I have a 1991 300zx TT

I just replaced my Head gasket and fuel injectors, before I had done that I didn't drive the car for 4 months or so due to leaking injectors. When I would start the car every few weeks the valves would tick pretty loud but go away after running the car for 5-10 minutes.

After I completed the job I started the car up. Tweaked a few things and while doing so I heard a Knocking sound at random. It seemed to be like a rod knock/Spun bearing. I shut the car off looked over a few things started it up again the car is running ok as far as idle goes but now the knocking/Very loud ticking is constant and gets a lot faster even with a very low rpm increase. The car seems like it is miss firing or something when it is revved up.

I read somewhere that the way to tell the difference between a valve problem and a rod knock/spun bearing is the speed change as the rpms increase.

If I do have to replace the bearings can I do it by just dropping the oil pan? Would I be able to pull the crank without pulling the engine?

Tutorials would be awesome if you guys know of any!

Thanks for the help!

 

You will need to pull the engine to replace rod and crank bearings. The oil pan has to come off (which couldn't be done in the chassis without dropping the entire front subframe/steering rack, which alone is harder than a motor pull), the oil pump has to be removed (which would require disassembly of the front of the engine, and timing gear, which won't come off easily and I couldn't IMAGINE doing with the engine the in the chassis), etc. Is it possible to do with the engine in the car? Perhaps... but I'd never bother trying to do it. It will be easier to pull the engine.

If you need a tutorial, the job is probably beyond your skill level. Work slowly, disconnect whatever's holding the engine in, and go from there.

There is a motor pull writeup on TwinTurbo.NET, though.

 

Valve tick and rod knock will both change with rpm's. I've heard both and they're distinctly different. The rod knock will be noticeably more pronounced if you kneel down and listen from under the car.

Hopefully, after having head gasket and injector problems, you changed the oil. Overly diluted oil can definitely cause a bearing to spin.

 

like zlover said if it is bearings then its easy to do when motor is out. i just replaced all my bearings like 2 weeks ago. and i dont think i could have did it in the car setting in the crank was the hardest part i had few friend guide the rod around the crank,

 

My Z sat for 2-3 weeks and when I started it up I had MAD lifter tick. I mean terribly bad. I almost crapped my pants because I thought something was majorly ****ed up.

Let it run for a while, put in a little MMO and after idling for a while the noise improved but wasn't totally gone. Took it for a drive around the block VERY gently (I mean shifting at 2000-2500rpm into 2nd gear (no higher) and by the time I got home the noise was gone.
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I had a lifter that knocked, and loud too. But, it did it when the engine got warm.

Listen to the frequency of the knock as well. A lifter will tick at half the rate of a rod knock.

I suspect you just lost prime in one of the lifters and it will pump up over time.
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Here are two posts from another forum, does it sound like this could be a possibility?

 

Dude, without hearing the car, none of us are going to be able to tell you if it's rod knock or lifter tick. Take the car to an expert. Tell us where you're located and we'll tell you where you can find someone qualified to touch a Z32.

 

I live in Sandy, Utah near Salt Lake City, Utah. I will put a video up on Wednesday.

Thanks

 

rod knock gets loud when drivin so does lifter tick if it sounds come from valve cover u got lifter ticking

 

It turns out it was just an extremely loud lifter! Thank god I just ran the car trying to see where it was coming from and it slowly dissipated and as soon as I drove the car a few feet it went away completely.

Anyone with a knocking sound it may be a loud lifter, it was loud enough to be a rod knock so check it out before pulling the motor.

Now the car is running amazing, except after driving the idle surges between 500-1000 rpms every few seconds about 5 or 6 times before leveling out at about 900 rpms, I found a few boost leaks and it seemed to help some but it still surges does anyone know what would cause this?

I still have 1 or 2 very small boost leaks no more than before the new injectors and head gasket though.

 

Could this be related to bad O2 sensors, I had a DSM and I could not stop the idle surge for the life of me took it to 3 different shops replaced repaired everything that related to the idle and no one knew what to do. I replace the O2 sensor and bam bye bye idle surge.

This morning I started the car let it run for 2 minutes and tried to drive away it felt like I was towing a 5th wheel trailer. The car would bog or something. I had a similar problem on a cooler day it went away after driving around the block. It seems like this could have something to do with an O2 sensor as well....? This morning was pretty cold by the way.

 

How does it react under WOT? O2 sensors are ignored upon full throttle, so if it's the O2 sensors, going WOT will run fine. If you still have problems under WOT, it's not the O2 sensors.

By the way, it is possible to do an ECU self diagnostic. (hint: search)

 

It runs fine other than the idle and I didn't go WOT because I didn't want to damage anything while it was running weird.

 

I searched around and couldn't find much for ECU self diagnostic. Could someone link me to a TUT? Thanks I must have just missed it or something.

 

before obd2, (obd1) u gotta ground ecu to flash check engine light to read codes.

1.Find the ECU! 300ZX it is under the passenger floor panel under glove box. Take the thing right out so you can see the ECU
2.Start the car and let it idle. If it doesn't start turn it over on the starter for 10 seconds or so.
3.Turn the diagnostic switch fully clockwise (Small plain screwdriver)
4.The LED should flash 3 times. When it has turn it fully anti-clockwise
5.Check the LEDs flash to confirm
6.The ECU will now flash the code. A red flash indicates 10 and a green flash indicates a single unit. For example, if the code was 23 the red LED would flash twice and the green LED would flash three times. Told you it was easy! The code will then repeat its self. Anyway, note the code down then switch the ignition off.



Trouble code Cause
11 Engine speed (RPM) sensor or Crankshaft sensor (CKP) intermittant signal
12 Mass air flow sensor (MAF) circuit malfunction
13 Engine temperature sensor circuit malfunction
14 Vehicle speed sensor
21 Ignition signal
22 Fuel pump open circuit
23 Closed throttle position switch
24 Park/neutral position switch (Automatics)
28 Engine coolant blower motor circuit malfunction (Cooling fan)
31 Additional Idle air control valve (IAC)
32 Starter signal
34 Knock sensor circuit malfunction
41 Intake air temperature sensor or fuel temperature sensor (Earlier models) circuit malfunction
43 Throttle position sensor
44 No faults stored
55 No faults stored
Just because a particular code is stored does not automatically mean that sensor/switch or assembly has had it. ALWAYS check the wiring to the component, the condition of the terminals and the fuses before legging it off to Nissan with your wallet flapping!


How to clear the codes
1.Turn the ignition back on
2.Turn the diagnostic switch clockwise fully
3.Let the LED flash 3 times then turn the switch fully anti clockwise
4.Check the LEDS flash to confirm then turn the switch fully clockwise again
5.Wait for teach LED to flash 4 or 5 times to indicate 'No fault found' (Code 44 or 55)
6.Turn the switch fully anti-clockwise and switch the ignition off again
7.Thats you! Put your centre console back in

Hope this all makes sense!

 

Thank you I will try this tomorrow.

 

I haven't had time to test the self diagnostic, I will try it this weekend.

I am still having weird power issues when the car isn't at running temp. It feels like when I had a leaking injector. I get boost but the car bogs.

I also noticed that when it is colder outside I don't have any idle surge problems.