Hi Rev Misfire as in past 6k

r2d2hp · Post by **r2d2hp** » Fri Sep 05, 2008 8:36 am

Tony,

Have you adjusted anything since being on the Rolling Road.

I recall you were looking at the dissy advance, have you changed it.

The other option is ditch the dissy,hyfire etc and move over to a fully mapped ignition - you know you want too.

Another thought - do you have the Hyfire bringing in any timing retard at all

Post by **Coops** » Fri Sep 05, 2008 12:22 pm

Hi Reg,
no not touched the dizzy etc,
only thing is changed a few things on the vems, but put the old o/e .msq back after and made no difference,

only time it retards is via the nitrous controller,
and thats only 6 degrees taken out,

On another note:
anyone got a unilite i could borrow?
a set of good leads?
and a promaster coil?
I can bypass the hyfire to run the dizzy only to eliminate that,

just so i can slowly eliminate my own parts etc,

Post by **Rossco** » Fri Sep 05, 2008 2:10 pm

Dont foget if you bypass the 685 you'll need to put a ballast resistor in there or you run the risk of blowing the module in the dizzy

Post by **Coops** » Fri Sep 05, 2008 2:27 pm

its still sat under the bonnet by the coil allan

Post by **Coops** » Fri Sep 05, 2008 7:59 pm

some one else just advised and said sure your not getting valve bounce

stevieturbo · Post by **stevieturbo** » Fri Sep 05, 2008 9:18 pm

Take the rocker covers off and inspect the springs.

But I'd be trying a conventional ignition setup first. Just in case.

What does the rpm log look like ? Does it sit stable at the missfire ? or is it all over the place ?

Perhaps a crank sensor problem ?

Post by **Coops** » Fri Sep 05, 2008 9:30 pm

rpm is up and down stevie,
the ecu is triggered via the tach output on the mallory cdi unit,
still using a dizzy you see.
im going to do the cdi unit bypass tomorrow and trigger the ecu direct off the coil, so all thats being used is the coil and the unilite,

stevieturbo · Post by **stevieturbo** » Fri Sep 05, 2008 9:38 pm

your ecu doesnt run a 36-1 trigger or similar ???

Post by **Coops** » Fri Sep 05, 2008 9:48 pm

not at present mate no

Post by **Coops** » Sat Sep 06, 2008 6:48 pm

did a test today,
set the hyfire with a rev limit of 3k
took for run and did a datalog,
and im 99% convinced its not an ignition problem,
as the datalog shows the car going lean (ecu not being triggered whne no ignition) when on the limiter,
where as when it hits 6k it goes mega rich,
so its either and ecu problem, or valvetrain problem,
im going to take the top half the engine apart next week etc to check lifters , cam etc, could the valve springs be weak after the rolling road giving valve bounce?

datalog here:
http://www.v8forum.co.uk/zip/log06.zip

stevieturbo · Post by **stevieturbo** » Sat Sep 06, 2008 7:16 pm

generally speaking, missfires will show a lean condition.

Although I'd guess valve bounce would too....but dont honestly know.

Anything that allows excess oxygen into the exhaust...will read lean.

I know that on my own car, I had been plagued by a high rpm struggle.....perhaps not as bad as a noticeable missfire, but still a struggle after 6000rpm.
In the end, for the most part it turned out to be a weak spark.

Can you try really dropping the gap down to about 20 thou or something to see if that changes anything ?

What sort of air filter etc is on the car ? Could any induction be getting restrictive all of a sudden ?

Are all the pushrods/rockers ok ?

Post by **Coops** » Sat Sep 06, 2008 7:44 pm

the car was fine until the rolling road stevie,

also today i noticed after a run i left the car running while i opened the bonnet, where you could hear 1 or more tappets rattling,
never had that before either

stevieturbo · Post by **stevieturbo** » Sat Sep 06, 2008 7:53 pm

maybe a dodgy lifter or something ??

Such problems are a real PITA to find.

Post by **Coops** » Sat Sep 06, 2008 8:11 pm

what i thought if i got a lifter or two playing up that would give the miss fire effect would it not?
and also give a rich reading possibly with the ecu.

stevieturbo · Post by **stevieturbo** » Sat Sep 06, 2008 8:21 pm

Not sure what way it will affect the readings.

With a V8, it can be so hard to tell at times when a car is off a cylinder !!!!

A visual inspection is called for.