Exhaust manifold temps
#1
Racer
Thread Starter
Exhaust manifold temps
I'm learning every time I try to work on my car and you guys on the forum have been a great help, thanks. My new issue is way above my knowledge base. A significant difference in cylinder exhaust header temps.
While checking the accuracy of my temp gauge, I happened to check the temps of each of my cylinder exhaust manifolds. All but one read 550* + or - 30* or so. However, the second cylinder from the front on the passenger side read 335*. The cylinder must not be firing. Where do I begin my search and how would I diagnose the problem?
Jim
'62, 327/340
While checking the accuracy of my temp gauge, I happened to check the temps of each of my cylinder exhaust manifolds. All but one read 550* + or - 30* or so. However, the second cylinder from the front on the passenger side read 335*. The cylinder must not be firing. Where do I begin my search and how would I diagnose the problem?
Jim
'62, 327/340
#2
Melting Slicks
First pull the spark plug to see if it's sooty or oily. If oily it could be just a bad plug or wire or both. If you have another plug try it. If sooty it could be vac leak or carb related. You can also trace the plug wire back to the distributor cap and, with the car running, pull the wire out of the cap and hold it just above it's hole (carefully or you'll get shocked) to see if you have spark. Worse case scenario, a dead hole (valves).
Last edited by Gary's '66; 07-05-2014 at 08:30 PM.
#4
Burning Brakes
I'm learning every time I try to work on my car and you guys on the forum have been a great help, thanks. My new issue is way above my knowledge base. A significant difference in cylinder exhaust header temps.
While checking the accuracy of my temp gauge, I happened to check the temps of each of my cylinder exhaust manifolds. All but one read 550* + or - 30* or so. However, the second cylinder from the front on the passenger side read 335*. The cylinder must not be firing. Where do I begin my search and how would I diagnose the problem?
Jim
'62, 327/340
While checking the accuracy of my temp gauge, I happened to check the temps of each of my cylinder exhaust manifolds. All but one read 550* + or - 30* or so. However, the second cylinder from the front on the passenger side read 335*. The cylinder must not be firing. Where do I begin my search and how would I diagnose the problem?
Jim
'62, 327/340
#5
Racer
Thread Starter
First pull the spark plug to see if it's sooty or oily. If oily it could be just a bad plug or wire or both. If you have another plug try it. If sooty it could be vac leak or carb related. You can also trace the plug wire back to the distributor cap and,
[IMG]https://cimg2.ibsrv.net/gimg/www.corvetteforum.com-vbulletin/434x504/80-
with the car running, pull the wire out of the cap and hold it just above it's hole (carefully or you'll get shocked) to see if you have spark. Worse case scenario, a dead hole (valves).
[IMG]https://cimg2.ibsrv.net/gimg/www.corvetteforum.com-vbulletin/434x504/80-
with the car running, pull the wire out of the cap and hold it just above it's hole (carefully or you'll get shocked) to see if you have spark. Worse case scenario, a dead hole (valves).
Jim
#6
Race Director
A dry plug is a good sign, although a little unexpected. I think I would try a new wire or set of wires. Probably check the inside of the distribuor cap also to see if there is any sign of carbon tracking on the electrode for that cylinder. Does the engine idle and run smoothly?
#8
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Are you running a traditional (points) ignition?
If yes, how long since you checked timing and dwell?
How old are the plugs/wires?
If yes, how long since you checked timing and dwell?
How old are the plugs/wires?
#9
Melting Slicks
A dry plug is a good sign, although a little unexpected. I think I would try a new wire or set of wires. Probably check the inside of the distribuor cap also to see if there is any sign of carbon tracking on the electrode for that cylinder. Does the engine idle and run smoothly?
Last edited by Gary's '66; 07-06-2014 at 09:31 PM.
#10
Racer
Thread Starter
Thanks, guys. Distributor is points type. Plugs are old, wires appear to be newer, as does the cap. Visual inspection of points, cap contacts look good. I've owned the car for a year. Car starts without hesitation and runs strong. I've included pics of the ohm readings of the suspect cylinder wire and a known good wire. There is a significant difference but not sure what the readings indicate. (Spark plug continuity/resistance checked out well)
Jim
Suspect cylinder wire
Known good wire, sorry for the orientation of the image.
Jim
Suspect cylinder wire
Known good wire, sorry for the orientation of the image.
#11
Team Owner
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Thanks, guys. Distributor is points type. Plugs are old, wires appear to be newer, as does the cap. Visual inspection of points, cap contacts look good. I've owned the car for a year. Car starts without hesitation and runs strong. I've included pics of the ohm readings of the suspect cylinder wire and a known good wire. There is a significant difference but not sure what the readings indicate. (Spark plug continuity/resistance checked out well)
Jim
Jim
#12
Racer
Thread Starter
Man, I'm confused now. The good cylinder is showing a suspect wire and the bad cylinder is showing a good wire. I am going to switch the plugs and wires (working cylinder with non-working to see if problem follows the plug and wire).
#13
Team Owner
Why don't you do a basic tune up and replace all that dicey/old stuff ? Plug wires can have intermittent resistance problems or only break down under load or cross-fire if the insulation is shot. You obviously have a subtle problem like this or you'd feel a dead miss in the motor instead of needing exhaust temps to find it. If so, swapping wires around that might work in one instance and not in another is gonna confuse the snot out of you.
New cap/rotor/points-condensor/plug wires/plugs is pretty basic service routine....and I bet your problem mysteriously disappears.
New cap/rotor/points-condensor/plug wires/plugs is pretty basic service routine....and I bet your problem mysteriously disappears.
#14
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If you're convinced the temp reading was accurate on that cylinder, I'd start out with a vacuum gauge check and see if intake vacuum is steady or not.
#15
Racer
Thread Starter
Thanks, all for the help.
Jim
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#17
Racer
Thread Starter
Jim
#19
Racer
Thread Starter
#20
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You must have missed post #14.
You also said it started quickly and ran strong.
Your spark plug isn't fouled so it's firing.
You might try adjusting the idle mixture on the carb. You might have a compression problem. You might be taking bad readings
Then again, your tuneup may fix something. I wish you well.
If the engine wasn't misfiring, I'd leave the hood shut and go for a ride.
You also said it started quickly and ran strong.
Your spark plug isn't fouled so it's firing.
You might try adjusting the idle mixture on the carb. You might have a compression problem. You might be taking bad readings
Then again, your tuneup may fix something. I wish you well.
If the engine wasn't misfiring, I'd leave the hood shut and go for a ride.