Mechanic Needs Help With This One??

[62Cobra]

I have a 302 with a 600 cfm Holly vacuum secondarys, and a mallory dual point ignition and coil. OK No 1 cylinder is dead! Its getting spark, the new plug and wires are firing, The compression is a good 150psi, the valves are opening and closing like the rest of the engine. The mechanical timing and timing chain are perfect. The carb and distributer are fresh rebuilt and everything appears to be in proper order, except No. 1 is dead. No change in rpm when the wire is taken off the distributer. Any idea what to look for next....Ive been working on cars for along time and I have to admit Im stumped!!!!!! Any help would be appreciated! Oh yea! The car is a 289 Slabside Aurora 1982.

[Ben]

This may not sound logical, but in the past, on more than one occation I have hade spark plugs that fired outside the cyl. but when subject to the adverse condition of compression + fuel would not fire. and they were new out of the box. this could also go for the plug wire ( test with ohmeter ) very little resistance for it to be good. Just my .02. cheap to test. good luck!!

[niles]

If all your asumptions are correct; it has to be plug or wire.
All you need for firing is: fuel, spark and compression. compression you have verified, mechical/ timing etc has to be OK if the other 7 cyl are normal.
Put in new plug.
If still not firing; change plug wire with one of the neighbors and see if the miss moves with the wire.
good luck

gn

[mr0077]

62, if you've verified you get spark across the #1 plug gap while cranking, that means you have to change the engine...LOL
seriously, if you do havea healthy spark all the way to the PLUG GAP, either it isn't getting fuel (but how if it builds compression - not likely), the spark is off time (rotor?) or it is not firing under compression pressure maybe? Try another distributor cap and rotor, easy and cheap to eliminate those two...that's a wierd problem!

[SCOBRAC]

ditto.. change the plug and the wire.

[poorboy]

I would look for a vacuum leak between the intake and head. A leak there would allow the cylinder to draw in air to make compresson, but not draw in any fuel mixture.

Poorboy

[62Cobra]

Thanks for the input, I've replace the plug in the number 1 cylinder with a plug from another cylinder and then a new plug. Also same for the wire....Ive tried 3 seperate wires and still not a hint of life in number 1. I have verified the plug is sparking as it operates a timing light just fine and about put me on my ass as I removed the wire from the plug. I manualy rotated the engine to compression stroke to verify compression on No 1 lined up with the right spot on the distributer. Its a new cap and rotor. I even borrowed a buddies distributer to make sure that wasn't the poblem......Man-O-Man Im stumped on this one! Im thinking mixture in that cylinder is lean but don't know why....I have adjusted the accelerator pump arm and travel....Im reaching here!

(Grover...Thanks for the put...Jerry C. says your cobra looks real nice and I look forward to seeing it as soon as I get mine back on all eight)

[KobraKarl]

62,

Is your #1 plug wet with fuel when you pull it?

Is your only indication of a dead cylinder audible ? or does it register on your tach?

KK

[750hp]

Longshot - but you might have a faulty camshaft that has ground the #1 lobe off. This could still allow a healthy compression test as the valves would be seated in the head. It's not likely that this is the problem, but you could quickly and easily check by simply pulling the valve cover off and cranking the motor. If the rockers are moving, at least you've eliminated one more option....

[Cobra20646]

Kim,

Curious question.... After starting engine from cold condition, how does the header pipe from #1 cylinder heat up as compaired to the others? Put your hand on it to compair, don't need any fancy IR tester Does it get warm, hot, or stay relitively cool?

- Jim -

[mr0077]

I'm leaning toward Poorboy's idea of a manifold leak at/near the #1 runner. Try spraying WD40 around the intake gasket and see if there is a change. Another long shot, could the motor have swallowed something that is disrupting fuel (but not air?) to #1? How would you check THAT!? Maybe 750 is on to it, check the rocker movements on #1 and #2 with a dial indicator, maybe a lobe has gone, but not completely. Let us know, interesting (frustrating) problem.

[trularin]

With the engine running, can you use some sort of thermal meassuring device to check if # 1 is hot at the header. A thermal imaging camera would be perfect. You may be able to just grabb the header pipe ( not after it has been running ).

With the engine running, take a can of carb cleaner and spray around the intake of # 1. If the Rs go up, you have an intake leak and will look like a dead cylinder.

Stupid as this sounds, I got a car in once that had two dead cylinders. Ended up disassembling the top end to find a rag in the intake manifold. I talked to the guy and he said his sons were "helping" clean the engine as dad was putting it back together.

Set the idle down to limp the engine. It will sound like it is going to stall at any minute. Then pull the plug wire. If # 1 is adding anything to the engine, it should die or at least sputter.

Read the plug. if it is burning fuel, it will have some deposits. You may want to force an issue but sraying WD40 down the carb.

Hope this helps.

Trularin

[trularin]

Is this a recent rebuild you are trying to get running?

Stupid as this sounds, are all the lifters in the engine?

Is it a hydraulic cam?

Is the valve train complete?

Take the rocker cover off and watch the valve train work.

Hope this helps.

Trularin

[boxhead]

Has this engine been running ok in the past and just started to play up?
A little previous history could help eliminate a few possabilties, (or open a heap of new ones).
Does the car miss when under load?
Are the plug gaps correct? I have seen engines with new plugs but wrong gap that missed only at idle.
The gaps i have found wrong have been too small.
I have also seen intake gaskets break away and end up inside the intake partially blocking intake runner.
Do as Craig (750hp) says and check the valves move when turning engine over by hand (worn lobe)
Move number 1 plug into another cylinder, does fault go with the plug to the new cylinder?
Let me know a bit of history on the engine.
Keep us informed

[frankym]

if this is a customer's car, was there a loud noise heard before the other symptoms surfaced? Could a single connecting rod have snapped? I would think it would continue to make a lot of noise while engine is running, but if it broke from the crank end, and the piston was near the top of the stroke, could it be that when the plug is removed, and a long screwdriver is inserted, the position of the piston is unchanged at sitting at the top after running? If the piston is moving with the rest of the crank, and the valves are all opening and closing, sounds like there's still some missing information about what happened prior to noticing the current problem.

[mr0077]

bent pushrod?

[KobraKarl]

yea, I like bent p- rod.
KK

[Junket]

Have you run a leak down test yet this could turn you in the correct direction ???
Ken

[tommyboy]

You need to rely on your basic mechanical skills ! If you can not easily find the problem, then go through each system of the engine and prove the system is working as designed then move on to the next system! Note the differences, what changes occur between a static and dynamic engine i.e. temperature, air flow, vacuum, cylinder pressures, timing, etc. Check the easiest systems/circuits first, prove them good, write everything down and move to the next system. A single carb application is common to all cylinders so carb problems should not affect only cyl #1. Primary and secondary ignition circuits seem in order. Timing also seems in order. Make sure you have checked every aspect of the engines mechanical integrity thoroughly! Prove it correct! If cylinder #1 is the only dead cylinder then check every component involved that would cause a problem with cylinder #1. A compression and cylinder leakage test along with a visual of the rocker arms should check the mechanical integrity of components for cylinder #1. While performing a cylinder leakage test rotate the crankshaft through one or two complete cycles and note the rate of leakage and sounds coming out from the carb, crankcase and exhaust. Make sure the spark plug is properly positioned in the cylinder head (depth) and in fact is the correct spark plug for that particular head. Make sure there is no airflow restriction from the carb all the way into the cylinder and out of the exhaust system wher they all become common again. Use your vacuum gauge!! Just make sure you can prove each system, cicuit and or component good before you move on. Good luck!! Let us know what you find.

[Monster]

I agree with many of the previous posts. Its possible that the intake valve is not opening. Remove the valve cover and verify that the valves are opening and you have proper lash. As you know you need fuel and fire. It sounds like you have fire so I would look to fuel (no intake= no fuel for #1).

Valve train possibilities: incorrect lash, bent pushrod, bad lifter, bad cam, broken/bent valve stem (unlikely), faulty rocker (cracked or in the case of roller missing/broken roller assy)

good luck,
Mike "monster"