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914World.com _ 914World Garage _ Anyone try this trick?
Posted by: pbanders Jan 4 2010, 11:19 AM
Saw a trick on "Motor Trend TV" the other day, I'm sure experienced mechanics know this one. To detect which cyclinder has a miss, you take a $30 infrared thermometer and aim it at each cylinder's exhaust manifold. The cold one is the cylinder with the miss. Obviously, not so easy to do on a 914 
, but still a good trick. Add in a noid light and a neon spark feeler, and you can diagnose a miss problem pronto.
Posted by: Vacca Rabite Jan 4 2010, 11:26 AM
Don't even need a IR thermometer.
Just reach under the car and feel. You do not have to touch the pipes. One will be radiating heat, the other will not.
Zach
Posted by: ME733 Jan 4 2010, 11:28 AM
![popcorn[1].gif](style_emoticons/default/popcorn[1].gif)
another way for those of us without an infrared gun ...is to spray water on the exhaust system. An absolutely dead cylinder will not boil off the water at all. a miss firing cylinder does so much slower than a properly firing cylinder.... Murray
Posted by: charliew Jan 4 2010, 11:45 AM
Both above very good techniques. At idle it's easy. I learned when I was just starting car stuff to just pull each plug wire and see how the motor reacted at the dist cap. You can also check the spark by putting the timing light on each plug wire. Unfortunately under a load is harder but after it gets worse it will be obvious at idle. I once completely rebuilt a holley on a sbc for a low speed miss only to find a high output aftermarket coil had turned the coil wire to dust inside the dist cap from arching. Thats when I decided to go to the gm hei. The boot and wire insulation was all that was left when I pulled it out of the cap. When my friend raced a t1 he built some gm hei dist.s for his motors.
Posted by: ClayPerrine Jan 4 2010, 12:14 PM
Take a standard, ordinary 12v test light. Hook the gator clip to ground. With the engine running, slip the tip of the test light down the spark plug wire boot at the distributor. It will kill that cylinder. If no engine speed drop, then that is the dead hole.
I have been doing this on MFI cars for years.
Posted by: markb Jan 4 2010, 01:57 PM
Take a standard, ordinary 12v test light. Hook the gator clip to ground. With the engine running, slip the tip of the test light down the spark plug wire boot at the distributor. It will kill that cylinder. If no engine speed drop, then that is the dead hole.
I have been doing this on MFI cars for years.
Now that is too slick!
Posted by: pbanders Jan 4 2010, 03:18 PM
Take a standard, ordinary 12v test light. Hook the gator clip to ground. With the engine running, slip the tip of the test light down the spark plug wire boot at the distributor. It will kill that cylinder. If no engine speed drop, then that is the dead hole.
I have been doing this on MFI cars for years.
Sweet. All the other tips are great. So, how come so many people here can't figure out their miss?
Posted by: J P Stein Jan 4 2010, 06:52 PM
I simply pull (& replace ) plug wires on a running engine till I find the one that is not firing. I can find the culprit in a minute or so on my motor. Don't try this, children, without having your plug wires in top notch shape at all times. Given the opportunity, electricty will go to ground thru you. 
This is pretty basic stuff. I has a dead hole in the 2006 Parade staging lanes.
Had a new plug gapped & in & the motor back to a purr in about 3-4 minures. Had it been a plugged idle jet, it would have taken another couple minutes. A Porsche guru (a real one) was watching this opperation. He said "why are you using a BP7 rather than a BP6?" "It runs better on 7s" says I....while screwing in the plug.
Posted by: rick 918-S Jan 4 2010, 07:09 PM
All good ideas, just don't use a chopstick to find top dead center.... 
Posted by: Al Meredith Jan 4 2010, 07:21 PM
I once used the heat gun method on a 4 cyl motorcycle where all 4 pipes came forward. you could tell which ones were lean or rich.
Posted by: Rand Jan 4 2010, 07:42 PM
All good ideas, just don't use a chopstick to find top dead center....
In this case, you hold the chopstick against each cylinder's exhaust pipe for several seconds. Watch for a wisp of smoke. The one that doesn't turn the stick black is dead.
Posted by: Eric_Shea Jan 4 2010, 07:46 PM
Does it work on non-MFI cars?
Posted by: ClayPerrine Jan 4 2010, 10:50 PM
Does it work on non-MFI cars?
Yes.
.. it kills the ignition. With MFI, you can't kill the fuel to one cylinder like on an electronic injection, so you have to kill ignition.
Posted by: championgt1 Jan 4 2010, 11:16 PM
All good ideas, just don't use a chopstick to find top dead center....
Posted by: 9146986 Jan 5 2010, 07:31 AM
I use the same method as JP.
After tuning carbs I connect an off board tach and one by one pull each plug wire. If the RPM's drop the same amount for each cylinder the carbs are tuned very close.
Posted by: pbanders Jan 5 2010, 11:25 AM
Pulling plug wires gets dead cylinders for sure. But what about an intermittant miss? Seems like the temp gun method would be able to detect even a very infrequent miss. Or perhaps the tach drop method Perry described.
Posted by: ME733 Jan 5 2010, 11:36 AM
I simply pull (& replace ) plug wires on a running engine till I find the one that is not firing. I can find the culprit in a minute or so on my motor. Don't try this, children, without having your plug wires in top notch shape at all times. Given the opportunity, electricty will go to ground thru you.
This is pretty basic stuff. I has a dead hole in the 2006 Parade staging lanes.
Had a new plug gapped & in & the motor back to a purr in about 3-4 minures. Had it been a plugged idle jet, it would have taken another couple minutes. A Porsche guru (a real one) was watching this opperation. He said "why are you using a BP7 rather than a BP6?" "It runs better on 7s" says I....while screwing in the plug.
Look J P...with deference to all your experience, and knowledge, I would like to say the following: DO NOT USE THIS TECHNIQUE (above) if you are using a high output MSD, or similar output ignition system. there is enough voltage and amperage to stop your heart. Certainly enough to have you swearing awhile, and I promise that when you do ground yourself you won"t try this technique again. murray
Posted by: 9146986 Jan 5 2010, 12:11 PM
Good point Murray! I ALWAYS use insulated pliers for this!!
Posted by: J P Stein Jan 5 2010, 12:12 PM
I simply pull (& replace ) plug wires on a running engine till I find the one that is not firing. I can find the culprit in a minute or so on my motor. Don't try this, children, without having your plug wires in top notch shape at all times. Given the opportunity, electricty will go to ground thru you.
This is pretty basic stuff. I has a dead hole in the 2006 Parade staging lanes.
Had a new plug gapped & in & the motor back to a purr in about 3-4 minures. Had it been a plugged idle jet, it would have taken another couple minutes. A Porsche guru (a real one) was watching this opperation. He said "why are you using a BP7 rather than a BP6?" "It runs better on 7s" says I....while screwing in the plug.
Look J P...with deference to all your experience, and knowledge, I would like to say the following: DO NOT USE THIS TECHNIQUE (above) if you are using a high output MSD, or similar output ignition system. there is enough voltage and amperage to stop your heart. Certainly enough to have you swearing awhile, and I promise that when you do ground yourself you won"t try this technique again. murrayI do have an MSD 6al. I do have 8.5mm Magnecore wires. I have gotten nialed on other guys cars. I keep nice thick insulated leather gloves around for them....it does get your attention. I am aware of the danger, thus the caution in my post. If ya get nailed it's time for new wires.
We're both old guys, right?.....you can tell me, you've gone thru life never doing anything remotely dangerous, eh?
Posted by: 6freak Jan 5 2010, 01:37 PM
I simply pull (& replace ) plug wires on a running engine till I find the one that is not firing. I can find the culprit in a minute or so on my motor. Don't try this, children, without having your plug wires in top notch shape at all times. Given the opportunity, electricty will go to ground thru you.
This is pretty basic stuff. I has a dead hole in the 2006 Parade staging lanes.
Had a new plug gapped & in & the motor back to a purr in about 3-4 minures. Had it been a plugged idle jet, it would have taken another couple minutes. A Porsche guru (a real one) was watching this opperation. He said "why are you using a BP7 rather than a BP6?" "It runs better on 7s" says I....while screwing in the plug.
Look J P...with deference to all your experience, and knowledge, I would like to say the following: DO NOT USE THIS TECHNIQUE (above) if you are using a high output MSD, or similar output ignition system. there is enough voltage and amperage to stop your heart. Certainly enough to have you swearing awhile, and I promise that when you do ground yourself you won"t try this technique again. murrayWell if it killed you you would be doeing something you like and not at the hand of some nut ball murderer or some sickness
...P.S you can detect bad wires in the dark ..pretty little blue spark
Posted by: ClayPerrine Jan 5 2010, 01:40 PM
...P.S you can detect bad wires in the dark ..pretty little blue spark
Why don't you just stand on the rear deck lid in bare feet and pee on the distributor?
Posted by: SLITS Jan 5 2010, 01:47 PM
...P.S you can detect bad wires in the dark ..pretty little blue spark
Why don't you just stand on the rear deck lid in bare feet and pee on the distributor?
Obviously a short Tejan style diagnostic tool. I just stand beside the car and pee on the dizzy ... I am tall enough to do that.
Posted by: Sleepin Jan 5 2010, 01:50 PM
I am tall enough to do that.
But not much else!
Posted by: 6freak Jan 5 2010, 01:51 PM
cause i dont want foot prints on it That would require more polishing it took me 2 hours to get my wifes ass print off the rear deck lid
Posted by: Sleepin Jan 5 2010, 01:54 PM
cause i dont want foot prints on it
That would require more polishing it took me 2 hours to get my wifes ass print off the rear deck lid Must......bite......lip.......can't....say...it...!!!
![yellowsleep[1].gif](style_emoticons/default/yellowsleep[1].gif)
Posted by: 6freak Jan 5 2010, 02:03 PM
no its not that big 
but shes not super model skinny either
Posted by: Sleepin Jan 5 2010, 02:08 PM
No, I was going to say that it only took me 15 minutes to get her ass print off of my car!
Posted by: 6freak Jan 5 2010, 03:31 PM
No, I was going to say that it only took me 15 minutes to get her ass print off of my car!
I dont use a buffer.......LMAO
Posted by: ClayPerrine Jan 5 2010, 03:35 PM
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