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Discussion Starter #1
2003, 20K miles. Took it out for a quick meal last week. Got on it, on the way home. Got a check engine light. It certainly seems like it is misfiring now. Runs like crap. Read out the code via the DIC last night, all are 'H'istory, but I did not have the car running when I read out the codes.

After reading some posts, and 0 time actually diagnosing this... I am fearing the worst, a broken valve spring? So is it safe to start the car and take it to the shop? If I diagnose it to the point of finding a broken spring, is it something I can replace myself? (I know if I am asking that question then the answer is no). I have rebuilt several motorcycle motors so I have the tools and not afraid to use them. But would I need a valve spring compressor?
 

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Discussion Starter #3
Since I don't drive it much, the battery has died a few times so I think these are all related to that:

from RDCM (right hand door module)
B2283, B2285, U1064

From LDCM (left hand door module)
B2282, B2284, U1064

From SCM (seat)
B0851, B0856, U1160 and U1064

Thank for any insight.

Carl
 

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Discussion Starter #4
I decided to pull the plugs and inspect them. Nothing obvious. No missing parts, all equally colored. Decided to pull the valve covers and look at the springs. Nothing obvious there. So I'll order new wires and plugs. At least I won't be afraid to start the engine again.

I do have the GM service manual, so I guess it's time to get familiar with the troubleshooting section:lookinup:
 

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A couple of things. Do you have a meter? Before you spend the money on plugs and wires, you could ohm the plug wires. They should be ~ 300 ohms or less. I can tell you that I had a few that were really high impedence..> 2 meg ohms and the car still ran, but misfired when I got on it.

You say you 'got on it'. Do you have a manual and possibly missed a shift or went from 3rd to 2nd instead of 4th? That is a common cause for an overrev which can cause valve float. If you bang a valve into a piston you could have a bent pushrod or valve. Do you have a 'tick' that wasn't there? A compression check and a leakdown test would tell you that.
 

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Discussion Starter #6
By "got on it". I mean I did a WOT to about 5,500 RPM, shifted to 2nd then 3rd as fast as I could move the shifter. There was no overrev, missed gears or shift to the wrong gear.
 

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By "got on it". I mean I did a WOT to about 5,500 RPM, shifted to 2nd then 3rd as fast as I could move the shifter. There was no overrev, missed gears or shift to the wrong gear.
:cheers: I wasn't deriding your driving skills. It happens a lot. I was just trying to determine what conditions your problem started under.

I would start by checking the resistance in your ignition wires since you've inspected the plugs already. Since a P0300 indicates random misfires it means they are, well random and not confined to a particular cylinder. If the wires ohm ok, then I would check you ground connections at the ground star points, and all the ignition and injector weatherpaks and make sure they clean and making a good connection. I would try this stuff first since it won't take much work or involve buying new parts.

If you suspect a mechanical condition you could try taking the pushrods out and rolling them on a glass tabletop. That should tell you if you have one or more bent pushrods. If they are ok, then with the pushrods out of the holes you can lay a straight edge across the the stem tops and see if any are sitting low. After that I would do a leakdown and compression test.

The manual has some good procedures for narrowing down the cause of a P0300 too. :cheers:
 

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Discussion Starter #8
No offense taken at all. Last night I was thinking I should have posted more details.:spanked:

I HATE pulling plug wires. I somehow managed to pull a wire out of a boot. I have no idea how it happened. I was twisting/pulling on the boot. s___ happens sometimes. I figured I would get new plugs and wires. since they are the original 7 years old. But I will ohm out the other 7.

Good thing I will not be at work for a few days. I will use the troubleshooting procedure in the service manual.
 

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Here's just a thought. You may want to check your battery voltage. You mentioned the battery had died a couple times. It wouldn't hurt to pull it out and have it tested, especially if its original. Low batteries can do some funny things to electrical components. This may effect your injectors and coils.
 

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Here's just a thought. You may want to check your battery voltage. You mentioned the battery had died a couple times. It wouldn't hurt to pull it out and have it tested, especially if its original. Low batteries can do some funny things to electrical components. This may effect your injectors and coils.
Doh! I didn't notice that since it was in subsequent posts...
A dead cell could lower the voltage enough to cause random misfires. Good call.
 

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Discussion Starter #11
Thanks for all the suggestions. Wires ohmed out, and battery voltage ok. Was talking with buddies and one pointed out that with hydraulic adjuster, all the valves should be closed.

I have one valve/rocker in the open position. I removed the rocker arm and inspected the pushrod. It rolls smoothly on flat glass. So my guess now is the hydraulic adjuster/lifter. Is this where the problem is? According to the manual, I need to pull the head to replace it? What have I gotten myself into?:surprised
 

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Discussion Starter #12
Follow-up for completeness sake.

Never found a smoking gun. New plugs, wires, fresh charge on battery, cleared codes. All seems to ok.
 

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Never found a smoking gun. New plugs, wires, fresh charge on battery, cleared codes. All seems to ok.
:thumbsup: Thanks for the update.
a couple of things
I've had a battery that read 13 volts and was very light on current, you need a special meter to test a battery under load which is where a battery is supposed to function...

You're friend is wrong that the valves should be closed with hydraulic lifters. If the maxiumum range of the lifter is .125" and the cam lifts .250" and is resting on thetop of the lobe, or even partially off the heel... you get what I mean.

However, the good news is it's running well again. I still vote for a drained battery. Might want to pick up one of those Battery Tenders and install the quick disconnect so you can use it anytime you park it in the garage.

:cheers:
 
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