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Author Topic:   motor misfiring
rogracer2
Dirt Maniac

Total posts: 119
posted May 09, 2004 08:03 PM  
My motor runs fine at low RPMs, but when it gets to higher RPMs, it starts to sputter and cut off. Does anyone have any suggestions on what the problem could be? I replaced the spark plugs, spark plug wires, and distributor cap so far.

nice_guy_wi
Dirt Maniac

Total posts: 120
posted May 09, 2004 08:47 PM  
Finish the ignition off with a new rotor, coil, and module.

juliaferrell
Dirt Freak

Total posts: 370
posted May 09, 2004 08:48 PM  
On the track under load or in the shop? Do you have an adequate valve train?

rogracer2
Dirt Maniac

Total posts: 119
posted May 09, 2004 09:03 PM  
it happens on the track. sounded fine while packing the track, even the first couple of laps at speed, but by the end of the heat race, and all through the feature, it was missing at the higher rpms.


mrteeshot
Dirt Maniac

Total posts: 127
posted May 09, 2004 09:46 PM  
sounds to me like once the coil is warm its causing your probs change the rest of elect system problem should go away also check that feul system is getting good flow

racer17j
Dirt Forum Champ
Total posts: 5390
posted May 09, 2004 09:59 PM  
do you run an alternator? sounds like battery could be getting low definately will cause this problem esp. with an hei

Raz_900
Dirt Forum Champ
Total posts: 635
posted May 10, 2004 09:14 AM  
If it runs fine at high rpm, under load for a few laps... I'd check

1.) module
2.) coil
3.) battery
4.) all connectors on distributor
5.) plugs wires

Spray some water (with a squirt bottle) on the wires in the dark. If there's any arching, get new ones.

I've had similar issues twice this year. Once was a module that finally fell over dead one night and wouldn't fire again, the other was the 3 wire connector on the dist. being lose.

juliaferrell
Dirt Freak

Total posts: 370
posted May 10, 2004 09:44 AM  
something ignition. check your engine ground!!! strap the engine to the chassis and make sure the ends are corroded. If you do have one put your hand on it and check to see if it is warm.

rogracer2
Dirt Maniac

Total posts: 119
posted May 10, 2004 08:16 PM  
OK...I've replaced the distributor cap, rotor, ignition module, condensor(capacitor), and ignition coil! Next I will check the spark plug wires and plugs themselves. I also plan on checking the ignition timing.


neil rucker
Dirt Forum Champ
Total posts: 799
posted May 12, 2004 06:46 PM  
tachometer? maybe? (seen it before)

racer17j
Dirt Forum Champ
Total posts: 5390
posted May 12, 2004 07:40 PM  
STILL HAVING THE SAME PROBLEM - I changed everything under the distributor cap - the cap, rotor, module, coil, condenser. I put a different carb on to see if a float problem could have been the issue - but that didn't help - the battery is fully charged - I have an alternator, but I had shorted out the wire a few months ago - so I have it turned off (via a switch) - I replaced all the spark plugs, checked the gaps, got new spark plug wires, the ignition timing is set. The only thing new I could find this morning under the hood was the ground wire from the battery to the exhaust manifold was a little loose. I don't have an engine ground (I have solid motor mounts) that should serve the purpose (right?) Should I take all the wires off the alternator? Rewire from the battery to the motor? What about the kill switch? Or the 3-wires under the distributior cap? I checked the fuel pump - that is working good.

I AM READY TO SHOOT MY CAR!!!

ANY MORE SUGGESTIONS WOULD BE GREATLY APPRECIATED!

waltonjr1
Dirt Forum Champ
Total posts: 516
posted May 22, 2004 12:05 PM  
Are you using a stock module, if so they are only good for about 6,000 rpm. If your turning more than that I would get an aftermarket module and see if that works.


BIGDADDYBOZ
Dirt Freak

Total posts: 466
posted May 22, 2004 09:17 PM  
I had a friend with a prob like this and his turned out being the fuel pump push rod. it sounds dumb but it had wore down enough that it wasn't getting full push on the pump.

mrteeshot
Dirt Maniac

Total posts: 127
posted May 22, 2004 11:40 PM  
I agree with fuel pump rod- been there fixed that -same probs as you explain - mine looked rounded and during next rebuild found bad lobe looked like some one used a grinder on it bad steel was our guess

Donnie Ross
Dirt Freak

Total posts: 264
posted May 23, 2004 04:41 AM  
move your ground from the exhaust manifold,
resistance goes up as heat does if grounded on an exhaust manifold this could be the prob.

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted May 23, 2004 05:19 AM  
I'm surprised nobody has mentioned weak or broken valve springs....

KP

bigcityracer
Dirt Freak

Total posts: 431
posted May 23, 2004 07:28 AM  
Disconnect the tach for a race. It maybe bad.

Gomer T
Dirt Full Roller

Total posts: 36
posted May 23, 2004 07:42 AM  
If you have a spare distrubutor laying around you might want to give that a try. The gear on the bottom could be getting worn or bearings could be getting bad. If you are using a high volume oil pump the gear will wear faster than stock. Sounds like this problem is happening after you are running a couple of laps and creating heat in your ignition system. The solid mounts will ground the motor, but you still have the chance of the motor twisting causing a loose conection. I run my ground from the battery to the back side of left head. If you are already grounded to the frame you can run a wire from the frame up also. Is your car getting hot?

Duane

rogracer2
Dirt Maniac

Total posts: 119
posted May 23, 2004 11:42 AM  
Yes - the car runs hot - after an 8 lap heat race the temp goes to near 230.

rogracer2
Dirt Maniac

Total posts: 119
posted May 23, 2004 03:10 PM  
What about a vacuum leak on the intake? Would that cause my problems? This afternoon while it was idling in the garage, I swear I could hear a hissing sound from the back of the intake, and I saw a little oil leak back there, as well as on the front of the intake.


Dsprintcar10
Dirt Newbie

Total posts: 2
posted May 23, 2004 09:58 PM  
Do you run an alternater? if so, check it to see if it's good,if you don't, check your battery to see how many amps it produces, if your battery gets low, it will not produce the proper amps that the HEI needs to run properly, and can be detected at high rpms as a misfire , 13 amps is what the hei usually needs, anything less may be your problem, hope this helps, goodluck..

tech355
Dirt Full Roller

Total posts: 73
posted May 25, 2004 08:42 PM  
Check your toggle switch,had the same problem.Also, a friend of mine had the same thing happen to him and it was his plugs.I dont remember if he changed brands or just numbers but he went back to his old plugs and that cured it.

rogracer2
Dirt Maniac

Total posts: 119
posted May 26, 2004 04:42 PM  
What about the pickup coil? I had a local mechanic say on the old Monte Carlos, this was a common problem...


19J
Dirt Freak

Total posts: 370
posted May 26, 2004 09:57 PM  
My guess is you found the problem. A buddy built a 350 bored 40 in his truck for the street. That thing idled awesome ran ok at low rpms but 4 barrels haha what a joke a metro has more power. Turns out his intake bolts are stripped and it leaks air. Also A LOT of people(mechanics) have told me if it has a vaccum leak it will get hot or warm. Change the intake gaskets on the front and rear dont use the lil gasket put a nice layer of silicon all the way across. Ive heard of too many motors sucking those lil gaskets in its not worth it to me though. Try that then go from there.

One more thing. Someone mentioned valve springs. That could be a possibility but do compression check. I had a motor that idled fine but it had dead cylinder and finally let go it had fine lower rpms but no higher rpms and it got hot every now and then when it felt like it.

On a side note it amazes me 24 replies and the car still isnt fixed and they the best thing in the world to work on LOL.

[This message has been edited by 19J (edited May 26, 2004).]

Raz_900
Dirt Forum Champ
Total posts: 635
posted May 27, 2004 08:19 AM  
If you've changed all the ignition parts (and it's not a stock module which is only good for 4500-5000 rpm) then I'd say the next step is to start looking at the fuel system.

Is your vent clear for the cell? Fuel filter not plugged? If a mud wasp plugged your cell vent or the filter's plugged, it'll run great for a couple laps then run outta fuel. Are the plugs white or black? The misfiring could very well be a lean misfire, but I'd double check on the module thing first. While I wouldn't rule out valve springs, usually weak springs will float out right away and not after a couple laps. Of course I say usually.....

carolinafast
Dirt Full Roller

Total posts: 72
posted May 27, 2004 01:13 PM  
had a similar problem......valve guides were
letting oil in 2 of the cylinders under race conditions.....go figure!
read the plugs??

[This message has been edited by carolinafast (edited May 27, 2004).]

Busch
Dirt Full Roller

Total posts: 46
posted May 27, 2004 07:53 PM  
pull the intake! Ihave seen more than one intake crack just under the carb. If you are using a stock cast iron manifold remove the heat shield and inspect the manifold. Also you may find this with a vaccum gauge with the engine at operating temp. Hope this helps

racerguy500
Dirt Maniac

Total posts: 168
posted May 27, 2004 11:42 PM  
I would say to look into the fuel delivery myself. A restriction or lack of adequate delivery would do exactly that. Regardless of the pressure, the volume could be killing you. Good luck.

rogracer2
Dirt Maniac

Total posts: 119
posted May 29, 2004 05:43 PM  
It is fixed!!! The car good last night. Thanks to everyone with the advice and ideas.


19J
Dirt Freak

Total posts: 370
posted May 29, 2004 08:43 PM  
WHOA WHOA WHOA!!!! What was wrong with it? Dont leave us hanging lol.

rogracer2
Dirt Maniac

Total posts: 119
posted May 29, 2004 09:30 PM  
I think changing the pickup coil did it!


ryan
Dirt Forum Champ
Total posts: 776
posted May 30, 2004 11:17 PM  
Kinda suprised nobody mentioned that he should try to phase his distributor.

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