Hi there, this is my first post so go easy. Had my car for a few months now (its a 1991 TT Manual Jap Import), and have been suffering with the age old 300zx problem of a misfire. Originally the car didn't want to idle, i did all of the usual things, connectors, plugs (replaced), changed the fuel filter (checked the pressure) etc. but still ran like a bag of Sh*t. Had it in a garage and they found the Drivers side O2 sensor was knackered. They changed this but it didn't seem to make a discernable difference. At this point i changed one of the coil packs as it was cracked around the stem, and also the Idle control valve. Still the same. Put it back into the garage and they found that one of the injector connectors was corroded. They cleaned this up and again it didn't seem to make much of a difference. Then the following Friday it really didn't want to run at all. The next day it didn't miss abeat, and now idles okay. The only problem i have now is that, every so often when i put my foot down the car doesn't want to rev above 2000rpm, unless i back off and re-apply it (even then it doesn't always clear). Like i said all the connections have been cleaned, but i still get this. I did have the car on a rolling road over Xmas and got a figure of 320BHP (woo hoo!), with an HKS Filter and 5Ziggen exhaust, but typically it didn't miss the entire time it was there (Doh!).

Looking through the threads on 'Misfires' it looks like the water temp sensor can have this effect, any other suggestions?

 

Any Help is appreciated

Yep water temp sensor (yellow connector on the front of the engine. Also check the PTU connectors (more than likely a silver box with fins on to the left of the water temp sensor as you look into the engine). If that doesn't solve it it may be up the duff. Tey to borrow one from a member or better still upgrade to a Series II one.

 

HTH

 

Ivan

Thanks Ivan, from what i understood the PTU usually fails due to the high tempuratures. The garage i had the car in tried heating up the PTU whilst it was running to see if it had any effect. It ran the same. Can they be effected by vibration?

 

Does anyone know how much a series II PTU is?

Thanks Ivan, from what i understood the PTU usually fails due to the high tempuratures. The garage i had the car in tried heating up the PTU whilst it was running to see if it had any effect. It ran the same. Can they be effected by vibration?

 

Does anyone know how much a series II PTU is?

 

not quite,

 

inside the series 1 ptu are lots of very fine soldered wires, vibration (& age) cause these to break. they tend to show up when hot due to expansion (they break contact when hot, then make contact again when cold), tho this isnt always the case.

 

i bought my series 2 PTU from Courtesy Nissan in the states for around $170 IIRC. a lot cheaper than here in the UK!

there you go:

 

http://www.courtesyparts.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=CP&Product_Code=22020-00Z32

 

$180, or about 5p at the current exchange rates!!! :D

Run an ECU diagnostic? Sounds like possible MAS failure (intermittent)...

Thanks chaps. I have carried out the ECU check a number of times and it always comes up with a code '55'. This is all clear from what i understand. Would the fault actually have to be happening at the time or does the ECU store the faults for checking later?

ECU error codes are only produced if the sensor in question is giving readings outside its normal operating conditions. Usually open or short circuit conditions will cause these. The ECU stores codes for (I think) 50 starts of the engine after the fault has occured last....

Andy, you mentioned the MAS. I have checked the connections to this and they are all okay (no corrosion). Is there any way to clean it or check it is operating correctly without replacing it completely? Do you think it could be something to do with the HKS mushroom filter thats fitted, i have heard stories of oiled filters clogging up the wires in Hot wire Air flow meters?

That could well have just hit the nail on the head! HKS type filters allow moisture in creating havoc for the MAS (water has a much higher specific heat capacity than air and will cool the hot wire much more, making the ECU think its just injested a massive amount of air). Try a known good MAS with a different type of filter installed (eg apexi) :)

Hi Markymark,

 

I´m a German Z32 owner since 3 weeks und i´ve the same problems

as you.

 

Have you checked the ignition-timining after looking for all elektrical

connectors?

 

Please give me an Info when you have found the problem

 

Utz

Update!!!!

Looks like I've found the source of all my problems. I removed the HKS Air Filter to check the AFM and discovered half of it was missing (what was left looked pretty manky as well). It must have rotted and got sucked onto the Hot wire in the AFM. I Cleaned the AFM with Carb cleaner and replaced the Filter and it has only hesitated very slightly once since. I may still need to replace the AFM at some point but I'll cross that bridge when i come to it. All i need to do now is find some way of protecting the filter from the elements a bit better. Hope this helps anyone with a similar problem.