Nissan 300zx Engine Issues

[Damien Hill]

Hey Guys, I have a 1989 Nissan 300zx with a VG30DETT Engine (Twin Turbo Automatic) which has only 164,800km. I am about to convert it from an Auto to Manual. I live in New Zealand, and I drove the car from Wellington to Auckland (650km) Because the engine was at highway speed the whole time I didn’t notice anything was wrong until I came to a stop in a small town about half way. The engine had developed a miss which only appeared to be there at idle. You can notice it a little bit more now while driving around, but if you put the engine under load it seems to perform rather well like it should. But as soon as you ease off the gas or let it idle it’s missing.
Now I have done all the obvious things here, It was due a cambelt replacement anyway, so I changed the waterpump, tensioners and belt myself.. and checked all the timing incase that was off but it was all good and made no difference.
From here I have done a power balance test and I can’t really say that any of the coils are at fault.. even though the engine is missing and you unplug a coil pack one at a time, they all run as rough as each other so there was no difference between each coil. From here I did a compression test and found one cylinder to be reading 100psi while the other 5 cylinders were around 145-150.. I took it one step further and did a leak down test.. and the cylinder with low compression read perfectly.. Now I did each cylinder at TDC on the correct stroke.. I just can’t get my head around this one.. The fact that a leak down test was perfect and compression not.

You can hear it in this video (Also don’t worry about the exhaust leak, i’ve fixed that)

This video is an acceleration under load with no issues:

If anyone has any pointer on this I would be truly grateful.

Thanks!

Topic

[Bryan]

I’d start by repeating the compression test, honestly.

Run it twice… one dry, and another with a shot or two of motor oil in the cylinder. Compare the two and see if adding oil ups the compression.

Most of these cars have had their engines ragged on their entire lives, so it’s not outside the realm of possibility that the rings are worn out. That’d be my first guess, especially on a twin turbo such as this. (I’m really starting to miss my old 1985 300z…)

The low compression is what catches my eye first and foremost… start there and see if you can resolve that.

-Hinoki

[college man]

That low compression cylinder is the misfire. what the leak down
test confirmed was the valves are sealing. Try a wet test to see
if compression comes up. If so rings.

http://www.nicoclub.com/FSM/300zx/1989/EM.pdf

[Author]

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