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jalexquijano

Random Misfire while cruising

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I have a question which has not been answered. Can one or two spark plugs that have been fouled due to traffic jam meaning some minutes of idle cause some random misfire? The reason i ask this is because the other day i experience some random misfire at 2nd and 3rd gear while cruising for a while after the engine experienced some idle during short stops and suddenly as i accelerated the misfire went away. Where should i look into? Im still considering it its worth replacing the fan clutch with twin electric fan to solve this issue or should i simply forget about this.

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 The only two reasons for switching to electric fans (IMO) are increased cooling at low or no speed and a slight horsepower gain. 

 I think you're on the right track suspecting plugs. Especially because you said the problem went away after a quick Italian tune-up. What RPMs did it begin to misfire? Normal for fouled plugs is around 3500 and above. 

 Is your engine still overheating in traffic jams? If so, I'd look into the electric fans. In extreme cases (hot weather and long waits) I just turned the engine off and when I did get moving slowly I kept the RPMs as low as I could. Fewer RPMs equals less heat generated. That said, I never had any percolation or vapor lock problems that would have prevented it from starting right away.

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Ok dude, electric fans won’t stop fouling plugs.

 

The first thing to look and adjust would be your mix.

 

But before any of that, go for a drive with a pair of cloth gloves, towel and a spark plug remover socket in the car. Re-created the scenario. As soon as it happens, turn off engine, pull over, pop the bonnet, lay the towel on the wing and pull your plugs (which will be hot) and lay them on the towel. Now look at what the plugs look like and if the ones from the front and rear banks are different in any way.

 

I also experienced similar symptoms but with fuel vaporisation as the header was heating up carbs and everything carrying fuel above them. A decent heat-shield works wonders. Good luck chap.

 

 

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 Good advice above, However, I'm not a fan of pulling spark plugs from a hot aluminum head. I've done it many times successfully but I hate the feel of the plug coming out. @jalexquijano Have you pulled the plugs lately and compared #1,2,3 with 4,5,6 and how many turns down are you running on the mixture screws? Both the same? Deja Vu!

Edited by Mark Maras
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I already have two heat shields installed. The stock one at the rear of the carbs and another aluminium one under the carbs. Thanks for keeping me away from buying an unnecesary electric fan.

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What spark plugs are they? If they're too cold then they can foul at idle and cause misfire until they're back in the self cleaning temp range and clean again.

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10 minutes ago, jonbill said:

What spark plugs are they? If they're too cold then they can foul at idle and cause misfire until they're back in the self cleaning temp range and clean again.

NGK BP6ES

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On 6/11/2019 at 4:13 PM, Mark Maras said:

 Good advice above, However, I'm not a fan of pulling spark plugs from a hot aluminum head. I've done it many times successfully but I hate the feel of the plug coming out. @jalexquijano Have you pulled the plugs lately and compared #1,2,3 with 4,5,6 and how many turns down are you running on the mixture screws? Both the same? Deja Vu!

Just pulled out all 6 plugs havent got into any heavy traffic. Plugs 4 and 3 came out a little bit more black. I will clean them up with brass wire brush and try again. The order of the pics is 6 5 4 3 2 1 left to right.

20190623_123637.jpg

20190623_123726.jpg

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 They look pretty good. Odd that 3 & 4 are a bit darker. As you said, clean 'em up and try again.

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The fact that 3 and 4 are different, makes me think you have an internal engine issue. If my plugs exhibited the same, I would check valve clearance and do a compression check to investigate further. Apologies if you have already done these checks and I am being repetitive.

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I have already done the compression test and there is now issue whatsoever. When i bought this car the engine was assembled by california datsun. 

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That is strange indeed, typically one side or the other will be darker.

 

Some other thoughts and forgive me if it’s already been said.

 

Let’s eliminate potential electrical issues:

 

1. Swap 3 and 4 with say 1 and 6 and see if you get the same effect. Could it be a faulty pair of plugs? And are the gaps the same (although that shouldn’t make a huge difference).

 

2. If 3&4 soot up again, try rotating HT leads from other plugs that aren’t sooted up.

 

3. Check the 3&4 electrodes on the inside of the distributor cap to ensure they are not corroded.

 

Looking at the mechanical side:

 

3. Have you checked manifold gasket for leaks?

 

4. Have you checked valve clearances lately?

 

5. On your comp test, what was the difference between 3&4 and the other cyls?

 

3&4 aside your plugs look a little too hot to me, how have you adjusted your mix? I have found that idling for a long time with a lean mix on a hot day, the car starts to misfire as if there is an electric problem, but it’s a heat problem.

 

 

 

 

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what about getting a spark plug extender. I still think it could be a valve seal as this engine was remanufactured by California Datsun. I am about to open the engine and change all the valve seals. Any other option? 

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On 6/23/2019 at 6:32 PM, Mark Maras said:

 They look pretty good. Odd that 3 & 4 are a bit darker. As you said, clean 'em up and try again.

Mark,

Sorry i couldnt keep up with your recommendations on solving this weird misfire issue on the car´s 4th cylinder but the starter engine went south and i had to purchase a new remanufactured one. I have read so much on this matter and even though the compression test results were good i still believe there must be a valve not working properly. I drive the car a couple of blocks or leave the car running for 25 to 30 mins and the 4th spark plug starts fouling. If you step on the gas pedal, the engine starts missing power until the spark plug is cleaned. Any other option other than getting inside the engine to change the seal or valve in that cylinder?  Should i purchase a 14 mm spark plug extender that avoids the spark plug getting fouled? 

https://www.amazon.com/Dorman-42000-Spark-Plug-Non-Fouler/dp/B000BYD9Z8/ref=sr_1_2?dchild=1&keywords=14mm+spark+plug+extender&qid=1602790752&sr=8-2

 

 

Edited by jalexquijano

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  Glad you got your starter problems resolved. I wish I could give you an opinion on the spark plug non-foulers but I don't even have an educated guess. I'm not familiar with the product at all. It's cheap and I doubt it can do any harm. I'd be interested in hearing about any change if you try them. Anyone else want to chime in?

 Have you tried all the things that @AK260 suggested in post #15?

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I’ve had misfire issues where the tip of the spark plug was loose. The end where the plug wire goes. On some NGK plugs, the end cap threads on, and I have found many that were loose. Check yours and tighten thoroughly with pliers.

Here is a screen grab showing plugs with and without the end cap and how they thread on

D149C2F7-A135-4710-88D6-99400FDC66E4.jpeg

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Should i try a hotter spark in cylinder 4 which is fouling? BP5ES? I want to test everything before opening the engine! Please advise.

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 I'd try a hotter plug. It won't tell you what's wrong but it might buy you some time.

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Should i try a hotter spark in cylinder 4 which is fouling? BP5ES? I want to test everything before opening the engine! Please advise.


My friend, you have to find out why it’s fouling - what you are suggesting here is a band aid not really fixing the issue. Until you solve the underlying issues, they will keep finding you.

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14 minutes ago, Mark Maras said:

 I'd try a hotter plug. It won't tell you what's wrong but it might buy you some time.

I bought this car already modified by california datsun so i really dont know if they rebuilt the engine correctly or not!

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Have you measured cylinder pressures? If they are correct then valve seals would be the next place to look.  Pretty easy to replace, easier than replacing oil scraper rings on the pistons.

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