Still struggling with car at idle after 8 years

[gundee]

I was going to mention it could have a weak spark at the plugs but then I saw

that one plug does not appear to be fouled. Confusing. If those valve oil seals were not snapped into place

properly then they could let oil buy I think.

An experienced engine and head builder should chime in if not already.

[Mark Maras]

4 hours ago, gundee said:

I was going to mention it could have a weak spark at the plugs but then I saw

that one plug does not appear to be fouled. Confusing. If those valve oil seals were not snapped into place

properly then they could let oil buy I think.

An experienced engine and head builder should chime in if not already.

 @jalexquijano Last year, as I recall, we were dealing with #4 plug fouling. Now it appears the problem has spread to all but one cylinder. What has been done to the engine since then? Were all the valve seals changed?

 Next time you're out driving find a nice steep hill, drive down the hill with the engine at around 4000 RPMs, and take your foot off the throttle pedal. Watch in the rearview mirror for blue smoke. Tell us what you see.

[Jarvo2]

I've said this years ago, and I'll say it again....I think its the crappy California Datsun engine and most likely the hot Cam that was installed in the head.  I've rebuilt these L6 engines and its not rocket science, unless you're an idiot.  Good luck.

[gundee]

Check if the camshaft timing is correct while you are at it too.

Like they say. California Datsun. You never know.

[jonathanrussell]

Reading the dialog of this extensive thread, the work that has been done with no progress, and the amount of time that has passed is super frustrating. I feel badly for you @jalexquijano. I am sure your frustration level is quite high. You have a nice car. It is terrible that you can't enjoy it.

I am not convinced that anyone who has worked on the car so far has been able to help. I have no faith that the efforts that have been done to adjust carbs, adjust float levels (critical), assess ignition health and valve timing, etc...have been done correctly. Now, when I think about the same local resources taking his engine apart, I think to myself...how does anyone know that they know what they are doing with an L series engine? 

Have you done an exhaustive search for someone in Panama who has experience with these cars and the L series engine?

Absent that, I would look for a great mechanic who is willing to read and learn about this car and the engine (factory service manual, online resources, etc). It feels like you and this collective forum have been attempting to tell the mechanics what to do. I would find a super smart mechanic that will read, assess the car, and tell you what needs to be done. Find someone who is also willing to engage here and ask questions.

Just my thoughts. I truly hope you get this resolved and are able to enjoy your car.

J

 

Edited October 19, 2023 by jonathanrussell
Panama...not an island.

[jalexquijano]

50 minutes ago, jonathanrussell said:

Reading the dialog of this extensive thread, the work that has been done with no progress, and the amount of time that has passed is super frustrating. I feel badly for you @jalexquijano. I am sure your frustration level is quite high. You have a nice car. It is terrible that you can't enjoy it.

I am not convinced that anyone who has worked on the car so far has been able to help. I have no faith that the efforts that have been done to adjust carbs, adjust float levels (critical), assess ignition health and valve timing, etc...have been done correctly. Now, when I think about the same local resources taking his engine apart, I think to myself...how does anyone know that they know what they are doing with an L series engine? 

Have you done an exhaustive search for someone on the island who has experience with these cars and the L series engine?

Absent that, I would look for a great mechanic who is willing to read and learn about this car and the engine (factory service manual, online resources, etc). It feels like you and this collective forum have been attempting to tell the mechanics what to do. I would find a super smart mechanic that will read, assess the car, and tell you what needs to be done. Find someone who is also willing to engage here and ask questions.

Just my thoughts. I truly hope you get this resolved and are able to enjoy your car.

J

 

Yes. Its super frustrating as i bought this car from a dealer in Colorado. You get stuck in traffic and the plugs start to foul. Once you accelerate engine starts misfiring. Its a real pain.

[Mark Maras]

21 minutes ago, jalexquijano said:

Yes. Its super frustrating as i bought this car from a dealer in Colorado. You get stuck in traffic and the plugs start to foul. Once you accelerate engine starts misfiring. Its a real pain.

Nine years you've been dealing with these problems. Were all the valve seals replaced and did the problem get worse (more plugs fouling) after that?

[jalexquijano]

15 hours ago, Mark Maras said:

 @jalexquijano Last year, as I recall, we were dealing with #4 plug fouling. Now it appears the problem has spread to all but one cylinder. What has been done to the engine since then? Were all the valve seals changed?

 Next time you're out driving find a nice steep hill, drive down the hill with the engine at around 4000 RPMs, and take your foot off the throttle pedal. Watch in the rearview mirror for blue smoke. Tell us what you see.

Just one seal was changed in cylinder 4. Let's go step by step as i threw away all those fouled NGK BP5ES spark plugs and installed a new set. Should we carry out a dry compression test and then a wet compression test before going any further? As i mentioned in the past this car does not have the original camshaft it has a Schneider 274F and a pertronix ignitor installed in the distributor: 

http://schneidercams.com/274FL6.aspx

Remember that California Datsun bored the cylinder to 2.6 and i was advised that the stock cam would not work. 

 

[Mark Maras]

 Well, I can't imagine why a stock cam wouldn't work. It might not be the first choice but it would certainly work.

 I think more compression tests (wet, dry, plugs out, throttle wide open) are a good idea. Fresh #s may show something new. I'm curious if you have any theories as to why more plugs are fouling now when it was only #4 in the past.

 Be sure to try the downhill 4000 RPM throttle-off test. It may provide a clue if there's oil consumption.

[AK260]

1 hour ago, Mark Maras said:

 Well, I can't imagine why a stock cam wouldn't work. It might not be the first choice but it would certainly work.

 I think more compression tests (wet, dry, plugs out, throttle wide open) are a good idea. Fresh #s may show something new. I'm curious if you have any theories as to why more plugs are fouling now when it was only #4 in the past.

 Be sure to try the downhill 4000 RPM throttle-off test. It may provide a clue if there's oil consumption.

That down hill test is a great idea. 

@jalexquijano on my old oil burning engine - when coming downhill and off the gas, I found that at the bottom of the hill when I went back onto the power, a puff of blue smoke came out. This signifies leaking oil from the head generally. When we cracked the engine open, I found that a UK Specialist who had rebuilt the head for me, had cross threaded one of the head bolts and it wasn't fully down, letting in oil into (coincidentally) cyl 4 😄 and cyl 3. So that test had proven the oil was coming in from the head. Try it. It's easy and free to do!

[jonathanrussell]

I read through this whole thread again. I have the following thoughts and suggestions.

In my opinion, your plugs are fouled with carbon / fuel, not oil. Maybe I would change my mind or confirm my opinion if I could touch and smell the plugs. Who knows. When I look at your spark plug photos, I think 4, 5, and 6 all look carbon fouled in varying degrees. 1, 2, 3 don't look great either, but I think they look weird probably due to the heat range plug you are using.

With your compression numbers, and assuming I am right about the plug fouling source, I would assume your engine is fine enough to run correctly. I would stop thinking about oil rings, oil seals, etc, etc....at least until you thoroughly follow some other paths first.

 

1) In my earlier post, I suggested finding a better mechanic. I still stand by that.

2) Take steps to make sure you have a perfectly functioning ignition system. Start with valve timing....camshaft sprocket, oil pump shaft, distributor all being in the correct position. Next make sure your plugs are connected to your distributor cap and spark plugs in the right firing order. Next make sure that you are getting spark at each spark plug. Also, I would suggest going back to stock heat range NGK plugs.  

3) Next, you need to get your carburetors adjusted correctly. If you are having to turn the mixture adjustment screw down 3.5 turns then your float levels are absolutely not adjusted correctly. If the float chamber levels are not correct, then it is possible, likely even that your mixture screw adjustments do absolutely nothing to affect mixture. You have Z therapy carbs. They are great carbs. They almost certainly have stock nozzles and probably SM needles (but it doesn't really matter which needles....you can get any of them to work well enough and not exhibit the symptoms you are having). In broad terms...your carb for cylinders 4, 5, and 6 is richer than the carb for 1, 2, 3. So...how can you get your carburetors adjusted correctly? 

a) One option is to find a great mechanic who is willing to read, research, focus first on float levels, and really learn how to adjust these carburetors. I read a lot of people saying it is easy. I agree it is easy when you have done it successfully and know what to do. The first time I really learned how though, it took days of trial and error....especially with the float levels. I prefer to take the domes off, turn the mixture screws down 10 turns, and set the fuel to the top of the nozzle hole. Others have different ways. All ways can work. And, getting the tab to the float tab that rubs against the needle jet to the right curvature so it engages smoothly and doesn't get caught is a big learning curve. So, can you find someone willing to go through this learning process and provide you with perfectly adjusted carbs? Probably not.

b) This is what I would do. Contact one of the great Z car shops (start with Z Car Garage) in the united states and ask them if you can ship your carburetor assembly (carbs, balance tube, etc) to them (dry out fuel first). Let them know you want them to tune your carb on a stock 240z or stock 260z (yes, I know your z engine has been stroked to 260z but you have a pretty much stock camshaft, etc). Tell them you want to be able to reinstall and run it. Key is to get the float levels adjusted. Yes, you may need to final tune with turns of the mixture screw, but you should be 90% there. 

I would also suggest purchasing a color tune device which will let you visualize how rich or lean each carburetor is running.

Those are my thoughts. I wish you the best and hope you get to enjoy your car someday soon.

J

 

[jalexquijano]

Thanks. Ill follow your and Mark´s continuous advice. Its a real shame i bought a car that i could never really enjoy. Should we start with a dry and wet compression test? All the spark plugs are new and gapped correctly. Can you confirm that i need to remove the plug from the ignition coil prior to cranking the engine while performing the compression tests?