I had my C5 Z06 out at the drag strip for the first time after buying it from copart and getting it road legal. The car has about 105k miles. Everything was running fine while driving it around town. But during the first pass I made down the strip, the clutch disc exploded as I was shifting from 1st to 2nd and caused the engine to over rev to maybe 7200 rpm. I immediately shut it off and towed it to a shop to have them put in a LS7 clutch. We immediately heard the engine knocking on the first start up after putting in the new clutch. It's also throwing a map sensor code and running very rough. I ending up towing it home so I could take off the heads and examine everything. I took the heads off and everything looks fine, no bent push rods, the lifters look fine, valves all look good. I am now stumped as to what is happening but I am still a little suspicious of the lifters. I never found any vacuum leaks that might explain the map code either. Does anyone have any ideas?

 

First off welcome to the Forum......you should put a scan tool on the car first (what was the MAP DTC ??) and I would do a compression test but you can do a "cranking compression test" just to listen to how the engine sounds when it is cranking over...put the accelerator pedal to the floor and HOLD it there...the car won't start but listen to any inconsistencies in the cranking cadence of the engine while you start it...should be nice and even...I'd put a vacuum gauge on the car and see what it reads...you'll need a smoke machine to find a vacuum leak so I'd suggest you do that and take the car to a diagnostic shop and ask the shop if they can do an "in cylinder pressure analysis" of the engine...you might have to look around to find an advanced shop that knows how to do it OR bring it to me here in SW Florida...LOL !!!...going in cylinder I can tell when the exhaust valve opens and when the intake valve opens and closes (can't really see EVC) and if any valves are sticking or not seating or maybe a bad cam lobe or incorrect timing (a cam-crank relationship)...this test will tell if anything is wrong mechanically...an in cylinder of my 01 at idle below...my EVO is 44.78 degrees before BDC...I can check IVO and IVC the same way ...please fill out your profile with all your info...model year, mods, tune, etc...it helps us help YOU !!

 

The map code shows up as P0106 "Manifold Air Pressure (MAP) Barometric Pressure Sensor Electric Circuit Output Range and Performance Problem". There was a code for multiple random misfires too. I did do a compression test and all cylinders read about 170-180 psi. I'm actually in the Tampa area, relatively close to where you are at.

Thanks for the reply!

 

Saw you put some things in your profile…what model year ??…differences in component location and wiring sometimes and if you put your location you may find someone willing to help !!…so is the car drivable ??…if not I could take a ride up your way if you want…could be an interesting diagnosis other than my usual O2 sensors, vacuum leaks and MAF sensors I’ve been seeing !!…wouldn’t be able to make it up there till next Friday or later…so basically it’s just running rough with some random misfires…you have a scan tool ??…seeing you had a clutch job it may be something like a loose or missing ground connection causing the misfire.

 

Whoops! Forgot to hit save for the profile info. Still new to the forum lol. It's a 2002 c5 Z06.

The car is not drivable. I've tried to take it around the block but it runs so rough that it gets close to stalling. And I also just took the heads off yesterday to look at everything so it's in pieces right now.

But yes.....long story short, the car is running rough, throwing codes for random misfires and the map sensor, and it has a top end knock that I can't determine where it is coming from. I do have a scan tool but it is a pretty basic one.

That would be great if you would take a trip up here! I've really been itching to get the car on the road and enjoy it but I just can't figure this out.

 

OK, so you are sure it's a top end knock and not bottom end one...spun bearing perhaps ??...well get the car back together and I'll swing by towards the end of the week if you'd like.

 

Yeah it sounds like the knock is coming from the top end. I will put it back together and let you know about later this week. Thanks!

 

Video???

 

One way to virtually eliminate a spun bearing, especially since you have the heads off, is to bring the pistons to TDC, one at a time, of course. Then SLOWLY turn the crank over until a piston just starts its downward travel. You'll need a dial indicator, or good depth micrometer to accurately verify measurements. Measure as close to the center of the piston as possible, to avoid false measurements due to piston "rocking" in the bore. Once ready to measure, push down with each thumb, again pushing as near to the center of the piston as possible. Then compare readings before pushing, to after. What youre basically doing is roughly measuring rod bearing to crankjournal clearances. You shouldn't see more than .003", maybe .004" max, allowing for some piston rocking. If you see all of them the same, except for maybe one that may reach .005"-.010", then you've trashed a rod bearing. If you're certain you "only" saw 7,200rpm, your bearings should be OK. My $$ would be on a damaged/broken lifter. Again, best to check the lifters and the rod bearings now, while heads are off. Best of luck my friend....

 

BTW, what strip did you run at? Welcome to the forum. I'm in Hudson, about 30 miles N. If Rob (C5 Diag) is coming tp help, Id try to eliminate the lifters/rod bearings being damaged ASAP. Rob knows his stuff. I just hope you haven't damaged anything mechanical......

 

Yeah I'm hoping I can get it back together by the end of the week. Going to be pressed for time but think I can make it work.

Thanks for the info on how to measure for a bad rod bearing! I'll certainly try that before I slap the heads back on.

This incident happened at a street heat event in Bradenton.

@grinder11 I attached a video. Please let me know what you think!

 

Zach, I listened, don't like it at all!! Sounds like my engine when I over revved it!! I had a broken lifter. This is obviously not an electronics problem. I would not run it again until your heads are off, and you've inspected the lifters. If it is a broken lifter, I'm hoping you can pull it up thru the lifter bore. I couldn't, had to remove the cam, and then push the lifter down into a special tool I made out of PVC pipe. If you keep running it, you'll make it worse.
NOTE!!!! Do not try to force the lifter up thru the lifter bore!!! If it has spread open, you'll be forcing hardened steel up thru an aluminum bore. Then you'll need to have the blocks lifter bore sleeved, which means removing the engine. Good luck.......

 

Anything happen with this yet? In to hear the diagnosis.

 

YO!!! Calling Zach!!! What didja find?