LT5 INTERNAL NOISE

[fred dosa]

CAN ENYONE TELL ME WHERE THE NOISE IS COMING FROM,
I KNOW ABOUT CHAIN RATTLE AT START UP THAT GOES AWAY AFTER 2 SECCONDS, MY NOISE STARTED LAST FALL INTERMINTANTLY AND DOES
NOT GO AWAY WHEN IT BUILDS OIL PRESSURE, I MUST SHUT ENGINE DOWN
AND WAIT 5 MINUTES AND RESTART. TO STOP THE NOISE I PUT ENGINE RESTORE IN LAST WEEK, SHOULD I HAVE DONE THAT?
SOMETIMES I MUST REPEAT START A NUMBER OF TIMES FOR NOISE TO GO AWAY. A COUPLE OF DAYS AGO I TOOK THE CAR FOR A RIDE ON THE HIGHWAY,
WHEN TO MY SURPRISE A PORCHE 911 WANTED TO RUN, I TOOK THE
MOTOR TO 7000 RPM AS I HAVE DONE HUNDREDS OF TIMES BEFORE
BUT THIS TIME THE MOTOR STARTED TO SOUND OUT OF TUNE
AND LOST A LOT OF POWER,I'M HEARING A LOT OF RATTLING NOISES
BUT OIL PRESSURE IS 30 LB AT IDLE AND 60 LB DRIVING
THIS MORNING I STARTED THE MOTOR HOPPING THE NOISE WAS GONE
TO MY SURPRISE I COULDN'T HERE THE NOISE, BUT WAIT IM STARTING TO HERE SOMETHING ITS GETTING LOUDER AS THE ENGINE WARMS UP
WHEN ITS WARM ITS AS LOUD AS BEFORE .

[tomtom72]

Hi, Look I'm just an apprentice Z owner and until one of the more knowledgable owners see this thread I'll offer up this:
Do you have any DTC codes?
If yes, did you look them up?
Did you put a scan tool on the data port? What did the scan show?

I own a 90 and when my primary injector coils started shorting the imbalance in cylinder output due to the lack of fuel caused my car's dual mass flywheel to start rattling. It made the car sound like a diesel...the noise was hurtful at times. It had a big miss or skip, and the hotter the motor got the worse the miss got. I learned the reason is that once the injector coil starts to short it will only get worse. The car ran almost fine when it was cold...you had to listen very closely for the miss from the bad injectors but after it reached proper operating temp...man did the miss show up! I used a scan tool to "view" what the motor was doing in "closed loop", by seeing the results of combustion in the O2 sensor numbers(cross counts & milivolts) and the block learn numbers & integrator numbers you will see that combustion is not normal. I'm not saying that this is your particular problem. The only reason I jumped in is because you said when it's cold it's not audible & when it gets warmer it starts to become evident & it seems the hotter the motor gets the more the miss & noise becomes evident.

Do you have a Helm manual set for the car? If not they are a very worth while purchase...Helminc.com...those are the genuine GM service manuals for the ZR-1.

Tom

[BBBAD94ZR1]

How many miles on the engine?

[fred dosa]

90,000 MILES ON MOTOR, NO DTC CODES
I TOOK SPARK WIRES OUT ONE AT A TIME WHILE RUNNING AND NOTICED
CHANGE ,ALL CILINDERS SEEM TO BE FIREING
HOW DO I TEST FOR ROD BEARING FALURE IT SOUNDS LIKE ITS COMMING
FROM BOTTOM END. NOISE GETS LOWDER WHEN I REV MOTOR AT IDLE

[We Gone]

Only way to check the rods is drop the oil pan

[tomtom72]

Rod bearing tests. Back before catalytic converters, yea I'm that old
We would remove one plug wire at a time & listen at the bottom of the "V" near each con-rod location. The theory was if the noise deminished when the combustion pressure in that cylinder was absent due to no spark ... then you had a fair bet you had a con-rod bearing problem. A piece of broom handle laid against the block near the bottom would transmitt the noise fairly well to your ear. If the noise was higher up along the cylinder bore & you had to follow it up & down thru the stroke...you could guess it was a wrist pin, if the noise stayed low down you could guess it was a rod bearing, if the noise stayed fairly constant it was a main bearing. I don't know how well that method would work on an LT5, as crank is burried fairly well.

If no one else has any suggestions, I would offer this up for consideration: Gordon Killabrew has a website..."foryourcar.com" and he has a paid trouble shooting phone line...it might be worth the $ to hear his opinion & suggestions? JMHO.

[TheLurker]

Anyone who has heard a rod bearing go should be able to tell you. Many times when one goes you will hear a high pitched squeel as the bearing rotates around the crank. Otherwise, you will hear a low pitched, sometimes metallic, knock from the center of the engine. Remove your oil filter and tear it apart. If there are filings in there do not run the engine again. If you have ever run the engine low on oil, perhaps taken a turn quickly then, you can toast a bearing in a fraction of a second.

[ZR1HOTC4]

Just went to an event this weekend and experienced the rattle & miss as described by tomtom72. Seems when it's warmed up it I get the miss and the rattle/knock starts. I trailered the car home in fear of losing the engine. It seems quite likely it could be the primary injectors going screwy since we just did a detail on the car and there was water going where it shouldn't have been - possibly doing something to the injector coils?

After the engine cooled after the event the car started fine and ran great for about 5 minutes (to the diner) - then it started again. To me this rules out rod knock and seems more ignition - temperature sensitive. When the truck and trailer arrived, car started fine to load it on the trailer, so I let run till operating temperature - then it started again.

My next step is to do a scan - thanks tomtom72 for your wisdom and experince. I love my car with 67,000 miles and hope I can get it running strong soon.

Dave McDonald, Santa Maria, Ca

[tomtom72]

Hi Dave,

I doubt that the small amount of water that escaped would cause a problem...unless you "hosed" it down very well & then your starter would be the likely victum. I do believe that after you let the car get to "closed loop" & scan it your numbers will not be like the numbers in the Helm manual. There is a page in section 6E, "Driveability & Emissions", and it shows you what the numbers should look like for a properly working motor on the scan tool. That's what brought me to the primary injectors being at fault in my case.

If you have a 90 or 91 it's a good bet that the ethanol in our gas has finally killed the injector coils...they weren't designed to resist ethanol like the 92-95 injectors were. Call RCEngineering.com & get a set(16) of their S/S injectors & don't look back, about $68.00 ea. I know it's a bunch of cash but they work great.

...welcome to the Fraturnal Order of the Knights of the Pulled Plenums!
Oh, while you're under there you may want to check the breather box gasket & hoses and eye up the 2* vacuum hoses and associated parts....test all the vac lines & actuators & the 2* control solenoid, ohm up the coils & wires & clean up the valley & drain tube....you know the standard house keeping for under the plenum. It's not hard to pull but the gaskets are expensive so you might want to consider giving the once over to everything that lives under there just so you don't have to make it a habit. Just a suggestion!


Tom

[haber rj]

Hello Fred, I had that same thing happen to me last year on my 91 "Z' car and boy without my buddy calming me down I was about ready to sell the farm. We traced the problem to a bad primary injector, called Rc Engineering and purchased a full set of 205 injectors (after a lot of help from my fellow form friends) who pointed me in the right direction and so far the motor is back to running great. All we did was pull each plug wire off one at a time when the motor was hot (running temp) untill we found the cylender that was bad. I also had access to a dyno and the problem showed up drasticly when we had the car on it. Aaron at South Georgia Corvettes was a great help also.