map747

Hi folks.
I have an 87 S4 auto. The issue is it wont start with the fuel pump relay in place. I have bridged the relay pins to activate the fuel pump and the car runs fine. As soon as I replace the bridging wire with a new relay, again the car does not start.
I have tried several relays but to no avail. It is almost like the relay is not getting any power to engage the fuel pump. But the wire is.

Any thoughts.
Becoming a pain to disconnect the battery and reconnect it every time I want to use the car.

Kind regards.
Martin.

FredR

Classic sign of LH failure?

As I am aware the LH unit secondary board sends power to energise the relay- jump the relay and the problem is circumvented or so I understand.

I dare say there may be something else that can cause your problem but I would initially suspect the LH unit- it is a common failure point now.

Time for JDS to chime in?

dzaprev

Check grounds , it could be a lot of different things .

Marti

Hi Martin

I could test your LH unit if you wanted to bring it over one evening. My S4 starts and runs fine so it would narrow down the search for you.

Mrmerlin

where is the OP located?
for your car it sounds like relay is bad,
you need 4 ...53 relays the
LH,
EZK,
Fuel pump,
and the ignition.

NOTE most will recommend to replace the first 3 of these, I also like to X relay (ignition)

NOTE relays can be damaged from not using a fully charged battery to start the car ,
this process takes time to manifest.

Best get some deoxit 100 and spray all the fuses with it ,
then pull the relays one at a time and spray them.

NOTE when fitting new relays ,replace the relays and test them one at a time to figure out what relay made the engine run.

NOTE if the battery is not in great condition replace it,
Also clean the battery and grounds before further testing so you dont damage new parts.

If the relays dont fix the issue then report back with the engine condition, some engine bay pictures and if the intake refresh has ever been done

John Speake

If the car starts and runs with the FP bridged then the problem could be an immobiliser, if fitted.
This is because they often act on the FP coil circuit

Alternatively, if the fuel pump relay has been jumped with the incorrect pins at any time, the LH drive circuit to the FP coil will have blown... this can be repaired.

worf928

Classic LH failure. Luckily there's a guy ---^ in Cambridge that rebuilds them.