Being a mechanic im just wondering what these vehicles are weak on apart from the general. Got a gt4 st205 jdm model as some may know and the last few weeks it has a slight hesitation when either full throttle of just cruicing, replaced plugs leads and coil just thinking is the mafs on these weak when uping the boost? its the only really thing i have left to change to be honest.So to clarify not really a misfire as such but a bit jerky hesitation when driving it.hope someone can help cheers

Coils are extremely rare to fail...

If you have an ignition problem then it is quite likely to be the rotor arm, dizzy cap, leads or plugs...

Change the rotor arm and cap and then re-set/check the ignition timing.

As you have a 205, you don't have a MAF, you have a MAP sensor. These are generally extremely reliable. I would recommend looking elsewhere for your problem.

As ever, check your fault codes before doing ANY further diagnosis...

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Kris
95 ST205 - slept for 10 years, now waking up...
Avensis
http://www.gtfours.co.uk
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Turbocharging - the replacement for displacement

I have known a coil failure, and this caused misfire at high boost but was ok cruising and below.

A few common causes of hesitation in a 205 (185 add leaks in vac / intake hoses as these have a AFM at the filter)

1. poor fuel in a JDM version. Use Vpower or next best is tesco 99.
2. ignition faults as you've already changed, plus dizzy cap and rotor arm. Have been a few rotor arms come loose recently.
3. Knock sensor fault. ECU light comes on and ECU limits boost and retards ignition.
4. Timing incorrectly set. Must be set to 10 degrees WHILE E1 and TE! ARE SHORTED IN THE DIAGNOSTIC CONNECTOR. It is common to people to set timing to 10deg without the link, leaving it quite a bit retarded.

Check for error codes which will also verify the engine light works (many dodgy sales places remove the bulb). This is done by linking E1 & TE1 (as above) then switching on the ignition. The engine bulb will flash constantly for no errors or will flash the error codes a digit at a time. e.g. code 52 (knock sensor) is 5 flashes then 2 flashes.

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If at first you don't suck seed, try drier grain.

I too had an on-boost misfire, that was traced down to corroded power cables going to the coil.

Hey guys good response i thought the basics would come out which are all perfect checked engine diagnostics and all is good, the cars always run on 100 ron which is what we have out here in nz, the rotor arm cap and leads are all brand new and uprated trd spec ones. there is no boost issues at all or leaks its just very hard to explain its a very slight hesitation not misfire through the rev range but maybe im being fussy as ive never had one of these before and i know they are hugely over fuelled. its running on 1 bar of boost and holding all the way so that really not the issue.Maybe earthing problem???As for the timing its spot on and the cams have just been replaced with the belt and tensioners etc and all is perfect.

What plugs are you using? Many people experience issues with Iridium plugs.

Try platinum ones if you aren't running them already. If the problem still exists gap them to 0.75mm and see if that solves the problem.

Aftermarket cams?

_________________
Kris
95 ST205 - slept for 10 years, now waking up...
Avensis
http://www.gtfours.co.uk
_______________________________________
Turbocharging - the replacement for displacement

with regards to a slight hesitation / misfire under boost mine had it was fouled spark plugs and the annoyance of the middle rocker gasket bolt working its way loose and leaking oil into number 2 & 3, some new grade 7 irridium's and tightening back up the rocker gasket and hey presto, no misfire, but as kris says, are they standard cams? or aftermarket?

they are platinum plugs guys and this week its got ever so slightly worse and has chucked a fualt code up for lambda sensor just got to source one now......huray hopefully once i get one it will fix it.Explains why the fuelling and use of it is all over the place aswell.
Oh and by the way they are aftermarket cams too.
Cheers guys just got to work out which o2 is down.

THere's only one O2, the 4 wire one right next to the turbo. If you see another sensor in the bottom of the downpipe/CAT it's actually an overheat sensor (JDM models only)

Replacements are available from Toyota but are quite expensive. General purpose ones should fit, it's a standardish 4 wire Zirconia sensor

I've bought a couple from SAP Motorparts for about £35 but neither has been quite right performance wise. Then again as a mechanic the local motorfactors + discount might work out well

cheers buddy yeah it is the jdm overheat sensor, im on the case of getting a geni one so all good.Hopefully have it within a few days shipping it from uk to auckland. since finding the fault code the other day its only got worse day by day.....

I believe the cat overtemp sensor will have little/no effect on engine running. In fact I have run without a cat and the sensor for years.

The O2 sensor at teh top of the downpipe however is critical to smooth running.

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JP
GT4DC Treasurer

Grey St185 RC
Silver BMW E46 M3
Multicolour yawn Honda VFR400
Silver Honda Civic Type-R

same as above, i have run for 2 years with no cat and no sensor and run fine, i only run the o2 sensor