It seems that every Zed owner and his dog has had rough running at some point, but I thought I'd ask the question in case these are characteristic symptoms....

 

Up to a minute or so after fire-up, the engine seems fine.

 

Once it's warmed up a little I get the following problem:

 

With the engine below 3000rpm and at low load, the engine note doesn't seem quite right and under light acceleration the car will judder/jolt. However, somewhere between 2500 and 3000rpm it will suddenly sort itself out and run smoothly. Similarly if you put your foot down below 3000, it will pull smoothly up through the revs.

 

When thoroughly warm, the problem's less apparent, but still there.

 

Originally I thought this was related to vacuum pipes as there were several which had loose connection with the plenum/balance bar, but having now replaced all the troublesome ones I've still got the problem. :(

 

My current thoughts are that this is a air/fuel regulation problem, but there's so much to check I thought I'd pick people's brains.

 

Any thoughts on where to start?

could be all sorts!

 

have you done an ECU diagnostic? also check the O2 sensors (diagnostic mode 2) as it could be down to one of those from the symptoms.

 

also check clean air mass & temp sensor & connectors.

 

check plugs for wear/fouling & do a compression test while there out

Check the left hand connector on the PTU :D Make sure the cable isn't too tight doubling back on itself...

Righty-ho. Thanx for that chaps- some small tasks for this weekend! :)

 

Mark

I reckon PTU aswell I had the same symptoms on mine before and I ended up buying a series 2 in the end...

Ok, I checked what I could...

 

Removed the PTU, which involved much swearing at the driver's side throttle air-pipe :x: , and more swearing and a rotating captive nut in the timing belt cover :x: :x: . Double-back cable is as gently bent as possible, but the connectors were a bit gunked up, so gave them a clean. Whilst it hasn't cured the problem, it's not quite as rough as it was. And I'm sure the car pulls a bit more strongly when booting it :hyper: .

 

ECU diagnostic- 55 :D

 

But here's the odd thing... both 02 sensors appear to be working to a point, but they're reporting differently for each side. The right-hand side worked how I thought it would- the indicator flashing briefly and frequently (about once every 1.5s), and it did not change in behaviour when the engine decided to run rough for a bit.

 

When testing the left-hand sensor and the engine was running ok, the indicator would stay illuminated for longer, and would also stay off for longer (in total flashing barely once every 2 seconds). More interestingly, the engine running rough would coincide with a sustained "off" period, and when the indicator finally came back "on", the engine would gradually pick up and run smoother again.

 

So the question is, is this indicative of an 02 sensor/ exhaust problem, or is the sensing ok and the problem lies in the fuelling of the left bank?!

 

(Going by the instructions via AndyP's site- when they say left does that mean passenger's side???)

 

I'll also get around to checking the other connectors and the AFM and temp sensors, but I didn't have time at the w/e. :slap:

 

Mark

I'd say the sensor is reading correctly - off being rich condition. That suggests you're dropping the spark on one of the left bank cylinders, pointing at either the PTU connectors or coilpack connectors ;)

Is off=rich definitely correct? The diagnostics I used (http://www.ttzd.com/tech/diagnostictech.html) say that on=rich.

 

Plus, if I've lost a spark wouldn't it run rough all the way up the rev range? Coz it seems to always get better around 3000rpm :confused:

 

Dunno, me!

sounds like a lazy O2 sensor IMO

http://www.300zx.co.uk/cgi-bin/manual.cgi?list=efec&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=53&design=default&total=190

 

I'm STILL going with the left hand connector on the PTU. Gets better above 3k rpm due to vibrations... Seen this before. May well be wrong but like I say I've seen it before :)

could it be the PTU sensor AND the O2 sensor?!?! :D

could it be the PTU sensor AND the O2 sensor?!?! :D

 

Whats a PTU sensor? ;)

OK- well in the first instance I'll :bow: to Mr. Duff's expertise here (no offence Paul C ;) ) If it's the PTU connector then which bit usually fails- the loom side or the PTU side?

 

I presume you suspect fractures in the wires...

One thing you could try is to tie wrap around the PTU so the connectors are held tightly in place. I'm not sure if its simply the pins in the connectors not making contact properly...

Buy a series 2 PTU...

Using Cable ties is deffo the way to go I even have them on my new series 2 as even the new connecters aren't that good. Where is your PTU at the mo ??? If it is in the stock location on the Cambelt cover try feeding all of your wiring over to the passenger side of the engine bay and re-mount your PTU on the inner wing by the fusebox, that way you can get to it easy and correct any bad connections...

Well either way it sounds like getting a series 2 is a good idea. And I like the sound of repositioning it- I take it the loom has enough slack to put it where you suggest without modification? Presumably a mounting bracket of some kind is also required.

The stock loom is long enough (A bit fiddly re-routing the loom) plus you also get a slightly longer lead with the series 2 PTU and it just plugs straight in to the stock loom. As for mounting it you just use the bracket provided with a series 2 and just use 1 corner tab underneath the fuse box, but still use cable ties to keep the connecters firmly in place though.... Good luck.

Got my nice, shiny series 2 PTU :) . Was a bit short of time this weekend, so I didn't have a chance to re-route it. The thing is, I took off the driver's side intercooler pipe and having seen davido140's post on hesitation had a better look at it this time, only to find about 3 massive cracks extending just past the jubilee clip! :cry:

 

Tried to shuffle the pipe around a bit so that the the crack was as far away from pressure as poss- drove fine yesterday, but this morning was running the roughest it's ever been, and boost gauge was reading almost atmospheric at idle.

 

Wonder if ChrisP still has that spare pipe...

I've got some stock intake pipes... one of them is cracked to buggery like yours but if it's not the same one you can have it - so is it the inner or the outer you need?

Thanks for the offer mate :), but ChrisP also has a spare one he's said I can have.

 

Cheers,

 

Mark

Sounds like you are getting there slowly but surely...

Well slowly anyway!

 

Had another look under the bonnet at lunch and found the tiniest vacuum hose in the whole engine bay had also split (goes to a small box-sensor thingy- boost gauge sender?). Wandered round a couple of motor factors and eventually found a pipe small enough that fits!

 

So that's cured the REALLY rough running, and I'm back to simply running rough now. :D

Cheers 4 starting this thread up, I had the same problem as yourself & i think I've located the problem with my Zed too. I waddled the connector on the LHS of the PTU & the engine developed a misfire, so rekon that's where the problem lies.

Good one...

Had an interesting discovery at the weekend, thanks to another problem!

 

Had cat overheat during the Xmas break (see this) Now up until this point, the rough running seemed to have largely gone away, but in order to stop the cat overheat, I pulled as many connectors I could find and gave them a clean. Hey Presto!!! The rough running came back! :headvswal

 

One thing I noticed while cleaning the connectors was the poor condition of the injector connectors- some of the contacts were bend so badly I'm not surprised I was running rough.

 

So- I made a couple of jumper cables and inserted them between the worst connector and its injector, in such a way that it was getting the best connection possible. And wahoo! Smooth as the baby's proverbial bottom!

 

Not a long term solution of course- I need some new injector connectors to replace the old ones, but it looks like I *might* have finally got to the bottom of it!

 

Oh I can't wait to alter my signature...

 

Mark

 

:nana2: