Hi

 

I know there's loads of threads about the stumble/hesitation issue that seems to be a common problem in the 300ZX, and I think I've read them all, and tried most of the suggestions within them, but I'd like some advice please.

 

I have a 1992 UK 300ZX twin turbo, with a +70BHP EEPROM upgrade and Apexi air filter.

 

The previous owner had the car for 9 years and had the EEPROM upgrade done when he first bought it. He thinks the stumble first started about 4 years ago but as he 'drove her like a granddad when she was cold' never really bothered about it.

 

My particular stumble/hesitation ONLY occurs in that first 10-15 minutes. Once the car is fully warmed up, it doesn't happen at all.

 

It seems to happen mainly when I'm doing 30mph or so in 2nd, or 40-50mph in 3rd, and the revs are between 2500 and 3500. It feels as if someone has taken the accelerator away for second, then it comes back. It may do it once or twice in a few seconds then it'll be normal.

 

Seems to do it mainly when I'm at that constant speed (30mph zone) but occasionally will do it when accelerating.

 

Even in those first 10 mins or so when it's still cold, it doesn't seem to happen at higher speeds/high revs.

 

Every so often it's more severe, and the 'drop off' will last longer than a second and feel likes it's going to stall. It did this really badly tonight. The car hadn't been used since this morning (2hr run, little bit of stumble in first 10 mins then absolutely perfect). I took it to the shops 9 hours later, 10 min journey. Stumbled maybe four or five times, not too deep, but annoying nonetheless. Shopped for 10 mins, came back, drove for another 5mins to another shop, couple of minor hesitations. Shopped for 20, maybe 30 mins. Got back into the car and headed for home, about 2 mins in had major, deep, drop offs, felt like it was kangarooing - would get 2 second without power, 2 seconds normal, repeated, probably about 10 times. All the time my foot was on the pedal consistently. Came to a roundabout and stopped for a sec; pulled away and was fine again.

 

Outdoor temp today has been 12 degrees, so not that cold really.

 

I've been following this document for the last couple of months and trying different things out:

 

http://www.zhome.com/ZCMnL/PICS/hesitation/hesitation.html

 

So far I've done:

 

Unplugged everything - injectors, all connections, cleaned all contacts up

Checked PCV hose/values (clamped as best I could, not fully closed, but there was no fluctuation at all)

Air flow meter - voltage fine

Air filter looks clean enough

Cleaned throttle intake valve

Voltage checked TPS - adjusted to 0.47V

Cold start temp sensor voltage check (readings here http://www.300zx.co.uk/forums/showthread.php?165253-Coolant-Temperature-Sensor&highlight= which I think are fine)

Checked spark plugs - have the correct PFR6B-11C, they look relative new/clean

Replaced Series 1 PTU with a Series 2 PTU

 

There are a few more bits and bobs that I could chec:

OHM check injectors

Replace fuel filter

Fuel pressure tests

 

BUT, reading through that doc above, and other posts, they don't sound relevant to my particular problem - i.e. the fact that the stumble is only when cold (in those first 10-15 minutes).

 

Any more ideas anyone?

 

Reluctant to spend any more time/effort/money on her!!!

 

I AM off to Zedworld in Birmingham at some point in the next month or two to replace an air compressor, I could ask them to take a look, but fear it may take them a long time (and cost me a lot!) to diagnose.

 

I thought the EEPROM upgrade could be to blame but it was installed 9 years ago and it's only been happening for the last 4 years...

 

Thanks

 

Ross

Hi Ross,

 

the issue (symptoms) sounds like a regular one, your particular problem/solution may be different however.

 

i would check the map on the eprom, maybe even replace with a more standard one.... see if it fixes it.

 

have you checked the timing with a light and taken the cas of and given the area where it goes a good clean?

 

did you say you did a boost/vac test?

Thanks for the response Medallion man... to be honest I'm not very mechanical. I have just about managed to scrape by doing that long list of checks/fixes above by the piercing together lots of different docs/guides and pictures. In one case there was a very bad u-tube video that was too dark but by following that, matching with static pictures and reading several forums I managed to work it out!

 

So no I'm afraid I'm not done any of the above, they may be beyond my capabilities. I have previous fiddled with maps on another car - an MX-5 with an Adaptronic ECU, but I had two local friends who had the same and showed me what to do - but again its a bit extreme for me.

 

I've seen people mention a boost/vac test but couldn't find any info on how to actually do this? All I did was "Checked PCV hose/values (clamped as best I could, not fully closed, but there was no fluctuation at all)" as per the section in http://www.zhome.com/ZCMnL/PICS/hesitation/hesitation.html although I'm not convinced I did this very well, I probably don't have the right tools but I struggled to get access to the pipes to clamp them very well, plus they are quite hard/not very flexible...

 

Thinking I may have to take it to the specialists.... unless someone has experienced this EXACTLY SAME issue and had ruled out the above already and says 'its this!'. Unlikely I know but crossing my fingers :)

lol.. I see.. well you've done well so far for someone without experience... :)

 

the timing is way to check but you'll need a timing light and it makes it easier id you have an extension for the coil pack for #1 cyl. (i.e. to connect the timing light to, but not essential)

 

you will also need the timing light if you're taking the CAS off, however you could mark the positions with a fine tipped permanent marker.

 

boost / vac test, you need a plug for the MAS inlet, ideally with tyre valve, so you can pressurise it form there. (easy to make).

 

what is the spec of your mods?

Thanks... yeah I didn't understand half of what you said then :)

 

Thank god for Google and these forums else I'd really be in the sh1te :)

 

I'll do some more research/fiddling and see what I can suss out... spec of the mods? Erm, I don't know to be honest, the only details I have on the mods are:

 

Upgraded eprom +70 BHP Nov 2004

Apexi induction kit Nov 2004

Turbo Boost increased from 9 to 13psi Nov 2004

In-tank “Broquet” fuel catalyst Nov 2004

Mongoose cat back stainless steel exhaust with twin 6” oval tips Mar 2005

PCV Valves Feb 2011

 

All done by Zedworld.

Ah, yes, so no lager injectors... that's good because you can test with a standard ecu.

 

if you are going to test the ecu (ie. change with another one) make sure you disconnect the battery and also don't over-tighten the connector when putting it back on.

 

there is a guide somewhere for accessing the ECU.

I'll have a look to see if I can find a cheap standard ECU then to test out the map theory - I guess if it IS a map issue, then with a standard map/ECU the car should run fine at lower speeds/off boost for those first 10-15 mins? I imagine it wouldn't be great at higher speeds/full boost (and would I have to be careful to prevent damage?) as the standard map wouldn't know how to 'handle' that extra boost - but I can at least rule out whether it's the map or not?

 

I'd forgot to say that I have accessed the ECU before - I did the O2 wideband diagnostic test (all ok).

Any idea where to find a cheap standard Z32 ECU?

Any idea where to find a cheap standard Z32 ECU?

 

Place an add in our wanted section mate :)

 

Ignore this, I see you already have..lol

ive replied in the wanted section budd

Thanks guys... I put a note in here as well as the wanted section as the wanted sections always seem to be less well browsed/searched than the problems, plus knew a few people were already watching/following this post :D

The easiest way to sort this out is to hook up some decent monitoring software and take a log when the issues are happening.

Are there any simple guides on how to do this/free software available?

Are there any simple guides on how to do this/free software available?

 

You need a Consult cable and a laptop. Cheapest cables are serial but can be used fine with a RS-232 to USB converter cable. Free software options include Conzult & ECUtalk. I use NIStune for any diagnostic issues & logging, it's not just for tuning :D

 

I take it you've checked to see if there are any fault code stored by the ECU?

its ok getting the software and pluging it in its knowing how to interpret it that matters

its ok getting the software and pluging it in its knowing how to interpret it that matters

 

Very true, but if he posts up his results we can take him through them :)

Thanks guys... yeah I've checked, no fault codes. I'll look into the software and cables then :)

its ok getting the software and pluging it in its knowing how to interpret it that matters

 

That's easy. If a sensor is showing a value under a certain condition that doesn't correspond with the published figures, you know that sensor (and/or circuit) requires investigating. The free softwares are simple plug 'n' play, it's not really possible to misinterpret anything IMO.

Ok well I was about to order a RS-232 to USB cable but a couple of things... erm... silly question, but is there even a RS-232 port on the ECU??? Looking at pics in Google I can't see one!!

 

Also, do you need a specific type of cable - see the reviews for this one, sounds like some cables work with some things and others work with other brands etc...

http://www.amazon.co.uk/product-reviews/B00077DJIQ/ref=cm_cr_dp_hist_one?ie=UTF8&filterBy=addOneStar&showViewpoints=0

Consult port above your right knee when you're sat in the driver's seat. Consult "cable" plugs into this. Cheap versions are serial, more expensive are USB. I use serial versions as I have a beast of a modern laptop with ports for everything, and I've been through a couple of the USB varieties, the ones I had weren't very well made.

 

Your ECU communicates with the software on your laptop via the Consult port, just like OBDII vehicles through the OBD port.

Ok well I was about to order a RS-232 to USB cable but a couple of things... erm... silly question, but is there even a RS-232 port on the ECU??? Looking at pics in Google I can't see one!!

 

Also, do you need a specific type of cable - see the reviews for this one, sounds like some cables work with some things and others work with other brands etc...

http://www.amazon.co.uk/product-reviews/B00077DJIQ/ref=cm_cr_dp_hist_one?ie=UTF8&filterBy=addOneStar&showViewpoints=0

 

Just in the middle of this at the minute, there are some cheap converters on ebay and I bought one which didn't work as you do need the driver software.

 

My advice get one of these for a tenner as it looks genuine and so will work with the prolific driver available for free on the website and comes with a cd, my cheap cable will not as it's all to do with the chip in the convertor I believe.

 

Sure you could buy a cheap one with a driver disc.....you pay your money and take a chance :biggrin:

 

http://www.ebay.co.uk/itm/230742488092?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Ah I see that makes more sense - a Consult to USB or Consult to Serial cable is what I need.

 

CRIKEY - the USB ones are around £60!! Just found a serial one for £20 on ebay... it's still £20 though when all I want to do is rule this out being the ECU, I'd never use it again! Oh and I quick scout of my laptop suggests it's not got a serial port either :(

 

I think getting a second hand ECU cheap and trying a straight swap might be an easier and cheaper (in terms of I should be able to sell it on again afterwards) option.

phutumsch - sorry post overlapped there - that would still be £20 for the Consult-Serial then £10 for the Serial-USB cable though right?

I've bought 3 cheap ones and all have been spot on as long as you install the correct driver. The discs are generic jobbies that cover 3 different types of cable. They all take a beating and I have used them for years for both consult cables and also for my wideband data logging (my laptop only has one serial port).

Just in the middle of this at the minute, there are some cheap converters on ebay and I bought one which didn't work as you do need the driver software.

 

My advice get one of these for a tenner as it looks genuine and so will work with the prolific driver available for free on the website and comes with a cd, my cheap cable will not as it's all to do with the chip in the convertor I believe.

 

Sure you could buy a cheap one with a driver disc.....you pay your money and take a chance :biggrin:

 

http://www.ebay.co.uk/itm/230742488092?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

 

Let me know which one you bought and I'll see if I've got the drivers

phutumsch - sorry post overlapped there - that would still be £20 for the Consult-Serial then £10 for the Serial-USB cable though right?

 

If you're in no rush, they can be bought for £12.51 but you've got to wait for it to arrive from China. They're all Chinese, mind. Think my last converter was about £3. Saying that, even £30 for Consult capabilities is nothing at all. It will allow you to monitor to your heart's content until the end of time :D