tcouty87

I have an 03 Z06 with 28,000 miles on the clock. Mods are a cam, intake, kooks long tubes w xpipe, nothing too big.

I was driving to las vegas from phoenix with my wife and all of a sudden power was slowly going down to the point where I could only go maybe 15 mph. Pull over, had it towed back home and got a rental car.

Coming back I checked the oil and it reeked of gas. Did a compression test and on the drivers side head compression read:

1-185
3-183
5-184
7-185

Awesome right?

The passenger side head was

2-75
4-60
6-60
8-120

Sounded like a head gasket issue to me. I have no idea what the hell would cause compression to go low on one bank besides a head gasket. So i pulled the heads, sent them off to the machine shop in town, replaced the gaskets, valve seats, seals and had the heads cleaned up and decked.

Buttoned it all back together and the car fired right up.
Oil pressure is at 40,
battery is at 14.1v, and
coolant is at 178. Perfect

After letting it run for about 10 minutes i check back and
Oil pressure is at 19
Battery is at 12.9-13.0
coolant still at 178

WTF! I pop my dipstick out and bam, smoke is still pouring out of that at the breather line to the throttle body.

Oil is 5w30, the 2nd time i used 10w40 and it wasn't any better.

1st off Im sure everyone will say it's piston rings.... but with only 28,000 miles (it's not a track car, the occasional once a month rpm run and thats it) how the hell would only one side of the motor be making that low of compression.

2nd, ofcourse fuel in the oil would cause oil pressure to drop which would cause blow by because it is too thin, but why just that side also? I checked the fuel pressure and it is at 68 at idle. way too high so yes a leaky injector could cause this (but again.... all 4 on one side?) I know the corvettes have the in line fuel pressure regulator, so is it possible that ruptured and would be causing my problem?

and to top it off, with a brand new battery and an altenator that tested good, i'm only at 13.0 volts as the high output? I checked this with a multi meter to confirm and it's the same reading as the DIC. I went through Bills ground cleaning forum and everything looks great, but I took them all off and cleaned them anyway. Same thing

I've worked on cars for over 10 years but this has me stumped

Ofcourse a leakdown test will be recommended, but I already know the outcome, it will point to the rings on the passenger bank.

I remembered getting an octane booster from a mobil one gas station and putting it in the tank and this **** happening about 40 minutes down the road so it's stuck in my head that that **** is what caused it, just stuck on what to do/check now outside of a full rebuild. Which is ridiculous with only 28k on the clock.


Thanks guys for any and all input, it would be well appreciated.

tblu92

Could point to many things--But i would start by 1st checking the manifold vacuum at idle
should be very high---15-20 ish
2nd a vacuum leak could be the cause--on the pass side--the ECM will try to compensate for the added un-metered air by dumping fuel via the injectors--causing tons of fuel to dump on the side with the leak--take some starting fluid or some brake clean and spray it around (while runninh) the intake manifold where it meets the head--around the MAP sensor--T-body PCV system etc--with the starting fluid the engine will flare up--with the brake-clean it will try to die----
Did you do a " crank relearn procedure" when you installed the cam? often overlooked but if the timing is way off you get lots of un-burnt fuel in the cylinders
The timing chain could be off one tooth--
While idling--if you remove the oil cap--is there pressure or vacuum being released??
if so report back-
Make sure the PCV system is all routed correctly--Often times with mods the system lines are changed or re-routed --A common issue is that a PCV line will get sucked flat and close off---creating all sorts of blow by-the hose has to be extra firm not to suck flat
Could explain why it was fine for awhile but as the hose aged it stsrted to suck flat
I believe the octane booster is just a co-incidence---Why are you using it anyway ?? Is your compression higer than stock ??
And finally--If you remove your heads and DON"T re-surface or clean flatten the block deck-- GM reccomends that you always use the graphite composition style head gaskets and NOT the multi-layer steel ones--- ( to allow for any deck unevenness) the graphite style gaskets tend to be more forgiving and will take up some clearnance for un-flatness (is that a word ?)---- good luck

tcouty87

Hey man thanks for the quick response. Vacuum is great at 18 inches of mercury with no fluctuation. The cam was put in over 3 years ago and the car has run great since then. There has been no changes of mods for over a year and then this suddenly happened.

Highly unlikely about the intake leak, however I will definetly give it a shot. I was leaning more towards o2 sensor if anything.

Just blows my mind my fuel pressure is so high.

The car was tuned by chuck cow over 2 years ago on 93 octane. I moved the car to Arizona with me so it's 91 octane here. That's why I used the octane booster.

I had the heads decked at the machine shop during the clean up and also deck cleared the block with no more than .001 clearance across the block deck. I also used the compose gaskets from Gmpp.

I'll for sure check out the lines for the Pcv system again.

Thanks for a quick response man. I appreciate it

lucky131969

First of all, what codes did you have? You are leaving a lot of information on the table here


How many times did you perform the test? Just once? Did you verify again on the good side(checking gauge)? Did you do a leak down? Shot of oil in the cylinders, and retest?


What did you find upon removal? The head would have to have a warp(or damaged gasket) about it's length to affect the whole bank? Did you see problem? What made you decide to send the heads to a shop? Also, what did the shop report?


What type of PCV system do you have? Is the valve functioning/properly connected?




Are you saying you did not change the oil, before firing it up again? Since you had a dead bank, did you change the plugs...they should have been fuel fouled. I do not see how a leaky injector can cause the fuel pressure spike. I would not even run the engine again, until you can get that corrected.

tcouty87

Zero codes. Ran through the dic at the time it happened, when I got it home and after the heads were done and back on.

Same numbers after 2 tests before the heads were off and back on. They fluctuated maybe 2-3 psi. But remained the same.

I had a 3 angle valve job done just to clean em up while they were off. Shop said there was slight (no exact number) of linear warpage but nothing that should have caused a problem

Stock Pcv system and did the shake test on the Pcv n it free rattles. The breather hose from the passenger bank that goes to the throttle body (not the Pcv hose) is also puffing smoke as well)

I changed the oil before firing it up after it was put back together with 5w30 and it smelled like gas again, drained it, put 10w40 in it and ran it for another 15 minutes and same symptoms. It hasn't been started since.

099blancoss

what color smoke is it puffing?

dougbfresh

Pull valve cover FIRST, see if anything is broken (like valve springs, Z's are notorious for this). I'm guessing a head gasket or head problem with those LOW compression numbers.

MikeV

Doesn't it have to be mechanical or it would set a code. Something is allowing just the right bank to go full rich. Low psi is probably rings are washing out. Make sure you let us know what you find as this is a new one.

Good luck
Mike V

tcouty87

Hey thanks guys. It's definetly nt valve springs or a head gasket (broken 3 springs before). When I have time I will do another oil change and view the readings Of the o2 sensors I'll go from there. I just started it yesterday after verifying the Pcv was hooked up. Runs great for about 15 minutes then just starts shaking and eventually dies. I get a "charging system failure" message and battery boys drop to 12.4 before dying.

New battery, new gm exact 130 amp replacement alternator, went through every ground wire and check alternator and starter wires. All is good

I'm leaning more towards an electrical issue that is makin the car run rich and die put like this.

I have a few more things I'll check out and get back as soon as I figure it out.... I hate when people post a problem on here and never write back what fixed it at the end

tcouty87

Oh and sorry smoke coming out of the oil fill cap is white/grey. It'd reeks of fuel

dougbfresh

Swap injectors with some from the other side and see what happens. Usually they fail CLOGGED but who knows, I guess they could fail open. How did you test compression (EXACTLY)??

MikeV

I could see one injector having a problem but not 4 on the same side. Compression was good on one side so thats not the problem.. Something is Telling the four injectors on one bank to go crazy and its not setting codes like a bad O2 sensor...Doesn't the fuel pressure regulator control both banks?

Mike V

dougbfresh

One cylinder was OK on the other bank, you need about 100psi of compression to fire OK. I agree it's PROBABLY a head gasket of funky head but I was trying to give him some options. With low compression, he will smell unburned fuel.

RonSSNova

Was this car tuned?
I wonder if maybe the DTC reporting for the O2 sensors was turned off?

My car was running fine. But looking at my tune file with HPT and lo and behold, all the DTC's for O2 were turned off. In fact, a lot of things were turned off. An interesting way to fool a buyer, or the DMV huh?

Also, I don't see how injectors sticking open would raise the fuel pressure.
An interesting check would be to check pressure with the ignition on and the engine not running, with the engine running and right after you shut it off.
How confident are you in the FP gauge you are using?

If the thing was washing a ton of fuel in the one bank, the piston tops would have been cleaner by far than the other side. You have it apart yourself? What did it look like?

It obviously doesn't have a vacuum leak.

Challenging for sure. You need to leak it.

Ron

dougbfresh

Who said anything about high fuel pressure. Since the fuel rail is always under pressure, a stuck OPEN injector would allow fuel in all the time. I agree 3 would be weird and I still think it's a head gasket or head problem.

RonSSNova

The OP did in the original post

"2nd, ofcourse fuel in the oil would cause oil pressure to drop which would cause blow by because it is too thin, but why just that side also? I checked the fuel pressure and it is at 68 at idle. way too high so yes a leaky injector could cause this (but again.... all 4 on one side?) I know the corvettes have the in line fuel pressure regulator, so is it possible that ruptured and would be causing my problem?"

had2have-it

Octane booster? Check O2 sensors

tblu92

When the eng is 1st started--it runs in "open loop" when the temp reaches 140* it should change to closed loop----After warmed it switches to a timer rather than ECT--usually around 20 seconds----Sounds like as soon as your ECM changes to closed loop stuff starts happening--That COULD indicate a FOULED or not working 02 sensor--also could be the cause of a rich mixture as the 02's are ONLY used when it switches to closed loop
--If you have a fouled 02 the ECM goes into a "open loop fault mode "on the fouled side and that is as a safety always pig rich--
Get any scanner that records data in real time and see if your 02's are bouncing around rapidly from .100-.950 millivolts--if one goes bad they usually flatline at .450 millivolts-that would ease your mind about the 02's failure and eliminate that issue

jpalamar

^ Thats something I would check. Def swap front O2s and see if the other bank messes up.

dougbfresh

What does this have to do with LOW COMPRESSION in 3 cylinders.