The purpose of this thread is to showcase some cases of automobile issues that are remain very challenging and unresolved for other mechanics that are brought to Autologic workshop for fix.
And the logical and scientific thought process that follow to achieve 100% definite diagnosis and resolution !!
Our work culture at Autologic Service Central is using scientific approach towards achieving on 100%
on- point diagnosis to achieve quality and manufacturer stipulated repair process !!!
Newbie and welcome are both welcome however ,trolls pls keep off .
Stay tuned!!

Case1

Car model :Nissan pathfinder 2003

Customer maintaince history :Mobil XHP 20w50 oil change 3000km change interval

Customer complaint: Car is unable to rev past 2000 rpm

Previous work attempt to fix the issue: ignition coil ,fuel pump and injector has been changed !!
Also the cam and crank sensor has been swapped all to no avail !!

Scope of Job Resolution :Fix to resolve the rev issue only

Diagnosis approach and procedure :

1.0 Physically inspection Result :subtle misfire felt !

2.0 Scan result :no misfire DTC
3.0 Live Stream conclusion :There is misfire at bank 2

Overall Conclusion :There is a subtle misfire within one of the cylinder not caught by the engine management computer to be registered as DTC .Hence all the existing DTC need to be erased and vehicle will need to be driven to complete the require cycle to register the misfire DTC.

1.Work Procedure
DTC erased and vehicle driven in a way to set the enable criteria for the engine Computer to pick and register the misfire DTC in its memory !!

2.0 Scan tool result after the drive cycle :
Misfire at no 4 cylinder !!

Well done!

More grease to your elbow!!

This is your best outreach ever!!!

Keep up the good work!!!!

Following keenly!!!!!

AutoElectNG:
Well done!

More grease to your elbow!!

This is your best outreach ever!!!

Keep up the good work!!!!

Following keenly!!!!!

Thanks

Thought Process to diagnose Misfire at cylinder 4 :
Misfire at a single cylinder can only be limited to issue of low compression at cylinder 4 cos previous mechanic had already changed swapped spark plugs and injector
So the diagnosis test to confirm the compression status of cylinder 4 will be the priority on the list of test to be undertaken before anything else
Therefore cylinder diagnosis compression test will be done to confirm the value of cylinder 4 and the adjacent cylinder 6 and their results will compared

Manufacturer stated value for cylinder compression
Standard compression value:185 psi
Minimum compression :142 psi
Difference limit between cylinder: 14 psi

Cylinder Compression diagnosis result for cylinder 4:
Dry test :140 PSI
Wet test :200PSI

Cylinder Compression result for cylinder 6 (adjacent cylinder)
Dry test: 160 psi
(No need for wet test cos this cylinder only serve for negative control purpose)

Diagnosis Conclusion :
From the test above ,we can boldly declare that we have a diagnosis :
The misfire is definitely due to worn piston ring due to long history of using wrong engine oil(20w50) for servicing .
The issue of rev not exceeding 2000 RPM is directly due to low compression at cylinder 4 !!!

Recommended Fix :
Completed engine change:
engines change: the cost of undergoing a genuine engine overhaul will exceed the cost of procuring tokunbo engine

I will update the thread for the progress report of the engines change!!!

Since we are of the opinion that the loss in compression is just a few psi below spec ,we can do a little bit of reverse engineering to raise the compression a little bit and if possible enable the car to rev past 2000
Fortunately for us ,with our home made trick we were ablw to achieve beyond expectation .
Lol and behold ,the car rev nearly up to 6000 RPM !!! ;

autologic:
The purpose of this thread is to showcase some cases of automobile issues that are remain very challenging and unresolved for other mechanics that are brought to Autologic workshop for fix.
And the logical and scientific thought process that follow to achieve 100% definite diagnosis and resolution !!
Our work culture at Autologic Service Central is using scientific approach towards achieving on 100%
on- point diagnosis to achieve quality and manufacturer stipulated repair process !!!
Stay tuned!!

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You mean your home made trick reversed in one fell swoop the disability represented by the supposed use of wrong engine oil?

autologic:
Since we are of the opinion that the loss in compression is just a few psi below spec ,we can do a little bit of reverse engineering to raise the compression a little bit and if possible enable the car to rev past 2000
Fortunately for us ,with our home made trick we were ablw to achieve beyond expectation .
Lol and behold ,the car rev nearly up to 6000 RPM !!! ;

Na that wan we dey interested in

Costee:
You mean your home made trick reversed in one fell swoop the disability represented by the supposed use of wrong engine oil?

Yes we thought about it that it possible to achieve some momentarily compression gain for case of a very subtle loss of compression(just for experimental purpose) and it works(we enjoy hacking a lot in our workshop) !! but the engine still later went back to its initial state after some few minutes.
Note that we can only achieve this gain cos it a very little below minimum!!! This cannot be possible wen the margin is high
Point of correction :Our supposed hack enable us to achieve a little compression gain caused by loss of Compression not use of wrong oil .

autologic:

Yes we thought about it that it possible to achieve some momentarily compression gain for case of a very subtle loss of compression and it works(we enjoy hacking a lot in our workshop) !! but the engine still later went back to its initial state after some few minutes.
Note that we can only achieve this gain cos it a very little below minimum!!! This cannot be possible wen the margin is high
Point of correction :The compression loss is caused due to worn piston ring directly not due to wrong oil directly .use of wrong oil is indirectly responsible not directly !!!hope u catch the drift

That's my point. I felt you announced your results rather prematurely as "the engine still later went back to its initial state after some few minutes." What is meant by wrong oil causing the issue indirectly? You stated the facts: compression loss----worn piston-----wrong oil. So in what way is wrong oil indirectly responsible, if not directly? The issue of oil viscosity is one universal controversy that has gone neither here nor there and has remained unresolved. Diagrams in owners' manuals will always graphically display variations that are permissible, though indicating preference for 0-30. Let me quote the owner's manual of the very 2003 Pathfinder you've used:"SAE 5W-30 viscosity oil is preferred for all ambient temperatures. SAE 10W-30, 10W-40 viscosity oil may be used if the ambient temperature is above 0°F (−18°C)." Would say that even at its coldest our ambient temperature here is lower than that stated? Your argument on the role of engine oil in this case appears to me rather far-fetched.
There was another thing you should have explained. The codes that came to your workshop didn't appear today. Yes, you suspected a misfire code, but which hadn't been there. Why was it that it was when you re-drove the vehicle that the misfire code came up? I'm not accusing you of any foul play, but an explanation would have given your procedure some respectability. You completely ignored P1130. I think you'd have to address it to fully resolve the issue at hand.
I appreciate the fact that you want to report real time measures and procedures, but leave your conclusions to when a vehicle that comes to your workshop has been certified as fully cured---and by none else than you!.

What was the characteristic evebts that took place on the cylinder 4 when it was physically inspected? Am just curios

mayor2013:
What was the characteristic evebts that took place on the cylinder 4 when it was physically inspected? Am just curios

Misfire event will cause an engine to vibrate and this jerking will depend on the severity of the misfire cos there are different degree of misfire.
Normal engine running without misfire will produce an even repeatative rhythm that a trained ear can easily distinguish from uneven rhythm produced by misfiring engine .Note that the phrase "trained ear"Not everyone can perceive this ,it is more of professional training that develop with constant practice!!!

Costee:

That's my point. I felt you announced your results rather prematurely as "the engine still later went back to its initial state after some few minutes." What is meant by wrong oil causing the issue indirectly? You stated the facts: compression loss----worn piston-----wrong oil. So in what way is wrong oil indirectly responsible, if not directly? The issue of oil viscosity is one universal controversy that has gone neither here nor there and has remained unresolved. Diagrams in owners' manuals will always graphically display variations that are permissible, though indicating preference for 0-30. Let me quote the owner's manual of the very 2003 Pathfinder you've used:"SAE 5W-30 viscosity oil is preferred for all ambient temperatures. SAE 10W-30, 10W-40 viscosity oil may be used if the ambient temperature is above 0°F (−18°C)." Would say that even at its coldest our ambient temperature here is lower than that stated? Your argument on the role of engine oil in this case appears to me rather far-fetched.
There was another thing you should have explained. The codes that came to your workshop didn't appear today. Yes, you suspected a misfire code, but which hadn't been there. Why was it that it was when you re-drove the vehicle that the misfire code came up? I'm not accusing you of any foul play, but an explanation would have given your procedure some respectability. You completely ignored P1130. I think you'd have to address it to fully resolve the issue at hand.
I appreciate the fact that you want to report real time measures and procedures, but leave your conclusions to when a vehicle that comes to your workshop has been certified as fully cured---and by none else than you!.

This is a long one and I will need to be careful to avoid the trap of getting engaged in unending loop of argument which will defeat the purpose of this thread but I will address this your question one by one subsequently with facts and figures .Every claim must be proof scientific not just mere talk !!!I am proudly a scientist !!
But still let me address the issue of ignoring P1130 .
Like I stated earlier ,we have a scope of work which is primarily to diagnose the issue of inability to rev beyond 2000 RPM.(This car is coming from mechanic) other DTC they is not a pointer to this issue will not be addressed .However ,P1130 is actually a reference code !!!
Secondly ,the issue of misfire is intermittent one and from years of experience I already know intermittent issues wil alwaysl evade the engine computer DTC arrest ,However I make my definite diagnosis not from DTC error code but live data and result from low level analyses (Scope waveform and DVOM readings )Is not compulsory the DTC record it before I can make my inference where it is coming from !!I have my own professional way of taking my reading !!But having it eventually is just a plus !!
Lastly ,U will need to read the conclusion again cos there is no where it is claimed that the issue has been cured by anybody. The conclusion still remain that there is a loss of compression at cylinder 4 responsible for the rev issue .What we have is an experimental session for our R& department after conclusion has already been drawn !!!

What scan tool do you use?

I intend to enter no polemic either, but I think in dismissing P1130 you proceeded by killing a fly with a sledge hammer. Scour the net, and you'll find it characteristic of the Pathfinder and QX4. Everybody who had it solved it because they found it ultimately easy. The Pathfinder of your client had all the symptoms. In no instance was was the worn piston/engine oil theory a causative factor (at any rate, they would always use the"recommended oil"), and neither was there a need for a whole engine to be replaced because of that small valve and gadgets working with it. A misfire code can be triggered by many many things, and I think by making it the central path of your diagnosis in this case you predetermined your conclusions. Endeavour to check that code (P1130) well and be convinced that it plays no part in this issue before advising your client to change his VQ35 engine. Why you intend to disparage/denigrate it as a "reference code" I'll never understand. I have and do understand Nissan's Factory Service Manual (not owner's manual), so I know what I'm about.
I don't intend to say more..............Well, until perhaps the next Nissan case

I think I may have talked with the owner of this car before. Just a thought process.

It's good to know a Nissan expert is around we have a few murano and altima/maxima going for 100k I believe it's time to occupy your workshop with them.

If it's only cylinder 4 that has been affected, why don't you change only that or the rest of the cylinders have started showing worn out symptoms?

Autologic, as Costee said, I think you need to revisit the P1130 code looking at the swirl control valve and the ECU.

nurey:
I think I may have talked with the owner of this car before. Just a thought process.

It's good to know a Nissan expert is around we have a few murano and altima/maxima going for 100k I believe it's time to occupy your workshop with them.

If it's only cylinder 4 that has been affected, why don't you change only that or the rest of the cylinders have started showing worn out symptoms?

I am a Nissan fan and Nissan is my first baby !!!
Let me use this profile to answer your question (my other profile Autologic has been banned I don't why )cc :marpol
In my workshop ,it part of our business policy not to engage in engine overhaul that is peculiar to low end part of engine (engine block ) as this is a confirmed worn piston ring issue .
Secondly ,the other cylinders are already following the same route ,so it better the fix is applied to all the cylinders once and for all
However if it still top end engine rebuilt ,we will readily do the job!!
The owner readily agree to go with the engine replacement!!!

autologic:
Diagnosis Conclusion :
From the test above ,we can boldly declare that we have a diagnosis :
The misfire is definitely due to worn piston ring due to long history of using wrong engine oil(20w50) for servicing .
The issue of rev not exceeding 2000 RPM is directly due to low compression at cylinder 4 !!!

Seriously?

autologic:
Recommended Fix :
Completed engine change:
engines change: the cost of undergoing a genuine engine overhaul will exceed the cost of procuring tokunbo engine

Really? So the next thing na engine change? Just like that? I am of the opinion that you went overboard sir.

praxisnetworks:


Really? So the next thing na engine change? Just like that? I am of the opinion that you went overboard sir.

Yes it is butter pill to swallow cos some considerable cost is involved ,emotion will set in natural but should not be allowed to cloud our thinking faculty. we need to be objective and logical in some decision making not to sacrifice standard and safety on the alter of era of buhari ecocomy!!
1. No magic can make a genuine and manufacturer spec standard engine overall become exactly like the manufacture built engine and will incur near the same cost.
(This is low end engine overhaul not top end) !!!
The resources that will goes toward sourcing for a good tokunbo engine like almost new for that particular engine will ultimately be cheaper than going through the time consuming process of undergoing genuine engine rebuilt that will rival manufacturer standard .
It will eventually be a win win situation for us and customer in term of quality and cost which is part of our mission statement
2.In autologic ,we are so conscious about safety and quality and we are not ready to compromise that #safetyfirst !!!!And to minimize return jobs to zero!!#quality
We want to minimize your cost as much as possible which is why we made huge investment in diagnosis to minimise wrong part swapping!!