Possibly not running on all 6 cylinders. Will a temperature reading work? (Page 1/6)
Cliff Pennock MAR 19, 11:56 AM
I suspect my Fiero is running on 5 cylinders. This due to the fact it feels like it's missing power and because of the sound the engine makes. What's an easy way to check? I was thinking of measuring the temperature of the exhaust header near each cylinder. But since they really all share the same pipe I'm not sure this trick will even work on a Fiero. Anyone ever tried it?
Raydar MAR 19, 12:43 PM
I have used a laser thermometer to do this. It should work. It may not be exact, but you should be able to identify the "dead" cylinder.
Or start it up in the dark, and have a look. Fiero manifolds - even in a properly running engine - will glow just a bit. Might need to rev it up a little, and hold it at a faster idle.
1985 Fiero GT MAR 19, 01:20 PM
Also theoretically you could try removing spark plug wires/fuel injectors, to pinpoint it, I've never tried this and don't know whether it would work at all, so let some other people say whether this would help before doing it, but you could unplug the fuse for one bank of injectors, then unplug 1 spark plug wire at a time, listening for a change in sound, if the sound changes/engine stalls, that cylinder works, move on to the next one, once one bank is checked, replace that fuse and take out the other to check the other bank, 1 plug at a time, a dead cylinder for whatever reason should make no sound/power difference when the spark plug is unplugged, all other cylinders should bog the engine down some when removed. Like I said this is all speculative.
Vintage-Nut MAR 19, 04:47 PM
"Possibly not running on all 6 cylinders"

Then Check the Engine's Cylinder Compression


"If your vehicle has been running roughly or losing power, there may be a lack of pressure in one or more cylinders. To determine whether pressure is escaping from the engine, you need to check the compression in the cylinders with a compression gauge, which measures the amount of pressure that the piston exerts on the fuel/air mixture before the spark plug fires the mixture. These gauges don’t cost much, and they’re easy to use. Some gauges screw into the spark plug opening, and others have to be held in place."

*Run the engine until it reaches normal working temperature, then remove all the spark plugs and coil lead to avoid possible sparking at the plug caps.

*Ask a helper to press the accelerator pedal to open the throttle fully and turn the ignition switch to crank the starter.

*Tell your helper to crank the engine for at least ten revolutions, or about six to eight seconds.

*Note the pressure, and how many revolutions it took on a chart. Then test all the other cylinders, in the same way, noting the reading after the same number of turns.

The figures should be within 10 per cent of each other.......

EDIT
If you found that one cylinder is 'dead' - my guess is a valve; my 'dead' cylinder was #6 exhaust.

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 03-19-2024).]

Stingray92 MAR 19, 05:19 PM
If you can get your hands on a thermal imager you'll see it pretty easy. Other options include IR gun, thermocouple, or spray some water on the exhaust before you start it up.
Patrick MAR 19, 06:04 PM

quote
Originally posted by 1985 Fiero GT:

Also theoretically you could try removing spark plug wires/fuel injectors, to pinpoint it, I've never tried this and don't know whether it would work at all, so let some other people say whether this would help before doing it...



You're on the right track, but never ever pull a spark plug wire and run the engine... without grounding the disconnected wire! Those thousands of volts want to go somewhere, and if it can't get to ground through the end of the wire/sparkplug, it'll instead try and find a path to ground within the ignition coil. Needless to say, this is not good for the coil!
1985 Fiero GT MAR 19, 07:45 PM

quote
Originally posted by Patrick:

You're on the right track, but never ever pull a spark plug wire and run the engine... without grounding the disconnected wire! Those thousands of volts want to go somewhere, and if it can't get to ground through the end of the wire/sparkplug, it'll instead try and find a path to ground within the ignition coil. Needless to say, this is not good for the coil!



Makes sense, good that my rambling wasn't entirely wrong haha!
pmbrunelle MAR 19, 10:08 PM

quote
Originally posted by Patrick:

You're on the right track, but never ever pull a spark plug wire and run the engine... without grounding the disconnected wire! Those thousands of volts want to go somewhere, and if it can't get to ground through the end of the wire/sparkplug, it'll instead try and find a path to ground within the ignition coil. Needless to say, this is not good for the coil!



I've had that current find its way to ground via my hand.

Not recommended / 10.

Generally comparable to a 120 VAC / 60 Hz shock, but perhaps more of a sharp piercing pain.

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That coil current, if it can't jump the spark plug gap, can also try to jump across the ignition points, or (if electronic ignition) zap the ignition module.

********************************************************************************

Clamping a timing light on each wire is a way to know if there is a spark to each cylinder.

[This message has been edited by pmbrunelle (edited 03-19-2024).]

Patrick MAR 20, 02:53 AM

quote
Originally posted by pmbrunelle:

I've had that current find its way to ground via my hand.



My introduction to 25,000 volts occurred in shop class about 1969. I was learning how to use the spark plug tester, and I figured if I held the insulated porcelain part of the plug with my fingers, that I'd be safe from any current. Hey, I was only about 13 years old. I soon learned that 25,000 volts can easily jump a half inch or so! It felt like my hand had been grabbed by the jaws of Godzilla.

theogre MAR 20, 07:49 AM

quote
Originally posted by 1985 Fiero GT:
Also theoretically you could try removing spark plug wires/fuel injectors, to pinpoint it, I've never tried this and don't know whether it would work at all, so let some other people say whether this would help before doing it, but you could unplug the fuse for one bank of injectors, then unplug 1 spark plug wire at a time, listening for a change in sound, if the sound changes/engine stalls, that cylinder works, move on to the next one, once one bank is checked, replace that fuse and take out the other to check the other bank, 1 plug at a time, a dead cylinder for whatever reason should make no sound/power difference when the spark plug is unplugged, all other cylinders should bog the engine down some when removed. Like I said this is all speculative.

While this test may help finding what cyl is "dead," this can Cause Really Dead Ignition parts because many just pulls a plug wire to each cyl.

HEI Hate this, DIS even more so & could hurt/kill you more too. Other Vehicles/Equipment also Hates this. Fry the I-coil ICM &/or many other Ignition parts.

You need to stop the engine & plug in a spark tester that doesn't need a spark plug in series then start or try to start w/ disable cyl, repeat until finding.
Example:

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave