running a CC306, rev limit set at 6600.

cuts out at about 6k, sometimes 5.5k going uphill, sometimes more than 6k going downhill. feels like it's hitting the limiter, which it is not because sometimes you can hear it break up over the last few hundred revs.

new fuel filter, new walbro 255, new coil, new vented opti, new icm, new 36# injectors, 6k mile plugs gapped at .050, new plug wires.

I'm running a Madz28 tune, think it's possible that the tune is just too aggressive for the crappy oxygenated 91 octane i have here in california? i desensitized the knock quite a bit, didn't seem to help much, i'm thinking about throwing in a gallon of when my fuel gets low and seeing if it eliminates it. Maybe my ignition can't handle the gap on the plugs at the high rpm? I'm using whatever plugs come on our cars stock, acdelco whatevers?

no exhaust leaks or unreasonable rocker noise, same results with the cutout open or closed. pretty much almost positively not false knock...
eh this weekend i'll datalog a few runs and send them off to ion for some finetuning, but if it's not in the tune


thanks for your input

 

Your post is very difficult to reeeeeeaaaaadddddd. Maybe you shouldn't post at midnight.

You say it cuts out at different rpm's depending on if you go up hill or down hill. This would appear to be fuel related. Either you are getting air in the line or you are running lean and under load it appears to be worse. If you put this into context with the next paragraph, where you say it has a new filter and walbro pump, the question becomes, was the pumps connection checked for leaks when it was installed? The hose in the tank between the pump and the hard lines that exit the tank is what I'm refering to. Does the problem you are having get worse with different fuel levels in the tank? Possibly another indication of a leaking hose. Maybe you should try topping it off and test it?

How does it appear to be cutting out? Is it just shutting down? Is it just bogging down as in loosing power? Or is it beginning to miss?

Have you ever monitored fuel pressure while the problem occurs?

In the next paragraph you state you have 36# injectors. But the only information you provide regarding your engine is that it has a 306 cam. Do you have any other mods that would warrant using 36# injectors? You also didn't tell us anything about the vehicle. Year, tranny, PCM mods or anything.

Was all the parameters given to Ion when he programmed it, like injector size etc??
Next. "i'm thinking about throwing in a gallon of when my fuel gets low and seeing if it eliminates it." OF WHAT? High octane? I doubt only a gallon of anything is going to make any difference. The next paragraph says you positively don't have false knock. Why the gallon of what ever then? Either it has knock or it doesn't.

Who put the cam in? Did you own it before it was put in? How did it run then? Perhaps before we can help you, you should give us more info.

 

i did the cam, with comp 918s steel retainers installed at 1.75, so i'm not dealing with valve float.

It's had this top end miss since before the cam, not really a miss, pretty much feels like it's slamming into the rev limit, stops reving completely.

no there's no air in the fuel lines, all connections are secure. doesn't matter how much fuel is in the tank, still same problem

i mean gallon of xylene-116 octane i think, so I could eliminate the possibility of it being real knock. when mixed with 2 gallons of 91 octane it'll be close to 100 octane.

i have 36# injectors because the heads are getting ported eventually, and there's nothing wrong with running 36# as long as the car is tuned for them, which it is.

my car is a 94 Z (Wckd94Z?) with a 6 speed, stock gears.

just because the revs at which the problem occurs changes with going uphill or downhill doesn't mean it's related to fuel, i'm curious what makes you think that. going uphill at full throttle increases cylinder pressure, which will show the weak points in the ignition system as well...

at this point i'm thinking its the plugs, maybe gapped a little too far. but i dont' really want to pull them if its not the problem

 

last time i datalogged it i was getting 6* or more of knock up top, but I had a header leak at the time. i don't think 6* of pulled timing will cause the engine to missfire like it does though

 

ttt

 

What is your fuel pressure reading at idle an WOT?

 

i'll get on that probably friday evening

 

What brand coil? I had some lame Autozone coil on mine and it was missing over 6000 rpm. I swapped out to an MSD coil and no more problems.

 

that is of much help kain lol... who put that coil on there?!

will check when my car is running again, electric water pump took a poop this morning on the way to work

 

I had that same problem and with the same cam it seems like my car was running to lean on the top end. Programed out the miss. and gained about 50 rwhp but i was still wanting to get about 20 more rwhp but ... my older brother blew my engine.

 

problem fixed, thanks kain, it was the autozone coil i had in there. they sell the msd blaster coils at pepboys here so i put that in today, revs to 6600 clean and smooth. definitely feels smoother and stronger 5k and above