Weird acceleration under boost !!

[nmx68u]

Hi all,

I drive an mr2 turbo, and just recently i had the accelerator cable adjusted as it had a bit of play.

Now what happens is on 100% throttle when the car hits about 3500rpm where boost comes on hard the engine starts to run rough, blows a crap load of smoke, and makes a weird exhaust note, kind of like a burbling noise.

On about 75-80% throttle, it does none of the above :T it has got me confused.

What could be causing this ???


If there is any more info required, such as mods etc, let me know!
Thanks :)

[Forg]

Had anything else done to it? It sounds like it's running rich; all of my cars have had a similar (but much less marked) response to an absolute flooring of the throttle, but if yours is fiddled a little then maybe the acceleration enrichment is a bit too much now the throttle's been adjusted to teh right spot?

[nmx68u]

Thanks Forg !!

It did have a service at the same time, which included plugs, leads, oil, fuel filter, oil filter and adjustment of the idle + accelerator cable.

Is it possible that something is leaking to cause the turbo to boost more than normal, because i know that its a built in function of the stock ECU to dump excess fuel when the boost is too high !

[Forg]

I can't think of a leak that'd cause it to be reading higher boost than it's really running; but hey, anything's possible. I know nothing about tuning an MR2, but I'd be ringing the place that tuned it & asking them these questions. For example, is it possible they've done something to a factory standard, and it's got an aftermarket chip or something?

I suppose that in short I'm saying that it doesn't sound drastic to me; could even be a loose wire. :)

[nmx68u]

:) cool.. thanks forg for your help !

I will be going back to my mechanic, but i like knowing the possibilities of the problem before asking the question.

[bitsMisin]

What colour smoke is it? When I did my first oil change it all started to smoke white cos there must have been stop smoke in the oil. Put some more in and it was alright, but since then i have had a recon anyway. Hope it's balck smoke though...

[RolinAuto]

If someone has adjusted the accelerator cable they may have accidently put the TPS sensor out.
May not be the cause but if the acc cable was the only thing adjusted, there's a good chance it put the TPS out of sync.
Throttle Postion Sensor!

[MWP]

Im thinking somthing different...
Most ECUs when at 100% throttle will squirt as much fuel as possible.

Before you got your cable adjusted, its possible that you were never reaching 100% throttle because your foot hit the floor or the pedal stop first (instead of the TB stop at 100%).

So now when you floor it you are getting 100% throttle causing the ECU to squirt a lot of fuel uncovering this new problem.

There probably isnt a lot you can do other than go with an aftermarket ECU or if you have one get it reprogrammed.

Probably the best idea is just not to floor it as early (drive it like a carbed engine). Flooring it later in the RPM range probably wont cause the surging problems.

[Cookiemonster]

Originally posted by MWP
Most ECUs when at 100% throttle will squirt as much fuel as possible.

I don't agree with that. The amount of fuel delivered is determined by many parameters such as manifold pressure, air temperature etc as read from a fuel map and then percentage changes to the fuel delivery can be adjusted by say an O2 sensor etc.

The ECU doesn't just drive the injectors at 100% when on full throttle.

[nmx68u]

My mechanic did say after the service that he thought my O2 Sensor wasnt 100%, and he said this because on a cold startup it would run rough for the first second before idling. Do you think that the O2 sensor can be related back to my problem im now having with the throttle ?

I still havent had a chance to take it back, and there is way too many variables that can be the cause of the problem, i think i might try adjusting the throttle back to its original position until i have the time to have it looked at.

Thanks for all your input guys !

[rony]

Sounds to me like the throttle is going past full open and is started to close again, if the ECU thinks that the TPS is past 100% it might think there's a bit of a fault and run really rich to protect the engine.

Most likely not going to be the 02 sensor as they are for light cruise(20-30% throttle) and idle conditions only, they are not used for cold start up as they don't warm until at least a min or two after startup, often longer.

Has it got aftermarket or standard ECU??

[nmx68u]

Just a standard ECU.... So does it sound like the throttle has been adjusted too much and is now opening past its 100% point ??? definately sounds feasible !!

[Cookiemonster]

Doesn't the thottle body have a metal stop point to prevent the throttle from going to far?

[TT]

are your new Plugs gapped properly?

[nmx68u]

Not too sure..

so many things could be wrong :(

car's are such a pain in the arse !!