Hello all,

 

(I promise I will be subscribing soon after all these Questions!)...

 

So, my 300 has developed an idle misfire (not bad but noticeable via the exhaust sound). here are the facts....

 

above 1200 rpm it disappears.

Smooth engine otherwise.

70k miles.

No smoke etc whatsoever.

have had the odd day of it not misfiring at all. but for the majority it misfires. Only started at the weekend after a week of running fine.

Misfires in a regular pattern: hovers at 1k rpm without a misfire for a few seconds, then drops to 750rpm and misfires, then slowly creeps back up to 1k rpm over 10 seconds, stops misfiring for 3 - 5 seconds, and then repeats this process.

When driving normally revs have occasionally stayed at 1.5krpm when the clutch is depressed, instead of dropping to normal... This also seems odd and may be connected?

 

Have done a lot of searching and I am yet to find someone who has fixed a misfire so I am slightly concerned. I will speak to JeffTT tomorrow hopefully but thoguht I would open this thread for some advice, and also for anyone else that has the same problem as it may help then resolve it as I am determined!

 

i know the PTU (is thats the right letters) can be naff if it is a series one, but my 300zx is a Jap import from 94 so imagine mine would have been a series 2 anyway... I know injectors or coil packs etc can be an issue, along with maybe o2 sensors, but I am hoping that the specific pattern that the misfire happens on may lend someone some clues??...

 

It is as if when running smoothly something then overloads and causes the car to drop the revs and misfire, then whilst the revs are lower it gradully gets it signal back to teh spark plugs and they work again until it trips out again...

 

Liek I say this isn't extreme misfiring yet, but annoying enoguh and I wan't to catch it befor eit gets too bad!

 

Anyway, rambling now! Here is the video:

 

http://www.youtube.com/watch?v=8MmvJ7K7ZoU&feature=youtu.be

 

All the best,

 

William.

Here is a question -

 

So I seem to remember this issues starting just after I came out of a junction and accidentally span up and bounced off the red-line hitting the fuel cut a couple of times.... This was only a week or so after buying it and it was ever so slightly dusty or damn and the boost just clicked me out. I have never bounced off a cars red line before, but could hitting the fuel cut have caused anything to foul and start playing up?.. Is kind of why I am leaning to o2 sensors.

It's best not to throw money at replacing components to try and solve issues. Did you get a proper diagnostic done as suggested back in July? I don't just mean checking for codes, but having the complete sensor readout whilst the engine is running and being driven. Even better, take it to someone and get an AFR readout for each bank. This is the most efficient (both in time & money) method of diagnosing issues.

 

Having just watched the video for the first time, that's not a misfire at all. A misfire is when you lose a cylinder. As per this post:

You dont have a misfire fella,just poor idle id say,the engine sounds rough because of the low tickover that develops.Id get a consult on that.

 

It's probably just a lazy O2 sensor in conjunction with a badly-adjusted AAC valve. Diagnose it properly, will save you time & money. As an aside, I had a car in for mapping not long ago that was very similar to that, but that was due to the injector latency value being so far out of whack (generic chip issue).

Hey Noz, I haven't had a complete readout, The trouble is I only ever get teh odd saturday to look into it, and I have been askign my mechanic to look into the issue for absolutely weeeeks but he hasn't been able to help much.

 

If I buy the "Datascan I" do you reckon it is simple enough to diagnose the issues from it?... If so I will go ahead and buy one now so next week I can potentially have it all plugged in and see what is happening... Not sure I would know what to look for in it though.

 

I have read from the ECU and that shows no fault codes (55), I tested the o2 sensors on both banks using the ecu diagnostics, at 2k rpm the check light blinks every couple of seconds which seems like a normal reading from what I can tell.

 

Best.

Otherwise I am happy to take it to a zed specialist and have them look at it, but I live down by Bournemouth and I can't find anyone this side of the country, so that mixed with only having saturdays leaves me a bit stuck! :(

...If there was any one or a garage within a 70 mile radius that could help me sort this out over a weekend then I will happily pay for it, just time and distance which is the issue....

Hey Noz, I haven't had a complete readout, The trouble is I only ever get teh odd saturday to look into it, and I have been askign my mechanic to look into the issue for absolutely weeeeks but he hasn't been able to help much.

 

If I buy the "Datascan I" do you reckon it is simple enough to diagnose the issues from it?... If so I will go ahead and buy one now so next week I can potentially have it all plugged in and see what is happening... Not sure I would know what to look for in it though.

 

I have read from the ECU and that shows no fault codes (55), I tested the o2 sensors on both banks using the ecu diagnostics, at 2k rpm the check light blinks every couple of seconds which seems like a normal reading from what I can tell.

 

Best.

 

I've never really used Datascan other than for a quick look years ago, Nistune does everything I need and I've used that for so many years I've never had to bother with any other diagnostic software for Nissans.

 

Got an idea, so PM coming your way.

 

Edit: ...or not, Mr Registered User. What's your email addy?

Hey Noz, I haven't had a complete readout, The trouble is I only ever get teh odd saturday to look into it, and I have been askign my mechanic to look into the issue for absolutely weeeeks but he hasn't been able to help much.

 

If I buy the "Datascan I" do you reckon it is simple enough to diagnose the issues from it?... If so I will go ahead and buy one now so next week I can potentially have it all plugged in and see what is happening... Not sure I would know what to look for in it though.

 

I have read from the ECU and that shows no fault codes (55), I tested the o2 sensors on both banks using the ecu diagnostics, at 2k rpm the check light blinks every couple of seconds which seems like a normal reading from what I can tell.

 

Best.

 

I've never really used Datascan other than for a quick look years ago, Nistune does everything I need and I've used that for so many years I've never had to bother with any other diagnostic software for Nissans.

 

Got an idea, so PM coming your way.

 

Edit: ...or not, Mr Registered User. What's your email addy?

Just registered for the year :)

 

But my addy anyway is wchestnutt@gmail.com

 

Best, W

Just registered for the year :)

 

But my addy anyway is wchestnutt@gmail.com

 

Best, W

So I have managed to book it in with Jeff for Thursday - My brother has agreed to drive it up there for teh day and (fingers crossed) he can solve it during that one day... If not my bro will be staying the night haha.

 

Jeff reckons it is probably an injector cable or connection that is breaking down and causing higher resistance, so when the voltage increasing by revving teh engine it kicks back in, but under low voltage/idle it becomes irregular.

 

best,

Would this also seem symptomatic of an ignition amplifier failure?... i.e. PTU?...

...I guess it could really be anything, I have to stop worrying now, the powers above that be Jeff will look after it! :)

.. So for a final update...

 

After I thought the initial vac leak had been fixed (corroded recirculation pipe) it turned out that it STILL had a vac leak and the recirc valve was rotting away and replacing taht fixed the rough idle and missfires!!!

 

5* for Jeff from ZedWorld, great chap, many thanks!! :)

yeah was a strange one .. nor jeff or me have seen a hole in the recirc

 

and if u knew it was your self there i could of tuck those wheels for u too lol

Thanks Mark, It wasn't myself there as I have work every day but i paid my bro to drive it up :) No worries about the wheels, haha thanks for the offer though, very kind.

 

Thanks for your time on it if you worked on it! It is SO nice to have a smooth engine again.

Just thought I would say again... She is running absolutely beautifully! :)

 

So happy