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.

Me and Jeff are not at the workshop tomorrow so if you want to contact us on Friday your more than welcome

 

but when was the spark plugs last changed ?

Me and Jeff are not at the workshop tomorrow so if you want to contact us on Friday your more than welcome

 

but when was the spark plugs last changed ?

 

Haha thanks Mark, Friday it is :) Bought some Gaskets for the gearbox off you guys last week and had some cracking advice from him with regards the gearbox noise and that is now all perfect! so thanks for that, hoping we can work some magic on this too, and then I will also get the cam belt and water pump etc through you guys if possible.

my money is on un-plugging the injector connections and finding a heavy green scale on the pins....;)

Thanks znut, I'll get that checked out! :) still very slowly learning my way around the bay, most daunting engine I have ever had that's for sure!

 

Also Mark, no idea when plugs were done!!... Never?!!

So which connectors are the injectors and which are the coils?... I can see the 5 directly on top of the block and the 6th is a bit hidden. But I thought that was a coil connector coming from the PTU...

ok the Injectors are the small 2 wire plugs tucked down with in the plenum . Coil packs are the Larger 3 wire plugs

ok the Injectors are the small 2 wire plugs tucked down with in the plenum . Coil packs are the Larger 3 wire plugs

 

Grand thanks Mark!

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.

Hi Jimmer, thanks for the input - I know from the video it looks like just an instable idle, but when you are around by the exhausts you can feel the gaps in exhaust gas when the miss occurs?... And it very much sounds like a miss on a cylinder or two rather than a hunting or general low tickover sounds, as sometimes it can tick over fine and low revs and sounds smooth... I'll try and get a sound file of the exhausts tomorrow with my big camera! :)

To get you started:

 

Hook it up to Consult and check all sensor readings are within spec

Determine if it's a single cylinder (play musical coil packs to find the culprit)

Check electrical connections

Check condition of plugs (they need changing going by what you've said)

Whilst plugs are out do a compression test

 

That little lot will take approximately 90 mins.

That's for the info, I will check that this week. Is it ok to pull the power from the coils while the engine is on?

 

I don't know if this is related or normal behaviour but if I sit at idle and touch the accellerator with the slightest pressure the minimum amount of change I can get is from 1 krpm to 2k rmp.. As it it jump to 2, and I can't get it to hover inbetween these numbers,... Whether this is normal or whether this may indicate sticky injectors or something I don't know?...

So this morning she was misfiring, went out for lunch and it cleared up! So inconsistent I can't attribute it to one thing...

That's for the info, I will check that this week. Is it ok to pull the power from the coils while the engine is on?

 

I don't know if this is related or normal behaviour but if I sit at idle and touch the accellerator with the slightest pressure the minimum amount of change I can get is from 1 krpm to 2k rmp.. As it it jump to 2, and I can't get it to hover inbetween these numbers,... Whether this is normal or whether this may indicate sticky injectors or something I don't know?...

 

 

Right... it's unlikely to be just one thing...

 

you need to do a full PM on the car first to rule out all the silly little things...

 

do run the ecu diags to see if there are any codes (best with a conzult or similar system) but you can just run the codes off the ecu.

 

check and clean all connectors, everyone you can see and find, including MAF (under the front panel), CAS, TPS, PTU, injectors, coil packs, ecu temp sender unit...

 

check filters, petrol, air... check plugs.

 

check TPS voltage (do a search there are guides) you only need a volt meter.

 

you really need a Conzult cable and software, even the free version will do so you can check readings from the ecu.

 

take your pic...

http://www.ebay.co.uk/sch/i.html?_trksid=p5197.m570.l1313.TR10.TRC0.A0.Xconzult.TRS0&_nkw=conzult&_sacat=0&_from=R40

 

you will also be able to use other software with it like ecutalk and dr300zx ..etc...

Hi Guys,

 

Ok i have had an air leak in the vac system fixed, cleaned the MAF but the issue is still here.

 

Thing is if the MAF is unplugged then there is no missfire or rough idle at all!... I reckon that points to a bad MAF? If it were coils or injectors/electric related then it would be consistent right?

 

Best,

 

William.

Have you checked the tps voltage recently?

Ahh no not yet, I will do that this week.

 

But have a reasonable result so far! Tonight on gumtree found a brand new maf and loads of other bits for £60 and it was just round the corner from me !!

 

Just installed into car and the rough idle is considerably reduced, by about 80% at least. It seems to REALLY big down around 3k rpm when you tweak the throttle, and smells MAJORLY of fuel, is this due to over fuelling where the ecu is now making it run lean??....

 

I have unplugged the battery to reset the ecu and tomorrow a bit if a drive will hopefully relearn the ecu with a working nF, unless this is some other issue uncovering itself?!?!

 

Ahhhgggrtr! Really hoping it wil be fine

PLEASE HELP??...

 

So I just took it for a drive after letting the ECU reset after teh batt being unplugged for an hour. man it runs like ASS!!!! any throttle means it bogs down BAD, and then I tried slowly accelerating in 2nd and at about 4.5k it was like hitting a brick wall!...

 

Is this just the ECU needing to re-learn or is this some other issue?! And if it does need to re learn what is teh best way to do that? as it stand it is almost un drivable.

 

This is with a supposedly brand new MAF in it. Before this it was a bit lumpy on idle but wouldn't ever hesitate or bog down, this is crazy and pretty worrying :( Any advice would be much appreciated as at the moment I have a long list of other things to get sorted on it ASAP including brakes, a clunking noise under braking (started today) and severely pulling to teh left.

 

best regards,

 

William.

... hmm or could this be that the MAF is shit even though it is unused!? arggg man am hating money going down the drain :(

When you say brand new MAF I cant help but think its one of the cheap shitty ebay ones with no label on, well known for being bad :(

 

is there no one local to you that will lend you a MAF to try?

Yeah I have just read about them... I didn't realise there was such a thing! I have asked a few people locally that had cars sitting there bring sold (and offered cash for their time ) but none were interested in letting me try theirs out :(

 

I'm gonna have to try and get my money back I think but reckon that is going to be hard :(

 

Also put a message on the forums asking if I could try anyone's but no takers yet!

 

Best regards, William

That sounds like the new MAF is pants. I had one that did this. Swap it straight back over and see if that sorts the 4.5k problem

Also might be worth checking the connector to the ECU, they can sometime sit incorrectly after being removed and give strange problems.

May be just coincidence but worth a look.

 

Scrub that. I have just re read post. Doh!

Edited September 2, 201312 yr by redwine300

Hi mate, I only unplugged the battery so ecu hasn't been touched but I will check it. Best, Will

Yet another Maf on order for this week, fingers crossed.

Ok So got another MAF and it ran exactly the same as before (slight misfire on idle)

 

Today I played with removing the coil packs one by one and also checking the plugs. Plugs all seem OK, nothing suspicious. So in pullign the coils one by one I would listen to the missfire and then try and hear the normal misfire behind that... Althoguh whenever I pulled one all I would hear is the misfire from the removed coil, The ECU was compensating by raising the revs to 900/1000 rpm so the normal rough idle wasn't noticable at all, I must say it stayed very steady idling at 900 the whole time I had a coil pack out!

 

So next on my list will be NOT to replace any coils or spark plugs, but try instead the o2 sensors and also today give the throttle bodies a big clean.