Help needed desperately people . 308 T400 one tonner, recently had new bearings, rings, cam, lifters, timing gear and reco heads fitted.
Straight gas GRA single throttle body 510 cfm.
Fit new set of plugs and the ute will run awesome for about a day, then it'll start a little miss here and there and by the next day will be missing sp badly you have to drive it hard to stop the miss. Change the plugs to another set, doesn't matter what brand and what heat range they are as they will be stuffed within a day.
I have full continuous battery voltage via a relay to the coil, coil has been changed to eliminate it as a suspect even though the old coil was less than 5 months old.
Leads have been changed, no effect to the problem.
Distributor cap checked for any scratches etc or arcing on the inside of the cap .
Inlet manifold removed and replaced with new gaskets just incase I stuffed up during the rebuild, no change.
I've gone right up to a 7 heat range in the NGK to see if that helped .. No change.
So far I've put 5 sets of plugs in the last 5 weeks and have become hesitant in fitting any more till the problem is found.
The dizzy is a HEI one that's been professionally regraphed to suit the gas also.
There was not this issue with the ute before the rebuild.
HELP!!!
Rodders
Has anyone heard of this problem before?

Are you running colder plugs. Maybe heat range 5

Hi Pete,
I've used 5, 6 and even 7 in the NGK. NGK themselves thought it may have been a plug heat issue, but the BP7FS plugs lasted just as long as the others....
Rod

Rodders, you might be onto something re the "too much/ too little voltage theory.

Have you checked the input voltage to the ign module- wondering if low or high voltage into it could cause low or high voltages out of it?

It's all I can come up with on a Saturday night !

Cheers.

you cant "fry the plug with too much voltage" because there only needs to be enough voltage to ionise the gap and start the arc, the maintenance of the arc for the duration requires far less voltage to keep it lit.

bang a timing light on it and rev and hold the engine in 500rpm increments to see what the curve is like and whether the timing is moving around, if driving it hard is "fixing" it, i reckon its tune related.

Edited by user Monday, 11 February 2013 2:05:33 AM(UTC)  | Reason: Not specified

g'day mr rodders ,
i think i have a solution for you , i had the very same problem+also burnin out points with a yanky car i purchased last year , it was eating plugs /points and even melting the plastic sleve on the points... , points in 2 days! ..the car would run fine then start to get a bad miss then it would get worse, then it wouldnt idle then die ......i checked changed everthing , points plugs/ leads/fuel pump /coil / carby/re earthed the motor/ balist resistor ....this kept happenin for around 1 month i couldnt figure it out , drivin me nuts my brother everythang ...then i went back fronm the start studied workshop manual crossed referenced parts+numbers..... bingo! the previous owner had instaled the wrong coil??? , i then just re newed it with a brand new coil that suited a car with a external balist resistor... when it need a coil with a built in resistor ....put in a ol coil from back yard ....whammmmo , no more burnt out pionts /plugs ...car has been running perfect for over a year!... i REALLY HOPE this work for ya

nascoman

Hi, I use a relay as I've changed from the original wiring that was in the ute when u bought it as they were using the original ignition wire to power the coil, 7 odd volts ain't enough. I use the gas switch wire as a trigger to pull full battery voltage to the coil.. Have tested it and battery voltage is evident throughout the wiring from battery to coil to distributor module. I have had one go on me before (ignition relay) and it won't bloody go at all when the relay craps itself! Happened to my EH prem wagon when ij was leaving for home after doing overtime on afternoon shift!!

Actually, I've just had another thought. What's the mixture like across the whole rev range? Have you had it on the dyno with a gas probe in the exhaust to monitor the mixtures? It may well be running out of air or gas flow at higher RPM. Might be worth finding a local car club running a dyno day & spend the $50-60 entry fee to find out. Could save you chasing a lot of other things if it turns out to be fuel/air supply related.

Hi, it's the Bosch coil. Originally it was the standard shaped oil filled one and now it's the Bosch high energy solid state one ( you know, the smaller almost rectangular shaped one). Changing the coil made zero change to the problem.

thanks rodders , but have you checked if your wiring is set up for balist resistor as the coil still may be incorrect as was mine ....my yanky car had no resistor , while the aussie assembled car had a factory resisto in the wiring harness this miss match caused all the problem ...mate i swore black and blue this could not be the problem with my car but once i triple checked this i was wrong ....and my car as no more probs....