1989 928 s4

[Baenzi]

I have no power to fuse 30-44, any ideas. Car does start but when I check 42 (Fuel pump), there is no power using a light tester.

[Baenzi]

Does the fuse receive power first or does the relay. What is th flow.
i THINK IT IS FUSE FIRST??
All hots on the top of the fuse block are hot.

Help

[chesireIsugaree]

"car does start"


But doesn't stay running?

[Baenzi]

It runs great
Can't quite understand this one. Also, I dont have a working headlamp motor relay in the hole.

[cwiert]

I don't have a specific answer to your question, but maybe this will help...
You can download the manuals for free here...

Manuals

[Baenzi]

Thanks, I have the manual but I think the only one that understands the wiring details is the technical writer who produced them.
Chasing wires on the back side i quite on an issue.

I don't understand how I can have power to the fuel pump with no power at the fuse. The other thing is, no power to the other fuses.
Does the relay get power first??

[Danglerb]

Look for non factory creative wiring, install or removal of an alarm, bypassing one, etc.

The only "tricky" bit about car wiring is that the connection to the Negative side of the battery runs through the body and chassis, and if the "ground" connections to the body get corroded screwy things can happen. Otherwise all wiring is a simple chain from the Plus side of the battery through the whatever and back to the Negative side of the battery.

[JhwShark]

Check the manuals link that has been provided and the appropriate current flow and/or wiring diagram for your model. I have an earlier more humble '79. A current flow diagram is best for trouble shooting.

Look at the FP circuit and you may find that there are two sources feeding the voltage one for start and one for running. Odds are there is a wire issue (obviously) at a ground for that bus, or connection and/or corrosion in run circuit wires which would usually come from coil or ignition circuit control even the LH cu which I no nothing about. Though a possibility is that you have corrosion and or bad wire in the wire harness that goes from the aforementioned components to the Connector which takes input back to the CE panel and relay then to the FP.

Just, trouble shooting an electronics system, trying..
Jon

[tlsmith1999]

I am curious, if you pull the fuel pump fuse out does the car still start?

[Baenzi]

I have never removed the fuse during operation, but I will to see what happens and let you know. My guess would be it would not affect it.

[Baenzi]

Sorry, I did not answer your question. Iwill remove a try it.
Thanks

[jstobo]

According to the electrical diagram there is no power to fuse 42 until the computer engages the fuel pump relay. The power is sent to the fuse and then to the fuel pumps and oxygen sensor.

The relay has power to one side as long as the key is on(pin 30) Pin 86 has power and when the computer grounds pin 85 the relay trips and sends power to pin 87 which then goes to Fuse 42-the fuel pumps etc. Pulling fuse 42 should result in a no run situation unless a PO did something funky. How do you fit a test light into the fuse holder? I don't see enough room to get a good connection with the fuses in there. Hope this helps.

[Xlot]

If its the whole block of fuses, check the (red) power leads to the top of the panel from behind it (under the clear plastic hinged cover). Make sure all are clean, and you've accounted for them all - from memory there are 5, but I'd have to go look see to verify.

Each of the leads should read full battery voltage when measured to ground.

edit: Your posts are a little unclear - by "30-44" do you mean no power to all those fuses? If the car does start and run, then they're working and it might just be surface corrosion on the test points on the fuses themselves.

[Baenzi]

sorry, yes fuse positions 30-45 no power with key on.

I had the central electric completely removed. I will check again to confirm all red power wires from the battery are connected properly.
I have been running the engine for some time now without the dash or pod installed. Only the Cluster. I installed the dash and the center console along with the POD. Now .....fuel pump is not cycling. I know that maybe something could have been hooked up wrong, but the ignition system is seperate?? If it did something wrong, it should not have knocked out my fuel pump. New relay, fuse...no start.

[Baenzi]

Thanks jstobo, I get it now.
OK, new problem.
I learned that the ignition circuit (fuse 42) is energized when the key is in the cranking position.
So, I do have power to that bus.

Now, it won't start and I have intermittent cranking and fuel pump not cycling. Tested pump with jumper and it works. I replaced all relays, fuses and even tried an LH that I know is good. NO START.

89 for sale.

[Maleficio]

Fuel pump died. happens all the time.

[Baenzi]

When I jump it, it works?? I can hear it. Are there two??

[Maleficio]

You may hear it trying to work, but you need to verify fuel pressure before ruling it out as being functional. Doesn't the fuel pump have a relay controlling it?

[Baenzi]

What do you mean by Doesn"t it have a relay controlling it??

So, if the pump does not turn on during cranking the fuel pump is bad?

The test by jumping the relay proves what?

[Maleficio]

You should be able to hear the pump turn on and run with the in run without cranking.

Mine is starting to get loud, and I wonder how much longer it will last.