Jc803

iTrader: (2)

I've replaced the plugs, threw the old ones back in, then put in brand new ones a second time just last night, all in the last week.

What is UDP?

If you mean under drive pulley it's fine

poltergeist 02

iTrader: (65)

Any updates?

LS1-450

iTrader: (33)

4K is a key point in the WOT tune. Are you sure that the WOT tuning wasn't tweaked when you tuned it just days before the plug change? Again, going rich @ 4K & "just tuned" point to a possible WOT tuning issue.

Jc803

iTrader: (2)

Nah the tune didn't change. I made a gas tune that ran 11.8 a while back. A couple weeks ago this high rpm miss made me run consistent mid 12s. I switched to e85 about a month and a half ago and it felt like it was pulling a little harder. Then out of no where i got this high rpm miss. I even went back to the 11.8 tune in gas and problem is still there

I bought new prc 650 springs. Tried to put them on last night but the damn keepers won't release. And i even bent all 4 bolts that came with the comp cams valve spring compressor. But i quickly realized that thing is a piece of trash and the angle isn't even right so i bought some $220 valve spring compressor that changes the angle as the spring compresses

1BADCTS

iTrader: (17)

I'm having a misfire in a similar fashion. Any updates from the OP?

Fry_

Did you check fuel pressure under load at WOT or just at idle?

Jc803

iTrader: (2)

Hey guys. Sorry I never got back to you. I did find the problem. It was 3 broken valve springs. It took me so long to find the problem because there wasnt really any signs of it. I had double valve springs and only the outer springs broke so the inners were keeping the valve up and still functioning, it just couldnt keep up after 4k rpms.

If anyone out there is reading this and has also checked everything like it did, check the springs. and check them GOOD. Valve springs was one of the first things I checked, but I only did a quick visual inspection and they all looked good. But after so long I said, screw this I'm just replacing everything and bought new springs along with some other stuff. It wasnt until I took the springs out that I realized they were broken.

big hammer

ever sick!

dr_whigham

iTrader: (49)

Were those the old springs? What brand are they?

Jc803

iTrader: (2)

Yea those were the old springs that I changed in like March I think. They are PRC 650 double springs. To answer the other questions from a while back, yes I did replace those with the same exact kind. Reason is, they only had 6k miles on them (I originally said 8k but that was off the top of my head), and the car and motor sat in the previous owners garage for years. Plus I rarely drive the car, if I do its either to the track or to a meet, either way if I'm driving it I'm running it as hard as it will go. So I cant blame the springs for breaking after 6k miles on them between sitting for years then I get the car and make the engine scream. So far the new PRC 650 springs are holding up great and I even cut .2 tenths off my 1/4 mile (comparing to before the springs broke) just after the spring swap

ThreeFitty79

[QUOTE=Jc803;18084360]I changed my spark plugs before I went to the track. I go to the track and notice a loss of power/slight vibration/rich air fuel ratios after 4k rpm and I'm running .8 tenths slower than normal in the 1/4. So I figure it must be the plugs since thats the only thing I changed. I change the plugs and that didnt work so I kept checking things.

Plugs - replaced
Plug wires - replaced
Coil Packs - Bought a new one and swaped it one for one, test drove, did that all 8 times
Fuel pump - checked and fuel pressure is fine
Fuel filter - replaced

Its not the tune, just tuned it days before the plugs
I also dont have a single check engine light.
Also tonight I data logged and I'm not getting any knock at all.[/QUOTE

Check your belt tensioner if it is slipping it will cause a misfire

G Atsma

[QUOTE=ThreeFitty79;20479735]And NINE years later, here you come o the rescue.... I have a feeling they solved this...