Z06Vette.com - Corvette Z06 Forum - HELP

SoCalSteve · 07-31-2008, 08:04 PM

OK, so I'm driving home from Santa Barbara per normal. Slowing traffic causes me to downshift. As I blip the throttle before the downshift, the engine exhaust note suddenly sounds noisy, with an unhealthy sound, and the CEL comes on. As I am slowing down, I notice that the car is going to stall and won't idle properly, so I pull off the frwy.

Get to a gas station - barely - and as I coast in, it stalls. Check under the hood - all seems normal. No dire engine sounds - feels like the Ford "limp-home" mode - running pig rich.

Wait 45 mins, try the key. After cranking and fluttering the throttle with my foot, it fires, but obviously ain't happy. Again, no dire engine sounds (didn't suck a valve, etc.) So, I elect to try to limp home - about 5 miles on a slow frwy.

Get home, and read the following codes:

P0300: Random/Multiple Cylinder Misfire Detected
P0101: Mass Air Flow (MAF) Circuit Range/Performance Problem
P0300: again...

By the way, I have a Halltech. It has not been re-oiled since I bought the car just before Christmas.

Remove the MAF to see if wires are fouled with oil from the Halltech. Some residue, light amount, black powder-like.
Clean them carefully with q-tip and No-Residue Electronic Cleaner.

Start it up. Same problem.

NOTE: Ran my first HPDE in the car last week. Has been running fine since then.

Any and all suggestions gratefully accepted. Maybe the MAF just gave up? Anyone know how to test? I've got a volt-ohm meter.

Thanks in advance!

SoCalSteve

**jub jub** · 08-01-2008, 06:37 AM

Sounds like you broke a valve spring. There was a guy on here a couple of weeks ago, same symptoms, same codes that did just that.

Don't drive it until you verify.

ScottPro · 02-07-2010, 02:45 PM

Was searching the forums and found this thread because I have the same exact problem, P0101 and P0300 DTC codes and the car barely runs. There is no mechanical noises like a broken value spring, just some serious misfires and the engine doesn't even idle (very difficult to start). I've replaced the MAF which cleared the P0101 code, also replaced the spark plugs and wires. No change at all. I hooked up an inductive timing lighting to each plug wire and found cylinder 3 was not firing at all. Swapped the coil pack with one that was firing and it still doesn't fire. Is this a PCM problem?

Everything on the car is stock engine wise.

SoCalSteve, did you ever find out the problem with yours?

Thanks...

SoCalSteve · 02-07-2010, 11:51 PM

Yes, it was a broken valve spring. I took it to Andy at A&A Corvettes in Oxnard, CA. (GREAT Guy! Very knowledgable - makes beautiful supercharger kits).

Only one broke, and lucky for me it didn't suck the valve or anything. He did a leak down test and found that the cylinder was unharmed. Replaced the spring (I'm outta work, so didn't do all). Car has been fine, runs great!

Except recently, got some random misfire and injector codes, again with pig rich condition, but without the same feeling as the spring. It would come and go, never lasting more than a few minutes. Took it back (remember, this is a year later). Andy said he needed to see the car when it was actually happening, but this was intermittant problem. However, after lifting the ground strap for a couple of days while he had it, the deep power cycle seems to have cleared some bad data, perhaps from the spring break incident.

In any case, this has solved the second problem which has not reoccurred since the power cycle.

ScottPro, my PM answer to you was wrong - I thought I had posted about the SECOND problem, which is what I wrote to you, but the original set of codes I had, which you have also, was the broken spring.

Hope this helps. Good luck!

SoCalSteve

ScottPro · 02-12-2010, 09:41 PM

Thanks Steve.

I'm going to do a compression check this weekend to see if I have a broken spring. It doesn't run like it's a broken spring because it doesn't even idle, have to keep it above 2000 rpm to just to keep it running. Barely starts.

ScottPro

SargeZ06 · 02-14-2010, 05:39 AM

Quote:

Originally Posted by ScottPro

Thanks Steve.

I'm going to do a compression check this weekend to see if I have a broken spring. It doesn't run like it's a broken spring because it doesn't even idle, have to keep it above 2000 rpm to just to keep it running. Barely starts.

ScottPro

Why don't you just pull the valve covers. Lot easier than compression check.

SoCalSteve · 02-14-2010, 07:27 AM

Quote:

Originally Posted by ScottPro

Thanks Steve.

I'm going to do a compression check this weekend to see if I have a broken spring. It doesn't run like it's a broken spring because it doesn't even idle, have to keep it above 2000 rpm to just to keep it running. Barely starts.

ScottPro

ScottPro,

Wait, that is exactly the symptoms I had WITH the broken spring - couldn't keep an idle, barly starting. I **may** have given you wrong feedback earlier because I had a recent different problem. But you have described exactly what it felt like when the spring broke.

Hope you have good luck!

SoCalSteve

ScottPro · 02-14-2010, 09:22 PM

Did a compression check (only took 30 minutes) and found cylinder #3 had no compression. Just ordered some Comp Cams 918's valve springs, Yella Terra YT6645 rocker arms and Comp Cams chromemoly pushrods 7.4" from Thunder Racing. I figure it's best to replace everything while I have the covers off.

I think I'm going to do a leak down test while the rockers are off to check for valve damage.

Thanks for everything,
ScottPro

SoCalSteve · 02-15-2010, 08:03 AM

Hey ScottPro, no problem.

Glad you found the problem. Sounds like you have a good plan on the replacements. Please keep us informed on how it goes! And if you can, take some pics. I'm lousy at posting pics, but I'm sure someone here can help (if you need any).

Hope it goes well.

SoCalSteve

ScottPro · 02-20-2010, 10:02 PM

Broken spring on cylinder #3

Broken spring next to new CompCam 918 spring

Box of old parts

New rockers, springs and pushrods. Had to use the shims with the Yella Terra rockers.

The whole job took about 3 hours. Did a leak down test on all cylinders and are all good, even with a 100K on the engine. Compression was good too, about 150 PSI, which is around 10.2:1 (figuring 1 atm is 14.6959 PSI).

Engine runs great again.

Thanks for all your help,
ScottPro

PMPN8EZ · 02-22-2010, 07:17 PM

Glad to hear the problem is fixed! Beautiful hardware under those covers now. Try putting up that box of old parts up for sale you never know if someone could use it.