly from idle if you free rev the motor. the ECU detects no load and sets the timing to around 30 degrees. If you want to see it work normally get someone to load the motor on the greabox while you stand to one side and look. I don't recomend you do that though in case something goes wrong and the car moves.

The original ducting off the valve block has only a ambient air temperature sensor which I have tested, and reads the correct value in omes, and is now fitted lower where the air comes in. I understood that the colder the air the denser the air, there for more fuel is needed to richen the mix, also the sensor tells the ECU the air need richening as if it were a cold day or started from cold.

One thing that did puzzle me was that the timing advanced very quick and not progressive through the rev range, kind of all or nothing if you no what I mean. So if I were to rev it gradually the timing would be about where it should be, but suddenly jump to its limit.

I've messed with cars for years but not as complex as this and can't remember a dizy that act's this way. The only parts on the dizy are the wires and pick up coil with no other parts to wear out, so I can only assume the ECU does all the calculations with the various info from different sensors, but all the readings from the diagnostic plug read within there limits...

air intake and a straight through performance exhaust system on. I have turned the timing back 3 degrees to try and stop the pinging but according to a emissions test it is showing around 0.4% and it has 200215 miles on the clock and sounds like new with no smoke or rattle/rumble what's so ever.

Generally a cold intake and exhaust are not worth the effort, TBH.

hard to find anywhere in the UK,

Its a 3SGE engine actually, and they are as common as muck. Well, relatively. I have the turbocharged big brother, the 3SGTE. Virtually any MR2 or celica of this age has the 3SGE or GTE engine.

rocker cover unlike all other G3SE engines including Jap spec designs.

If you have the plenum and intake OVER the rocker cover (pointing towards the exhaust manfold) its either a 3sgte or its something some has modified to be somewhere in between - the 3sge has a side-feed manifold.

All the top parts are nearly all squared of and almost hiding the plugs from view and the only thing that seems to be adjustable is a spade ended screw on the top of the throttle valve block that the air intake ducting attaches to. Does this screw adjust the air, to increase/decrease the mixture?

Drop me an email with a picture. But the point is you wont be able to adjust the mixture as its entirely electronically controlled until about 80% WOT. If you adjust the base-bypass amount it will barely effect the on-throttle mixture and will screw up your idle. You may want to adjust your air flow meter but thats risky - as that adjusts timing advance also and shouldnt be attempted without exhaust gas analysis tools and a rolling road.

You're feeling flat because you backed the timing off, I'll wager, so if you have pinking try running some shell V-power in it instead - this will help. If you got excessive pinking you may have damaged the knock sensor but you'd likely throw an ECU code for that. Set your timing back to normal and use V-power or optimax (anything 98/99 RON) and see how it performs.

J

grade of fuel in it to stop the pinging as the 3sge heads are very very prone to cracking when the motor pings.

Errr are they? Ive seen engines with pistons blown apart through detonation but with no head damage. In fact ive yet to see anything other than overheat-warpage damage on a 3sge/3sgte head!

meter if you have one. it adjusts the amount of air bypassing the flap inside. screw it out to allow more air past and lean out the mix. You can also pop open the top of the airlow meter and loosen or tighten the clock spring that profides resistance for the flap. this will affect the amount of fuel and the amount of timing the motor gets. If you have a map senser I would look for a vacuum leak in the system, this is proberbly causing the pinging and flat running.

to change the mix that way, kind of running with the choke on.

unichip installed, this is the most expensive but will yead the best results and should you make any more mods such as using a 5s crank to stroke it you can account for them as well.

Bypassing the AFM and adjusting the water temp sensor without the relevant AFR measuring tools is dangerous for the health of your engine. Too rich and you'll get bore wash and oil contamination, too lean and detonation/pinking problems will do damage (usually to the piston ringlands first).

Cold intake and exhaust should not cause this level of performance change - in fact id be amazed if it caused any level of performance change that was feelable. He needs to address the cause of the pinking

- to lean it out to the point where pinking was a problem he'd have to have had a super-cooled intercooler fitted :D Its far more likely he has introduced an air leak somewhere or other such fault. Remember the EFI system on the 3SGE engine measures intake temperature and includes that as part of its calculations for fuelling so it should not require change due to the intake. The exhaust wont effect the pinking so id be looking elsewhere and not using supermarket fuel!

the diagnostic adapter bridged and at the speed a Haynes manual said turned to

15 degrees.

sensor which I have tested, and reads the correct value in omes, and is now fitted lower where the air comes in. I understood that the colder the air the denser the air, there for more fuel is needed to richen the mix, also the sensor tells the ECU the air need richening as if it were a cold day or started from cold.

progressive through the rev range, kind of all or nothing if you no what I mean. So if I were to rev it gradually the timing would be about where it should be, but suddenly jump to its limit.

a dizy that act's this way. The only parts on the dizy are the wires and pick up coil with no other parts to wear out, so I can only assume the ECU does all the calculations with the various info from different sensors, but all the readings from the diagnostic plug read within there limits...

Find me a picture of the engine mate. Sounds like you have a totally non-standard installation - id be asking the previous owner exactly what had been done to it - to be runnign with no AFM you are either running an ST20X series engine or an aftermarket ECU - in which case you need to know what its up to to make modifications.

When you set the timing at 10 degrees you bridge the terminals in the port and it holds the ECU from moving it while you adjust. When you remove the bridge the ECU will push it back up - the idle timing of the

3sgte is best around 24-27 degrees BTDC so it wont even show when the terminals are de-bridged!

Unlike carb cars or more simple versions the celica (and certainly one with aftermarket ECUs) are not a case of tweaking screws to adjust. You will feel flat on performance if youre car is pulling too much timing and pinking - the ECU notices this and pulls the timing back as far as possible. If you are still getting pinking you have a problem or the ECU cant pull it back far enough (i.e. your base timing is screwed up, not at 10*)

Firstly MAF, this is for Mass Air Flo, am I correct? Gary says its got a G3SE lump that reads on the on the computer as a ST182 series.

The Plenum chamber squared and fitted directly over the rocker with the 4 branches pointing to the bulkhead and 4 valve system and the Air intake snorkel is from the right of the car body as you look at it from the front to where the original filter was fitted.

The car body is the is the rounded shape not the squared pre 1990 shape.

No Cat

No flow meter on the air box

1 previous owner

No previous modds, and all stamped at Toyota from new.

Slow take off

Shitty on fuel

At around 90 miles an hour it seems a lot more responsive, topping out at

120+ miles an hour

With the rev limiter jammed it goes nuclear at 140+ miles an hour at nearly

8000rmp

Yes, "MAF" is mass air flow.

I am not sure what you or Gary mean by "G3SE lump." Toyota does have a

3SGE engine (1st 2 characters reversed). "Lump" is not an automotive term that I am familiar with, perhaps you mean "block?"

The "ST" in "ST182 refers to the series, and the 182 refers to the model within the series.

You still have not responded as to whether you have checked the stuff I recommended previously. Before you make more changes and adjustments, check the basic stuff, or you will end up making it worse before you make it better.

Lump is just a term for engine

I got it now!

Work on the other stuff I suggested, and we'll get you motoring down the road. ;-)

Thats a 3SGE engine, of about your generation IIRC. Does that look similar?

Follow Rays advice - as he says sort the simple stuff before looking to adjust it to compensate for a fault.

Yes your right, that's the same engine and plenum set-up. Some of the pipe work is different on the snorkel but the same engine never the less.

Sorry I'm a bit slow with posts, it may be Friday before I get to work on the problem as I'm going to borrow another strobe, as I think mine is arcing and giving false flash times or I have the first lead going down it connects to.