Power Loss On St-185

[RichardCrafts]

Hello All,

Hoping someone can help me out. I've recently bought an import GT4 and I'm in the process of trying to iron out a few bugs.

Firstly, it runs like a dog from cold and goes flat if you try to give it any gas until it is completely warmed up. Even when warm, it still bogs in the lower rev range. I've cleaned out the MAF sensor and that's helped a little, but it still doesn't seem right.

The fuel economy seems a bit low. I'm acheiving about 18mpg, although about half to two thirds of my mileage is around town. Is this normal?

If I really launch the car in first gear and get my foot down hard, the power backs off at about 5500rpm like hitting a rev-limiter. Second and third gear are fine. Is there a gear specific rev-limiter on these engines? I've already checked for over-boost and that isn't the cause.

Any advice or suggestions would be greatly appreciated

Thanks,

Richard

[mikeb]

That could be many things. Firstly, I would do a compression test to check that there isn't a mechanical problem. Having said that, if the idle speed is correct and stable, mechanically it should be OK. I doubt it's a split hose if it is fine once the revs pick up.

From a sensor point of view, it might be worth checking for any stored fault codes. Then test the throttle position sensor (my first guess), followed by the air intake temp sensor and coolant temp sensors. I assume that your car doesn't have a MAP sensor as it has a MAF sensor instead?

This document discusses how to test some of the sensors:

http://www.autoshop101.com/forms/h24.pdf

I think boost is restricted in 1st and 2nd gear to protect the transmission/make the car more drivable. It is often disabled though. I am sure someone will be along shortly who has done it.

[mad welshman]

what should the bhp of a gt4 st185 be? a friend has just bought one, had a few problems, new clutch etc...... does 210bhp sound ok?

cheers

[daktari]

That could be many things. Firstly, I would do a compression test to check that there isn't a mechanical problem. Having said that, if the idle speed is correct and stable, mechanically it should be OK. I doubt it's a split hose if it is fine once the revs pick up.

From a sensor point of view, it might be worth checking for any stored fault codes. Then test the throttle position sensor (my first guess), followed by the air intake temp sensor and coolant temp sensors. I assume that your car doesn't have a MAP sensor as it has a MAF sensor instead?

This document discusses how to test some of the sensors:

http://www.autoshop101.com/forms/h24.pdf

I think boost is restricted in 1st and 2nd gear to protect the transmission/make the car more drivable. It is often disabled though. I am sure someone will be along shortly who has done it.

←

Yep. Easy job to disable. Take all the trunking and gubbins to the turbo from the airbox off. Then you can see a vacuum pipe going from the actuator into a thinmetal pipe which goes back over the gear box bellhousing. Simply disconnect the vacuum pipe and plug each end with something like a small bolt and some silicon to prevent leaks.

As for the poor running, try resetting the ECU first. This will clear any fault codes and you can start with a fresh slate. It may even cure the problem as everything is reset to default. Give it a try and let us know.

what should the bhp of a gt4 st185 be?  a friend has just bought one, had a few problems, new clutch etc...... does 210bhp sound ok?

cheers

←

Sounds about right give or take, depending on whether it`s an import or UK model. UK cars run slightly lower BHP (Around 200)

[RichardCrafts]

All thanks for the advice. I recently had the fault codes cleared, and nothing has shown up since. Now you mention it, the idle is a bit eratic. It runs about 1500-1800 when cold, then levels out to about 800-900 once it's warmed up, which is pretty normal, as I understand. However, it jumps up to about 1100 after running a while. Could that be the engine itself, or is it more likely a faulty sensor or hose?

In answer to the BHP question, the UK spec GT4s put out 201hp@6000rpm/ 200lb/ft@3000rpm and the JDM models ~220hp@6000rpm/ 220lb/ft @3000rpm. As far as I understand, the increased power is due to an extra 2psi pressure being generated by the turbos.

[GT4 BOOSTER]

imports run better on 100 ron fuel also , try optimax.

[Sirius]

In answer to the BHP question, the UK spec GT4s put out 201hp@6000rpm/ 200lb/ft@3000rpm and the JDM models ~220hp@6000rpm/ 220lb/ft @3000rpm. As far as I understand, the increased power is due to an extra 2psi pressure being generated by the turbos.

←

Your power figures are pretty much right - but the pressure provided by both the UK and the JDM is identical - the extra power of the JDM is due to the 100+ octane fuel they have in Japan meaning that the car can run more aggressive ECU settings.

For your problems I would look at the ingnition system - plugs, leads, distributor cap and rotor arm. The issue your having at 5500rpm could be knock sensor, but just a guess.

For information you do have lower boost in 1st and 2nd with the standard setup, however it is a common misconception that the boost is restricted. The Turbo VSV allows an EXTRA 2-3psi in 3rd+ gears. If you disable the Turbo VSV you will end up with the lower boost setting in all gears.

The correct method is to disable the Turbo VSV and then add some form of boost controller to raise the boost in all gears.

Hope this is of use. :)

[RichardCrafts]

Just changed the leads and plugs, but I'll get the distributer checked out.

I stand cheerfully corrected on the turbo point. If the JDMs run more aggressive ECU set ups would that explain my relatively poor fuel eonomy?

Thanks to everyone for their help.

[GT4 BOOSTER]

from 20 quid i get on average 120 to 160 miles , thrash it and you can half that.

[RichardCrafts]

From what I've read Toyota claim about 23mpg for the ST185s, but about 29mpg for the 205s. Does that sound plausable, given that they carry almost the same engines?

I get about 90 miles from £20, regardless of my driving style

[GT4 BOOSTER]

the 185 is a fat old thing weighing in at an enormously fat 1420 kg , the st205 however is a slimlined version weighing in at 1380 kg , the 185 however is more tourquey through the gears ,the 205 having more top end power , so i guess those figures are about right, if i do a steady 56 mph with no boost my returns are well in excess of 160 from 20 quid.

[mikeb]

the 185 is a fat old thing weighing in at an enormously fat 1420 kg , the st205 however is a slimlined version weighing in at 1380 kg , the 185 however is more tourquey through the gears ,the 205 having more top end power , so i guess those figures are about right, if i do a steady 56 mph with no boost my returns are well in excess of 160 from 20 quid.

←

Careful with the fat and old, that's only 60kg difference there. ;)

There are lots of differences between the st185 and st205 that will affect fuel economy:

weight (all 60 kg!)

different turbo

different cams

different c/head (compression ratio?)

gear ratios

pop up headlights (night only!)

+ other things I have probably overlooked.

As yours is a JDM model it should have closed loop fuel control which would improve fuel economy. Fuel economy depends massively on what type of journey you are doing. Town driving will be lucky to see you more than 15 mpg.

From your figures, you are getting ~18 mpg which isn't too bad. Unless you are doing lots of motorway driving. First thing to check is the lambda sensor (it's pretty easy, I think it's wired directly to the diagnostics port).

[RichardCrafts]

You're right. Half my mileage is in 6 mile journeys, too and from work, through 30/40mph zones, so it sounds like I'm lucky to see even 18mpg.

At least thats one problem solved, or at least reclasified, which is good enough for me.