Need some ideas, I'm having an issue with the car laying over above 5000 rpms.(well, wot is pretty much just above 5000rpm with the 4000 stall, lol)

Quick details of the car...

355, small cam, ported heads
Real Quick's header kit
GTS 76
th400/4000 stall
72lb low impedence injectors with resistor box
stock pcm(obdI) tuned via tuner cats by myself

CLIFFS...
at wot rpms will go up and down then back up again then down....repeat
new coil, new opti, new plug wires, new plugs, new coil wire
One night it ran perfectly strong without doing anything to it, then cut out again...then fixed it for 1/2 a day once by pushing on the coil wire better on the old coil that was corroded, and fixed it for one night another day by replacing the coil, then it went back to laying over.
Verified fuel pressure is rock solid at wot also, not dropping off

Sorry for the novel below, but want all my details out there....

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Ever since putting this car back together it's been down on power, now I can blately feel it laying over above 5000 rpms. Little background...

Got the car running with 4lbs and the transmission immediately started slipping. Even with the slipping transmission I could pull my buddies 115mph 3rd gen on the highway punches. Got the transmission fixed and had a boost creep issue, wouldn't hold solid boost, anywhere from 4lbs to 9lbs with the 4lb spring. I had some 110 gas in it, so we threw in my 8lb spring to see what it would do at about 10pm on a Friday night. We tried a pull with both 255 fuel pumps on and the car went 9.6:1 AFR and cut out. Ended up realizing my 2nd pump was jumping my fuel pressure about 5lbs(stock return line) and causing my AFPR to jump crazy high in pressure.(once it his about 65lbs it just jumps to 80+) So turned it down, got the pressure correct, and we double checked over everything on the car, which I do remember pushing on the coil wire.(you'll see later why this is handy information) Went out and made a few pulls and it pulled exactly 11lbs, and with 14 degrees of timing the car flat out MOVED OUT HARD. Probably 133-135mph, which is what it should do on 11lbs. Went out that night and it started boost creeping on me again, up to 13 or 14, so I was backing out of the throttle. Next day found out the flex cupler collased from the WG back to the downpipe, which caused the boost creep, so I switched to open atmosphere on the wastegate, but didn't make any pulls really since I was back on pump gas, still not having the tune dialed in exactly as I wanted.

Fast forward one week, pulled out the tr6 plugs(gapped at .032) and put in some tr7ix that I had laying around. Went out and at 6lbs it would blow out the spark. Next day, pulled them out and put in some ngk br7ef plugs gapped at .026. Threw in the good gas, and had the 4lb spring in it, so I could tune it from 4 all the way up to 15lbs.

Hit the dyno, car didn't make nearly the power it should. As we turned it up(8lbs up to 15lbs), the shop owner said he could feel it lay over around 5600rpm. The graph was a little wavey up top so I added timing, from 14 to 23(since it had good gas anyway) and it picked up right at 50rwhp at 8lbs. I pulled it back down to 18 degrees, but we didn't make another pull at 8lbs. As we turned it up to 11lbs and up, the afr would go through the floor, 10.0 afr. I kept pulling fuel in the tune, but it would stay 10.0 afr.(even after pulling out over 25% fuel)

Pulled it out on the street, and knew it would be way to lean, went out and on 9lb setting it leaned out immediately. I put the fuel back in it and afr was about 11.2 across the board. Went out and raced it that night and could tell it was just down badly on power, even at 14lbs it pulled WAY less than it did before on 11lbs.

So I started checking over everything and noticed the coil wire(taylor) on the coil wasn't going on completely and clicking like it should. We looked closer at the coil and the post inside was eroded away really bad. Well we FINALLY got it to click on the post. Went out and the car felt a million times better. Back on 8lbs the car pulled strong like it should. Bumped it up to 11lbs and the car moved out hard, but not quite as hard as before, still probably 130mph range.

Later that night the power died off again, I figured the coil wire came loose again and it did. So next day when the parts store opened up I bought a new coil and put on the car. Car felt AMAZING on 8lbs, and great on 13lbs! Didn't cut out at all, and went out racing. Made probably 15 pulls on it, all smooth and perfect.

Next day headed to the track, on the way there got on it and felt it completely lay over like it did before when the coil wire wasn't clicking on the coil. Got to the track, pushed the wire on, but still didn't run any better. I made no changes from the night before, even on the same tank of gas(mix of 110/pump).

So, since then I've been trying to figure this issue out. I've replaced the opti, a few coil wires, few coils(including the huge msd hvc-2 that ponyhunter had to switch to get his miss gone), replaced the plugs(back to the tr6's even), replaced plug wires, hooked up a mallory 685 box. I've tried about everything I can think of, but it still keeps laying over.

Best way to describe what it is doing, is if your spraying a car with a 100 shot and just let off the button around 5000rpms, then maybe tap it again, then let off it.

Sometimes it will make a clean pull though, I went to the track last week and hot lapped it. It made a few low 12 passes on 8lbs, laying over. Then made a great 1/8th mile pass, didn't lay over until the end of the first 1/8th and it went 7.1 at 100mph in the 1/8 and I was backing off the gas to see if it would quit cutting out on the back 1/8th and went 11.12 at 122mph. This is where the 1/8th should be on 8lbs without launching it hard, last year I went 6.9 at 100mph in the 1/8th and 10.80 at 128mph on the back end, which I think it should do on 8lbs this year.

Today, I made some pulls and datalogs will show the rpm going up then BACK DOWN! Timing stays at 18 degrees, afr is FLAT at 11.3.

Example from datamaster...

4125rpm
4925rpm
5425rpm
5025rpm
5350rpm
5075rpm
5125rpm
5325rpm

This was all 3rd gear on a highway pull.

Another one....

4400
5275
5700
5750
5525
5050
5100

This is all while I am still WOT.

Anybody have any ideas, I'm trying to make the ltx shootout, but this has been my problems for the last two weeks, not to mention the rear end I've replaced already, and on my 3rd transmission. This year isn't starting out good.

 

my CC306 car is doing the same thing around 5800 rpms in a M6.... itll be like 5750 5850 5975 5700 5800... etc etc... and my rev limiter is set at 6800

 

It could valve train related. If your valve springs aren't up to task it could cause valve float. Are the heads stock besides being ported?

 

Crane valve springs that should be up to the task. I was thinking this could be a problem also, except putting on the coil fixed it for that night.

 

ugghhhh.... what a headache Justin! I feel for ya dude! I hope you get this worked out. I would think valve springs too, but if the spark did indeed cure it before... then I think it is still spark related.


I am stumped.

 

Had the same problem, was the opti.

 

which I really thought as going to fix it, and I put a known GOOD working opti on it off a friends car, but still does it.

 

Something in the tune maybe? I duno, i had the same problem with my car and for right now i have the car set to shift at 5500 (before it started messing up)

Maybe try gapping the plugs smaller?

 

Plugs gapped at .026 should be tight enough.

How long have you had the problem and did you just give up on trying to fix it?

With my coan 4000 stall, I can't shift below the problem really.

 

I had the problem for over a year.
Replaced everything ignition related over that time. Saw some improvement with the new opti and some with a small plug gap. Replaced the trans, Converter, Computer, Tune...

The next thing on my list to try is larger injectors and pump. If that doesnt work then i will just give up on shifting that high and wait till i get my new motor in the next few years.

I never looked/tested my springs, maybe one of yours is bad, it wouldnt be a bad idea to take a look at them.

My problem started when i put the current engine in, guy that sold it to me said he reved to 6200 no problem... But who knows.

At that high of an RPM enven sometihng small can become noticable.

 

do you have a ignition box?

 

justin, as i said earlier, check your opti harness. You have something definately spark related. A higher end RPM stumble sounds opti related, but you have that already replaced. So, check your harness. Even though it means pulling your W/P

 

mallory 685 ignition box on it, it went on after the problem started and still hasn't fixed it.

 

i had the same problem with my car, had the box in the back of the car. i ran 16g wire to the front, the car would fall on its face at about 4800 to 5300. changed it to 12 gauge and wraped the ignition wire in aluminum foil and electrical tap, shes clean to 7000 hope it helps

 

Damn, that is a thought. I am running 12 guage wire from the box to the coil and the box is under the dash, but I am only running 14 guage wire to the box's main power/ground, and to the stock harness side.