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L28 sounds like it's running on one cylinder


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Hi everyone!

 

Back at it again. 1978 280Z. L28 with ALL emissions deleted including cold start and bcdd valve. 

 

The problem is, when I start the car it is very difficult to start, and it sounds like it's only firing on 1 cylinder. I have tried re-adjusting the AFM at idle and at higher RPM. seems to have made no difference. The motor is solid. Good compression and strong spark (although I may visit this again). It was running great last time I drove her after repairing a blockage in the fuel return line. Fuel pressure is perfect around 36psi +/-. Only change made was taping up a small crack on the throttle body to AFM boot (temporary fix) and replacing the battery. 

 

All thoughts and ideas are more then welcome. 

 

Thank you! Happy motoring! Wish I can be a part of it, but my car won't run right hahah 😩 

20210911_155030.jpg

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Does the problem go away after she is warmed up? Start running OK after 10 min? 
 

If so, the cold starting capabilities of your OEM EFI have been compromised. I don’t know Enough about the OEM system to help diagnose though. Usually and easy fix is to artificially increase your idle with the throttle body set-screw, but you will be running higher rpm’s at idle once warmed up. 
 

unless there is something mechanically wrong, it can only be fuel, spark, or air. Air is unlikely since you have a single throttle body, and you have already tried adjusting your idle Screw. Spark is easy to check with a timing light. You can also pull each plug, ground the threads, and watch for a spark as you turn the engine over to confirm each plug is sparking. Make sure your plug wires have not been crossed, or out of order. 
 

Last and most difficult to diagnose is fuel. Check for fouling (black soot) on your plugs and smell gas out the exhaust pipe, indicating a rich mixture. If lean, the plug ceramic insulation and electrode will look white, but that will not happen until the engine is warmed up and under load. Proper mixture will yield a brown/dark grey electrode. 
 

I tune adjustable EFI and carbs, so I’m not much help on OEM EFI. Sorry 😕 

Edited by AydinZ71
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17 hours ago, Mike33Stig said:

 it sounds like it's only firing on 1 cylinder. I have tried re-adjusting the AFM at idle and at higher RPM. seems to have made no difference.

 

It was running great last time I drove her after repairing a blockage in the fuel return line. Fuel pressure is perfect around 36psi +/-. Only change made was taping up a small crack on the throttle body to AFM boot (temporary fix) and replacing the battery. 

 

If it was running great before the first thing you should do is to put the AFM back exactly as it was before.  "Adjusting" AFM's ruins most of them.  Nissan puts glue on the wheel because they're only meant to be adjusted when calibrated then never touched again. 

 

One cylinder must be an exaggeration, right?  Post a video.

 

Are you sure that you didn't bump something or do something that you think "should" have no affect?   Because there's nothing you've described that is a clue.  "Engine ran great, worked on engine, engine runs terrible" is all that's here.

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@AydinZ71 I will try adding more fuel through the intake and see if that will clear her up. And I will check the points on the distributor again and check all the plugs this afternoon.

 

@NewZed The AFM has already been tampered with. I re-calibrated it using the information from Atlanticz. But would not run in this orientation. I then did the yogurt cup test and had great results and a strong vacuum at idle. My only leaks were at the butterfly valve on the TB and the small crack in the TB boot. 

Now I have not made any permanent adjustments to the AFM. But usually I can find the sweet spot by fingering the AFM at idle and at a higher rpm and get it close to where it's happy. Can't be 100% until I get a wideband.

In my previous post on this forum I had an issue with a blockage in my fuel return line causing high pressure 95psi. And at that time I checked all my injectors and made sure I'm getting a good pulse with noid lights. I still suspect the AFM at this point because I had a similar issue before and it was the culprit. But now I can not get it to run correctly by adjusting (fingering) the AFM. 

I do have a 2nd AFM I can try. But I think it's in worse condition. I will try to upload a video this evening. 

 

Thank you!

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1 hour ago, Mike33Stig said:

fingering the AFM

 

More fuel or less fuel?  "fingering' doesn't really tell much.

 

I don't think the engine will run on one cylinder.  So, it's still not clear what you mean.

 

Don't overlook the simple "fouled plugs".  When the cylinders don't fire the plugs tend to get dirty.  Plug examination usually tells a story.

 

And - bad fuel.

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@NewZed @AydinZ71 Problem solved! Never be afraid to re-visit the basics. 9/10 it's something so simple hahah. 

... Fouled plugs. I had been running too rich. Now I set her up on the lean side to help burn the crud off that I couldn't get myself, then I will richin up the mix after my next short drive cycle. 

Before and after videos attached. Thank you all for the help!!!!! 😁😁😁

 

 

20210930_180944.jpg

Edited by Mike33Stig
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