Tech Thread Only?

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Re: Tech Thread Only?

scanner
909 Smog wrote
That was smart of Nissan to use the same color connectors with the ability to plug into each other.  One question I still don't understand.  If the connectors are crossed and and Bank 2 oxygen sensor measures .8, why is the Bank 1 Alpha adding fuel with a reading of 125?  The same with Bank 1 oxygen sensor measuring 0 and bank 2 Alpha subtracting fuel?  Seems backwards to me.  Please explain Scanner.
On the scanner, the PCM sees Bank 1 Low,  so Bank 1 Alpha is trying to bring it up.   The PCM thinks Bank 1 is low, but it's actually seeing Bank 2 which is already high.

A couple was traveling on the open highway and it was getting late.  They decided to stay at a motel.  It was cold, but the owner of the motel said they had electric blankets with separate controls for him and her.    They went to sleep, and both set their thermostats to their liking.   On his side, it was getting to hot, so he turned his thermostat down.    She was noticing that it was getting too cold, so she turned her thermostat up.    He was getting hotter and hotter, and she was freezing.   They didn't sleep at all that night, and when they discussed how terrible the electric blanket was, they suddenly realized that someone had switched the thermostat controls.    

Why make it simple, when it will work equally as well complicated.
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Re: Tech Thread Only?

D Rochells 150861
In reply to this post by 909 Smog
The pigtails are different colors, and if someone had bothered to backprobe and read the wiring diagram. Plus anytime one of the ziptie peg holders isnt in the hole indicates sloppy work. Not saying I would have caught it without a lot of headscratching. Im only good at diagnosis when Im not being paid to do it.
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Re: Tech Thread Only?

Just the Facts
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Re: Tech Thread Only?

Just the Facts
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Re: Tech Thread Only?

FiendFX
In reply to this post by scanner
Scanner,

Did a wiring diagram led you to the answer?
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Re: Tech Thread Only?

scanner
FiendFX wrote
Did a wiring diagram led you to the answer?
No, I never looked at a wiring diagram for this diagnosis.  

The fuel trims told the whole story.  The PCM was putting a boat load of fuel into Bank 1 because it looked like B1S1 was dead lean.     It was taking away fuel from BANK 2 because it looked like it was pegged rich.  

What other conclusion can you come to?

I jumped out of the driver's seat and looked at the connectors above the exhaust manifold and figured the easiest way to switch them back to the correct position.   Took me longer to document the case study than it was to provide the fix.  

I'll wait a week or two, and I'll put another one up.   I would like to see what others have done.
Why make it simple, when it will work equally as well complicated.
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Re: Tech Thread Only?

FiendFX
Scanner,

Ah I see. Nice catch.
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Re: Tech Thread Only?

barrym95838
Administrator
In reply to this post by scanner
scanner wrote
... I'll wait a week or two, and I'll put another one up.   I would like to see what others have done.
Please don't wait that long, scanner.  I doubt that anyone else could do better, but I also don't want to discourage anyone else from trying.

I don't see why we couldn't have more than one case study going at the same time, as long as the responses are clearly labeled.

And with all due respect, dmlusmc, sir, if you decide to post one, please try to provide solid clues from the beginning, not "I think it said ..."

BTW, that mid-eighties Thunderchicken didn't have crossed O2 sensor connectors, but it did have crossed injector connectors, with the same symptoms.  The Jag did have the O2 connectors crossed.

barrym95838
EO/EI144107
“Never attribute to malice that which can be adequately explained by stupidity.”
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Re: Tech Thread Only?

909 Smog
Barry,

Would the crossed injectors on the thunderchicken need to go to different banks in order to give the same symptoms as Scanners case study?  What would the fuel trims and O2 sensor graphs look like on a 4cyl. engine with crossed injector connectors if it only had one bank?
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Re: Tech Thread Only?

barrym95838
Administrator
In the high-pressure CFI era, the 3.8L and the 5.0L both had an injector over each throttle plate, but only the 3.8L could have separate left and right fuel trims, due to the internal shapes of the intake manifold passages, which were a direct result of the firing order.  On the V8, each injector fed two cylinders on the right and two cylinders on the left, making left and right fuel trims impossible, but on the V6 each injector fed the entire bank associated with it.  The V6 firing order is LRLRLR... and the V8 firing order is LRRLRLLR... (at least for a conventional 90° crankshaft).

Swapping the two injector connectors would have no effect on the 5.0L, but swapping the injector connectors on the 3.8L produced the same symptoms that scanner described for the Nissan.  That early EEC-IV system didn't have live scan data, though, so I had to figure it out with a two-channel scope, after a bit of head-scratching.

Regarding crossed injectors on a single-bank system, I would think that it could cause a driveability concern and maybe an HC problem in a sequential system, but the last time I saw something like that was on an old beat-up 4.0L Cherokee, and it ran like straight shit before and after I hooked the injectors up correctly, for a variety of unrelated reasons.

barrym95838
EO/EI144107
“Never attribute to malice that which can be adequately explained by stupidity.”
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Re: Tech Thread Only?

dmlusmc
In reply to this post by smgmn
So I took a pop quiz at my friends mechanic shop as to what the first thing to check when diagnosing a high HC misfire is reading was 430ppm at idle 02 level 1.0 passed at 2500 fine.the dodge van had GPd so its compression as far as what your supposed to check first, I didn't know at first. I would think doing a cylinder balance test to locate the misfiring cylinder and find out whats causing it to miss. but yea compression and engine integrity make perfect since as the first thing to check. and the plugs will be out during the compression test so those can be checked as well. But its better to find the root cause of the problem when diagnosing and check the little things rather than just be a parts changer. This also failed the EGR functional test so I would clean the egr passages first and retest before replacing the valve if it was me.
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Re: Tech Thread Only?

justa
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scanner
just another shop owner wrote
First thing I would do, and I will get told no is. Vacuum gauge to manifold source.
That sounds legit to me.  A fluctuating needle will instantly tell you there are valve train problems.  

Depending on the platform, I'd disable either fuel or spark, and then do a flatrate relative compression test.   I'd crank it over, and listen for a cylinder that doesn't have compression.  Apparently some don't have the ear to be able to do that.  

 Next time give us the CO reading also. Rich engine will cause high HC
You've said it before, an I don't know how many times you can say it,  Make, Model, Year, Engine size, and all the gas readings.  
Why make it simple, when it will work equally as well complicated.
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Re: Tech Thread Only?

FiendFX
knock knock
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Re: Tech Thread Only?

you rang
You rang?
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Re: Tech Thread Only?

Kriss Vector
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Re: Tech Thread Only?

FiendFX
I think it's unnecessary.. Pumping gas already has additives.
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barrym95838
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In reply to this post by Kriss Vector
I get that question all the time, and I say that I have nothing good or bad to say about most of them, but also that I don't use any of them for my personal vehicles.

barrym95838
EO/EI144107
“Never attribute to malice that which can be adequately explained by stupidity.”
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Kriss Vector
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FiendFX
In reply to this post by scanner
Bring it back
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