Ok here is the deal. SBC, with 3x2 Offy intake , Rochester 2g's , Pertronix Distributor, New wires, new plugs. 150# of compression in effected Cylinder. (#1) valve train appears to be working properly as i run this engine i took a heat gun and pointed it at each exhaust tube where it exits the head. #1 Cylinder registers really low on the exhaust gas temp..180 to 190 on a warmed up engine ( operating temp ) all the remaining Cyl. show an exhaust gas temp of 400 to 412..(all the other cyl. show relitvely the same temp give or take a 10 or 12 degree change) Well this leads me to believe #1 isnt firing. why? I have moved plugs around to check for a dead plug..nope not it. still need to completely rule out the spark plug wire, but i tried another one and it still did the same thing so i think its ruled out, not a plug wire. distributor is firing on that cyl. and i can see the rockers for that cyl doing their dance of intake and exhaust...so wtf gives? plugged intake runner???
What RPM? If it's at idle,raise the RPM and see if it changes. How does the plug look? Any possible coolent in the cylinder?
Same..dont matter.. Now i havent layed into it, (opened up the other 2 carbs they are in a progressive link) but taking the center carb to about 1/2 throttle and it doesnt change anything in that cyl. when something doesnt seem right i hate to rake on an engine unless she is living right , i have had bad things happen when rageing on an engine that is telling me somethings not right
what does the plug on that cylinder look like?? you get a nice blue spark on it?? what is the compression on the other cylinders?
the plug looks good, but of no sign of ignition, did a resistance test on the plugs , they are new, and all seem fine all the other cyl. are good comp...and are running fine its almost like theres no fuel to that cyl. or very little? Idk? still need to do more testing tonight it got late and i was tired of F-ing with it. looking for suggestions to check tonight, and if anyone has ever run into this I am taking some tools home to check valve lift and such on that cyl. tonight
no coolant..i can see its a dirty hole in other words, carbon and no loss of coolant I looked in the bore with a light and the top of the piston is typical with a bit of carbon
No , i plan on that tonight..I have a dial indicator i use at work, so its coming home with me tonight. with the naked eye, it seems they are moving as much as the others, but no definet measurement yet
Thats a good thought. Lots of older factory cams had #1 exhaust lobe issues. If RPM has no effect it should not be a Vacuum leak. Testing the Vacuum may also reveal something.
it would seem that they are moving enough (if not the same as the others) i would still get some ignition in that cyl.? 180 to 190 EGT..is dead...that is the engine temp. if any fuel was getting in there and being fired..it would have to be a bit higher than that? right?
Thanks i will definetly work on those two issues tonight. the vac for my pcv is on the back side base of the front carb. I dont think there are any leaks in the set up , but will check.. could only one cyl. be affected by a vac leak?
Depending on where it is and this being an outside cylinder it could but generally just raising the RPM just off idle should show a change. Good luck keep us up to date
First does the engine run properly?? or does it have a miss?? Which cyl is it?? OK this will involve a bit of work but should bring some things to light. Remove front carb Remove valve cover Remove plug Rotate engine until intake valve is open on malfunctioning cyclinder. Snake a piece of # 12 or 10 wire down the runner into the hole. You should be able to see the wire through the plug hole. If this works then the runner is open. You could pour some gas down the intake to make sure it gets to the hole. Take an extra plug and ground it to the block Fire that mother up and see if you are getting good spark.
A few other questions need answering: what lead you to begin testing for this condition; do you think that #1 was proper at some point recently; does the engine run as normal, but power is s bit low? These questions come to mind as well as a few others. A pic of the plug would help, but is it wet? Raw fuel kinda wet? Like maybe the front rochester is dumping raw fuel and washing the plug out? I havn't done the egt thing with a 3 X 2 motor but i'd expect the outboard cyls (1,2, 7 & 8) to be lean and likely hotter than the inboard - this is at idle only-because of the cenetr carb having the idle ckts and the shape of the plenum. If the front carb is dumping fuel (bad power valve gaskt etc where you can't see it) it may have washed out your rings in number 1 as well and account for the lower compression. I'm just making a swag here, a couple pics of that plug would sure help. Good luck, oj
I always do this when firing up a new engine to me..and i was testing a new coolant system on a new build, so the car or chassis in this case hasent been driven yet to see whatt or how it acts on the street. the plug isnt wet enough for the dump issue on the front carb. I dont think, but i will not rule it out yet is 150# low?
the plug looks like it just came out of the box..in a way it just did. it only has an hour or less of run time on it..it shows no combustion taking place in #1
it isnt noticeable when it is running..not popping, not back firing.. I havent done a full throttle check on it yet, and am not sure i want to in this condition. so its only running on the center carb. and i have opened it up as far as it would go on the center carb with out intoducing the other 2 carbs progressive link..center carb opens to almost 1/2 and than the front one comes in and when the front one is at almost 1/2 the rear one comes in progressively when the center carb is fully open all 3 are fully open...I havent pulled them all open yet, while running
No, 150# is not low if the other cylinders are reading the same. All cylinders should indicate a pressure reading that should not vary more than 10% from cylinder to cylinder.
i didnt think so ..i will be testing all 8 tonight to give me more of an idea if the others fall in line with #1
Ahh, all new. That explains a lot. New car/engine blues is what you're dealing with. Yes, in this case i'd say the 150# compression is significant. But then again, it hasn't been run and the machineshop may not have the rings & vavles seated/meted up as well as the others - check it again after a few hunderd miles, maybe a thousand. Being new and all i am thinking it is unrelated to the plug issue. The plug looking brand new can be from being washed out with either fuel or coolant - or it just isn't getting spark. I assume it is getting spark and firing because you must have had a timing light on that cyl to verify timing, right? Have you double check your header/gasket seal? If it isn't sealed good at #1 it'll suck air and the plug'll look stupid, run stupid and likely be egt stupid. Being all new, the problem is something simple. Something during assembly you hurried thru or left partial undone because more parts were coming etc. When you go back thru your basics you'l likely spot it.
Ok, go back to basics. You need spark, fuel, compression. You say you have spark. Verify it's not weak spark (Bad dist cap, wire, defective plug). Check fuel (vac leak on that intake leg,...). Check compression and valve sealing. Pressurized air into cylinder, valves closed, listen for air at exhaust and intake.
pertonix ..electric no points.. I will be going thru all the possibilities tonight..was hopeful some one on here ran into this before i will be making an air fitting for a test also
My 2 cents,I had a dead cylinder on my sbc.pulled my hair out for half a day,it was a vacuum leak on that runner.
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