Smoking ZR1 - 1990

[HOTZR1]

In the last 5 years I've driven the ZR1 about 200 miles. I start it occassionally and have seen some blue smoke on startup and figure that's normal. The other day I ran it for about 20 minutes and there was quite a bit of blue smoke... to say the least, it just doesn't look cool!

I ran a compression test and here is the results:

Cylinder Dry Wet (tsp oil)
1 205 225
2 205 220
3 180 215
4 205 210
5 185 220
6 190 225
7 180 215
8 220 225

Service manual states 150-200 psi is acceptable and low to high within 25%.

I did a search for some insight on the smoking condition. There is a post regarding pulling the plenum and see if oil has accumlated in the "breather box" or that "seal at the base" of the breather box has gone bad which can cause loss of vacuum and some oil build up (PCV doesn't work effectively). If the PCV isn't working right it will smoke. Another mentions the PCV as it enters back into the injector housing. Oil can accumulate in there from the PCV, especially if it isn't functioning correctly.

Today I'll do a leak down test.

Does anyone have any additional insight to this smoking issue. Thanks Dave

[Pete]

1990 ZR-1's do not have exhaust valve seals,normal for them to have start up smoke.

How many miles on this Z?
Test seems good.
I would drive it some more and retest.

Pete

[HOTZR1]

The car has 69K on it. Not hard miles. Most all the miles were put on by the original owner between 1990-95. I bought the car in 2005 with 65K on the car.

Very embarassing with the smoke. Just hope there isn't anything internal going on which is going to cause more damage... if something is damaged.

Thanks, Dave

[bad-zr1]

I have run the dry compression test many times on my 90 with 56K on it and I am always over 200 psi by the third revolution. The 4th brings me to 225 for my low reading. This is on a "cold" engine. The leakdown test will let you know what you have and where its going.

[HOTZR1]

Just finished the leak down Test:

Cylinder - % Leak
1 - 15%
2 - 23%
3 - 18%
4 - 18%
5 - 15%
6 - 14%
7 - 20%
8 - 25%

All air escaping seemed to come through the crankcase. I took the oil cap off and slight air was escaping. I could tell by the smell coming out rather than any rush of air. No air was escaping through the valves out the intake or exhaust.

Do these %'s look reasonable. They were all in the green on the tester.

I'd like to add the spark plugs looked pretty black and some wet (#8 especialy) which had the smell of gasoline. I'd also like to add most of the smoke was coming out the passenger exhaust. Could it be possible the injectors are leaking?

Thanks, Dave

[Hammer]

Just finished the leak down Test:

Cylinder - % Leak
1 - 15%
2 - 23%
3 - 18%
4 - 18%
5 - 15%
6 - 14%
7 - 20%
8 - 25%

All air escaping seemed to come through the crankcase. I took the oil cap off and slight air was escaping. I could tell by the smell coming out rather than any rush of air. No air was escaping through the valves out the intake or exhaust.

Do these %'s look reasonable. They were all in the green on the tester.

I'd like to add the spark plugs looked pretty black and some wet (#8 especialy) which had the smell of gasoline. I'd also like to add most of the smoke was coming out the passenger exhaust. Could it be possible the injectors are leaking?

Thanks, Dave

Dave,

Was the leak down done on a warm motor? Not sure on the ZR-1 but on regular small blocks, the dipstick tube is the place to check for ring problems as the oil is added to the valve covers. I'm not sure if the oil cap on the ZR-1 goes into the head or the pan. Just a thought.

Your leakdowns to me, look like a ring job is in order. From What I know, anything over 15% on a street engine is indicative of that and you show over that on 5 of the 8 cylinders.

You might try the same thing you did with the compression test. Warm the car, do the leak down (listen at the dipstick tube for ring problems), put a teaspoon of oil in the cylinders, turn the car over a few turns and then do the leakdown again and see what happens.

I had a ring problem on a Pontiac Sunbird once and put some Mopar (ouch) combustion cleaner directly into the cylinder, turned it over a couple revolutions, let it sit overnight, started it the next day and it did wonders. Smoked like a sum beotch when I first started it. I think there was a stuck ring or something. Sounds like your car sat for a long time so that might help.

To me there isn't enough miles on the motor to be having this problem if it was taken care of and it sounds to me like it was. I sold '91 #458 with 72k on the clock and it was running strong at that mileage.

Good Luck. Keep posting on this problem if you would please.

[HOTZR1]

John, Thanks for your insight.

I ran another compression test and leak down test with the car hot and no oil. Here are the results:


Compression Leak down%
1 195 21%
2 205 21%
3 190 20%
4 195 24%
5 195 20%
6 205 20%
7 185 21%
8 200 23%


The hot test seems to present less variation. As mentioned earlier, compression on the 4th stroke should be higher above 220. This time there's higher leak numbers http://zr1.net/forum/images/icons/icon11.gif than the cold test and the ranges are close. The difference could be the setup on the leak down guage... has to be set at zero. I was very careful this time and even retested to verify the results.

If the numbers should be below 15%. I've even seen 5-6% would be good. If so, then there is a problem in every cylinder. There were no bubbles in the coolant... to rule out a head gasket. There was only slight leaking detected out the oil filler cap - which was more of a oil smell than hissing air. I pulled the dip stick but couldn't hear anything from it. Nothing out the exhaust or throttle body.


When I started it before the test to get her hot it was smoking pretty bad - mostly from the right exhaust. I tried a camera, but the camera end was too big to go into the spark plug hole - bummer.


Next step is to tear the engine down. I've been under the plenum a couple times, but this will be a first time in the heads and cylinders.

I've looked throughout the forum and see there is plenty of guidance regarding cylinder/piston replacement. What would be the "best" most reliable replacement?

Thanks for the replies. Dave

[Polo-1]

Your left bank to right bank show, maybe a little cam timing off from each other.
How old is the engine oil ( I'd like to add the spark plugs looked pretty black and some wet (#8 especially) which had the smell of gasoline. )
Put in a fresh load of 15-50 M1 in it. Drive for a good 30 mile loop with the secondaries used well. See if the start up smoke goes away, or at least minimal.

[Hammer]

Do you have a dual guage leakdown tester? The numbers seem wierd to me in that they went down for the most part, whereas the compression readings went up indicating a better seal. Try Kevin's advice before tearing into the motor and don't rule out trying the Mopar comb. cleaner, you could have gummed up ring lands from it just sitting.

As far as a rebuild, the parts, special tools and headaches required to rebuild the engine could add up to more than you anticipate. Especially considering you are ready to get rid of the car and there aren't really machine shops on every corner that can work on this motor.

Trust me, I am no expert on this motor by far and the advice I have thrown out is from general engine building in the past.

I still find it hard to believe you have engine problems with the miles on the car though.

[FU]

IMO........change the oil and filter. Replenish with prpper AMO oil . Then take the car out and beat the snot out of it.
Then , get a dual guage leak down tester and check . The reading's that you are getting now aren't that bad to warrant a total engine rip down (IMO).