350 chevy missing on 2 cylinders in the same bank?

Hey i hope this is the right section to ask a technical question if not forgive me in advance, and tell me where to put it. I have a 350 chevy motor with a msd ignition and msd ignition box, new cap and rotor, new plug wires, new plugs. The problem is it runs like ****, i drove this chick i know in it, and it ran ok till i put my foot on it for her, then when i slow down the idle drops and it tries to die when your idling. I checked all the plug wires,plugs, and cap and rotor and they all appear to be ok. but if i pull off the 3 and the 5 wire the rpm doesnt change at all, but if i pull off the 1 wire you can hear it drop. i put a plug in the wire, and they spark and did a compression check on the same 2 cylinder and both are around 135, does anyone have any other ideas of why these 2 cylinders arent firing? i also tried 2 other plug wires on the 3 and 5 and its still the same thing..i am so frusterated..any help is greatly appreciated..thanks guys....adam

 

Maybe a blown head gasket between those two cylinders.

 

sure it aint 5 and 7 ,if you cross those 2 as they fire 1 after the other they can cancel each other out so make sure 5 and 7 aint crossed......Marq

 

I would agree with the head gasket, whats the compression in the other cylinders? Did you take out all the plugs or do them one at a time? I ask this because if it is blown between cylinders and you leave the plugs in, it will push compression from one cyl to the other. If you take them all out, you will have a much lower reading in those 2 if that is truly the case.

 

I'd make sure the wires are all in the right place. Follow that with a compression check. I'm betting on the wires.

 

Is the chevy over carbed,or has it been flooded lately?You said you checked the plugs,how?What I mean is did you ground them to engine and turn her over and saw spark.Or did you just look at the color or what.With that much compression i would doubt a valve problem .If it is a head gasket there would possibly be coolant in the oil .I think you should change the plugs and try it again .I suspect you have a couple that are gas fouled.Good luck.

 

Is the chevy over carbed,or has it been flooded lately?You said you checked the plugs,how?What I mean is did you ground them to engine and turn her over and saw spark.Or did you just look at the color or what.With that much compression i would doubt a valve problem .If it is a head gasket there would possibly be coolant in the oil .I think you should change the plugs and try it again .I suspect you have a couple that are gas fouled.Good luck.

 

ok, so the plugs we pulled out and grounded to the motor, and appeared to have agood spark, i have double checked the plug wire order, and all appears to be ok. i pulled out the other plugs and did a compression check and still shows good. i am completely lost, oh and i have also put on a new coil thinking it might be that, and it is still the same..any other suggestions?? thnaks guys, i did not know of the gasket blown beetween cylinders,and still reading ok with the plugs in. i will always remember that one...any other suggestions would be great

 

Check the dissy cap a crack on the cap could cause this.

 

Do you have fuel injection?

 

I just thought of something else..If you have spark, and compression,,then you need fuel. I had a BB Chevy with an edelbrock manifold on it. It lost the two middle cyls on one side, the outer 2 on the other side were weak. There was a crack in the intake, leaning out that side of the manifold enough to misfire. Its also possible you lost 1/2 the carb. Since you said it was OK till you got on it, maybe something got stuck in the carb, like a metering valve, etc...

 

Desertratrodder may be dead on. You've probably already replaced the two plugs but if you haven't I'd try that as well. Had that problem with a new set of Champions years ago and haven't run them since.

 

Could have ****ed in an intake gasket to.

 

I'm with Desertratrodder, I also think it might be a manifold leak of some type .Try spraying some starting fluid around the seal on that side between the head and intake with it running and see if it idles up. The bolts may be loose or the surface warped or both.

 

If you are running a dual plane intake, check the other cylinders that are on the same plane. Mine drove me ****ing nuts, and come to find out 1/2 my carb was dead. Slapped another carb on there and it run like it useta. I opened the choke and with the car running sprayed starting fluid down inside each side of the carb. It instantly came back to normal idle when I hit the correct one....Good luck....Fido

 

Ok guys i have sprayed starting fluid all around the entire intake, and it didnt change the idle at all, still running bad. I dont have another 4 bbl carb over here that i know is good, so what do you guys suggest? pulling the valve cover first then the intake? see what i find? or is there anything else i can check before tearing it apart...?thanks guys

 

5 and 7 crossed...like Marq says

 

My 283 was missing on one cylinder and I tried the usual stuff. Grounded the plugs and all seemed to have a good spark, but a mechanic friend suggested that the plug may not be firing under pressure, (I was skeptical but he knew cars inside out) so I replaced the plugs and it ran fine.

 

i have triple checked the plug firing order, and all the wires are run correctly, it seemed to run fine till i put my foot in it..i have also replaced the plugs, didnt change anything....?

 

i think you might have a blown head gasket.

 

i'm new to this site but not to cars(specially chevy's)
what kinda carb are you running? got an egr valve?

if it was me i'd run a leakdown test on those 2 cylinders.
that will absolutely tell you if there's a major problem on the inside of the motor...mel

 

Have you noticed any extra blowby?Did you check the oil for coolant,which would indicate a blown head gasket?I'm also begining to suspect that MSD setup.Do you have an HEI or even an old single point,that you can use temporarily to see if it improves the problem.Atleast then you can rule that **** out if it dont.

 

if the gasket is blown in the center of the cylinders then you might not notice oil/water transfer yet,and the cylinders will both have the same compression reading.
if it started right after you stomped on it i would bet that this is the problem.

 

i have also checked the oil, and it shows no water... and i dont have another distributer either, plus that would mean re wiring alot of stuff to get another one in there, it shocks the **** out of you if you pull it off a plug, thats why i dont think it is a distributer problem..