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Discussion Starter · #1 ·
Recently had a fuel injection system tune-up done on my '77 280Z. The mechanic, Steve Ehler of Rising Sun Performance in Fort Worth, Texas, did a great job.
He changed the oil & filter, adjusted the valves and then hooked the beastie up to his tailpipe tester. He then proceeded to adjust the AFM, the throttle switch, and check out ad correct the outputs from the engine temperature sensor and thermotime switch. The good news is that there really is such a thing as a fuel injection system tune-up and it really improves the cars performance. The bad news is that he discovered that a previous mechanic had misadjusted the AFM and the throttle switch which set my car up to run rich and it has suffered irrevocable damage. Camshaft scoring, rings going bad, etc.
This type of tune-up requires an exhaust gas analyzer like the Nissan Shops and safety inspection boys use. Not something the average guy would have in the garage. Not having this done six years ago when I first got the car problably took 100,000 miles off the engines expected life. The cost of the work was about $250 and is worth every penny. Even though it has significant internal wear my car runs stronger than ever before.
Phantom
 

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I paid the bucks and was told the AFM needed replaced. Mechanic took me aside and told me about the resistor trick inline with the water temp sensor. Not temp gauge sensor.. Works good.. Was running too lean..
 

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Discussion Starter · #3 ·
Joe,
It definitely works but it is a band-aid. It doesn't cure the original problem. You probably didn't need a new AFM either - they are restorable. Just need a very experienced Z mechanic that knows how.
I always confirm the following:
1) Is he Nissan certified
2) Has he been working on Z's for at least 15 years - 20 is better
3) Does he have a certifed exhaust gas analyzer. Must have one to set the cars up correctly.
Phantom
 

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Re: Why does it kill it??!!

> Recently had a fuel injection system
> tune-up done on my '77 280Z. The
> mechanic, Steve Ehler of Rising Sun
> Performance in Fort Worth, Texas, did a
> great job.
> He changed the oil & filter, adjusted
> the valves and then hooked the beastie up to
> his tailpipe tester. He then proceeded to
> adjust the AFM, the throttle switch, and
> check out ad correct the outputs from the
> engine temperature sensor and thermotime
> switch. The good news is that there really
> is such a thing as a fuel injection system
> tune-up and it really improves the cars
> performance. The bad news is that he
> discovered that a previous mechanic had
> misadjusted the AFM and the throttle switch
> which set my car up to run rich and it has
> suffered irrevocable damage. Camshaft
> scoring, rings going bad, etc.
> This type of tune-up requires an exhaust gas
> analyzer like the Nissan Shops and safety
> inspection boys use. Not something the
> average guy would have in the garage. Not
> having this done six years ago when I first
> got the car problably took 100,000 miles off
> the engines expected life. The cost of the
> work was about $250 and is worth every
> penny. Even though it has significant
> internal wear my car runs stronger than ever
> before.
> Phantom

Phantom,

A couple of questions from someone trying to learn:

Why does running rich score the camshaft and wear out the rings, etc.?

And how does he know the rings are worn? Do they always go hand in hand or did he perform a compression test or something?

Thanks,

Matt
 

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Re: Why does it kill it??!!

I agree.
Whoever told you running a motor rich scores cam lobes and wears out rings can't know too much about how engines work.
If you believe it can, please explain why in detail...
 

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This is why!!

What happens is that the extra fuel that dosent burn runs down the cilinder walls and past the rings. This in turn washes all the oil off the cilinder walls and causes scoring and eventual loss of compression. When the fuel hits the oil it breaks it down and dilutes it. The oil then can no longer lubricate all bearings and cam lobes properly.

I can tell you this from experience because i bought a 240 that had been running rich for quite a while and dissasembled the motor for a rebuild. I ended up replacing all the valve trane parts from the cam wear and lack of decent oil. The bottom end was wrecked too: my machine shop had to grind my crank back to smooth and use ovesized bearings in the block holy **** was the term used when i brought it to them. The cilinders were severly scored and had to be rebored too.

If you are running rich, you need to replace your oil immediately and get the problem corrected, i spent a fortune fixing this damage!

I hope this clears things up- evan
 

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Discussion Starter · #7 ·
Evan is exactly right!!! Please read following

Evan's description of what has happened to my car is exactly correct. The other thing that the mechanic told me is that he strongly recommends oil changes every 2,000 miles on the high mileage Z engines just to try to keep this from happening. The fuel management systems on these cars tend to become less than optimal over the years - corroded contacts & sensors - and the usual result is engines that run rich. If you are wondering if you may have a problem check the tailpipe test that was done at your last safety inspection. If your cruise RPM had a CO reading above .5% you are running rich!!! I was running 6.0%. 7.5% is leagal for a '77 but it is not right for the motor. I found out the hard way.
Phantom
 

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Re: Not bad for a 18yr old huh?

Not to create an issue, but I think you have it backwards.

If your rings are bad to begin with, blowby will force the mixture past the rings into the crankcase. That does dirty the oil and makes for a pretty poor environment down there.
But if your compression is fine and ignition working ok, any extra fuel will exit the exhaust valve. It can't go anywhere else.

Rather than blaming the mixture, it sounds like your damaged motor is a result of poor maintenance and high mileage.

--1970 running 10:1 compression, rich mixture, and clean oil : )
 

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Re: OK, OK, maybe, but...

> Not to create an issue, but I think you have
> it backwards.

> If your rings are bad to begin with, blowby
> will force the mixture past the rings into
> the crankcase. That does dirty the oil and
> makes for a pretty poor environment down
> there.
> But if your compression is fine and ignition
> working ok, any extra fuel will exit the
> exhaust valve. It can't go anywhere else.

> Rather than blaming the mixture, it sounds
> like your damaged motor is a result of poor
> maintenance and high mileage.

> --1970 running 10:1 compression, rich
> mixture, and clean oil : )

Both answers sound plausible, but what do I know? I'm just a marketing guy that took highschool auto shop.

Here's another one for you though: Assuming there's truth to both, ie.-- unburned gas can pass the rings and corrode the oil (regardless of the cause), does running pure synthetic change the scenario any?

Also, how bad would the oil have to get to score your cam, rings, bearings, etc. Seems to me it would have to have lost all it's lubricating qualities to do such dammage. Wouldn't this be more evident in the outward appearance of the oil in question?

Don't be shy! Let's get to the bottom of this.

Matt
 

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HERE'S THE DEAL

Oil is a suspension made up of many molecules. The problem, is that with time and heat, they break down. This causes the oil to become more viscous, which means it does not flow as well.

Areas of the engine that rely on the viscocity the most, are areas that are not under direct oil pressure. For examle, the rings get oiled by the 'splash affect' of the rods rotating through the oil. When the oil is higher in viscosity, this affect is lost, and is why worn cylinders/rings are the first part to go on a engine that was not well maintained. Places that get direct pressure (main bearings, cam, etc...) are not AS affected, but still feel the affects of unwanted friction, thus further breaking down the oil. So, once the viscosity starts to break down, it really begins to snowball. This is why regular oil changes are important.

Another thing to consider, is the formation of deposits and acids. As the oil breaks down, it starts to form long Carbon chains, which can block small oil passages. The acid will start to score the highly polished surfaces of exposed metal, and begin the corrosion process.

These are all reasons why oil changes are recommended. Synthetic would help in any situation, because it is not based on the same carbon molecules as 'dead dinosaur juice'. It won't break down the same, and create all the acids and deposits. But, it WILL break down over time, just as any suspension will, but it takes alot longer, and provides better protection in the meantime, without as many nasty side affects.

240Dave
 

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Re: Thanks, & clean oil ?

> Oil is a suspension made up of many
> molecules. The problem, is that with time
> and heat, they break down. This causes the
> oil to become more viscous, which means it
> does not flow as well.

> Areas of the engine that rely on the
> viscocity the most, are areas that are not
> under direct oil pressure. For examle, the
> rings get oiled by the 'splash affect' of
> the rods rotating through the oil. When the
> oil is higher in viscosity, this affect is
> lost, and is why worn cylinders/rings are
> the first part to go on a engine that was
> not well maintained. Places that get direct
> pressure (main bearings, cam, etc...) are
> not AS affected, but still feel the affects
> of unwanted friction, thus further breaking
> down the oil. So, once the viscosity starts
> to break down, it really begins to snowball.
> This is why regular oil changes are
> important.

> Another thing to consider, is the formation
> of deposits and acids. As the oil breaks
> down, it starts to form long Carbon chains,
> which can block small oil passages. The acid
> will start to score the highly polished
> surfaces of exposed metal, and begin the
> corrosion process.

> These are all reasons why oil changes are
> recommended. Synthetic would help in any
> situation, because it is not based on the
> same carbon molecules as 'dead dinosaur
> juice'. It won't break down the same, and
> create all the acids and deposits. But, it
> WILL break down over time, just as any
> suspension will, but it takes alot longer,
> and provides better protection in the
> meantime, without as many nasty side
> affects.

> 240Dave

Thanks 240Dave.

If I understand you correctly, its more of an acidic corrosion that scores the parts. I always pictured something more extreme only could cause such damage-- like no oil or dirty, gritty oil.

So, if your oil is looking clean/clear, is it safe to say it's still doing it's job? And if not, how can you know if your oil is breaking down?
 

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Re: Thanks, & clean oil ?

> Thanks 240Dave.

> If I understand you correctly, its more of
> an acidic corrosion that scores the parts. I
> always pictured something more extreme only
> could cause such damage-- like no oil or
> dirty, gritty oil.

No, Not really. The acidic corrosion and carbon buildup are bad side affects. Like I said, the cylinder walls/rings are usually the first parts to feel the affects of the lowered viscosity. Since these are dependent upon the 'splash affect'. This is one of the prime causes of engine failure. Dirty, gritty oil, is more harmful than just acid buildup. Over time, acid buildup will do it's deed, and then you'll have more than just scored cylinder walls.

> So, if your oil is looking clean/clear, is
> it safe to say it's still doing it's job?

Yes, I would say so. It's just like you said, if it's clean, then it's not holding alot of crap in suspension, which means that it's molecules are holding together tightly.

Look at it like this. Most manufacturers, recommend an oil change every 3000mi or 6mo., whatever comes first right? The reason for this is that oil breaks down with heat (it breaks the bonds of the molecules), but it also breaks down over time.

> And if not, how can you know if your oil is
> breaking down?

You really can't tell just by looking at it. But, if it looks clean, and is was put in recently, then don't worry about it. If you can't remember the last time you had an oil change, I'd say get it changed, even though it may look alright. It's just cheap insurance. $20 every 6mo or so is not bad if it saves your engine. Besides, a free flowing oil system (low friction) = more hp!!!
 

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Re: Thanks, & clean oil ?

> No, Not really. The acidic corrosion and
> carbon buildup are bad side affects. Like I
> said, the cylinder walls/rings are usually
> the first parts to feel the affects of the
> lowered viscosity. Since these are dependent
> upon the 'splash affect'. This is one of the
> prime causes of engine failure. Dirty,
> gritty oil, is more harmful than just acid
> buildup. Over time, acid buildup will do
> it's deed, and then you'll have more than
> just scored cylinder walls.

> Yes, I would say so. It's just like you
> said, if it's clean, then it's not holding
> alot of crap in suspension, which means that
> it's molecules are holding together tightly.

> Look at it like this. Most manufacturers,
> recommend an oil change every 3000mi or
> 6mo., whatever comes first right? The reason
> for this is that oil breaks down with heat
> (it breaks the bonds of the molecules), but
> it also breaks down over time.

> You really can't tell just by looking at it.
> But, if it looks clean, and is was put in
> recently, then don't worry about it. If you
> can't remember the last time you had an oil
> change, I'd say get it changed, even though
> it may look alright. It's just cheap
> insurance. $20 every 6mo or so is not bad if
> it saves your engine. Besides, a free
> flowing oil system (low friction) = more
> hp!!!

I just recently changed to Mobile One synthetic-- engine revs real smoothly. I thought since my engine burns about a quart about every 1,500 (thus dumping fresh lube in every month or two) that I would try changing only the filter when the oil starts to get cloudy. See what happens to the appearance. I'm curious about this because supposedly the synthetics are not supposed to break down like the fossils do. So, theoretically, if you could filter out the bad stuff, you should still have good oil.

I certainly wouldn't do this indefinitely, but 5,000-6,000 miles of clean oil without having to crawl under the car???

Is this faulty logic?

Matt
 

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Re: Thanks, & clean oil ?

> I just recently changed to Mobile One
> synthetic-- engine revs real smoothly. I
> thought since my engine burns about a quart
> about every 1,500 (thus dumping fresh lube
> in every month or two) that I would try
> changing only the filter when the oil starts
> to get cloudy. See what happens to the
> appearance. I'm curious about this because
> supposedly the synthetics are not supposed
> to break down like the fossils do. So,
> theoretically, if you could filter out the
> bad stuff, you should still have good oil.

> I certainly wouldn't do this indefinitely,
> but 5,000-6,000 miles of clean oil without
> having to crawl under the car???

> Is this faulty logic?

> Matt

Well this I m not sure about but I had other people tell me with a turbo engine u should still change it 3,000 miles. Synteics oil. with me I know I can do 36 trips then I have to change the oil that 82 miles a day
 
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