Help me understand how this system can work. I have been driving my 87 Volvo with 300,000 miles on it and the fuel consumption on the highway has been down to about 16-17mpg for a while. I have been going through replacing all the sensors and fuel regulator stuff. I finally got to the Coolant Temperature Sensor located in that great location under the intake manifold. During the process I tested both the old and new sensors and the were both good. At this point I went with the new because I did not want to think about replacing it again. Now I focused on the circuit wiring and found I had 300 ohms on the one wire to the connector on the end of the wiring harness. So I began thinking about running a new pair of wires. Somewhere along the way, I began looking at the wires in the harness (all of them). I had long ago replaced the Oil Pressure Sensor wire and the altenator wire (small field wire). Well, I found a number of wires in the main harness that I will reinsulate. This will not be a problem. It will just require a little time, it won't be that difficult for me as I pulled the whole main harness out of the car.

Here is what has me scratching my head. The wiring to the fuel injectors. First, the insulation on both wire was shot and the wires were about 90% bare, so there had to be some shorting. Secondly, I discovered that there are only two wires that feed all four injectors, one brown ground and the other is obviously the power supply. I am at a loss for understanding how individual injectors know when to open. It would seem that this system would cause all injectors to open at the same time. I have searched the FAQs? How can this system work?

You definitely do have a fuel supply issue. You should be getting at least 25 MPG on the highway. The injector system is pretty primitive it only fills the intake manifold with gas vapor and the cylinders suck it in when the intake valves open.

they all open at the same time.

this is not sequential fuel injection.

Well, Goatman, I thank you for confirming that this is normal as I could not see how it could be otherwise. Nonetheless, it seems crazy to me to think that the injectors are apparently opening at four points in the cycle. It would make sense to me if this was like the throttle valve injection system. I am going to have to look and see where the injector ports are located and then do some reading about this type of injection system. In the meantime, I will take accept your input and simply work on reinsulating my wiring so I can get to work on Monday.

Thanks.

The "batch fire" fuel injection isn't really *that* insane for the vintage. Lots, if not most, of European cars of the 1980's were running K-jet, which didn't stop spraying fuel.

The computer power back then was fairly primitive.

-Ryan
--

Athens, Ohio
1987 245 DL 324k, Dog-hauler
1990 245 DL 142k M47, E-codes, GT Sways/Braces, Dracos, A-cam
1990 744GLE 189K 16-valve
1991 745 GL 304k

Re: the insulation, you have the biodegradable engine harness of those years. You may find help on Dave Barton's site. He used to and maybe still does sell good harnesses.
Some have made their own new harness; I think I once read that someone did it in an afternoon.

To everyone who has replied, I thank you for your help. I am going patch up what I have. I will reinsulate some wires and replace a couple. I really did not understand the system before and your comments helped a lot.

I still marvel that my car ran at all with the missing insulation. This is particularly so on the wiring to the injectors as both hot and ground wires were bare and I would think that they had to be shorting out. That would have likely caused a leaning out of the mixture though and I have an over rich mixture.

Once I replace the high resistance (300 ohms) wire on the Engine Coolant Temp sensor, I am hoping this will lean out my mixture a little bit. Probably not a lot. We'll see. After this, I am going to start thinking about the engine control unit. I have already cleaned up the grounds so I am about at the end of the list. Oh yeah, the only other thing I have done since I have been off the road is to seal the small holes I had on my air intake duct. While it seems counter intuitive I am told this may help lean out my fuel-air mix.

Well, gotto go get started and that wiring. If I learn anything from this I will post it.