HI Guys,

I finally took my car to get it dyno tuned...was able to lean it out some which was good, but one major problem...it pulled good up to 5000 rpm (380rwhp) but then was breaking fire and or missing. We tried a couple of diffrerent things...un pluging msd box...changing coil...The tuner seems to think it is a ignition problem of some kind...he tried changing fuel and timing tables in various ways, but still did the same thing...I was about 400 miles from home so I could not really try and diagnois the problems all sensors are functioning properly according to his scanner....A little background on the motor..383, 12to1 comp, all forged, lt4 ported heads, lt4 edlebrock intake,
42lb injectors, welbro fuel pump, msd distributor, gm 847 cam, 130lb seat pressure springs, 1.52 pro mag roller rockers, 4.10 gears, msd coil, msd 6a box,long tubes, 3inch y pipe, all new sensors etc...It consistantly started to misfire and/or breakfire at 5000 rpm at every run...we made 8 runs...Like I said I was way away from home and did not have the ability to check things like spark plugs or wires. I was wondering if any one has had any problem similar to this....Any help would be appreciated...Also how does the igintion control module function on these cars...I know on older carb hei distributor ignitions the car can break fire above 5500 with a stock module...Thanks for any Help!!MM

 

PLEASE HELP THIS IS DRIVING ME CRAZY!!!!!!!!!!!!

 

breaking up like uneven sounding? sure it just wasnt exhaust my car sounds like it is but is still pulling..

 

or is it bucking or fighting to climb? mine did that so i changed opti, fuel pump, coil and then it dawned on me that maybe my brand new Taylors were bad so i went onto a pitch black road and turned off the lights. went under the hood and reved the engine and it was a light show under there. Damn wires are bad after a year oh well some new AC Delco's goin' in today Try that as it may be the same for you...

 

The car was on the dyno and you could start watching it surge on the dyno graph...it sounded just like when you hit the rev limiter only the rev limiter is set at 7200 not at the 5000 which was exactly where it started breaking fire on every dyno run..we made 8 runs and the guy was also making tuning adjustments..he said all the sensors are functioning properly and he had the timing a/f tables and fuel tables dialed in he feels it has to be ignition related....anybody else have any ideas....thanks for the responses given so far.....MM

 

No it would not be the exhaust you could see it steadily pulling on the dyno
graph until you hit 5000 then it would start spiking on the graph and as I said
it sounded just like you hit the rev limiter...Thanks MM

 

another vote for the opti. sounds like the screws hoding in the optical sensor are slowly releasing themselves. same thing happened with my car.

get ready to swap the opti

 

Same thing was happening to me, it drove me nutz...I had the plugs, and wires changed, and had a top engine fuel injection service done at the dealer...and no more problems.

 

Post up the dyno graph no one is going to be able to tell you what it is by that post. And what springs are you running with what installed height, and did you check the installed height on the springs or just assume it was correct?

 

speaking of injector i needa run some more marvel fuel injector cleaner through mine

 

maybe rocker arms are too tight, especially if you have comp r lifters (they like zero lash). i had the same problem on the dyno, power just fell off at 5000 rpm. re-adjusted rockers and she kept on pullin well past 6500.

 

i'm voting for the opti..

 

I don't have the sheet yet...I am running 130 lb spring pressure 1.750 installed height...it is not falling off in power at 5000 it starts studdering like i said as if you hit the rev limiter