Right under the stock air box behind the headlight. What do they do, and what are they wired to.

 

Its for the fuel injectors on a 86-87.5 model

 

why is it on my 89gtu then. I am fighting to keep a consistent idle and from time to time it will hold rock steady other times it will drop all the way down then the relay clicks it bounces up for a second and back down repeating the process. once in a while it will bounce up and hold. Its starting to drive me crazy

 

Well that's not exactly correct. The fuel pump relay resistor as shown in your picture actually controls the voltage going to the fuel pump. Under normal cruise conditions, the 12v power goes thru the resistor and then fuel pump sees less voltage and delivers less pressure/flow. When the ecu sends a signal to the relay, it closes and bypasses the resistor sending the full voltage to the fuel pump. I don't know the exact conditions that trigger the ecu to do this but I've heard it occurs under boost.

Hope that help out.

Scott

 

whoops I guess I confused resistor packs...

 

About your idle.......What is happening, according to YOUR description.....is that the bac is trying to maintain a 750 rpm idle after the idle drops waaaay low.

The most likely reason for your problem is actually NOT bac related. The problem is that the idle is not set right.

To set your idle right, you need to install the initial set coupler and adjust the idle according to the fsm to as close to 750 as you can get it. Once you have done that, you remove the initial set coupler. Usually the engine will rev up and down about three or four times then hold an idle at approx 750rpm.

After you have done the above, and the problem persists.....then you MIGHT have a bac issue.

YOu need to download the fsm, the Fuel Section, and set your idle according to the fsm. It's similar to what was described above, except it asks you to set your timing right on first and maybe one other thing or two....like set the tps first also.

 

Due to some reading in the fsm. I came upon this diagram and found it interesting that only the use of components that are associated with the electrical load control system cause the problem

But if I have any of these or all on and press the A/C button the idle goes up and stays rock steady. So what is this electric load control system and where is it at?

 

It's the ECU. See the words just at the top of the page?????? Engine Control Unit...is what it says. It's inside the ECU. Part and parcel of the ECU.

 

DOH! now I truly feel like an idiot. I don't know how I missed that one.

Could that be the cause of my problems. Would there be any other signs the ECU or that section of the ECU has failed. The only other thing of suspect is the alternator could be on its way out but its done this for about a year. Guess it's time to find another ECU to try to trouble shoot the problem.

 

When you turn the a/c on the bac's duty cycle goes up creating a touch higher idle.

An alternator that is putting out a low voltage at idle WILL mess with your ECU and cause an irregular idle. Especially if you have your foot on the brake at the same time. Those stop lights put a heavy load on the alternator/battery...which in turn lowers the voltage to the ECU....which in turn causes PROBLEMS at idle.

You might put a meter on the alternator or battery and see just how low the voltage gets when the engine is fully warmed up and the brake pedal is stepped on.

 

When you turn the a/c on the bac's duty cycle goes up creating a touch higher idle.

An alternator that is putting out a low voltage at idle WILL mess with your ECU and cause an irregular idle. Especially if you have your foot on the brake at the same time. Those stop lights put a heavy load on the alternator/battery...which in turn lowers the voltage to the ECU....which in turn causes PROBLEMS at idle.

You might put a meter on the alternator or battery and see just how low the voltage gets when the engine is fully warmed up and the brake pedal is stepped on.

 

Thanks again, I will give that a shot. What wires should I be connecting to on the alternator.

 

Just put your positive lead of the meter to the large output wire on the alternator and the negative lead to a good ground.