Bosch Fuel pump Relay

[AndyH2K2]

8 minutes ago, PaulTWinterton said:

I still don't understand why you have 2 fuel pumps in use.  Wouldn't the low pressure pump get fuel directly from the tank and feed the carb?  It seems you could eliminate the tii pump altogether.

 

Sorry if I was confusing - there's only one fuel pump, in the rear back of the car, right of the differential. And yes, it does like you've said, takes the fuel directly from the tank and feeds the carb. 

[JLENHAM]

Andy, if you noted the year of your car I missed it.

 

It is almost certain these have been disconnected by now... but some models (74 and 75?) have a seat belt interlock that will prevent the car from starting.  "Back in the day" the likely scenario was a bag of groceries on the passenger seat and... no start.  I believe the fix for this is just to unplug the connector found under the seat.  

 

I don't know if the fuel pump circuit would be cut off as well as the 12v to the starter.  

 

If the circuit to the fuel pump is the same it is #12, but if that were bad I don't think you would get the oil pressure light.

 

It is also not difficult to remove the screw and pull up the fuse block to check all those connections into the fuse block.  I would disconnect the battery before doing this.

 

You can jumper from the battery to the 12v on the starter to test it.  Do look up Rob Siegel's guidance on this and be sure the car is in neutral!  Having a helper or a remote starter switch is helpful.

 

Good luck

 

 

Edited October 19, 2020 by JLENHAM

[AndyH2K2]

It's a '74. Good thinking... those interlocks are unplugged already, unfortunately.

 

Thanks, I'll disconnect the battery and take a peek fuse block, hopefully later today. I'm a novice here but a motivated one! Wisconsin winter is coming and I'd prefer to drop it into storage under it's own power. 

 

I've had this car since July or so. It's run (poorly) a handful of times (anemic at 4000rpm), despite that still a joy. But I can dig into that later once I get it running again. The most recent time it left me stranded it just felt like it ran out of fuel (I puttered to a stop). Upon inspection of the previous fuel pump's performance, it definitely was short on fuel delivery. 

 

Here's a few photos of the wire nest below the dash for viewing displeasure... more updates later. Thanks for viewing. 

 

 

[Son of Marty]

The 74 interlock system just cuts the power to the started solenoid all the warning lights will come on and fuel pump will run just no starter. Unplugging it at the seats doesn't bypass the system it just assumes theres no one in the seat and the relay works as designed this relay can fail over time and especially if you crank it with a low battery and burn the relay points. To really bypass the system just connect the large wires at the relay together and your done.

[FunkyLaneO]

If you still suspect the relay, test it by applying power and ground to the 85 and 86 terminals (they are usually labeled and it doesn't matter which is ground and which is power) it will click if it works.  If it is indeed dead let me know, I will send you one.

[AndyH2K2]

Thanks a ton, but I went ahead and bought a new universal fuel relay from a store down the street, which fit fine. Still nothing though. I tested the red wires going to the ignition switch (behind the key) and they've got strong charge. However, saw there's no power on the green wire back to the fuel tank (well duh), where it attaches to the tank in the trunk. It has to be something simple. Hope to find some time to disconnect the battery check the connections to the fuse box this morning.

 

 

 

 

[AndyH2K2]

It lives! 

 

Got in the fuse box and made sure everything was connected tightly. Began turning over right away, then had some difficulty starting. Recharged the battery then gave it another whirl and it started better than I've ever experienced. Going to monitor over the next few days and see if this battery holds charge. Otherwise I'll have to get a new one. That'll be the second replaced part that was supposedly "new" from the chump who worked on this. 

 

Thanks everyone! I'm sure I'll be back here pretty soon.