Random Misfire while cruising

[jalexquijano]

3 hours ago, Mark Maras said:

 @jalexquijanoWere those readings with the throttle wide open? Also before or after checking the valve lash?

9 hours ago, Mark Maras said:

Yes, and after they've been reset another compression test would be helpful to rule out low compression in #4.

Compression readings attached.

 

3 hours ago, Mark Maras said:

 @jalexquijanoWere those readings with the throttle wide open? Also before or after checking the valve lash?

No throttle wide open. Just turning the car key with all six plugs removed. Cranking the engine. One by one. 

[jalexquijano]

This is whats inside my engine

 

9 hours ago, Mark Maras said:

Yes, and after they've been reset another compression test would be helpful to rule out low compression in #4.

Compression readings attached.

[Mark Maras]

 Ok, the closed throttle explains the low numbers on all of them, however it still doesn't explain the misfire on #4. Back to the simple things. Are you absolutely sure the number four wire has been securely attached to the plug. It should have the same noticeable click as the others when you snap the plug wire onto it.

[jalexquijano]

Its secured. Should i try hotter plugs? I sent you the specs of this engine. I will need a camera to see if a seal inside is broken or damaged valve guide. 

[Mark Maras]

Yeah, Put a hotter plug in #4. It's a band-aid but it may buy you some time until we discover WTH is going on. Is the dark color on #4 plug oily, smell like fuel or is it dry carbon? I'm beginning to suspect a bad valve guide or valve guide seal on #4 if the colorization is oily. Looking at your latest pic of #4 it looks like the plug is trying to fire (clean near the center electrode) but is being overwhelmed by either fuel or oil. Fuel can be crossed off the list so it is likely oil. One more test please. Pull #4 plug, put the wire on it and ground the plug (With an insulated gloved hand) while turning the engine over with the starter. Watch the spark and note the color. It should be bluish, not yellow and you'll probably be able to hear it.

Edited October 22, 2020 by Mark Maras

[AK260]

Yeah, Put a hotter plug in #4. It's a band-aid but it may buy you some time until we discover WTH is going on. Is the dark color on #4 plug oily, smell like fuel or is it dry carbon? I'm beginning to suspect a bad valve guide or valve guide seal on #4 if the colorization is oily. Looking at your latest pic of #4 it looks like the plug is trying to fire (clean near the center electrode) but is being overwhelmed by either fuel or oil. Fuel can be crossed off the list so it is likely oil. One more test please. Pull #4 plug, put the wire on it and ground the plug (With an insulated gloved hand) while turning the engine over with the starter. Watch the spark and note the color. It should be bluish, not yellow and you'll probably be able to hear it.

 

Wot he said!!! [emoji115][emoji115] ^^

 

It won’t be fuelling as the other plugs fed by the same carb are fine. Also all your plugs except the oily one look too lean to me (but that means nothing as it could be that you just have a lean idle but good on WOT). Having said that, a lean idle is a hot one and will cause you other issues not related to this.

 

I am of the very strong opinion that you have oil coming down your valves or past a point on your head gasket. Once my” professionally” rebuilt head by a UK “specialist” came off, we found that one of the head bolts was not put in properly and oil was going down the bolt, feeding oil nicely into 3&4.

 

Do you get any blue smoke out of your exhaust? On my engine I found that if I let it idle for a while then blip the throttle, I got a lovely puff of blue. Typically that is head related not ring related.

 

Check your valve clearances, check the torque on your head bolts and look to the valve seals / guides as a potential cause.

 

Look at the plug on no. 4 in this pic compared to the rest!! Then look top right from no.4 and you will see the oil around the offending head bolt hole.

 

[jalexquijano]

22 hours ago, Mark Maras said:

Yeah, Put a hotter plug in #4. It's a band-aid but it may buy you some time until we discover WTH is going on. Is the dark color on #4 plug oily, smell like fuel or is it dry carbon? I'm beginning to suspect a bad valve guide or valve guide seal on #4 if the colorization is oily. Looking at your latest pic of #4 it looks like the plug is trying to fire (clean near the center electrode) but is being overwhelmed by either fuel or oil. Fuel can be crossed off the list so it is likely oil. One more test please. Pull #4 plug, put the wire on it and ground the plug (With an insulated gloved hand) while turning the engine over with the starter. Watch the spark and note the color. It should be bluish, not yellow and you'll probably be able to hear it.

Mark,

I really need to move forward with this matter as i would like to drive my car in all conditions, traffic or non traffic. I bought this car in 2014 and after visiting 10 mechanics nobody has a clue on how to solve this issue in Panama. Only one  knowledgeable bike engineer believes that its useless to keep adjusting valves as the problem is clearly in the valve guides or seals. This engine was rebuilt by California Datsun and has the specs described above. I wouldnt like to open and remove the cylinder head without having all the parts required for this job.  Please advise if there is a kit that comes with the valve seals, valve guides and valves to carry out this work accordingly. If not which brand and parts would you recommend? 

[Mark Maras]

 Before proceeding to valve guides, I need you to test the #4 plug (use a new plug) against a ground by turning the engine over with the starter. That will ELIMINATE a possible electrical cause of the fouled #4, then we can move on to oil fouling. But while I'm thinking about it, how much oil does the engine use in around 1000 miles or 1600 kilometers?

[siteunseen]

You say no one in Panama can work on the L motor.

How/who put that Schneider cam in? As I recall it came from Ebay crook California Datsun with a "Far 311" cam. Please correct me if I'm confused. Very often occurence with me. 

 

[jalexquijano]

California Datsun

[siteunseen]

Yeah I get that spec sheet, seen it a lot but who put the the Schneider 274 cam and componets in?

[jalexquijano]

Okay after i did the spark plug boot to ground on cyl 4 i could only notice blue spark. So the problem is not electrical.