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Just put the jumpers in the relay socket and drive it a little, per the second paragraph in post 21 above. It completely removes the relay and triggers from the options list. Then if the car runs OK, you'll try the new relay and see if it runs OK.
Save the old relay for me please if it turns out to be the problem.
Just put the jumpers in the relay socket and drive it a little, per the second paragraph in post 21 above. It completely removes the relay and triggers from the options list. Then if the car runs OK, you'll try the new relay and see if it runs OK.
Save the old relay for me please if it turns out to be the problem.
Which prongs of the relay am I jumpering with a continuous wire in order to make the pump run all the time?
30 to 87 causes the pumps to run continuously. For this duty I like to have a jumper with a heavy-duty switch in the middle so the pump can be turned on and off without fiddling with the wire connections.
The pin numbers are on the relay itself, BTW, so use your mirror-image sense to determine the right places in the socket.
30 to 87 causes the pumps to run continuously. For this duty I like to have a jumper with a heavy-duty switch in the middle so the pump can be turned on and off without fiddling with the wire connections.
The pin numbers are on the relay itself, BTW, so use your mirror-image sense to determine the right places in the socket.
Perfect. Thanks. Good idea with the switch. I'll make one of those and put it into the car's toolkit.
How many amps should the switch be rated to handle? The fuel pump fuse is either a 16 or 25 Amp fuse, depending on which resource diagram I look at so I'm assuming a 30 Amp rated switch would work, right?
Some of the relays have 2 separate 87 pins, so another pigtail may be needed. I don't remember which relays though. You'll see the two 87 pins on the relay itself if it has them. Your spare is handy for that.
At this point, I think it was the fuel pump relay. I installed the switched jumper I made and was able to drive the car around the neighborhood 3 times (only made it around once last week after the problem first occurred), then installed my new spare FPR and drove around 2 more times without the AFR gauge leaning out or any hiccups.
Figured for good measure, I'd change the fuel filter too since it was the original from when Carl did the supercharger build after the car had been sitting for a few years while the previous owner was working on it as his project. Since then, it had done a round trip from SC to WI, a couple round trips to Charlotte (2 hours each way), the round trip to SITM, and a bunch of local driving - figured it was time to start fresh with whatever gunk from sitting was now trapped. I'll add a can of Seafoam at my next fill-up to help lubricate the fuel distributor and see how she runs during a more extensive test drive.
Thanks to everyone for the help and suggestions. I'll update the thread if it turns out I still have an issue. drbob, if you want the old FPRs let me know where to send them as I think the one I changed last year (on the right in the photo below) may be a collectors item with a separate fuse on-top - that one stranded me at a gas station while I took apart the interior to remove the board and swap it out with a spare I was carrying).
Perhaps the most amazing part of your last post is the idea that the installed relay failed while you had a spare in the car. What are the odds of that ever happening?
Perhaps the most amazing part of your last post is the idea that the installed relay failed while you had a spare in the car. What are the odds of that ever happening?
I'll PM some info when I get home. Thanks!
I know, right? I would have thought that just keeping the spare in the tool kit would mean I'd never have to use it
I've now replaced a FPR about once every 12-18 months in this car. The first one I understand since it was really old and an odd design, but this last one was only 12-18 months old and just seems odd that it would fail that quickly just by doing a longer high RPM pull. Any idea what the cause and effect relationship is here or do they just fail kind of randomly?
I'm hoping that was the actual problem and that it's not something intermittent that is going to come back.
What do you do with the old relays? Do you somehow test them to see what the failure mode is, rebuild them, etc?
We encourage every 928 owner to carry a spare fuel pump relay in the glove box, and if not that, at the very least a fuel pump relay jumper wire. Between the damage caused by less-than-careful tow truck drivers and the worry of leaving your 928 parked somewhere you did not chose, a relay or a wire shunt is a little cheap insurance.
I've now replaced a FPR about once every 12-18 months in this car. The first one I understand since it was really old and an odd design, but this last one was only 12-18 months old and just seems odd that it would fail that quickly just by doing a longer high RPM pull. Any idea what the cause and effect relationship is here or do they just fail kind of randomly?
It has gotten harder for us to get genuine German-made relays. The China relays are everywhere, and packaged as "Made in Germany" and "Bosch" and the like. That's one guess as to what caused your last relay to have a short life.
Also possible is your fuel pump is failing and starting to draw extra ampere loads... an ammeter in the circuit temporarilly would tell you what amps the fuel pump is drawing.
I don't see a Fuel Pump relay for a '79 in the list on that page. Does another one crossover and work? If so, I'll take 2 of the German made FPRs for my car. You can send them USPS Priority Mail if that's OK and I think you still have my account info and card on file - if not, just have Gretchen give me a call.
Lots of confusion available on Bosch relays these days. Problem starts when Bosch goes to the lowest-cost suppliers, who may happen to be in China. When made to original Bosch specs, these are fine. Of course, the original packaging spec still shows a "Made In Germany" on it, so that is dutifully added to the new part too.
Else a nearby factory sees a demand, figures out how to make one that's "just good enough" but looks the same, and floods the market with their look-alikes. There is no way to tell without opening the can if the contacts are good, and even then a silver-plated contact looks like a tin-plated pot-metal contact when it's new.
The original relays are contact-rated for ten amps. The pump motor presents an inductive load that encourages arcing at the contacts when they open. With two motors connected, that's higher current load and more tendency for arcing.
The basic logic function for the relay is easy to duplicate with a simple IC timer, a few resistors and a capacitor for the actual "timing". A premium relay will have higher-rated contacts, along with a 15.5V suppression diode and resistor to kill some of the contact arcing. My thinking is to make a plug-in base with the smarts inside, with a second socket on top that will accept a common 40A Bosch 53b-style relay for the dirty work. I think we have a '79 "test mule" available locally if I can convince the owner to share. It will be another summer project though, as the rest of winter and spring are already overbooked.
Well, I'm happy to report after today's test drive to the gas station where I added a can of Seafoam with this fill-up that the car is running perfectly. Did some long 2nd and 3rd gear pulls without any issues and AFR gauge stayed between 10-14 at all times.
I'm curious to see what the fuel filter I replaced may have captured - what's the best way to open that up and take a look? I don't have a pipe cutter large enough and my oil filter cutter has the blade right next to the flat plate which won't work with the fuel filter's end fittings. Thought about using the band saw but that doesn't seem like a good idea since it might be like holding a bomb in my hands once the blade sparks with the metal canister. If I can't open it up safely, so be it.
What do you do with the old relays? Do you somehow test them to see what the failure mode is, rebuild them, etc?
The failure mode for yours is definitely the output relay contacts.
My last CIS cars had a similar relay, for which I incorporated the trigger circuitry into the fronkensteen fuel injection controller. Then a standard and easily-replaceable relay plugged in to do the heavy lifting. I ended up with two sequential pumps on the last project car to feed the pressurized manifold reliably, and the single tiny-contact relays didn't last very long. Even 25 years ago the darn things were pretty expensive, so the decision to add the pump relay to the electronics for the CIS was easy. Job now is building the sensor/timer bits into a plug-in adapter. Yours will give me the exact contact dimensions for the base.
02-18-2017, 12:51 AM
