Santana787

i need help with my new project 1990 nissan 300zx n/a. I just got this car from my pops. The car turns on and drivings. but the only only problem is the car at time runs on 3 cyclinder. i know my dad had the car rebuilt(sand blasted head,new head gaskets and seals,etc). He resently had two mechanics come by to looks at the car. The car gives spark and fuel. So they came to the conclusion that the engine has 3 cyclinder with no compression. But i dont know if tfhat really the problem. i just want to see if there is someone here thats good and knows 300zx z32z If they can come by and give the car a look and give me a definite answer whats my problem before i buy a new motor! Vg30dett

Empire

I would be willing to bet it is the PTU. (power transistor unit)
they go bad. and even the ones that got replaced during the recall, the plugs themselves get loose.
I'm not talking a matter of IF, I'm talking a matter of When. They will go bad sooner or later, and the plugs will get loose and corrode sooner or later.
Without the PTU, there is no spark. The PTU has a circuit for each cylinder so it is likely that one a few will work.
Beyond that, since it is believed to be a compression problem. you need to get the engine warmed up and do a compression test on each cylinder. It isn't difficult as you can easily pull the coils off and yank the spark plugs out without having to do anything crazy like pull the manifold or anything like that. A compression tester is cheap, especially from Harbor Freight, and it is really straight forward on how to do it. Don't need a mechanic to do it.

When you say it is only running on 3 cylinders, how do you know it is only 3?
Are you pulling the plugs for the coils to figure out which cylinder isn't firing?
A simple misfire on these engines can shake the engine all over the place.
What is going on when this happens? Is it hot out? cold out? worse when the engine is warm? When the engine first starts? Does it go away? When it goes away, what happens? Does it go away on its own? Do you fiddle with the plugs? Do you have to re-start it and then everything is good?

I can list off a dozen things to check, but it would all be useless without knowing more of what is going on.



p.s. You can call the dealership and give them the VIN number and they can look it up to see if the car has ever had the PTU replaced under the recall. If NOT, then they should do it for free, and it is very much worth having done. If it has, see if there is anything they can/will do to replace the new one since it is more than likely faulty again. I suggest that because there are stories of people getting the new one replaced because it failed and it should have lasted the lifetime of the car, and the dealership took care of it. If they won't do anything (and after you've called a different dealership) then replacing it is going to cost 150-180 bucks for a new part.

Santana787

Yea I going to call the dealership to check that out. But yea I know the car is running on three cylinders buy disconnecting the plug. But checked all plugs but the give spark. When I drive and its cold it sputters. Then after heat up it drives smooth but when you try to speed up it sputters and you feel the lag then after it speeds up quick.

Empire

What 3 cylinders are misfiring?
Is it the same 3 every time?
That makes me believe the fuel injectors are bad. Which is another really common issue with these engines. The problem is, Nissan used an old style injector in these engines, and an old method of powering them. the injectors have 12 volts of power to them all of the time. Because of this, they die out faster than the newer style injectors. Also, Ethanol kills these injectors even faster. So if you are getting solid spark, then I would bet on the injectors being bad. The most simple way to test them is to get out the multimeter and test the Ohms between the two contacts. They should be right around 11-12. Less than 10 is bad, and anything over 15 needs replaced too. You can do this without pulling the manifolds off.
IF one of them tests bad, you're going to have to pull the manifold, which, if you have never done before, can be a bit of a pain, but it is rather straight forward. I don't remember any "hidden" bolts or anything like that. Once you pull the manifold, I would highly suggest pulling the fuel rail so that you can visually see the injectors spraying (or not spraying) properly when you turn the key. I suggest this because it is possible for an injector to, for lack of a better term, be jammed, and not spray even though it tests well with a multimeter. The spray pattern could also be garbage, and if you're buying injectors, might as well replace everything at once instead of having to pull it all back apart in 6 months.
This really sounds like classic coolant temp sensor.
There are two sensors. one controls the gauge, the other tells the ECU the temp, so the ECU can adjust the fuel as needed. From what I remember, the sensor for the ECU is rather cheap. There really isn't any accurate way to test it. If you have the spare cash, I would suggest replacing it. It should have technically been replaced at 100k miles anyway.
Now, having said that, a fuel pump/fuel pressure issue could also cause this kind of symptom. When the engine is cold, the ECU tells the injectors to spray more fuel. If the fuel pump can't keep up, it is going to be the worst when the engine is cold. Also, if the fuel pressure regulator is/has failed, then it won't be able to keep the pressure high enough, and again, will be the worst when the engine is cold. Getting a fuel pressure gauge on there would tell you a lot about what is going on.
And this is what has me thinking it is very possibly fuel related.
in my experience, there are really only 3 reasons to have this kind of sputtery/laggy symptom.
#1 - not enough fuel. either the pump isn't pumping enough, or the pressure isn't high enough.
#2 - The throttle position sensor has either gone bad, or at least needs adjusted. It should be 0.45 volts at closed throttle and just over 4 volts at wide open. In my experience, the TPS usually needs adjusted if it hasn't been in a long time due to build up and all of that.
#3 - a vacuum leak. There are lots of vacuum lines especially for all of the emissions things. It can be tough to trace them all down, but you very much need to. Nothing else is really going to matter unless you know there are no vacuum leaks. All of my suggestions have been based off of the assumption that there are no vacuum leaks. Even a minor one can cause a sputter and lag when you give it gas. It is a bit time consuming, but it is worth the time and effort when trying to get one of these engines running properly. The ECU will do everything it can to keep the engine alive so it will compensate for a vacuum leak. I've seen cars with hoses just flopping around, dumping vacuum, and the engine still started and ran "ok"

One more thing I'd suggest doing if it hasn't been done yet is to clean the Mass Air Flow sensor. The MAF gets dirty, and because it is under the nose and out of the engine bay, it gets forgotten about and never cleaned. I've used MAF cleaner on some and had everything from visibly cleaner, to pouring black stuff out, to literally having chunks of dirt fall out. Makes a HUGE difference in the performance of the car.

Seems like a lot, but without seeing the engine in person, all of that is what I would suggest doing, given the info available thus far.