Well after getting the car back together this year I have a little gremlin walking around somewhere........ive been struggling with injectors and ignition and I finally got pretty damn close.........but.....still seems like i have some intermittent misfires here and there.........

I took the car to the dyno saturday with 29* of timing at 11.7 AFR it made 435 on the first pull...........I bumped the timing to 31* and it made 469 @ 11.9 AFR.........then I backed fuel out to 12.4AFR and it made 480...........the last pull i heard one little misfire at about 7100 then it cleaned right up.......

another issue i started noticing as i revved the car up is the power was falling off at 7300 or so......the car made peak at 7400 last year and made power out to 8000+rpm........i am atribuiting the loss of power to the plugs being to warm and detonation starting to occour......i re-checked the valve train and everything is good......no valve float or other mechanical issues.....

the last pull i put 33* in the motor and it pulled to 7200 then started detonating badly......so i backed off the throttle.......after examining the plugs i determined that a 7 (NGK) heat range is too hot for a gapless ring 14.25:1 motor operating in the 7000-8000 rpm range.......so im ordering 8's and 9's to try today......


i still seem to have an issue however......at part throttle its got random misfires through the exhaust........also at idle it will sit just fine at like 1350 then randomly drop for a split second and come right back up........almost sounds like somebody is shutting off the ignition for a second........the fueling is good at idle 14.5-15.0 so i dont think the car is loading up........


system is a FAST XFI with a MSD Pro Billet Dizzy in the intake.......with a MSD Crank Trigger on the balancer and a MSD 7AL-2 Plus box with a Pro Power HVC coil........and Moroso Ultra 40 11mm Plug Wires......Plugs are BR7EF but that will be changing..........

im maybe pointing towards the Magnetic Pickup on the Crank trigger sometimes not picking up the signal......it was soaked in antifreeze a couple of times.....(my fault)......not sure if this affected it......


any ideas would be apprieciated........i've already done quite a bit of troublshooting but a new thought from another mind will always help.....

 

Is the dizzy brand new, have you pulled the cap off of it to see what it looks like?

 

yep dizzy is brand new......and i checked the cap and rotor and it looks fine....

 

Can you take the pick up of your crank trigger and test it? Did you check continuity in your plug wires. bad gas?

 

i drained the fuel and tried another source that didn't do it......i checked the wires they all ohm'ed out good.............i didn't test the trigger pickup yet...im gonna call msd today and ask whats the best way to test it.......this is driving me nuts

good thing is it made killer power even with the tune still being off and this problem being present.......485 through a dana 60 w/4.56's slicks and a unlocked 5300 converter aint bad lol

 

No ****! not bad at all. Well it sounds like youve done everything i can think of. Ill put the money on the crank trigger for now.

 

me too.........thats all i can come up with...

 

when you find out, let me know. My car does this and it's basically stock. lol I've been chasing it on and off again for the last 2 years, and everything I do doesn't help any.

 

I had a problem like this years ago and it turned out a few of my plugs had cracks and it would arc occasionally and I would get a miss. Some suggestions/ideas: Where you datalogging when this occured? If so, did the battery voltage change rapidly at all (wiring/battery related issues)? What about connections for the ignition box/coil? I wouldn't think the crank trigger would be an issue, it is just a simple magnetic pulse with not much to go wrong. How many degrees do you have between the cam position sensor and the crank trigger? I think you need a min of 10 degrees for the computer to have the time to adjust/track timing events.

 

How fast can you log the pickup? If your logging rate is too slow, you may have to scope it to catch it glitching.

A few dyno sheets would help in figuring out your early power drop off.

 

i know what you mean about the plugs........i think im gonna ditch ngk and try an autolite plug......the batt connections and everything are good i got 14.2 volts at the xfi and the box at all times while the car is running......i rechecked the coil wiring but im going to again tonite.......im not even in sequential right now i have the cam unplugged im running just bank to bank........

thats what i was thinking i was almost gonna hook my o-scope up to the crank trigger........im gonna put my timing light on the coil and tape the button down and go for a spin and see if i can catch the misfiring......

i have the dyno sheets being emailed to me now.....should have em within an hour or two

 

and i appreciate the help!!!!!

 

Mike, post this up on yellowbullet. You will get 100 replies from guys that have been there done that and will have tips to offer.

Side note, a good datalogger would troubleshoot this in a heartbeat, especially one of those crazy$$$$$$$ ones with egt sensors.

 

+1 on posting it at yellowbullet. Lot's of great info there. And lot's of ********* too..... Never mind nothing new. jk

 

I have seen this a few times and was able to remedy it by providing additional grounds. Alot of time the ground in the harnesses are too small and when you start adding the other electronic components they dont bleed off the harmonics as well. Try adding a bare braided ground strap fom chasis to motor, as well as inspecting the rest of your grounds.

Any idea what the duty cycle was?

 

What are your plugs gapped at? With the 7al2 you can tighten them up, it will help with the higher rpms.

 

yea i talked to a bunch of ppl today........seems like we came up with a solution


the plugs in my car showed signs of too hot of a heat range and my timing pointer moved a couple of degrees on my motor.......so what we thought was 33 degrees was really 37.....that plus the too hot of a plug explains the severe detonation we heard on the dyno........luckly no dammage occoured...i also ran a compression test and with the motor hot it put out 270psi...as for the motor running like crap yesterday the way the plugs looked it explains it.......becuase before that the motor ran fine with new plugs........i spoke with a few guys today and after speaking with someone at autolite i was refered to in the race plug division we determined to run a ar473 or ar474 in the motor......the br7ef is just too hot of a plug with 14.25:1 operating above 7000rpm..........


i had them gapped at .037 ....apparently a hair too much......also yes he said they come gapped at .027 and to leave them there and not open them up......he said that also that with my ignition it will help hi end misfires and stop the spark from jumping to other ground sources than the ground strap.....



we'll see what happens this week i got the plugs comming tomorrow im going to start with the colder ones first......

 

So what ended up fixing the misfire and detonation issues.?

 

Just read the post above yours

 

Sorry I thought until the new plugs and gap were actually installed and tested it was jus an educated guess...that's why I asked to confirm that's all..