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?
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.
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.
"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.
------------------ Original Owner of a Silver '88 GT Under 'Production Refurbishment' @ 136k Miles
[This message has been edited by Vintage-Nut (edited 03-19-2024).]
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.
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!
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!
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.
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.
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.
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:
------------------ 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)
A safer way to check if a cyclinder is dead is to take a water dropper and drop a few droplets on each manifold near the ports. The one that doesnt boil instantaneously is dead
I have a plastic spark plug wire puller. I do it all the time while it is running. If you pull a wire and the engine does not change RPM, you found the bad one.
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.
Will one of these work? (and test it at the distributor cap, not the spark plug)
Will one of these work? (and test it at the distributor cap, not the spark plug)
Only if you ground it to the block, and not connect it to the spark plug cable. Remember, you're purposely trying to prevent the spark plug in the tested cylinder from firing.
But but but if I put it between the distributor and the spark plug (cable), the "light" inside the tester only lights up when the spark plug fires, doesn't it?
Cliff, I don't think you're quite grasping the point of disconnecting the spark plug lead from one spark plug at a time. You don't want the spark plug firing!
[This message has been edited by Patrick (edited 03-22-2024).]
I'm trying to find out if one of the spark plugs isn't firing (and if so, which). Pulling spark plug cables is one way of doing it. But I tried that once and even though I was wearing rubber gloves, got shocked pretty bad. Not doing that again. Another way of doing it is using a spark plug tester. If the spark plug fires, I will see it in the tester.
Originally posted by Cliff Pennock: But I tried that once and even though I was wearing rubber gloves, got shocked pretty bad. Not doing that again.
Ya big baby. It's only 40,000 volts.
You can have the plug spark, but the cylinder could still not fire because of a fuel injector, or lack of compression, or the plug could be shorted with a buildup of carbon.
Google "plastic spark plug pliers" See if anything comes up locally for you. They're cheap.
I guess even metal plyers with a wire connected to it and then attached to metal on the engine would work too. (very small probability that you would be the path of least resistance, but I'm not making any promises)
[This message has been edited by buddycraigg (edited 03-22-2024).]
Attach a copper wire (ie 2 ft length of house wiring) at one end to the block, and the other end to the metal shaft of a screwdriver with a plastic handle. With all six of the rubber boots (one for each cylinder) pulled up clear of the distributor, stick the tip of the screwdriver into the top of each spark plug wire tower on the distributor cap while the engine is running. The high voltage will want to find the path of least resistance to ground, and that'll be to the metal tip of the screwdriver and then down the wire to the block. Just make sure to hold the end of handle farthest away from the metal shaft. Easy peasy. No pulling of spark plug wires is required, and no chance of frying the coil.
[This message has been edited by Patrick (edited 03-22-2024).]
Playing around with electricity is no joke! If you're gonna try visual spark check method at least ensure you got some decent insulating device between you and the plug. As the starting part of thus thread stated you believe that not all cylinders are firing, aka you need to look for hot exhaust at the manifold port. The exhaust manifold will get very warm quickly upon start/running. Could be bad fuel injector, fouled plug, etc. How you choose to verify what your engine is doing from here is up to you.
So if I understand correctly, you want me to in fact short the outputs of the distributor to ground one by one. If the RPM goes down, that plug has spark. If the RPM doesn't go down, that plug doesn't spark.
So if I understand correctly, you want me to in fact short the outputs of the distributor to ground one by one.
Correct.
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Originally posted by Cliff Pennock:
If the RPM goes down, that plug has spark. If the RPM doesn't go down, that plug doesn't spark.
You're still not quite getting it. Buddy understands...
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Originally posted by buddycraigg:
You can have the plug spark, but the cylinder could still not fire because of a fuel injector, or lack of compression, or the plug could be shorted with a buildup of carbon.
Cliff, you're just trying to find which cylinder isn't working... whether that be due to lack of spark, carboned up plug, no compression and/or no fuel. When you short out the spark to a cylinder and it makes no difference with the RPM, then you need to figure out what the problem is with that cylinder. Right now, you're just trying to find which one (or more) it is!
[This message has been edited by Patrick (edited 03-22-2024).]
You're still not quite getting it. Buddy understands...
No, I understand quite well. I think you're not understanding what it is I'm trying to do. I'm trying to find out if the engine is running on all 6 or not. Nothing more, nothing less. That's the first thing I want to know. And the test you described will tell me that. For now, I don't care (yet) what the possible cause could be if the engine isn't running on all 6. Like I said, I first need to know if the apparent drop in performance and the sound the engine makes is indeed caused by the engine not running on all six cylinders.
So in short, I'm not trying to find out if a plug sparks (because like you both said yourself, that is no guarantee the cylinder fires), I'm trying to shut off one cylinder at a time while the engine is running to easily hear if it makes a difference or not. So engine running, I short one of the cables. RPM drops, then that cylinders is firing. If it doesn't drop, then I have found the problem cylinder. I can then troubleshoot what actually is wrong (spark plug, injector, compression, etc).
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Cliff, you're just trying to find which cylinder isn't working... whether that be due to lack of spark, carboned up plug, no compression and/or no fuel. When you short out the spark to a cylinder and it makes no difference with the RPM, then you need to figure out what the problem is with that cylinder. Right now, you're just trying to find which one (or more) it is!
Exactly. That's why I initially asked if taking a temperature reading works. The spark tester was just an inquiry if these things actually work (in case I do find a non working cylinder, so I can rule out a spark plug problem) since I read many contradicting reviews. Some say they don't work at all, others say they work perfectly.
So I'm guessing because of this second discussion about spark testers (which is really a reply to TheOgre's advise that if I want to test spark, I need one of these), you are under the (false) impression I only want to know if a cylinder sparks or not.
Oh for fuksakes don't be a pussy, your not gonna fry the coil or anything. this is a 80's GM Do or die ignition system. put a heavy glove on, welding gloves work great. pull a wire off the Distributor with it running , when you did all 6, the one that did not make it worse, there is where you look..................
Everyone is replying like this is something exotic and Spooky, NO it's GM. pull a damn wire and see what happens.
[This message has been edited by jelly2m8 (edited 03-23-2024).]
I'm waiting with bated breath, to hear what you find out.
BUT... I have a story.
I had a V6 car, 85 maybe 86 Very underpowered, bur still seemed to run *smooth* by my opinion. one of the fuel injector fuses was blown. 1,3,5, and 2,4,6 are on separate circuits.
It mystified me that I couldn't feel a misfire. The 2.8 is just so perfectly balanced.
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Originally posted by Cliff Pennock: So I'm guessing because of this second discussion about spark testers (which is really a reply to TheOgre's advise that if I want to test spark, I need one of these), you are under the (false) impression I only want to know if a cylinder sparks or not.
The spark tester thingies really only give you 1/3 of the story. and are almost useless. I would GIVE you the ones I have, but would cost more in shipping than what they are worth.
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Originally posted by jelly2m8: Oh for fuksakes ....
I don't know that I can put it as eloquent as you. But you are right. The GM HEI system would make Storm from the X-MEN proud.
[This message has been edited by buddycraigg (edited 03-23-2024).]
The spark tester thingies really only give you 1/3 of the story. and are almost useless.
Yes, but it's 1/3 of the story I would like to rule out if it turns out one of the cylinders is out.
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I would GIVE you the ones I have, but would cost more in shipping than what they are worth.
I already bought one. In fact, I bought the one from the picture.
If I had a garage, I would have taken the thing apart long time ago and fixed every damn issue the car has. But I don't and I need to work outside on a public street. Also, this is The Netherlands. Meaning this time of year, it rains, it's cold and it storms. As in every freakin' day. I've been able to do one hour of troubleshooting this year so far since that was the only time it was actually not raining and/or "warm" enough to not freeze my nuts off.
Originally posted by Cliff Pennock: Will one of these work? (and test it at the distributor cap, not the spark plug)
CLICK FOR FULL SIZE
No. & often not even if you but the end direct to ground as often the bulb would fail because make to have a plug in series.
Is made to see if HV side sends power to a plug in the first place like trying to see if coil(s) etc works and still runs the plug in series. This maybe you problem & need new spark plugs, plug wires or cap/rotor set but often will "blow" the bulb etc if you try direct ground test try to find a "dead" cyl.
If have old spark plug... cut/break the ground electrode & clamp the metal body to the engine. Not as good as above Examples but should help short term.
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Originally posted by buddycraigg: I have a plastic spark plug wire puller. I do it all the time while it is running. If you pull a wire and the engine does not change RPM, you found the bad one.
Do whatever you want but Every time you to this to HEI and others... High Volt side will find another path to ground farther upstream & often damage HEI or DIS coils & more but damage may not be seen right then. HV/Secondary Can: (Not limited to these...) Jump secondary to primary in the coil. Burn the ICM because of above. Start at minimum Carbon Tracking in/on Dist Cap or Rotor.
[This message has been edited by theogre (edited 03-23-2024).]
...you are under the (false) impression I only want to know if a cylinder sparks or not.
No, I was correcting/clarifying your following comment.
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Originally posted by Cliff Pennock:
If the RPM goes down, that plug has spark. If the RPM doesn't go down, that plug doesn't spark.
If the cylinder has spark (and a good spark plug), but no compression and/or no fuel, that would also cause the RPM not to go down if you ground the spark.
Anyway, I realize you're getting somewhat conflicting advice from all sides. I'll just say that the procedure I outlined is a helluva lot easier than pulling individual spark plug wires from all six plugs.
If the cylinder has spark (and a good spark plug), but no compression and/or no fuel, that would also cause the RPM not to go down if you ground the spark.
Exactly. So removing (or grounding) the spark plug wire from a properly working cylinder, (one that has spark, compression and fuel) will always cause the RPM to drop. But if a cylinder has no spark, no compression or no fuel, pulling the wire would make no difference (or hardly any difference). So it's still a valid test.
Exactly. So removing (or grounding) the spark plug wire from a properly working cylinder, (one that has spark, compression and fuel) will always cause the RPM to drop. But if a cylinder has no spark, no compression or no fuel, pulling the wire would make no difference (or hardly any difference). So it's still a valid test.
I would add an additional step. The ECM is going to try to maintain a certain RPM. "Killing" a cylinder may not make a noticeable difference - at least in RPM - because the IAC will try to correct for it. Before killing cylinders, I would be inclined to unplug the IAC.
Cool. But what is it then that I misunderstand? Because I never thought otherwise.
Perhaps it's a language issue, because what you "thought" and what you posted didn't entirely agree with each other. Anyway, you're now on the right track.
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. 
