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Old 10-04-2008, 01:30 PM   #1
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Idle/Misfire?

Ok guys, Im new to the site here, but a long time lover of all things Z. I have a 1990 300ZX Twin Turbo, and this morning she presented a problem to me that I have not yet been able to understand or research.

The car usually fires right up as soon as you turn the key, but this morning when I sat down in it, she turned over and died out. Turned over again and failed. On the 3rd start I got her running, but had to give it a bit of throttle to keep it running from the get go.

Now I said it started, but it was running very poorly. The RPM's usually sit between 5 and 7, but now it fluxes between 5 and 12. While the fluxing the car will occasionally have the slightest "bump" and the exhaust sound has a quick break in the note. Under any acceleration in first gear she has random hesitation in the throttle.

Under the hood, the sounds are a little more pronounced. I can hear the hum of the engine and the momentary break in the tone which sounds to me like a missfire, but I am not a mechanic. While all this is going on, there is a ticking coming from the top of the engine somewhere, which sounds much to me like and electrical contact firing improperly. This light ticking noise sometimes has a pattern to it, and sometimes it does not.

When this problem persists, the engine smells almost like it is running rich.

What I have done:
I have checked all the wires on top of the engine to be sure everything is connected, but nothing seems to be amiss. I did not check the TPS. I did not check anything below the manifold area of the engine. I ran the ECU in diagnostic mode, and flashed me a 55 so nothing on the ECU list is going wrong, then ran the ECU Mode II check on the O2 sensors, both right and left, and when I hold the throttle at 2000 RPMs, the check engine light flashes like I suppose it is meant to, though the flashing is by no means uniform. I have not yet called nissan to see if the PTU was ever replaced in this car.


As before stated, I am not a mechanic but I love these cars and I love to learn, so if you have any insight, I would appreciate any of your wisdom.


Thanks a ton.
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Old 10-04-2008, 03:53 PM   #2
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from a newb's view sounds like a valve issue. on my 260z (I know a world of difference but) it threw the rocker off the valve and had some of the same symptoms.

try getting the engine running and pull each plug wire and have someone watch the tach to see if there is an rpm drop. If you pull one and the rpm's stay the same you have a misfire on that cylinder.

good luck and get someone who knows more than me tho help you further.
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Originally Posted by JPerkins
Handles like......something......that doesn't handle well at all.
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Old 10-05-2008, 07:55 PM   #3
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Test the resistance of your injectors. It doesn't 'completely' sound like an injector problem, but it's an easy place to start and the injectors are common problems on the 90-93 Z32. Resistance between the two leads should be 10-14 ohms.

Other possible problems (which we'll address after you test the injectors) are TPS, MAF, and IACV.
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Old 10-05-2008, 08:04 PM   #4
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Quote:
Originally Posted by at-jefft
from a newb's view sounds like a valve issue. on my 260z (I know a world of difference but) it threw the rocker off the valve and had some of the same symptoms.

try getting the engine running and pull each plug wire and have someone watch the tach to see if there is an rpm drop. If you pull one and the rpm's stay the same you have a misfire on that cylinder.

good luck and get someone who knows more than me tho help you further.

He said plug wires...... thats cute.

JK

The injectors is a good place.

I had an issue like that (with the rpms) and it turned out to be an injector, luckily enough it was a middle one and i was able to replace it without having to tear apart the motor.

The injectors also wont show up on the ECU either.

I had an issue like this with my z31 and it was the MAF. There is a code on the ECU for the MAF, but lets face it, computers arent always right.

If its a misfire, it could also be one of your coil packs.

Good Luck.
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Old 10-05-2008, 08:25 PM   #5
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Little known fact: all 6 injectors can be replaced without removing the plenum or even grinding away at any metal. All that's needed are bent-nosed locking pliers and hose pliers.
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Old 10-05-2008, 10:15 PM   #6
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a way to tell if the PTU was replaced is see if there is an adapter in the wiring harness. it's a couple extra plugs in the middle of the wiring harness. also, for the old style, the bolts go right through the unit. on the new ones, they bolt to an adapter that mounts to the timing cover
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Old 10-06-2008, 09:15 PM   #7
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An even easier way to tell if it is the new style is this:
The old style has cooling fins on it, the new style does not.
The old stlye was recalled and can be replaced by your local dealer.
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Old 10-06-2008, 09:52 PM   #8
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i was about to say that one, but i decided on the others.

i don't know if you've heard my story, but i'm betting that that recall has been voided because the car's almost 20 years old. i had the old style, and i called the dealer and even the nissan customer service hot line and gave them all my numbers, and they said there are no recalls on my vehicle. the vin confirms that the car is a 1990, so it did come with the old style PTU. so, one of two possibilities that i see:

1. the recall is no longer in effect and any Z32 owner that didn't act fast enough is screwed

2. my car had the PTU changed, so the recall was removed from my vin, then the engine got swapped with another early engine that hadn't had the PTU changed. the recalls go with the body VIN, so this is a possibility. i looked into it a bit, and basically they are not obligated to perform the maintenance on the same body twice, no matter how it ended up with the recalled PTU in it.

i'm still betting though that the recall is over, because i don't have any other good reason to think that my engine has ever been swapped, and also, if it had been, someone would have had to have been stupid to not switch the PTU's during the swap.
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Old 10-08-2008, 06:30 AM   #9
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I'm totaly car-stupid, hey I can own it, but when I had an injector go out on me a couple years back this is exactly how it started. It didnt take very long for my car to go from "a little hard to start and idels rough" to full blown "Lucky to be on he road at all and god DAMN look at all that smoke!!"

It was an easy fix, just swapped out hte number 5 injector and good to go...at least until the O-ring that was pinched on install blew out completely and I had to go BACK to the shop, but that was a simple fix too.

Just my 2 cents.
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Old 10-08-2008, 06:30 AM
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