How much injector cleaner can I safely add to a tank of gas, and then just drive the car. I put alot of highway miles on this car so driving long distances is not an issue. For example, last Sat my wife and drove to the mountains and back in one day for a nice drive on the blue ridge parkway, then dinner and back home, over 700 miles. We love driving.

 

Spot on Mark.

 

As long as there is no boost you should be able to run with loads of it.

 

The fuel pumps will run for several seconds when turnng the key on, which mine do. Then they will not run again until the engine fires to cause the throttle plate to move. So after they have run several seconds to prime, they really have no effect on starting the car, only keeping the car running after it has started!

 

Thankyou.

 

That is not correct. The pumps should only run when the engine is cranked over. They should not run at all when you turn the key on only. Not even for a second. The electrical connection on the back of the sensor plate supplies the ground for the fuel pump relays. It only supplies the ground when the plate is pushed down off the stop which only happens when there is vacuum produced by cranking the engine over. I recommend you fill your tank full and add a can of cleaner. Run that tank down to 1/2 full and add another can and fill your tank back up then run that.

 

I agree, the pumps do not run until the air flow plate moves.

I think the noise you are hearing is actually the CDI, not the pumps. Check it out.

 

1986 930, My rear fuel pump runs for approx 2-3 seconds when I turn the key on, then it will not run again until the engine fires causing the plate to drop. I assume the front pump runs also but I just can't hear it. I know what a fuel pump sounds like, and the difference between that and the CD.

 

Sorry, The first part of the above in correct, they do in fact run for 2-3 seconds. Then do not run again until the engine fires, moving the plate which as you stated is then picked up by the elect connector and sends a signal to the FP relay to run the pumps again.

Please check the operation of the fuel system for an 86 930.

 

I don't mean to sound "brash" at all, and I apologize if I came off that way in the above responses, but please believe me that I know what I am hearing when I turn my key on. The fuel pumps do briefly run for approx 2-3 seconds, then stop. They do not come on again unless I turn my key off and back on, or the engine fires and a signal is then sent from the throttle plate to the FP relay's signaling the FP's to run. I assumed this was standard on all 930's, but maybe not. But the other two 86 930's that I looked at before I bought this one operated the exact same way, other than that I cannot say.

I do really appreciate the help you guys have been on this problem, and the injector issue seems quite logical and I am following up with that.

Tim

 

Tim, you did not come off wrong to me.... I am very aware of the wiring for the fuel pumps. What your car does is not proper. The pumps should not run until you crank the engine. If they do then something is not correct.

 

Sounds like your sensor plate may be a little out of adjustment or sticking a little bit from age or grunge on the pivot points of the arm underneath, and not quite coming up all the way and tripping the switch at rest.
Then if your fuel pumps are actually coming on as you say, maybe the fuel control pressure in the fuel head pushes the plate up enough to trip the switch and shut them off. Just guessing there...
When I first got my 930 the pumps would come on with the ignition sometimes but not always.
I cleaned all around the sensor plate and squirted some carb cleaner into the mechanical pivots and levers underneath it while the big 90 degree hose and diverter valve housing was off to get at the driver side intake valves to adjust them and it stopped doing that.

 

I just don't think that is correct. Not sure what to say, but again, both 930's that I looked at prior to buying my car did this, my car does it, and I have a friend that has a shop, just called him, he has three 930's in his shop right now and they all do it, and he said the FP's run on his personal 930 for a brief second when the key is turned. Stan told me that this is in fact normal.

That is 7 cars, three of which I have personally experienced, where the FP's run for a second (maybe my earlier 2-3 sec's was wrong, it is actually about 1 sec, I just timed it).



Tim

 

Strange. If my car was not in pieces I would test it. Maybe the noise of the CDI makes me think that the pumps do not run when turning on the ignition. A good test would be to unplug the CDI, turn on the ignition and listen if the pumps could be heard.

 

This just gets more curious by the minute! I love a good debate.
My '87 930 pumps don't run until the engine has pulled some vacuum through the sensor plate, which I THINK they're supposed to do fresh off the showroom floor. But face it, these cars aren't available brand new anymore, so who really knows what the ravages of time have done to the sensor plate pivot points or the sensor switch itself. My guess is that...if we were all to vote on it...that we would find a significant percentage of 930's experiencing the same problem.