Tony @ MPH

Hey guys,

After finishing a valve spring swap and painting my valve covers/coil pack rails, my car started running really poorly. I did an EFILive run tonight and it's easy to see from the data that something is wrong. My LTFTs are pegged at 25% and when I hit the throttle hard, I get 10-20 misfires per cylinder as read from EFI and on cylinder 5 I got as high as 50 misfires.

My understanding of the misfire counter in EFI is that it's a count of misfires per 200 crankshaft revolutions. Knowing that a cylinder fires every 90 degrees on the crank, that means that inside 200 revolutions each cylinder should fire 100 times. First off, is it bad that most of the cylinders are misfiring 10%-20% of the time? Obviously the cylinder 5 misfiring 50% of the time is REAL bad.

My suspicion is that when I removed the coil packs and wiring from the coil pack rail, the brittle wires may have gotten messed up. The factory electrical tape was literally flaking off the wiring harness which I assume happens because of 2.5 years of use and a really hot engine. But I do not know this for sure.

Is there anything that I could have done wrong with the valve spring swap (assuming that the retainers, locks, and springs are all in the right places and that the rockers are all torqued down properly, and the valve stems are attached to the springs :D)? I can audibly hear a little more valvetrain chatter on cylinder 5 than other cylinders. Could the increased chatter be a result of the misfires, or are the misfires a result of the chatter?

I'm not sure if I should take the car to my dealer (still under warranty) on the suspicion that it's the coil pack wiring harness or coil packs themselves... especially if they are going to find that I somehow messed something up on the valve spring swap.

btw, I already tried replacing both the spark plugs and wires, so all these misfires are happening on brand new wires/plugs. It seemed the car improved some after doing the plugs/wires but it's still bogging HARD on acceleration (although not as bad as it was just before the plug/wire swap).

Thanks for your help guys.



[Modified by diynoob, 11:47 PM 2/28/2004]

Bill Curlee

My recommendation would be to go back to where you were working last before the problem existed.

I would check to see if you have spark on that cylinder (#5) Remove the wire from the spark plug and insert a philips screw driver into the terminal inside the boot. Then use another screw drive to make a spark gap to ground with about a 1/4" air gap. If you get a good spark, my next check would be to investigate what that valve noise is all about! Hydraulic lifters should NOT make any noise. Something is wrong on that set of valves and that will also cause a misfire.

Bill

SideStep

Hey man... how many miles are on your Vette??? This is starting to sound like a collapsed lifter...
:confused:

:cheers:


[Modified by SideStep, 10:53 PM 2/28/2004]

Tony @ MPH

I have 30K total miles on the Vette... doesn't seem like the lifter should go that early? Also, just before the valve spring swap it didn't have these same symptoms. It wasn't making the peak HP I was hoping for, but at least it ran smoothly. Right now it is the complete opposite of smooth :mad

Bink

+25% LTFTs - probably an air leak. All cells?
More at idle and less as RPMs increase?

SpinMonster

Binks, I think he said the ltft's were high when he hit the throttle.

Check the wire/spark plug connection and the screw on ends of the spark plugs to be sure they are tight. Irridiums will reduce misfire count too. I had 125 misfire count in my #7 from the end of the spark plug being loose.

runamuk

What kind of plug wires are you using, I put MSD 8.5mm plug wires on my car and had the same problem your describing. Then while watching the engine run (roughly) you could see the plug wires were arcing to anything and everything nearby, it looked like a real cool lightshow only this one cost me $80.00 to see :crazy:

Tony @ MPH

Hey runamuk,

I am in fact running the MSD 8.5mm wires. Where was the arcing occurring in your setup (between coil pack/wire or between plug/wire)? Did you switch wires after that or was there a simple fix?

Bink

Spinmonster - They shouldn't be maxed out, regardless. If he doesn't have a Wideband O2 who knows how lean he's running?? A Lean condition would cause the stumble on throttle transition. If the heads are milled the intake may be hanging up/ not seating completely - resulting in too lean/ unmetered air.
Maybe it's just me but running Unknown Lean scares me. :eek: :eek:

joel

dpd

if the ltft's are +25,you are lean[air leaks,low fuel pressure/volume,etc].if this started after changing valve springs,i would first do a plug check and see what they look like.if your problem was with the ignition i would expect to see the fuel trims go the other way[-,due to the cylinders not firing fully].you also state that #5 is banging away and all cylinders are skipping.did you go to a lighter spring?if so,maybe you don't have enough spring pressure to close the valves and they are floating.another possibility is maybe the lifters aren't pumping up and are staying collapsed.sounds like the valves are not closing all the way[if the car was fine prior to the spring change].start with a plug check and take it from there.JMO

Tony @ MPH

I went to the LS2 spring from my LS1 spring. The LS6 springs are no longer made and are superceded by the LS2 spring.

My spark plugs prior to the change were a nice black/golden brown color. Can you get at the lifters by just removing the cylinder head? Maybe I'll get some ARP studs and peel off the head and see what things look like on the inside. Maybe I'll find a bent valve or some other tell tale sign of what the problem is.

Andy@A&ACorvette

Are you sure you put the left coil pack on the left side and the right coil pack on the right side? It will run like that, but very badly.

Tony @ MPH

Uhhh... no, I am not sure.. I had no idea that the coil packs were meant to be on a specific side of the engine... going to the garage now to check it out and see what happens.

Thanks for the tip Andy.

:leaving: <--- me going to the garage in shame


[Modified by diynoob, 10:16 PM 2/29/2004]

Tony @ MPH

Just swapped the coil packs from side to side. It helped some, but my problem persists. At WOT the car hardly accelerates and the engine makes a funny choking sound.

I'll call you tomorrow to order some ARP studs and whatever else I'll need to open up the heads and see if there's anything visibly wrong on the inside.

Thanks..
Tony

z0sense

I would make sure the coild packs are plugged in correctly, make sure the plugs wires are correctly installed, and make sure none of the plugs are cracked.

Also the one time I had this problem it turned out being that my injector was unplugged.

Make sure all your injectors are plugged in to.

Tony @ MPH

Visibly, everything looks OK. I have checked the packs, plugs, and wires twice. The plugs and wires on the car now are brand new and exhibit the same behavior. If the problem is on the outside of the car, my gut says that it's the coil packs or the coil pack harness. When I was taking the coil packs off the rail the harness wire and electrical tape was brittle and cracking. I am going to head over to my Chevy dealer and see if they'll give me two new harnesses under warranty. I bet they are probably $75 a piece if not.

vetterdstr

Check the coil packs with a timing light (hooked up to the plug wire) to see if they are firing correctly. If you have a bad coil you will see it skipping a beat or two right away.

VR :cheers:

Tony @ MPH

Thanks VR -- I bought an inductive timing light at the auto parts store on Saturday and gave that a shot. Either it's reading incorrectly, or ALL of my coil packs are misfiring. I really can't tell which is the case.

EFILive does say all cylinders are misfiring, but it only generally picks that up on hard acceleration. The timing light was showing misfires at idle.

z0sense

It may be that all of your coil pcks are misfiring.

I would definitely check the connection of the coil pack harness.

You didn't get paint inside of it did you?

vetterdstr

Is there a chance that your computer is corrupted? You may need to get a new one and reflash with your current program... I have seen this be a problem before and so has JR..

VR :cheers: