Its hard to express how a professional would do it. To you it looks like a mountain to climb. To me its what I do every day. Likelyhood is that the problem is so simple I wouldn't even see the car in my shop (I only do the hard ones).
Most problems, even for experienced techs, boil down to something simple camaflaged under some poor assumptions. How about another example of one that toasted our...you know.
My best strategic tech does most of our BMW diagnostic work. He wound up on a 93 Audi 90CS 2.8l v6. The car is brought to us by the cheapest car wholesaler (that is cheapest wholesaler not cheapest car) in town. Knowing the source we should decline the business, but we are good guys.
The story is that it is a no start. He has already replaced the crank sensor. (keep track of the camoflage). We test the car and sure enough it has no spark signal or injector signal. After doing pin-outs of every terminal of the controller we have found that the controller is awake and capable of displaying fault codes. We cause a couple to be sure. Other than the codes we cause there are no codes. While testing all the controller inputs we come across some problems with the signal from the cam sensor and we replace it. Still no ignition or fuel pulse signal outputs from the controller. We are about to bail as with the known status of the customer we know he will whine after we charge him for the first hour of labor and there are a shop full of real customers cars.
Our diagnosis at this point leads us to thinking it is a controller issue. We spend some time finding a real cheap used one ($125) and with it installed there is still no ign or fuel control. *****!
At this point the professional says: I'll deal with it tomorrow! (as of course this problem has risen to my level - I of course suggested the cheap used controller at my tech"s controller diagnosis - diagnostic risk management is also my specialty).
Well what would you do??? I did the same thing, I went to the iATN archives and looked the problem up and in about three posts I had the answer. Those damn "A" fools have a engine protection strategy that turns the ign and thus fuel off when ever the syncronicity of the cam and crank are off by more than one tooth.
About an hour latter that thing was running like ***** with its cams adjusted and 65psi compression in each cylinder. This is where the professional really can get beat up. I should have turned down the job knowing the source. I/we were lead astray by his original work with the sensor and the further finding of no electronics. Normally we probably would have went right to cam timing. OF course when we take it apart we see the crayon marks and new belt where they had screwed it up... do you think they would tell you they did such? The job is just packed with irony, a psych would maybe have done better. The fact that we didn't know Audi used this unique strategy without setting a code amazes me but we will chock it up to learning and the fun of the final kill.
A professional handles it anyway necessary. A real professional then figures out what that problem should cost and charges for it. As it turns out a real professional wouldn't of had the problem as he would have known that startegy, least all those archive replies were from guys who had been there!
It wouldn't be fun if it was easy, but it is unfortunate that there is no way for me really to give you all any clue how far in the dark you are compared to a professional. The typical DIYer only lacks three things to keep you from having the same problems I do: Training, Experience and a half million in tools. Otherwise we could all do brain surgery!
Bosch Master, ASE Master, L1
33 years MB technician