missfire at stress • The Dodge Challenger Message Board

by **Jimiboy** » 23 Jul 2007 3:55

Hi

Can anyone give me a suggestion to solve my problem with missfire...
My car run's fine at idle and gives a quick response at the gas true the rpm range... if i run the car with a little throttel or 3/4 gas it runs with no doubt and respons nice... the problem comes when i stress the car with full load and max throttle. It then runs quick and nice up to say, about 4000rpms, then it start missfire like hell.... (?!?)

I have tested to set the timing at 10-12 degrees at idle and then i have misfire at a bit lower rpms (4000rpm-) when a friend helped me to set timing at about 34 at 4-5000rpm it put the problems higher on the rpm curve (4500rpm-) :s022:

Is this a problem with timing, sparks or a fuel, jet problem? what do you guys think?

I recently mounted an Edelbrock Air Gap with an mechanical Holley 650..
i have a bit bigger jets on the carb (69+83 and bigger accelerator pump (i dont know the word in english) there is practicly new cables to the sparks and new distributor cap and sparks also....

///Regards Jim :shock:

by **dave-r** » 23 Jul 2007 8:08

Sounds like an ignition system problem to me.

Describe your ignition system. Contact points? Electronic? Mopar? Other make?

by **Jimiboy** » 23 Jul 2007 9:17

I got mopar original electronic ignitionsystem. Could it be broken?

by **dave-r** » 23 Jul 2007 13:28

The "orange box" unit might be faulty.

by **dave-r** » 23 Jul 2007 13:37

Have a look at this.

http://www.4secondsflat.com/a688dropcyltest.html

by **Jimiboy** » 23 Jul 2007 14:57

Ok, i have borowed a new aftermarket unit. i am about to test that one. It was bad fitting to the contact do... :disbelief:

by **Jimiboy** » 29 Jul 2007 11:02

Ok, i dont know if this should be a bit embarassing to tell.. but i got things rockin' by playing with the timing a bit more :s006:

humm....
i am totally confused! i really dont know the degrees of the timing now, but i dont be surprised if its close to 40 at peak(?) but i dont hear any knockings so... it should be allright, right? :s022:

by **Eddie** » 29 Jul 2007 14:11

Need more info. Be careful Jimiboy, you could "get" detonation at higher rpm's and if you have headers or a "loud" exhaust never hear it. Then someday engine damage from detonation,(usually in the form of broken ring lands or cracked pistons). Simple solution. Dial back timing light. Put one on it and "see" what your total timing or timing minus vacum advance is at a specific RPM's :thumbsup:

BTW, have you checked your timing chain slack? Easy to do, pop your dizzy cap, put a breaker bar on the front and remove the spark plugs although it's not necessary but makes the engine much easier to turn over by hand, then observe rotor movement, there should be very little "play" between the two.

by **Jimiboy** » 29 Jul 2007 20:30

I get your point there... I am running with headders and loud pipes, so i hope i dont make damage to my engine and miss it due to the "noise" like you say! :roll:

I havent checked timing chain.. But yesterday as i was removing intake/ replacing lifters, i moved and tried to feel the play between the rotor/ cam, and it looked ok... :s022:

I have a regular timing light. Guess you mean a timing light i can set degress on? I might have to search for someone with proper tools to set timing correct after all... :?:

by **dave-r** » 30 Jul 2007 8:45

I have instructions on setting the timing on here somewhere. More than 35 degrees at 3500rpm is probably going to give you problems. But you want at least 12 degrees at idle. Possibly 14-16 degrees would be better if you can tune the distributor advance curve.

by **Eddie** » 03 Aug 2007 21:51

Another thing I just thought of was, JimiBoy check that you didnt overtighten the base fasteners to the carb. Too tight will possibly cause the back secondaries,(throttle blades), to delay or hamper the opening of them under load. Easy thing to check, they should openly smoothly with no bind or click if so, they are too tight. Just thinking out loud man! Let us know! Another, did you try and disconnect your vacuum advance? try it and see if this eliminates your problem. If so then you need to work on your timing curve. You have three curves. base, initial, and vacuum, Dave is right on! :thumbsup:

by **Jimiboy** » 04 Aug 2007 14:07

I like you guys

Thanks for all nice points here... This is good stuff to have in mind....
I do think the car is ok (no worries that i am gonna worn it driving with this timing) even do i have that feeling somethings not mounted right maybe in the cam, timing/gear ?!?

Let me try to describe my problems from the start...
This may be a long story, how big can a reply in this board be? :biggrin:

Why i had that idea with faulty mounting in "cam timing gear"
I never checked timing earlier, so maybe this is why i never got the car running normal with normal timing setting 8-12 degress without wacuum at idle. after i switched my *magnet pick up* in distrubitor...
It all began with sudden difficulties to have the machine starting. I first switched the ballast resistor and checked sparks and so on... i did not get the problem... at first i thought it was that ballast resistor do it was really bad (isolation protecting the springs on the back was history) and i think i got it fixed up when it started the first time... no more then one time? so this was real fretful and i started to switch my sparks. I thought this was a good thing to do since i had'nt done it since i bought the car, and the wirings was in bad shape also... and i also buryed the distrubitor cap and the pickup there looked like it had been brutaly abused, so i believe this can have been my problem... :s006:

it may have been scary timing before, and i did'nt notice about it, have all stuff switched and drop the distrubitor in and was about to set timing "after the book" and by all rules correct.... and can it be that somethings not right in camshaft, crank gear or something? if my setting was totally faulting i should not be able to this great idle and running at all rpm registry? it must be correct, do it seems scary?

I had it at 8 and then at abot 10 and 12 at idle, no vacuum, result: good idle and rpm up to somwhere in 3500-4000 rpm, then missfire! Then set by hand a bit more backwards (higher timing at small block) and managed to have this missfiring problem at a bit higher rpm instead, somwhere in 5000rpm...
My friend has a 383 and we messured his timing and marked this messure at my flywheel to be able to set my timing at 34 degrees (you sure get our idea?) and this was not helping my engines missfire no more... then i tried to borrow a new ignition unit from our excellent local u.s car part store (it wasn't fitting) :s023:

so i thought this MUST be to little fuel or wrong timing setting... i was trying once more and filled air in the neigbourhood with sound of thunder and set timing bit for bit more higher, and wow! or maybe what a h*ll? the new marking (54 mm below standard timing marking) was now where the ordinary zero marking should be?!? at 0 degrees without vacuum. this was the idea from beginning but it was only a bit more to this fine result! and 8-10 at idle!!! this i dont understand :!:

You all guys must think i am a strange, crazy guy or something! But i have helping friends that are most confused also :hmmm:

and i heard abut a similar story with a guy and his mustang...

Phuiiii.... :s023:

But now it working! really fine! :V8:

Did you fall a sleep reading Eddie?

(now i hope i was not totally excited abot getting engine running fine, that i dropped my eyes... this marking at idle is for 99% sure the new one)

by **dave-r** » 04 Aug 2007 17:59

Didn't understand a word of that.

But can i make a few points?

The timing figures and proceedures I outline on this message board will ALWAYS make your car run better. Small blocks do like a bit more advance at idle. Anything from 12 to 18 degrees. But never more than 34-36 degrees at 3500rpm (vacuum disconnected in both cases).

If you find that the timing figures you need are way out from my specifications then there is some error in the reading of the timing.

The usual problems with reading the timing are;

1) Not dissconnecting and pluging the vacuum advance first.
2) Not adjusting the vacuum advance when it is plugged back in.
3) Having vacuum at the distributor advance port at idle.
4) Using a basic/cheap timing light instead of a "dial back" timing light where you set the degrees on the light and look for the zero mark.
5) On small blocks they changed the position of the timing tab on the timing cover from side to side. Sometimes this does not match the damper being used.
6) When a damper starts to fail it can slip around and give false readings.
7) Some people get confused as to which cylinder is #1.

I hope that sheds some light on the possible problems you might come accross. :wink:

by **Jimiboy** » 05 Aug 2007 7:03

Thanks Dave!
(at least i tried to explain) :roll:

I have tried to find a "Dial back " light, nobody has one... This sure is something i want from myself in christmas... (to bad a guy cant have both a Girl and all his money for the car?) :mrgreen:

I am not sure i understand the number two?

I set timing with vacuum plugged, then put it back when i am done and check timing again without touching the distrubitor no more! And then i consider it done(?) :s006:

That number 6 in your list sounds like something(!) :idea:

by **dave-r** » 05 Aug 2007 9:42

With regards to 2).

You can vary the amount of vacuum advance in the vacuum can. Most are adjustable. You only want about 10-20 degrees vacuum at most. Or do without the vacuum at all. Otherwise it can put too much advance into the timing.