HarleyZ28

So I got out of the car scene for awhile.


I have a 1997 Z28 with 70k miles. For anyone old school members on here it used to be Gregg97z's car.



I had my car stored in a barn covered for a couple years. I moved two years back and drove the car to my new place with no issues at all. Recently I went to take the car for a small drive and noticed it wasn't running right.


So I popped the hood and noticed immediately the dipstick tube popped out and threw oil all over the place. So my first thought was this oil is several years old, while it had under 1k miles on the oil, it had been sitting for years in the car, so maybe the oil is bad and causing blow by issues. So I changed the oil / filter.


Now I can start and drive the car and the dipstick doesn't blow out,, however I'm still having issues with the car.


The car starts perfect and idles fine, however if I rev it up to 2-2500 rpm and just hold it there I start to get serious backfiring and smoke from the exhaust, and not a sweet smelling smoke either very harsh to the point it will gag me out of the garage. As far as the smoke color its definitely not bright white , maybe a grayish color smoke?


So, I went ahead and replaced the spark plugs. They were all almost completey black.


Fired the car up, same thing. Idles fine, starts right up, but if I blip the throttle it definitely doesn't rev nearly as quick as it used to feels like some hesitation, and again if I try to rev it up to 2-2500k rpm and just hold it , it will start to backfire horribly and smoke starts rolling.


So the only things I have really done so far are

1. Oil change

2. Spark plug change

3. Put fresh gasoline in it.


This car is far from stock.


Also I should mention it has Slp midlength headers with egr delete. No cats, no 02 sensors. The car has a mail in order tune.


This thing ran perfect before I parked it , not a darn thing wrong with it, I'm at a loss as to whats happened to cause this.

Injuneer

Sounds like excess pressure in the crankcase blew the oil dipstick out. May be indicating gummed up/stuck piston rings allowing significant blowby. That could also account for oil entering the combustion chambers and burning to create the smoke.

Were the plugs we with oil?

Another possibility is excessive piston ring blowby, combined with a plugged up PCV valve. With a faulty PCV valve, pressure can build, and it relieves the pressure by flowing out the PCV vent hose on the passenger side valve cover, and into the throttle body, where it eventually gets mixed into the ar entering the combustion process. Pull the hose off the valve cover and see if it has oil in it. Take the top cover off the throttle body and see if there is a puddle of oil.

HarleyZ28

I will check these out when I get home after work and report back,

So where does the backfiring come into this? Idles fine, when I hold it at 2-2500k rpm it starts making loud backfiring / popping sounds, like excess unburnt fuel detonating, and I have my exhaust dumped at an angle towards the ground, there is a black spot on my garage floor where the exhaust points.

Also, it doesn't rev as fast as it used to.

Injuneer

Trying to sort out the problems one at a time. Dumping oil in the intake manifold may account for the other problems as well. Definitely accounts for the black spot on the ground.

Best i can do..... maybe someone else can add to it.

HarleyZ28

No oil in throttle body , hose did not have oil, and the pcv valve seems fine, but I went ahead a got one and put in due to how cheap it was and the auto part store is across the street from my house.

I did start the car and let it idle for about 30 seconds and shut it off, I then started feeling every exhaust port on the header to see if they all were firing. Every one was hot minus #5 it didn't even seem warm. So I think I have atleast narrowed down to where the major misfire is happening. I put a new plug in and that didn't help, the wire looks fine to the eye but maybe its bad still?

WhiteWS6

Plug wire could be arcing elsewhere, best way to test this is by spraying it down with water or looking under the car while it's totally dark. You should check for spark at all cylinders, auto parts stores usually sell an inline spark tester. #5 is an easy cylinder to put it on compared to the passenger side. If you're getting good spark to that cylinder maybe you have a fuel injector not operating properly or the wiring to it may be disconnected or not correct. Take my 2c with a grain of salt, I'm sure Injuneer likely has a better game play for the issue, he's definitely helped more than a few on this forum to say the least.

-Grant