Sudden Running Lean Issue

[chaseincats]

A friend last night suggested checking the resistance of my NGK spark plug wires (bought in 2021).  I set my multimeter to 20k ohm and here is what I got:

 - plug wire cylinder 1: 6.40

 - plug wire cylinder 2: 6.03

 - plug wire cylinder 3: 6.03

 - plug wire cylinder 4: 6.68

 - plug wire cylinder 5: 7.07

 - plug wire cylinder 6: 7.2

 

Is any of this suspicious?

Edited February 17 by chaseincats

[Zed Head]

Does it have a miss now?  You're on Page 4, hard to tell what the current state of the situation is.

[chaseincats]

1 minute ago, Zed Head said:

Does it have a miss now?  You're on Page 4, hard to tell what the current state of the situation is.

It doesn’t, but plug wire resistance was my friends theory yesterday when I showed him cyl 3 was darker than the rest.

[Zed Head]

Is there a problem?  On my engines, a 76 and a 78, 5 and 6 were always darker and 1 was always whiter.  I don't think that air flow is well-balanced through the EFI engine intake manifold.  They all get the same amount of fuel but diferent amounts of air.

[chaseincats]

21 hours ago, Zed Head said:

Is there a problem?  On my engines, a 76 and a 78, 5 and 6 were always darker and 1 was always whiter.  I don't think that air flow is well-balanced through the EFI engine intake manifold.  They all get the same amount of fuel but diferent amounts of air.

interesting and a really good point.  I'll pop the wires back in then

[chaseincats]

Update: the car is running great now.  Here is what I did and found:

• New plugs did not help (car lean running issue continued after installing these)
• Pulled new plugs from the head and watched them spark - spark level was identical
• Measured HT wire resistance - all within spec
• Went through the fuel injection bible and confirmed all components are within factory spec when measured through the main ECU connector
• Fuel pressure at 32 not 36
  • changed engine bay fuel filter but did not re-measure fuel pressure
• Pulled the fuel rail, put all 6 injectors in separate cups and measured the fuel output volume while cranking
  • All injectors output identical volume with identical spray pattern (injectors are ~1.5 years old)
  • Cleaned injector connector teeth - cylinder 1's injector teeth were green but this did not affect injected volume

 

I did notice a couple small black pieces in the injector inlet size so it may have been the fuel filter which was odd since it was only about 2 years old.  I will change the tank to fuel pump filter this week although it looks clean

[Zed Head]

Seems like you're implying that your fuel filter was clogged.  But in Post #36 you said you got 39 psi.  ???  I assume that gauge was between the filter and the fuel rail.

Might be that you had a vacuum leak at an injector or two and you fixed them when you removed and replaced the injectors.

Wahtever it was, good luck with it.  On to the next problem...

 

[chaseincats]

5 hours ago, Zed Head said:

Seems like you're implying that your fuel filter was clogged.  But in Post #36 you said you got 39 psi.  ???  I assume that gauge was between the filter and the fuel rail.

Might be that you had a vacuum leak at an injector or two and you fixed them when you removed and replaced the injectors.

Wahtever it was, good luck with it.  On to the next problem...

 

Interesting idea and good point with the 39 psi 

[chaseincats]

Final update: Culprit found - case closed

The weatherstrip (the rubber rectangular gasket that goes inside the efi connector) for cyl1 was working its way out of its mount when the car warmed up and prohibited cyl1's efi connector from fully seating.

I noticed that today when I needed to pull over to the side of the road due to the engine (now I know as cyl1) running prohibitively lean on my air/fuel ratio gauge.  I found I was unable to push cyl1's injector power cable fully in so I removed that piece of rubber, could plug the connector in firmly, and now the car runs awesome with power throughout the rev-range for the first time in a while.

I originally noticed this issue when I pulled the fuel rail to run tests on injector flow and reseated the rubber piece back in the connector - but I guess it had other ideas.  I have permanently removed that piece and may pull the others to prohibit this in the future.

 

Thanks for all of your help with this

-chase

Edited March 10 by chaseincats
Added image

[Captain Obvious]

I'm sure you already know this, but that seal (in theory) should not affect the electrical connection function. In theory.

But it's completely conceivable that mixing and matching different vendors parts with various levels of design and manufacturing pedigree... Seems something wasn't done quite right. And if pulling that seal out fixes it, so be it!  I'm glad it's that simple!   

[chaseincats]

4 minutes ago, Captain Obvious said:

I'm sure you already know this, but that seal (in theory) should not affect the electrical connection function. In theory.

But it's completely conceivable that mixing and matching different vendors parts with various levels of design and manufacturing pedigree... Seems something wasn't done quite right. And if pulling that seal out fixes it, so be it!  I'm glad it's that simple!   

Honestly, I feel a bit silly posting this, but I did take a second look today in the light and there were actually 2 of those rubber seals in the plug instead of 1.  There was no way that was ever going to make good contact like that - there isn't enough physical space inside the connector for that to happen.

That said, I'd rather feel like a doofus than have the car run like it had been and at least now I know all of the other systems are working as intended.

[Captain Obvious]

Haha!! You know... I was gonna suggest that as a possibility! I should have! Would have looked like a rock star!

Don't worry about looking like a doofus. I do it all the time!  Hahaha!!