Engine Harness Repair
Many 944s are plagued with electrical problems. Many of these are not from the sensors themselves, but from the connection to the sensor. The plastic housings easily break and wear out. Most of the time, the wiring itself is just fine, as Porsche was really good about properly protecting their wiring. The problem lies within the plastic electrical connector housings themselves.
The Bosch L-Jetronic fuel injection system uses electrical connectors at all the sensors and fuel injectors, known as Bosch/AMP connectors. They are similar in fashion except for the number of pins each connector uses. They are fairly hard to find in the United States. If you want to just replace the connector, boot, and terminals; they can be ordered from an excellent vendor known as KayJay Company. Some of these connectors may be available at the dealership, but many are discontinued. I prefer the aftermarket connectors as the retaining spring is located further from the plastic housing and allows you to disconnect and reconnect the connector much easier. If you want to replace a two terminal connector with a pigtail, NAPA #CRB 218457 can be used. If you want to go that route, just solder the pigtail wires onto the existing two wires. This write up will explain how to replace the entire housing, terminals, weather seal, and boot.
NOTE: Porsche had the habit of injecting epoxy inside the boot of the connector. This creates a super hard plastic mass that makes things very difficult. You can't extract single wires, and you can't see inside the connector to double check things when putting it back together. Supposedly, at one point they stopped doing this. The following write ups show a harness with epoxy injected boots.
Harness Repair Using New Bosch/AMP Connectors
First let's look at the inner workings of the Bosch/Amp connector. You can see that the terminal is un insulated and slides through an individual hole on the back side of the connector. The front of the connector has a retaining tab which keeps the terminal from backing out of the plastic connector. This is a very positive retaining tab, you will hear this tab loudly "snap" when it passes through. Finally, you can see the horizontal alligator mouth that connects to the male terminals on the sensors.
To repair the connector, first pull the boot off the one you plan on replacing. You may want to cut away as much epoxy as possible until you can see where the individual wires are going. This is to double check things when putting the new wires in place. Be sure to double check the wiring order with the factory electrical schematics. These can be downloaded in the documents section of this web page.
Cut the wiring about 5 mm behind the housing. This is so that there is enough wiring to see where the original wiring went. If the wiring is damaged past the connector, you will need to cut even further back. This may happen on the knock sensor connector as it sees more heat than the other sensors.
Next, you will have to cut away some of the plastic covering on the factory harness. The more terminals a connector has, the more of the plastic covering you will need to remove. This is to give you room to spread the wires around. Next, slide the new boot onto the harness. If you forget to do this before you crimp the terminals, you can still get it down. However, if you forget to install the boot and you have the plastic housing attached; it's too late unless you have the $30 terminal extraction tool.
To crimp the terminals on the wires, you will need an open barrel crimp tool. This is different then the normal closed barrel crimper you're used to. The little "points" in the bottom of the opening cause the ears of the open barrel terminals to curl over into the wire when the terminals are crimped. These are hard to find. You might find one at a specialty computer/electronics store. I went to many tool and electronics places before I finally just ordered one online. If you're ordering connectors from KayJay Company, they carry a reasonably priced crimper. You could also just go to Google Product Search and find a crimper.
Now that you have the crimper, it's time to crimp the terminals onto the connectors. You will need the terminal and the weather seal (green thing). First, strip the wire 5mm (0.2"). Then, slip the seal over the end of the wire just covering the insulation. Then crimp the terminal with the end tabs capturing the seal. The assembled wire is now ready to be inserted into the housing. To test your crimp, pull onto the end of the terminal with one hand while holding the wire with the other. A good hard pull should not disturb the crimp. To crimp the tabs over the weather seal, I found that the open barrel crimper would tear through it. I ended up using a regular style insulated crimper to make that crimp. TIP: Order a few extra terminals when you order your parts from KayJay Company in case you end up with a bad crimp.
Now that you have the terminals crimped onto the wires, you can install the wiring through the plastic housing. Double check yourself! Check the factory electrical schematics as well as the connector you cut off. Make sure that the plastic housing is oriented properly and not upside down. Some of the Bosch/AMP connectors will also have the terminal numbers labeled onto the housing just like how the factory schematics have them labeled. So, once you're sure the wire is going to the right place, slide the wiring as far as it will go inside the connector. Make sure that the terminal is rotated to where the alligator mouth is horizontal.
You probably won't be able to get the terminal fully seated into the plastic housing just by pushing it in with your fingers. So, once it gets pretty far inside, use some needle nose pliers to grip the wire right behind the seal. This will give you some good leverage to push the wire inside the plastic housing. When the terminal fully seats, you will hear a fairly loud "click" sound.
Slide the boot over the plastic housing. Now you have a brand new electrical connector. This should eliminate your electrical problems.
