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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
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.
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
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).
Pulled the plug from the suspect cylinder, as you can see it's dry and sooty. Connected the wire with the plug out,grounded it while cranking and plug spark looks weak but it is present (yellow spark). What would be advisable at this point? How would you check the vacuum issue?
Jim
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?
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?
I would also pull the rest the plugs on that bank to be sure you have the right cylinder and to compare them to each other, also be sure to check the gap on each. Do you have an ohm meter? IMO an ohm meter is the best way check a plug wire. I've had brand new wires that showed continuity until I pulled on them or wiggled them. Almost always the bad spot was at the plug boot, or you could also try what Jeff suggested. As SDVette points out, I also think we need more info about your motor and ignition system. I think you should wait to check for vacuum leaks until you've gone through the electrical checks.
Last edited by Gary's '66; 07-06-2014 at 09:31 PM.
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.
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
A good plug wire should show about 3000-4000 ohms per foot (less is better); you have one at about 45,000 ohms, which is WAY out of whack.
A good plug wire should show about 3000-4000 ohms per foot (less is better); you have one at about 45,000 ohms, which is WAY out of whack.
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).
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.
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).
Thanks, Frankie, you remain a solid point of reason, especially for novices. .After switching plugs and wires, I find no significant differences in operating temps of the suspect exhaust tubes. I also have at least one other cylinder running at the same temp as suspect. I believe all the cylinders are working, just at various I levels because of everything Frankie said. Well, off to NAPA.
Thanks, all for the help.
Jim
You're going to NAPA to spend $100 and a whole afternoon swapping parts.
What is it you are trying to "fix"?
After considering the different scenarios, it appears a good tune up would rank reasonably high on the "risk-reward" scale. But just trying to make the best decision. What are you thinking?
Jim
07-05-2014, 07:47 PM
Exhaust manifold temps
I would also pull the rest the plugs on that bank to be sure you have the right cylinder and to compare them to each other, also be sure to check the gap on each. Do you have an ohm meter? IMO an ohm meter is the best way check a plug wire. I've had brand new wires that showed continuity until I pulled on them or wiggled them. Almost always the bad spot was at the plug boot, or you could also try what Jeff suggested. As SDVette points out, I also think we need more info about your motor and ignition system. I think you should wait to check for vacuum leaks until you've gone through the electrical checks.
