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 Post subject: Idle Misfire ST205
PostPosted: Thu Dec 15, 2016 6:50 pm 
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Joined: Mon Dec 12, 2016 9:30 pm
Posts: 11
Location: Farnham, Surrey.
Car Model: ST205
Hello all,

Sorry for my first post to be related to an issue that i am having with my car, but it is something i am keen to try and sort before putting it into storage this coming week. I have owned the car since June and in that time have made quite a significant amount of changes to it. As i am now reaching a stage that i am somewhat happy with this issue is something that is bugging quite a bit.

The car is fine when cold started, but misfires when the Aircon/Econ is off and the engine is up to full operating temperature. The car is absolutely fine in regular driving (well as good as, it doesn't miss under load). If i use Aircon/Econ and it raises the idle, then the misfire disappears. Otherwise, sat at lights or a junction it will jerk and miss. I have looked everywhere online and no where sheds any light.

So far i have done :-
- Denso Rotor / Cap
- o2 Sensor
- Plugs (NGK7BREIX)
- Static timing
- Cleaned ICV
- Reset ECU after each item.

Anyone had anything similar?


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 Post subject: Re: Idle Misfire ST205
PostPosted: Thu Dec 15, 2016 9:27 pm 
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Joined: Sat Sep 02, 2006 3:13 pm
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Location: Bournemouth
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Check compression, compression testers are cheap enough and could save you spending a load more on the off-chance. Since you've covered most of the other likely candidates it could be the first signs of ringland failure.

To set timing correctly, you need to use a timing light and with E1 & TE1 linked in the diagnostic connector set to 10 degrees BTDC at idle. (the link is vital or it will end up quite a bit too retarded)

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 Post subject: Re: Idle Misfire ST205
PostPosted: Thu Dec 15, 2016 9:36 pm 
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I'd suggest get a wideband on it at idle to see if it is fuelling related.

Just a quick point that Mij has had a new O2 sensor recently as well as the old one was faulty, the new one appears to be outputting the correct voltage.

I've briefly passengered in the car and it drives fine, boosts smoothly and as quick as you'd expect at 1 bar. I'd describe it as a minor miss-fire at idle.

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 Post subject: Re: Idle Misfire ST205
PostPosted: Thu Dec 15, 2016 10:28 pm 
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Location: Bournemouth
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My first ringland failure, the car drove fine apart from misfire at very light throttle & idle, funnily enough compression test was fine at this point. It steadily got worse until compression started dropping on No. 3.

If the O2 sensor is swinging between about 0.2 and 0.8V at idle then I doubt it's mixture related.

If you get a petrol smell on boost it could be an injector seal.

I don't see leads listed so could be those - worth a resistance check with a meter at least. Could be an injector. Could be many other things.

I seem to remember one of the manifold runners (No. 4 I think) has an outlet near the head - if this is open to air it could cause a slight misfire at idle, though I'd expect it to raise the idle slightly.

Could also be worth checking for dipstick blowing out / clouds of smoke from dipstick tube as another sign of ringworm.

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 Post subject: Re: Idle Misfire ST205
PostPosted: Thu Dec 15, 2016 10:40 pm 
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Hmm, Over to your story regarding dispstick Mij :-(

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 Post subject: Re: Idle Misfire ST205
PostPosted: Thu Dec 15, 2016 10:41 pm 
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Nibbles wrote:
ringworm.
:shock:

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 Post subject: Re: Idle Misfire ST205
PostPosted: Fri Dec 16, 2016 10:59 am 
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Joined: Mon Dec 12, 2016 9:30 pm
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Location: Farnham, Surrey.
Car Model: ST205
So i have compression tested the car and it came back at 170 +/- 5 accross all cylinders, i have also tested the resistance of the leads and all are below 25 ohms. The timing was checked again yesterday and was bang on 10 degrees with the timing locked out using TE1/E1.

No petrol smell apart from the corner of the engine bay that used to house the carbon canister, the O2 sensor swap has made the car a lot smoother and nicer to drive in general. As JP said above, the car pulls quite well and has no issue when moving, only at low idle speeds.

The dipstick does pop out under full boost of circa 1 Bar and has done since i have owned the car. I fully understand this points to ringland failure, there is no smoke from the filler or dipstick tube though and i would expect blowby on a car with 150k on it.

I have just read on an MR2 forum that the guy disabled his fuel pump relay / resistor pack and that solved the issue. So i will try a bypass of that to see if that solves the problem. I will also have a look again for any air leaks, although as mentioned, because it is a Gen 3 and therefore MAP, an air leak would only really cause an increase in idle speed.

I definitely feel like the more i look into it, the more my head is just in the sand because i don't want it to be piston failure.


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 Post subject: Re: Idle Misfire ST205
PostPosted: Fri Dec 16, 2016 11:13 am 
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Joined: Wed Dec 14, 2016 8:25 am
Posts: 78
Location: Russia, Izhevsk
Car Model: ST205
knock sensor look.
Errors check there?

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 Post subject: Re: Idle Misfire ST205
PostPosted: Fri Dec 16, 2016 12:29 pm 
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Joined: Mon Dec 12, 2016 9:30 pm
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Location: Farnham, Surrey.
Car Model: ST205
No error codes, they do work as i can cause 54 to pop up. Unfortunately it hadn't realised the O2 sensor was duff and never threw a code for that!


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 Post subject: Re: Idle Misfire ST205
PostPosted: Fri Dec 16, 2016 12:40 pm 
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Joined: Wed Dec 14, 2016 8:25 am
Posts: 78
Location: Russia, Izhevsk
Car Model: ST205
on the oxygen sensor 21 and the error is not displayed.
The knock sensor is working properly?
Distributor Cap old?

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 Post subject: Re: Idle Misfire ST205
PostPosted: Fri Dec 16, 2016 12:44 pm 
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Joined: Mon Dec 12, 2016 9:30 pm
Posts: 11
Location: Farnham, Surrey.
Car Model: ST205
Oxygen sensor is now fine, checked that through the diagnostics port.
Not sure how to test the Knock sensor, it isn't throwing a code. I would have thought that would have caused issues up the rev range rather than idle?
Distributor cap is new Denso.


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 Post subject: Re: Idle Misfire ST205
PostPosted: Sat Dec 17, 2016 12:00 am 
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Joined: Sat Sep 02, 2006 3:13 pm
Posts: 3580
Location: Bournemouth
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Knock sensor failure, if detected, retards the ignition greatly, mostly in the midrange. Won't affect idle.

A small air leak in one runner close to head will make one cylinder run a bit weaker. Injector seal or gasket failure / loose manifold are all possibles for this.

Is it a regular '3 cylindering' misfire or random ?

My old 205 engine pushed it's dipsick up half an inch on full boost most of the time I was running it, but then it was a tired engine to start with and I must have added another 100K ish. (It didn't suffer ringland failure). It's a warning sign for ringworm, but also normal on an old engine. Clouds of smoke out would be more worrying. If the misfire is ringlands, you'll be scratching your head for the next couple of thousand miles as it gets steadily worse until you find the clouds of smoke and compression loss in 1 cylinder (normally No. 3).

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 Post subject: Re: Idle Misfire ST205
PostPosted: Mon Dec 19, 2016 6:40 am 
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Joined: Wed Dec 14, 2016 8:25 am
Posts: 78
Location: Russia, Izhevsk
Car Model: ST205
In a range of engine speed change?
for example 800-1200? or 500-800? or something else?

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 Post subject: Re: Idle Misfire ST205
PostPosted: Mon Dec 19, 2016 3:22 pm 
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Joined: Mon Dec 12, 2016 9:30 pm
Posts: 11
Location: Farnham, Surrey.
Car Model: ST205
It is a random misfire and not limited to a single cylinder, it pherhaps misses once every 3 seconds on differing cylinders. As JP will atest, it runs perfectly fine on boost with no smoke etc, so that is a good sign. The dipstick in mine doesn't have an Oring at the top of it, however i am unable to compare it as i don't have another one to compare it to.
It also idles low, circa 500-700 RPM, which is odd, as it isn't adjustable on the Gen3 3SGTE.

One thing that has been mentioned is the use of NGK7BKREIX plugs, it coincides that i started to get issues when these were fitted to the car. Anyone had a similar issue?


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 Post subject: Re: Idle Misfire ST205
PostPosted: Mon Dec 19, 2016 5:29 pm 
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Joined: Wed Dec 14, 2016 8:25 am
Posts: 78
Location: Russia, Izhevsk
Car Model: ST205
Yes, the low idle speed.
I use a spark plug PK-20 R8. I do not much twist the engine, so they are fully satisfied with me.
The engine is running, and then as if startled, then works again?
I'm sorry, but I do not understand 40% of what is written for the translation problems. But really I want to help you or suggest.
Therefore, I ask you questions.

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