foggedz

iTrader: (1)

The spring hight was checked, and rechecked before the heads were put on, and they are all setup at a 1.800 install hight. Again, the car had this same exact miss with a completly different valvetrain on the car.

As for what the O2s read, I have also had a wideband hooked up on the car for the past 3 weeks tweeking the tune. I have put probably 20 different tunes in the car making very small adjustments each time, and currently at WOT the car is a 12.8-9 AFR. Except, when it misses in the top of 1st and 2nd there is a lean spike, then it drops right back down to 12.8-9 all the way to 6800. Opposite to what most would think a miss fire reads as a lean spike not a rich spike.

I think I should try and describe this miss a little better also. This doesnt feel like a normal misfire, where the car has a slight stumble. When the car reaches 62-6400 it feels like the motor completly cuts out for a small faction of a second and then picks right back up and pulls to 6800+. Last year when I had the car on the dyno it would drop 40hp for a spilt second and then pick right back up and keep pulling.

I have said the it seems to miss more when the car is warmed up. But I would say I has a better chance when warmed up. The other night I took the car out, drove it for about a half hour and then made pass from stop to about 120mph and the car did not miss a beat. Since this is so unpredictable I almost have to rule out anything mechanical. Plus the motor is fresh with virtually everything new. If it was mechanical it should have been fixed.

foggedz

iTrader: (1)

I got a spare PCM from a friend last week, flashed my tune into it, and the miss was still there. I installed a brand new set of 30lb svo injectors last summer. I had noticed my stockers were at 103% duty cycle so I thought AHH HA. THat must be my miss. Put in the brand new 30lb injectors.... Still misses. The 30lb injectors are currently at 78-80% duty cycle at 43psi of fuel pressure.

jimbob

iTrader: (4)

OK...
If the coil wire and wires to the coil don't fix here's one last thing that happened to me..

....When my car was a manual years back it would sometimes just die at the top of 4th gear running thru the traps.... Anyway, I never quite figured it out as it only happend once in a great while. When I swapped over to a 4l60e I changed the engine harness with tranny control harness. After I swap it the problem never came back. It was obviously a harness issue some how...probably a pin that was pulling or bad connection.....Maybe that's what you have going, however it should never happen at the same rpm if that is so.....

I sure hope something here fixes it....Don't overlook something you have asssumed was good....And maybe you'll find the problem....I'm still going with the coil wire and or wires feeding the coil....

speed_demon24

iTrader: (6)

1.8" is too high for the 918's, set them up at 1.75". And if you have a miss it will cause a lean spike, it will just pump fresh air in the exhaust which will make the wideband read a lean condition. My friend also had a miss he couldnt figure out on his LS1, it turned to out to be crankwalk. It would miss around 5200, then pick back up all the way to the shift point.

foggedz

iTrader: (1)

Thats interesting that your car used to be a 6 speed also. My car was a 6 speed for the first 3 years I owned it, and then I decided to swap in a th350. The car had the same miss back when it was a 6 speed. I never had to change the harness because the th350 was not computer controlled. I just had to desable a few codes to keep the check engine light off and the car has ran great. Even with the miss the car has gone 11.7 at 115 with a cam only CC305 setup. With the CC305 setup I used to shift at 6300, so when the car missed I was all ready at my shift point. In that situation I dont think the miss was costing me to much time. Now with the miss 5-600rpms less than my shift point I really want to try and figure this out.

I barrowed a coil wire from a friend yeasterday, and that didnt seem to help the problem. Ill check out the wires feeding the coil today.

dhdenney

iTrader: (53)

You can check with EFI Connection or Speartech for those connectors. Last time I got quite a few pigtails from Speartech. I did buy the black coil connector from them, they said they were really short on the gray ones so I made mine work even though the wire was like 1/2" long. Anyway, just so you know where to look......

foggedz

iTrader: (1)

I have some what of an update. No good news. I droped $100 on a brand new set of MDS plug wires, with a new coil wire. No help... Someone in an earlyer post had mentioned that the stock coil was better than the MSD replacement coil. Borrowed a stock coil and ICM of of a friends car that has a little over 30,000 mi on it. Still no help. I also tryed all kinds of combinations of ICMs and coils that I had, and none of them fixed the problem. I closely inspected all of the wires going to the coil connecters, and couldnt find any problems with them. My options are running down to slim and none. If I dont get this figured out soon, I can tell you my winter project is gonna be standard SBC intake, carb, distributer setup.

infinitebird

iTrader: (11)

you could try the ltcc or delteq, I know that's fixed some high rpm problems similar to this for others.

GTP PWR

iTrader: (24)

or use a msd crank trigger and cam position sensor and coil packs and completely eliminate the opti system. Sound Performance in Chicago have opted to make me an entirely new system. they have it on a few drag cars and have had no problems, and rev some engines to over 7500...no problem.

I have decided to go that route for the solid roller. I had comp R lifters in it before and it loved high rpm. parked it for winter, got it out in spring loved it, then a month later this misfire. everything was replaced earlier. then he rans decided to go yet again for a 3rd time, so I have ripped everyhing out and started new.

I have contacted LTCC, they areable to have one shipped out 7/6/07. they JUSt got more supplies in to make them up.

Kevin97ss

Hey foggedz, I usually hang on cz28.com, but your issue caught my attention. I've had a similar issue since my cam install in '01, before that on the stock cam w/1.6 rockers, crane double springs it would pull to 6600 with out a hiccup... no power cause it was out of air but it still got there.

After the cam it would hit a wall @6200 which is usually where I shifted. Have never figured it out, now it kinda surges above 5200 and hits the wall around 6100...so I'm back on the hunt.

Anyway I wanted to ask does the motor make any noise during your power drop out? Reason I ask is my motor would clatter loudly @6200 and just stop pulling, I never tried to pull through it though thinking it was either detonation or valve float....but now I'm not so sure.

One more thing, does your problem happen in every gear or just pulling through high gear?

foggedz

iTrader: (1)

No it doesnt make any noise during the miss, or above a givin RPM for that matter. My miss is actually more common in 1st gear, less in second, and virtually never in 3rd. I have a th350, so I only have 3 gears.

If you only have a mail order tune from PCMForless, I would get a wideband on the car if I were you. I got a tune from them early this year, to brake the motor in with, and since the 847 cam is so popular I figured they would have a really good chance of geting the tune right with out me having to mess with it. After driving the car around for a month or so I hooked up a wideband and found out that the car was somewhere in the 11.6 AFR range around 4500, and in the 13.8 AFR range at 6500. So, it went from way to rich to way to lean.

If your tune is ok, I would say you probably have a valve train problem. Esp if you get to certian an the car just will not pull anymore.

Kevin97ss

Thanks for the heads up on the tune. The 12 bolt is blown up at the moment and I need to get it back together so I can continue troubleshooting.

Back to your issue, have you checked the opti wire harness? Couple people on cz28 had an issue with that connector corroding and causing big problems, anything from hi rez codes to random misfires and no starts....but for it to stay unchanged for so long(6 years)....