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How to find a "miss" or misfiring cylinder?

Chief Brody

Chief Brody

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I am trying to locate the source of a miss. It is there at Idle..causes the hood to shake...gets worse up to about 2500 rpm and then tails off or is less noticable.

Whats the best steps to take to pinpoint the source of the miss?

Vacuum gauge or just start pulling plugs and wires?

Note: I did see a video where a guy warmed up the engine and used a thermal temp gun to find the "cool" cylinder by pointing it at the exhaust manifold ports. Does this work, or should I just start pulling plugs or something else?
 
IR temp gun works good. Even dropping a drop or two of water on the manifold where it exits the cylinder will tell you plenty. If it vaporizes/boils, that cylinder is firing. If it does nothing you have a dead hole.
 
Chief Brody said:
My dad used to start the car and and start pulling a wire from the distributor and the one that made no difference was it...but I am afraid to do that.
Click to expand...

That's what I've done. Just don't use your bare hands, haha.
 
Like Rene said...I use a spray bottle with water in it. Just squirt the manifold or headers. You’ll see right away if the cylinder is dead.


Engine running obviously.
 
Just be careful with the water trick, too much water can crack you manifold. A little dab’ll do ya.
 
Chief Brody said:
I am trying to locate the source of a miss. It is there at Idle..causes the hood to shake...gets worse up to about 2500 rpm and then tails off or is less noticable.

Whats the best steps to take to pinpoint the source of the miss?

Vacuum gauge or just start pulling plugs and wires?

Note: I did see a video where a guy warmed up the engine and used a thermal temp gun to find the "cool" cylinder by pointing it at the exhaust manifold ports. Does this work, or should I just start pulling plugs or something else?
Click to expand...



sorry I've missed all your issues.. pm me anytime... generally a plug reading will tell you exactly what's going on....
 
Whew! Finally found the issue with the misfire / dead cylinder.

I thought I had a stuck valve because I did the "paper test" at the tailpipe and it was sucking the paper towards it intermitently. So I went O'Reilleys and got some Marvel Mystery Oil and ran that till it warmed up. Then I got the IR gun and wow, that was amazing. Every exhaust port but one was at around 325*. #2 was at 170*. I removed the wire and the plug and replaced them and voila! No miss.

It is running as smooth as it ever has.

Now the only issue is, it is STILL running hotter than I like. The temp gauge is still hanging out at the 3/4 mark when I always used to stay at exactly the 1/2 mark.

I tested the water housing with the IR gun when it was at the 1/2 mark and it read 193*
I tested it when it was at the 3/4 mark and the water housing was reading 208*. Both of these just idling in the driveway.

So I feel like I resolved the misfire issue, but apparently I have not resolved the overheating issue. The new severe duty fan clutch just kept it cooler longer but when it gets up to the 3/4 mark it doesn't come down.

I open for suggestions at this point. I think maybe the cheapest thing I could do is change the thermostat, and since we average 95* every day in the summer, I probably should go with a 180* thermostat.

Does anybody still think it could be timing?
 
Oh...and my oil pressure is running a bit higher than I normally see also
 
If you are running a 195 t-stat and its sitting @ 208 the lower temp thermostat won't help, just will just open and heat soak everything quicker. Factory thermostat is 205 or 210 I think? I had all kinds of problems with my quadrajet trying to get the engine to run "cooler", because i thought that was better. Turns out the choke would never pull off completely due to the lower temp.

The higher oil pressure doesn't add up, unless you have changed oil viscosity recently?
 
I think I will plan to change oil and filter and thermostat next weekend.
bigjimmy82 said:
If you are running a 195 t-stat and its sitting @ 208 the lower temp thermostat won't help, just will just open and heat soak everything quicker. Factory thermostat is 205 or 210 I think? I had all kinds of problems with my quadrajet trying to get the engine to run "cooler", because i thought that was better. Turns out the choke would never pull off completely due to the lower temp.

The higher oil pressure doesn't add up, unless you have changed oil viscosity recently?
Click to expand...

Yep...I went to 10W40 istead of 10W30 and changed oil filter brand as well...all because of a sale price.
 
Factory T-Stat on mine is 195* but forever my Temp gauge was dead center straight up the middle no matter what..maybe a tick to right if I ran the air conditioner.
 
I guess this really could be a sticking thermostat though maybe it open at 195 sometimes then doesn't or not enough?
 
In case anybody is curious, I always use Valvoline. I have always used Valvoline 10W30 in it with an AC Delco Filter.

This time I bought Valvoline 10W40 Long Life with a WIX filter.
 
That 100% explains the oil pressure. It's a 40w when hot vs a 30w.

The thermostat could be sticking. If you have the temp gun you could start it cold and monitor, you should see a big temp swing the first few cycles as it heats up all of the coolant. I notice that with my mechanical gauge, once fully warm it only swings 5-8deg vs 20 or more with the first few open/close cycles and "cold" coolant.

edit: a fully open thermostat or no thermostat is bad since the coolant doesn't get any dwell time in the radiator to get cooled off

Edit #2: in my opinion that oil won't hurt anything. I run 15w-40 in mine, admittedly trying to stop rear main leak. Going to have to pull pan and change it ☹️
 
GM used a 195 degree thermostat in all their engines after 1968,when the "controlled combustion system" was introduced to help lower emissions..anything lower will only open faster and not have much effect on the temperature once the engine fully warms up..
As noted running a cooler thermostat might create other issues like it running richer,staying on choke longer,even oil dilution in colder climates,fuel economy will drop too..
Coolant wont boil until it hits 258 degrees when the radiator has 15 psi in it..I've had several GM vehicles that ran as high as 220 degrees in hot summer weather,with no overheating issues or coolant being peuked out after shutting them off..

I had a VW Beetle that had a rear main oil leak-I put in SAE 40 oil instead of SAE 30 ,thinking thicker oil would leak slower,but instead the oil pressure went higher,which made it drip even worse!.
I put 10W-30 in it and it almost stopped leaking completely,and I could go a lot further before having to add a quart,until I was able to yank out the engine and replace the rear main seal..

Torquing the huge "gland nut" that holds the flywheel on was a "fun" job..it requires 200 ft/lbs and about 50 ft.lbs will make the engine flip over!..had to use a special "tooth"tool, that bolted to the engine mount bolt hole to hold the flywheel still,and I had to have two friends stand on the engine's heads to keep it on the ground while I jumped on a breaker bar with a 8 foot hunk of pipe on it..:eek:
 
I wouldn’t get too hung up on a factory gauges accuracy. Plumb in a good aftermarket gauge and see where you’re really at. I’ve seen factory idiot gauges read high, low, everywhere.
 
I got all my parts in, I will be changing the thermostat anyway just to eliminate that, thought I might flush the coolant too and make sure my mix is good. I am changing the oil again back to 10W30, need to change the oil since the overheat. Then I'll see where it is going on the gauge. I may replace the gauge to be sure, but I am keeping mine original, so I will replace it with an original.
 
Chief. I don’t think your getting it. You cannot monitor engine temp with the factory gauge. Until you have the overheating issue knocked out zip tie one in. Then when it’s running nice and cool take it out.
 
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