Sudden Running Lean Issue

[Zed Head]

Is it running well now?  Intermittent problems are hard to diagnose.  You have to catch them in the act.

An ECU going bad or maybe an ignition module might cause rough-running.  How does it drive now?  If it's running right but the gauge numbers are off maybe it's just an AFR gauge problem.

Turbo engines can get damaged by running lean but an NA engine won't be hurt.  It will just run like crap.  I'd focus on how the engine runs and ignore the gauge.

[chaseincats]

2 minutes ago, Zed Head said:

Is it running well now?  Intermittent problems are hard to diagnose.  You have to catch them in the act.

An ECU going bad or maybe an ignition module might cause rough-running.  How does it drive now?  If it's running right but the gauge numbers are off maybe it's just an AFR gauge problem.

Turbo engines can get damaged by running lean but an NA engine won't be hurt.  It will just run like crap.  I'd focus on how the engine runs and ignore the gauge.

It was definitely running worse than it had in the past, and the rough hot-start idle was new.  That said, it was running great today and didn't even have the hot start issue so I'm not sure what's going on.

I will take the rental gauge I have to my friend's place tomorrow and test it on his z to see if it reads 36 at idle or if it says 32 which would mean the gauge is just off.

[chaseincats]

6 minutes ago, siteunseen said:

When I was trying to figure out my lean running '77 I ran a fuel hose off a T to my driver's wiper blade, put the gauge on and zip-tied it to the window wiper and went for a drive. Mine was losing pressure while driving I discovered (couldn't see the engine mounted gauge while driving) so I ask an '80's Nissan Certified mechanic about it. He clamped off the return line which increased the fuel pressure on the rail and it ran much better. Told me to, basically, throw new parts in. Well after a lot of reading on this lovely forum I did the CTS tweak with a potentiometer from Radio Shack, $5 volume knob. Runs great when I drive it. 

This rainy day long read was my "ah ha!' moment.

This was the fix.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Good to know this exists.  This was a problem that just cropped up while driving so it has to be something mechanical rather than aging ecu related I'd think.

[siteunseen]

Do you have a fairly new fuel filter? The sediment falls down when they sit so it'll crank and idle for a minute then the crud stops them up.

Edited February 3, 2024 by siteunseen

[chaseincats]

2 minutes ago, siteunseen said:

Do you have a fairly new fuel filter? The sediment falls down when they sit so it'll crank and idle for a minute then the crud stops them up.

I believe its a few years old

[siteunseen]

If you have the Fram G3 between the tank and the fuel pump it should catch the gas tank trash before it gets up to the metal one in the engine bay so you are probably okay on the filter. That's just a knee jerk response from me. As Zed Head says, "carry on". 

[chaseincats]

38 minutes ago, siteunseen said:

If you have the Fram G3 between the tank and the fuel pump it should catch the gas tank trash before it gets up to the metal one in the engine bay so you are probably okay on the filter. That's just a knee jerk response from me. As Zed Head says, "carry on". 

I don't remember which make/model it is, but there is one of those clear plastic filters between the tank and pump.  I checked it yesterday and looked fine.

[Zed Head]

How about bad fuel?  Or water in the tank?  It happens.

https://ktla.com/news/california/were-californians-filling-up-on-bad-gas-for-years/

[chaseincats]

1 hour ago, Zed Head said:

How about bad fuel?  Or water in the tank?  It happens.

https://ktla.com/news/california/were-californians-filling-up-on-bad-gas-for-years/

Interesting - It did run really well yesterday but granted I didn't drive it, just idled it until it got to temperature so I could get readings with the fuel pressure gauge. so maybe not?

[Zed Head]

No telling.  If it runs well, what would you change/fix?  There's nothing to fix now.

p.s. next time it acts up watch the tachometer needle.  It's a good way to see if it's a spark problem or a fuel problem.

.

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Edited February 3, 2024 by Zed Head

[chaseincats]

12 hours ago, Zed Head said:

No telling.  If it runs well, what would you change/fix?  There's nothing to fix now.

p.s. next time it acts up watch the tachometer needle.  It's a good way to see if it's a spark problem or a fuel problem.

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Good call on watching the tach needle.  It is a fuel problem, as the needle behaves itself haha.

I will pull the injectors in the coming week and see if they are all firing at the same rate.

[chaseincats]

Hi gang,

So I pulled my injectors, put them all in individual cups and cranked the engine for a bit and all seem to have the exact same level and spray pattern (see video here).  I did however notice cylinder 1's injector connector teeth had a pretty solid amount of green corrosion on it which is weird considering these are only a year or so old with brand new harness connectors.  I did also notice small black particles in the gas coming out of the injectors - I'm not sure if that is just dirt from them resting on the head while waiting to be put in the cups or not.

Long story short here is where we are:

• I filled up the injector's plug area with caig de-oxit and let it sit all night and ill remove the corrosion this morning
• I will get a new engine bay fuel filter just in case it's not just dirt sitting on the engine intake plenum while they were resting there
• Switch injector #3 with a different one to see if the darker plug on cylinder #3 darkens darkens on the cylinder with the moved injector or not

 

Edited February 11, 2024 by chaseincats