154 random frequent misfire

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Duner
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154 random frequent misfire

Postby Duner » Mon Jan 23, 2023 10:03 am

154 will start at slightly off idle and not miss. Increase RPM and engage mower and misfire starts.
BUT let it warm up for about five minutes and misfire goes away and it runs good.
I had another vehicle that did about the same for misfire but misfire would not go away ,ever.
Replaced the condenser on other vehicle and all was well.
Anyone ever have a condenser act like I described on my 154?

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Re: 154 random frequent misfire

Postby 64/67lo-boy » Mon Jan 23, 2023 6:48 pm

Yes thats a very common symptom of a bad condenser.
Pete from Virginia Beach

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Re: 154 random frequent misfire

Postby 64/67lo-boy » Mon Jan 23, 2023 6:50 pm

64/67lo-boy wrote:Yes thats a very common symptom of a bad condenser.

That is when it miss fires and miss fire doesn't go away.
Pete from Virginia Beach

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Re: 154 random frequent misfire

Postby Eugene » Tue Jan 24, 2023 8:12 am

Most likely misfiring one cylinder. Automotive Oscilloscope would easily identify the problem.

Lacking the O-scope, timing light on one plug wire at a time will identify the problem area - which cylinder. Then you will have to diagnose the problem.
I have an excuse. CRS.

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Re: 154 random frequent misfire

Postby Gary Dotson » Tue Jan 24, 2023 8:22 am

Usually, when I encounter a miss fire like this, it turns out being a spark plug or a bad plug wire. A scope would be very helpful, it’s been a long time since I’ve had mine out. Make sure your plug wires and coil wire are fully inserted in their respective towers, I’ve seen that cause a miss like this.

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Re: 154 random frequent misfire

Postby Duner » Tue Jan 24, 2023 8:54 am

It acts exactly like a failed condenser would in this respect.
Starts and idles fine. Increase RPM and RPM and load it completely breaks down.
Let it warm up for five minutes and it runs perfect. Been doing this all last mowing season. Thanks for the thoughts.

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Re: 154 random frequent misfire

Postby Larry B » Tue Jan 24, 2023 10:35 am

If you want to test for a bad condenser just disconnect it. It is only there to extend point life. Running for a short time won't hurt the points. If you disconnect it and the misfire problem goes away then bad condenser.

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Re: 154 random frequent misfire

Postby Eugene » Tue Jan 24, 2023 11:43 am

Larry B wrote:If you want to test for a bad condenser just disconnect it. It is only there to extend point life. Running for a short time won't hurt the points. If you disconnect it and the misfire problem goes away then bad condenser.
The condenser does reduce the arcing at the points. But it has other functions such as discharging back into the coil to improve the spark quality.

Without the condenser in the ignition circuit the engine may run, just not very well. Frequently the engine will not run.

The condenser is either good or bad. No in betweens.
I have an excuse. CRS.

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Re: 154 random frequent misfire

Postby Duner » Wed Jan 25, 2023 9:26 pm

I can tell hear if it was one cylinder. It is 2 or more and random ,frequent and sporadic.
I have owned and fixed points ignitions for over 60 years.
If it would not cure itself after 5 minutes I would say condenser.
Thanks for the replies.

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Re: 154 random frequent misfire

Postby cubbrian » Tue Feb 07, 2023 4:45 pm

I had a similar issue when i purchased my 154. It would start and idle perfectly. Give it throttle and it sounded like it was missing/starving for fuel. After many hours of troubleshooting, I found that the coil was bad. Go figure.

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Re: 154 random frequent misfire

Postby Duner » Wed Feb 08, 2023 12:27 pm

I will try a different coil. Thank you. Did yours run better after five minutes or so?
I have had bad condenser that acted like yours.

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Re: 154 random frequent misfire

Postby Duner » Sat Apr 01, 2023 8:54 am

I tried timing light as suggested and it misses on all cylinders. Tried it on coil to dist wire (Packard 440) and still shows missing. Tried Bosch Blue Coil, new cap, rotor, points and condensers. still misses.
Disconnect Delco 10si alternator, miss goes away. Install Delco 12si . Still misses. Tried many different wiring combinations , still misses. Last thing I tried was separate stand alone battery to coil only . Works fine , no miss.
I have never had an alternator affect points ignition before. Anybody ever run into anything like I described.

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Re: 154 random frequent misfire

Postby Gary Dotson » Sun Apr 02, 2023 8:24 am

Is your coil an internal resister or does it have an external ballast resister? I’ve seen issues where an ignition system didn’t like increased voltage. I think the extra voltage kind or overloaded the points and condenser. So, make sure you are using either an internal resister coil or an in line 1.5 ohm ballast resister.

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Re: 154 random frequent misfire

Postby Duner » Sun Apr 02, 2023 4:22 pm

My coil does NOT have external resister. I did try a different coil. Same results.

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Re: 154 random frequent misfire

Postby Eugene » Sun Apr 02, 2023 6:09 pm

Duner wrote:My coil does NOT have external resister. I did try a different coil. Same results.
Gary Dotson wrote:Is your coil an internal resister or does it have an external ballast resister? So, make sure you are using either an internal resister coil or an in line 1.5 ohm ballast resister.
Are your coils labled with internal resister?
I have an excuse. CRS.


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