tirod
09-05-2012, 12:02 AM
One of the more difficult aspects of working on cars is discovering there is a completely unknown system installed in them that diabolically ages with every turn of the key. Each time you fire up the monster, it gets another startup older, and like the morning you realize you can't just bend over to tie your shoes, you have to face the reality:
It has a electrical system that is aging faster than you are.
Old cars - just twenty year old cars - are plagued with resistance and voltage drop issues. As our cars keep getting more and more electronic stuff installed, and communicate to a computer with more wiring, more defects keep popping up.
Lets look at one such case, a Technical Service Bulletin issued less than one year after a certain model was equipped with a new motor. It's dated May 23 of 1989. That's quite a while back, over 23 years ago. It details, in short, a method of correcting the low signal issues of the crankshaft position sensor and the no start or long cranking it causes. In short, the TSB directs the mechanic to simply cut the entire wiring of the CPS off, drill a hole in the firewall, and install a new CPS and harness that connect directly to the 32 pin plug at the computer.
It was already a problem - the wiring harness was developing corrosion beyond the ability of the low voltage signal to send data. The answer was to eliminate the connection to the ECU wiring harness and connect it directly. The TSB was issued before they even built my Cherokee - BUT - they did NOT alter the harness or change the way mine was built. Millions went out like that.
As far as the factory was concerned, they'd bother to do it if and when it became a problem on a customer car under warranty, when someone could complain.
23 years later, it's a bit late. But, I can take the lesson for it's actual value and perform the TSB. If you use an donor, it would certainly help to research what the factory suggested might be valuable for you - especially since it's highly unlikely they bothered to improve it. And it certainly should give pause to even consider a donor harness, especially one that is nearly twenty years old, removed from a car, dieted, and then reinstalled. That is a lot of manhandling and corrosion to put up with. In the worst case, it will make a car a garage queen until it's replaced.
The perspective of those who have driven old cars a lot for a long time is that the wiring harness is the #1 cause of much of the car's infirmities. Whether a '60s or '90's, it's a major "tell" of factory wiring that the cure for a bad voltage drop issue that prevents the car even starting is to bypass the wiring completely and connect it directly to the computer. As the car continues to age, the relative replacement interval of these CPS units comes more quickly. They aren't making them worse and worse, the wiring is getting worse and worse.
Don't install that problem child to begin with, and you are already on your way to a long lasting relationship with a reliable runner. Upgrade to an even better system, and you can avoid the symptoms of corrosion for another decade longer. It's up to you - would you rather be driving it in the rain, or under it trying to get it to start?
I've done both, and it's not getting any easier when it breaks down. But, it's getting more frequent.
It has a electrical system that is aging faster than you are.
Old cars - just twenty year old cars - are plagued with resistance and voltage drop issues. As our cars keep getting more and more electronic stuff installed, and communicate to a computer with more wiring, more defects keep popping up.
Lets look at one such case, a Technical Service Bulletin issued less than one year after a certain model was equipped with a new motor. It's dated May 23 of 1989. That's quite a while back, over 23 years ago. It details, in short, a method of correcting the low signal issues of the crankshaft position sensor and the no start or long cranking it causes. In short, the TSB directs the mechanic to simply cut the entire wiring of the CPS off, drill a hole in the firewall, and install a new CPS and harness that connect directly to the 32 pin plug at the computer.
It was already a problem - the wiring harness was developing corrosion beyond the ability of the low voltage signal to send data. The answer was to eliminate the connection to the ECU wiring harness and connect it directly. The TSB was issued before they even built my Cherokee - BUT - they did NOT alter the harness or change the way mine was built. Millions went out like that.
As far as the factory was concerned, they'd bother to do it if and when it became a problem on a customer car under warranty, when someone could complain.
23 years later, it's a bit late. But, I can take the lesson for it's actual value and perform the TSB. If you use an donor, it would certainly help to research what the factory suggested might be valuable for you - especially since it's highly unlikely they bothered to improve it. And it certainly should give pause to even consider a donor harness, especially one that is nearly twenty years old, removed from a car, dieted, and then reinstalled. That is a lot of manhandling and corrosion to put up with. In the worst case, it will make a car a garage queen until it's replaced.
The perspective of those who have driven old cars a lot for a long time is that the wiring harness is the #1 cause of much of the car's infirmities. Whether a '60s or '90's, it's a major "tell" of factory wiring that the cure for a bad voltage drop issue that prevents the car even starting is to bypass the wiring completely and connect it directly to the computer. As the car continues to age, the relative replacement interval of these CPS units comes more quickly. They aren't making them worse and worse, the wiring is getting worse and worse.
Don't install that problem child to begin with, and you are already on your way to a long lasting relationship with a reliable runner. Upgrade to an even better system, and you can avoid the symptoms of corrosion for another decade longer. It's up to you - would you rather be driving it in the rain, or under it trying to get it to start?
I've done both, and it's not getting any easier when it breaks down. But, it's getting more frequent.