340 misifre

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MOPARTEEN

MOPARTEEN

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Hello,

I recently built a 340 with a hughes engines whiplash cam and put it in my Dart. I am having a misifre at high r.p.m.'s or under load. 0 - 65 is smooth and effortless but once I floor it from 0 or at 65 m.p.h. I have a misfire and cant get the car to go over 80m.p.h.

I have good compression, spark in all cylinders, voltage regulator is fine, no wires are touching, standard mopar performance orange ecu box, distributor. eddy 660 carb. Vaccum advance, idle time is around 20-21 and all in is 32 or 33. I cant seem to find out what it is I have great spark in all cylinders. I have basic wires from an auto parts store, and 3.23 gears. I think I should be able to do over 80 m.p.h in this car as I took it to the track and it ran 18's at 80 m.p.h. I believe it can do better.

When I do a burnout it misfires like 2 or three times and then stops missing and then it really takes off like it should. Sometimes a backfire can be heard in the headers. I have richened the fuel mixture, leaned it out, adjusted timing to 35, checked all my wires, changed my plugs and still cant figure it out. Perhpas it is my coil but the resistance seems fine(around 1 ohm)

I want to floor the car and twist the distributer untill it stops missing but I dont think that is a good idea.

I think it is timing.
Can anybody help? I would really appreciate it.
 
What trans? Comp ratio and fuel octane used? MPH doesn't really help, is there an RPM it cuts out? Does the orange box have a good chassis ground? Have you ran it with a vacuum gauge hooked up?
 
More information is surely needed. But if you are certain(& make certain you're certain) the mechanical condition of the engine is right, no broken valve springs, tight valves etc. then I'd take a good hard look at the ignition for any high scondary resistance & make sure the primary connections at the distributor & coil are sound & correct.
 
I have a 727. I havent checked for ground or my secondary, I just assumed since it was running it was fine, but I wil check(i have a multimeter).

I dont know what r.p.m it cuts out except when I go to floor it, no matter what r.p.m. I am at. It seems to cut out at like 900 to 2000 and 4000 to 5000.
*complete stop to acceleration backfires/connects and goes/back fires alittle through exhaust twice while going/connects and goes and then stumbles and fights to get past 80* its like it just maxxed r.p.ms and the tranny is saying NO.
Connects=all 8 cylinders igniting.
I think I need to play with timing.

I had a vaccuum gauge hooked up, the vaccum is around 12, it fluctuates a little but it is with the stroke of the cam because the idle is sort of choppy and the needle kind of goes with the sound. However when I raise the r.p.m. up to about 1100 or so the idle really smooths out and the needles acts like it supposed to and steady's. I know on a properly running engine the needle is supossed to be steady but my cam isn't stock so I am thinking it is just the cam making it wiggle.

2 weeks or so I pulled the valve covers and all the rocker arms were moving and I had oil shooting all over, I observed the valve train and dont believe to have a sticking valve, plus the heads and valve train are all brand new and recently installed.

I may have burnt valves, I am thining about buying a valve retainer tool and checking my valaves out and cleaning them.

So far my plan is to check my secondary ignition and grounds, research some timing and play with my air fuel mixture. Also scope out a valve tool.

Thanks.
 
This problem could be your orange box or you should check your distributor.Sounds like an ignition problem at higher RPM,s.I had the same issues when I first put my 360 in.I went MSD ignition and my problems were gone.Good luck.
 
Im getting a misfire at the top end of second gear, getting ready to shift into third. It stumbles and then shifts into third and fires like it should. Im stumped.
Any help would be appreciated, in the meantime I will keep at it.
 
I think may be lean. What fuel pump are you running and what kind of pressure. I may seem like a misfire but may be just running out of gas. May have vacuum leak which would also lean it out. Need to make wide open run and shut it down and read plugs.
 
Hey guys thanks for the replies.

Turns out I have a collapsed lifter. I thought it was just the unadjustable rockers clacking together because I have no spacers.

I called up Hughes Engines and they said to pull a lifter and check it out for dirt. I pulled the lifter due to the spongy pushrod and took it apart.

When I took it apart It had small shavings or hard deposit like particles in it. Supposedly the lifter is much like a check valve and I geuss it got cloggged and would not let the oil in to prime it.

I bought a new set even though I can clean them out and reuse them but I figured I would keep a secondary set.

Now I need to reassemble and run her!

Thankls again.

Rob.
 
make sure you keep the old lifters in order of what lobe they cam off....
 
Throw the old lifters out! What good is it to have a set of lifters lying around that you know have had failure issues? If you ever need another set you don't want to install problems from the old set. JMO...
 
Good point lone wolf.

Jimmy I dont believe it is the pickup coil because I popped the cap off and it doesnt look burnt or corroded and looks fairly new.

Thanks for all the help and replies. I am waiting on the intake to be powder coated so I can reassemble.

Rob.
 
MOPARTEEN said:
Good point lone wolf.

Jimmy I dont believe it is the pickup coil because I popped the cap off and it doesnt look burnt or corroded and looks fairly new.

Thanks for all the help and replies. I am waiting on the intake to be powder coated so I can reassemble.

Rob.
Click to expand...

a bad pickup coil does not need to look corroded or burnt...a simple ohms test will tell ya whether it is good or bad..


Unplug the wire going to the dizzy and check the pickup coil ohms. Set your voltmeter to ohms and you should get anywhere from 375 to 900 Ohms. Switch to AC volts and spin the dizzy and you should see at least 1 volt AC.
 
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