1990 with gas in the oil

Nissan 300ZX technical discussion forum: Maintenance, performance, installations, modifications, how-to's and troubleshooting.
branden0502
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Car: 99 I30

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Hey guys. i'm lookingto pick up a 90 300zx mT, and they guy says that it has fuel in the oil. The searches i've done point to faulty injector or Fuel pressure regulator. has anybody delt with this before? is it common on these cars? is it something to worry about or an easy fix?

Thanks


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Ace2cool
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If gas is getting into the oil, it's pushing past the piston rings. So yes, you could have a leaking injector that is potentially hydrolocking a cylinder and forcing the gas past, or you've got blown piston rings. Even if it's a stuck injector, your rings are still probably toast from the force of having fuel pushed past them. I'd start with a compression test. Is there rough idle or a misfire?

branden0502
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Car: 99 I30

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no misfire, but it is hard to start

amc49
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'17 Nissan Altima

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A personal preference to lower problems of course, but that is one of those situations I would never buy a car under, previous overheating being the other. The issues just often later turn out to be worse than originally thought at first.

Just the potential of a hydrolock means the engine could pop a connecting rod at any point later, I avoid deals like that, or he better be giving it away.

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DCaff300ZX
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1993 CRP TT- Modified
Location: Tacoma, Washington

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amc49 wrote:
Mon Sep 17, 2018 2:31 pm
A personal preference to lower problems of course, but that is one of those situations I would never buy a car under, previous overheating being the other. The issues just often later turn out to be worse than originally thought at first.

Just the potential of a hydrolock means the engine could pop a connecting rod at any point later, I avoid deals like that, or he better be giving it away.
+1 to this, people get rid of problems and too many aren't honest (or knowledgeable enough) to be able to pass on the correct info, and wanting to be rid of the problem may well gloss over things hoping you just take the car.
I'd pass unless it's a fire-sale and you need good parts it may have, and only you'd know that.

branden0502
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Car: 99 I30

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Thanks for the help guys. It was definitely a steal so I went ahead and grabbed it. It was too good to pass up. I’ll be tearing into it later this weekend and next week. I’ll keep you updated

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DCaff300ZX
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1993 CRP TT- Modified
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branden0502 wrote:
Wed Sep 19, 2018 6:52 am
Thanks for the help guys. It was definitely a steal so I went ahead and grabbed it. It was too good to pass up. I’ll be tearing into it later this weekend and next week. I’ll keep you updated
Oh...wow, OK. Hope you got it for under a grand because you will most likely be spending 3-4 times that to get a good vehicle out of it.
Be prepared for a lot of service work most likely, expensive enough for parts if you DIY and VERY expensive and risky if you send it out for the work unless you know a reliable Z32 mechanic, who will still be expensive.
Most common issues (especially with Z32's that have sat for long periods unused) are the old style fuel system you have needing complete overhaul/replacement, problems are idle/misfire and other fuel-related issues and sometimes more. Included and also a common and difficult issue is the non-shielded connectors to a myriad of important engine devices (PTU, CAS, IACV, CTS, injectors/harness) that are often troublesome to test and a bit expensive to deal with as well. Cooling issues are common especially when the PO has put in electric fans in place of the OEM system, but also from other issues such as the heater core and deterioration in other areas.
These will most certainly be your first issues in a fire-sale Z32, and plenty more to come as you dig deeper...most likely, again, why the PO is selling the car. Take a look at the variety of issues being asked about in the tech section for some ideas of what's ahead...and don't be afraid to ask away here as we all have been through most if not all of the things talked about here, and more in some cases.
Good Luck!

branden0502
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Joined: Sun Oct 15, 2017 6:05 pm
Car: 99 I30

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a little bit a doom and gloom there....luckily I don't think most of that will apply to me. hopefully....I know the guy i bought the car from. it wasn't his daily driver but he drove it often. I think it was actuallu sitting about a month before i picked it up. one day it wouldn't start for him, and in his checks he found the oil smelled like gas. I guess his mechanic told him it was the piston rings and it would need a new engine, so he just wanted to unload it. Yes i got it for under an grand. It was definatly a steal. I do have some experience with cars and things that go zoom zoom. I've just never owned a 300 before so i figured i would check with the real experts on the subject. I know that the rings could possibly be bad, but hopefully it turns out to be a bit simpler than that and i find a injector stuck open or something.

Thanks for the help and Ill keep this updated as i go.

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DCaff300ZX
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branden0502 wrote:
Thu Sep 20, 2018 5:46 am
a little bit a doom and gloom there....luckily I don't think most of that will apply to me. hopefully....I know the guy i bought the car from. it wasn't his daily driver but he drove it often. I think it was actuallu sitting about a month before i picked it up. one day it wouldn't start for him, and in his checks he found the oil smelled like gas. I guess his mechanic told him it was the piston rings and it would need a new engine, so he just wanted to unload it. Yes i got it for under an grand. It was definatly a steal. I do have some experience with cars and things that go zoom zoom. I've just never owned a 300 before so i figured i would check with the real experts on the subject. I know that the rings could possibly be bad, but hopefully it turns out to be a bit simpler than that and i find a injector stuck open or something.

Thanks for the help and Ill keep this updated as i go.
Doom and Gloom, or reality...your choice in how you interpret it. The Z32 is well-known for the issues detailed above, and more...It's not "if" with these things, it's "when". Or already happening, you just didn't know it yet.
That's why we are here, to help people understand what they have and how to approach it dealing with the things that most commonly occur with it...especially considering that most mechanics know nothing about the car and will screw it up in most cases.
I do wish you Good Luck however!

branden0502
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I was talking about your first paragraph and mostly joking. At first read it sounds kind of like...don’t buy these cars because....

I know your trying to help and I definitely appreciate it.

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DCaff300ZX
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1993 CRP TT- Modified
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branden0502 wrote:
Mon Sep 24, 2018 7:11 pm
I was talking about your first paragraph and mostly joking. At first read it sounds kind of like...don’t buy these cars because....

I know your trying to help and I definitely appreciate it.
Yeah, I guess my own current issues I'm dealing with played in, these cars are awesome fun and I love mine to death but they DO have a way of getting under your skin with some of their issues.
For that reason I do tend to lack sugar-coating to my advise, and go right to the guts of the matter and let it fly... :chuckle:

branden0502
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So i finally got a chance to get in to it. I ran a compression test. this is what i got

1 140psi
2 175psi
3 150psi
4 110psi
5 160psi
6 60psi

Then i put some oil in cylinders 1,4,and 6 then re checked and got

1 180psi
4 160psi
6 130psi

So im guessing i have a some new piston rings in my future. does anybody have anything throw in the ring.....before i begin

amc49
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Car: '11 Nissan Versa
'17 Nissan Altima

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Make sure the low ones were not among the last checked. Battery going low can make low numbers. Need ALL plugs out too if not and throttle held wide open.

Never do just one reading, do at least 3-4 and more on 'bad' cylinders and tear down the plug tool install and do it again, the o-ring sometimes does not seal. Compression testing is one of the most error prone tests you can do and you get multiple readings before making any assumptions. One is absolutely NOT enough. And spin the engine until the gauge quits increasing, some advocate only spinning it 3 or 4 times and that can lead to error too. Watch the gauge increase, the speed with which it goes up tells you bad or good along with the number itself and also can point at leaking o-ring.

If someone unlearned has changed the valve you use to relieve pressure in the gauge then that too, they are NOT tire valves like so many think, they have maybe 1/5 the tension to override that a tire stem does. Made specifically for compression gauge only.

branden0502
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Thanks for the heads up. i had removed all of the plugs, and had the throttle open the whole time. yes 4 and 6 where the last ones tested, but i had a battery charger hooked up the whole time.
turned over until the gauges stopped every time.

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Ace2cool
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Especially if the numbers increased with the adding of oil, you're looking at rings. But I'd caution to make sure that there were no issues with fuel delivery or anything. There's usually a cause when there's one piston with that low of compression. If it's original injectors, I wouldn't be surprised to find one sticking.

branden0502
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Car: 99 I30

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Based on how the injectors looked when I took them out I’d say they where original. I figured with the mileage and half of them at the low end of acceptabile it would probably be in my best interest to just get it done now. I’ve got it down to just the block and heads. I should have the block out tomorrow

I plan to also replace the timing belt, injectors, plugs and probably the clutch since I’ll have the engine out. Do the coolant bypass, egr delete and what not.

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Ace2cool
Posts: 12672
Joined: Sun Apr 20, 2008 5:21 pm
Car: 1991 Nissan 300ZX TT
1966 Datsun Fairlady 1600
2005 Suzuki GSX-R 600
1974 Honda CB550 Four
2009 Ford F150 Lariat
Location: Murfreesboro, TN

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If you're gonna replace the injectors, go ahead and get the adapter kit and swap to the new style. A little bit more $, but well worth the future headache, especially since you'll already have everything apart.

branden0502
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Joined: Sun Oct 15, 2017 6:05 pm
Car: 99 I30

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I did order that one From z1

Thanks

branden0502
Posts: 13
Joined: Sun Oct 15, 2017 6:05 pm
Car: 99 I30

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after i pulled it all apart. i have the old valves. should i replace them while i have it out?

kevin43734
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Joined: Thu Oct 18, 2018 6:05 pm
Car: 1996 300zx z32 with an early style engine.

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I had a fuel leak in my engine bay and traced it down to injectors. Swapped the o-rings and smell went away but suddenly noticed the gas in the oil. Stuck injectors. I purchased the new style nismo 615cc injectors and no more fuel in the oil. Nice little upgrade from the stock size too.


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