GR86 Jerky acceleration when cold?

[Triggaaar]

I would guess the transient fuelling is rather lean, to contribute to getting the CO2 and NOx figures as low as possible.

But what's that got to do with how the throttle is mapped to be all on or all off?

 

[Itcaptainslow]

But what's that got to do with how the throttle is mapped to be all on or all off?

Transient fuelling is the part of the map to do with fuel delivery/mixture when coming on/off the throttle.

 

[Triggaaar]

Transient fuelling is the part of the map to do with fuel delivery/mixture when coming on/off the throttle.

A couple of things:
1) If the mapping is changed such that the car has more emissions, surely it will be in danger of failing later MOTs
2) People are complaining about the inability to gradually add throttle - I don't understand how a leaner fuel mixture would affect that. Indeed you can gradually add throttle, power, revs, it's just not as easy with the pedal for some as it should be.

 

[RedGR86]

There is light at the end of the tunnel!!



Fensport now have a GR86 test mule.

 

[Itcaptainslow]

A couple of things:
1) If the mapping is changed such that the car has more emissions, surely it will be in danger of failing later MOTs
2) People are complaining about the inability to gradually add throttle - I don't understand how a leaner fuel mixture would affect that. Indeed you can gradually add throttle, power, revs, it's just not as easy with the pedal for some as it should be.

I’m not sure - I would guess it depends on the quality of the remap. I can only speak from most recent experience of owning a live mapped Focus ST170, which always passed MOT emissions tests with no issues. Beyond that, hopefully someone with more expertise and knowledge will be able to advise!

 

[Itcaptainslow]

There is light at the end of the tunnel!!



Fensport now have a GR86 test mule.

It’ll be interesting to see what they can achieve - although it would somewhat bugger many people’s plans I’m sure of servicing the car at a Toyota dealer & retaining warranty cover up to ten years (mine included).

 

[RedGR86]

It’ll be interesting to see what they can achieve - although it would somewhat bugger many people’s plans I’m sure of servicing the car at a Toyota dealer & retaining warranty cover up to ten years (mine included).

It they are doing it with ECUTek it might be a switchable map, but will wait and see. If they can't sort it I will be selling mine come the spring (unless I can get a decent offer from Motorway etc etc).

For me it's such a major flaw in what should otherwise be a brilliant little car.

 

[Vimes]

The direct and port injection transition is complex with different maps when cold to bring the cat up to temperature, plus the camshaft profile will need to be fairly aggressive to enable the (near) 100bhp/litre NA output. Which will make smooth cold running difficult.

Good explanation of the injection side covered in this YouTube video:

 

[ZN8]

I think the jerky throttle is amplified by the top heavy mapping of the throttle travel.

Hopefully somebody will remap it soon enough

There is quite a lot of movement/slack in the the drivetrain, this will amplify the jerkiness as it all bounces around, the diff bushes in particular are very soft.

 

[Conscript]

There is quite a lot of movement/slack in the the drivetrain, this will amplify the jerkiness as it all bounces around, the diff bushes in particular are very soft.

That's a very good point. The previous gen had notoriously soft engine and transmission mounts. I upgraded them to the TRD/STI mounts (I was trying to fix a different issue at the time, I had an aftermarket exhaust manifold which was making contact with the engine undertray on acceleration), but I seem to remember it really helped throttle response too.

When look at the below comparison video (for Stock vs Cusco engine mounts) you can really see how much the engine moves under load.

 

[RedGR86]

There is quite a lot of movement/slack in the the drivetrain, this will amplify the jerkiness as it all bounces around, the diff bushes in particular are very soft.

That's interesting, as there have been times where I wonder how much is the suspension / drivetrain and how it's interacting with a less than perfect road surface, plus the mapping / fueling issues that have been discussed.

 

[AdamST205]

How does it help emission readings?

The throttle is kept open after you take the foot off the accelerator. Also known as rev hang. This is done for emissions to help for a cleaner burn. Someone who is used to flat shifting or heel toe. This can become annoying very fast. It also seems to be in the lower gears only. If I blip the throttle while coasting it works instantly but after a gear change up or down there is a little bit of rev hang.

I think the clutch adjustment helps because you are pushing the bite point closer to the bulkhead so the travel isn't as far masking the throttle issues a little. I still need to do mine lower and match it with the brake pedal.

My 2004 Saab 9-5 Aero is easier to rev match on the downshift than my new GR86 which shouldn't be the case. That car is also drive by wire. My old Ignis Sport was sublime but that was cable clutch and accelerator.

 

[FRAJ]

The throttle is kept open after you take the foot off the accelerator. Also known as rev hang. This is done for emissions to help for a cleaner burn. Someone who is used to flat shifting or heel toe. This can become annoying very fast. It also seems to be in the lower gears only. If I blip the throttle while coasting it works instantly but after a gear change up or down there is a little bit of rev hang.

I think the clutch adjustment helps because you are pushing the bite point closer to the bulkhead so the travel isn't as far masking the throttle issues a little. I still need to do mine lower and match it with the brake pedal.

My 2004 Saab 9-5 Aero is easier to rev match on the downshift than my new GR86 which shouldn't be the case. That car is also drive by wire. My old Ignis Sport was sublime but that was cable clutch and accelerator.

Daft question please @AdamST205 : I have seen this issue mentioned before but never really understood why it affects rev matching. When down changing I am blipping the revs up where the key point is how quick the revs rise. Whether they fall artificially slowly doesn't matter - or am I missing something? I mean it could be a benefit in giving you longer to get the gear in and clutch up to meet revs

 

[AdamST205]

Daft question please @AdamST205 : I have seen this issue mentioned before but never really understood why it affects rev matching. When down changing I am blipping the revs up where the key point is how quick the revs rise. Whether they fall artificially slowly doesn't matter - or am I missing something? I mean it could be a benefit in giving you longer to get the gear in and clutch up to meet revs

What I mean is it is almost as if I press the accelerator and nothing happens because the ECU is overriding my input on the accelerator

Like I said if I jab the throttle when coasting it is instantaneous yet if I do it while downshifting nothing happens yet push it down further and it just revs really high.

Maybe I just need practice but I have tracked plenty of cars over 10+ years and never had this problem before but they were all older cars too so maybe this is just a modern thing from the past 5 years with manual transmissions and I need to reteach myself or something.

 

[Triggaaar]

The throttle is kept open after you take the foot off the accelerator. Also known as rev hang. This is done for emissions to help for a cleaner burn. Someone who is used to flat shifting or heel toe. This can become annoying very fast. It also seems to be in the lower gears only. If I blip the throttle while coasting it works instantly but after a gear change up or down there is a little bit of rev hang.

Thanks. Would fixing the issue cause any problem with passing emissions in MOTs?

 

[AdamST205]

Thanks. Would fixing the issue cause any problem with passing emissions in MOTs?

No because Euro 6 is the certificate for the vehicle which is where all this stuff comes from. A bit like when VW did that cheat thing with their dieselgate.

Mot emissions is different.

 

[Triggaaar]

No because Euro 6 is the certificate for the vehicle which is where all this stuff comes from. A bit like when VW did that cheat thing with their dieselgate.

Mot emissions is different.

I don't quite follow.

When my current car has its MOT, it doesn't have to pass a set standard of emissions, it has to pass what the manufacturer stated it should pass. So I wondered if that meant Toyota stated the 86 meets one standard, and our changes could mean it no longer does (therefore I don't understand how VWs pass),

 

[leosayer]

There is quite a lot of movement/slack in the the drivetrain, this will amplify the jerkiness as it all bounces around, the diff bushes in particular are very soft.

I agree it almost feels like the engine and gearbox mounts are worn.

Whilst the bodyshell feels really stiff giving the suspension a great platform to work from, the transmission feels the opposite...loose and imprecise.

I know from experience the benefits of replacing worn engine mounts with stiffer ones. I replaced the hydraulic mounts on my 993 with the semi solid RS version which improved the whole driving experience with a slight increase in noise and vibration.

I'd be happy to make the same compromise on the GR86.

 

[AdamST205]

I don't quite follow.

When my current car has its MOT, it doesn't have to pass a set standard of emissions, it has to pass what the manufacturer stated it should pass. So I wondered if that meant Toyota stated the 86 meets one standard, and our changes could mean it no longer does (therefore I don't understand how VWs pass),

The M.O.T is quite simple in comparison to the Euro 6 test. M.O.T test you will just hold the car at certain revs and record the figure (idle and fast idle). The test for making a car Euro 6 compliant is far more vigorous and tests the car in a "real world" environment. A manufacturer for example will build a car to a certain spec then hand it over to a regulatory body to pass for Euro 6 emissions. Once it has passed it doesn't need another test and all cars built to the same standard will not need one either.

This is why DPF and EGR removal is highly illegal as you are messing with your Euro certificate. It will still pass M.O.T no problem as that is a different UK based test.

There are plenty of people who mod their cars for example and remove one of the two cats if it has one. You might still pass an M.O.T but if it went for a Euro 6 test (which doesn't exist). It would most likely fail.

I am sure once Fensport have a play they will be able to make a map that gets rid of the rev hang and still passes M.O.T test. The only problem we will have as owners is it will most likely invalidate warranty.

 

[Triggaaar]

The M.O.T is quite simple in comparison to the Euro 6 test. M.O.T test you will just hold the car at certain revs and record the figure (idle and fast idle). The test for making a car Euro 6 compliant is far more vigorous and tests the car in a "real world" environment.

Ok cheers.

The only problem we will have as owners is it will most likely invalidate warranty.

The 'only problem'. It's quite a big problem.