Today with the Red Fuel Pump Relay

[zakthor]

Driving to coffee this am, 1979 930 running fine. Got three blocks and engine dies and wont restart.

Grab my baggie of spare relays from the glovebox (relay C), swap the first (relay a) and still no start, reinstall A and swap the second (relay b) and it stumbles and then starts. Drives fine. I guess B has failed. Took it easy, about 35 minutes of driving and car seemed a little placid, i didnt push it and stayed off the gas thinking something is wrong.

Home and i hook the bad relay B to my dc power supply. It switches great. 0.5 ohms resistance on both legs. Hmm. If thats bad what is good?

Pull the original good relay A from car… it wont switch! 0.5 ohms on the off leg.

Pull the swapped relay C from car, it is indistinguishable from relay B - they seem good.

Relay A no clicky but car drove fine… its really not good.

Do these cars start and drive with only one fuel pump relay? Starve engine at high rpm?

Now with two relays that i tested as working, car still feels good but im still wary. Whats going on? I think id like to know how many watts are going to fuel pump while driving. How do i test that the relay is correctly letting amps through?

How many amps can fuel pump use? Could relay test low resistance but not pass higher amps?

And does anyone have theory as to why car stalled and wouldnt start? Relay B broke but then fixed itself?

Edit: more info, in above description relay A was in 2nd from windshield, relay B, C were in socket nearest the windshield.

Cheers.

[zakthor]

Hooked up the non-switching relay A this morning and now it is switching just fine. Venus was transiting Sagittarius?

I’m going to test a bunch of relays and see how many volts before they switch. Could be cracked solder joint and the bad behavior is random.

[Alan L]

The car will run on one pump/relay - but sluggish. Like you describe.
If the relays are baffling you, you can flip the tops off them and observe what is going on. Then pop them back on.
Alan

[zakthor]

Originally Posted by Alan L

The car will run on one pump/relay - but sluggish. Like you describe.
If the relays are baffling you, you can flip the tops off them and observe what is going on. Then pop them back on.
Alan

I know how they work inside, stamped sheet switch plate with a spring and a coil

Relay wasn't working yesterday evening, now it is. Im guessing both relays were dead when car stalled and wouldnt start. Probably when i swapped first relay i didnt give it enough of a crank, after swapping second relay the car took 20 seconds of stumbling before it would idle.

Now miraculously all work fine in the light of my dining room. Im glad i found they are intermittent.

Btw they all switch fine even down to 6 volts. All pull the same watts, same resistance, etc. i cant tell them apart electrically.

Years ago i bought a pile of red relays from our host and 4 of 6 were non op so i returned them all. Living with collection of old relays now. These stupid mechanical things.

Maybe i should make an adapter for a modern solid state relay.

Tempted to wire up a 12 volt led to each relay socket so i can tell at a glance that the relays havent flaked out.

[Alan L]

I have cleaned the contacts on them before. That might explain the intermittent behaviour. Either that or you have a bad/intermittent connection in the circuit feeding them - via the 3rd relay.
Alan

[zakthor]

Originally Posted by Alan L

I have cleaned the contacts on them before. That might explain the intermittent behaviour. Either that or you have a bad/intermittent connection in the circuit feeding them - via the 3rd relay.
Alan

Last night relay A was not responding to voltage - no click - and today it is responding great. It at least explains the behavior I saw. I guess there could be other issues too.

I'd like to pop the relay open and have a look, maybe reflow the solder for the wires to the coil, but it is not obvious how to get the cover off. Any advice?

[mark houghton]

0.5 ohms makes me think you were checking the connections to the points, but perhaps not..500 mA may seem a lot of resistance through points in good condition. To test the coil, make sure you're at posts 85 and 86. And yeah, pop off the can and take a look. I had a bad relay once and just resoldered where the coil wires were spot welded to posts 85 and 86.
EDIT: Funny, I just realized you responded lately to a YouTube response I left awhile ago.

[zakthor]

Originally Posted by mark houghton

0.5 ohms makes me think you were checking the connections to the points, but perhaps not..500 mA may seem a lot of resistance through points in good condition. To test the coil, make sure you're at posts 85 and 86. And yeah, pop off the can and take a look. I had a bad relay once and just resoldered where the coil wires were spot welded to posts 85 and 86.
EDIT: Funny, I just realized you responded lately to a YouTube response I left awhile ago.

It does seem like a lot of resistance. Do you know how many watts or amps go through the relays? I could load and see if they get hot.

My worry is that all my relays now work great but I know some are intermittent. And I've no faith in the ones I can buy. If I just reflow the solder I won't know if its 'fixed'. I'll do it but I won't be happy.

These damn things.

[Alan L]

They take a high load - over 10A. Thats why I cleaned the points - they do get burned - which I suspect is the main reason they start to fail - under load. And probably intermittently.
Prise the cap off carefully with a stanley knife. You can always glue it back on. But I have left mine unglued - they sit back snug enough. That way I can always get to them to see what is hapening and clean the contacts.
Alan

[flightlead404]

Originally Posted by Alan L

The car will run on one pump/relay - but sluggish. Like you describe.
If the relays are baffling you, you can flip the tops off them and observe what is going on. Then pop them back on.
Alan

Sometimes it helps to take a razor blade and sort of spread those split pins a little bit.

[Chinook]

Isn't there a company called Resoration Design that currently mfrs solid state round relays? I purchased two awhile back. They claim that their relays are geometrically compatible so that one can use an original plastic cover to satisfy the judging dorks.

[zakthor]

Originally Posted by Chinook

Isn't there a company called Resoration Design that currently mfrs solid state round relays? I purchased two awhile back. They claim that their relays are geometrically compatible so that one can use an original plastic cover to satisfy the judging dorks.

Woo! That appears to be the correct answer.

Just ordered 2 red ssr from them. Canadia to the rescue.

[HaroldMHedge]

Another manufacture for the round relays is 914 Rubber.

[ToySnakePMC]

Originally Posted by Chinook

Isn't there a company called Resoration Design that currently mfrs solid state round relays? I purchased two awhile back. They claim that their relays are geometrically compatible so that one can use an original plastic cover to satisfy the judging dorks.

Here's one from R.D. Have had it in use for only a few months and anticipate many more years of service life.
It has a red anodized alum appearance, so it won't pass a concours judge's sharp eye - but it looks A-OK to me!
Edit -- I see what you're suggesting on reusing the red plastic cover. I get it!

[zakthor]

I just didn’t want to pay money for another electromechanical relay. The restoration design relay uses a solid state relay. No more worrying about if the contacts are clean.

Edit: anyone know if the r.d. Relay has the diode?

[Jhalsey]

Anyone have a good technique for removing the red cover without damaging it? I just received two RD relays without covers so would like to move my old covers over. I spent 1/2 hr yesterday running an exacto knife around the perimeter, no bueno. Thanks.

[mark houghton]

Originally Posted by zakthor

.Edit: anyone know if the r.d. Relay has the diode?

I can't see why a diode would be necessary in a solid state relay, since there is no coil to open and close contacts.
In a mechanical relay, when the relay coil is de-energized, the collapsing magnetic field generates a high voltage counter EMF spike which the diode can safely block.

[Alan L]

Originally Posted by Jhalsey

Anyone have a good technique for removing the red cover without damaging it? I just received two RD relays without covers so would like to move my old covers over. I spent 1/2 hr yesterday running an exacto knife around the perimeter, no bueno. Thanks.

They are only held on a small lip. I removed mine many years ago and just pop them on and off when checking them. Pretty sure I just used a cutter knife. That may only get you around the base of the lip, but I expect they will ping free eventually. It may help to squeeze them gently around the base perimeter to try and free that lip, which probably has glue on it.
Maybe a bit of gentle heat to soften the cap a bit.
Alan

[mark houghton]

It would be a relatively simple procedure to wire in SSR relays. 10A relays readily available at considerably less $$ than the red cans we are forced to use. A guy could take a toasted standard relay, minus its' guts just to keep the 5 pin male socket. I looked around a bit but can't find a relay small enough to fit within the standard relay can dimensions. A person would almost have to create one from scratch with off the shelf components. Probably what the guys at R.D. have done.

Those of you that know me, know that I'm a DIY freak of sorts...born that way, my middle name is MacGiver. I look at things like this as a challenge.

[dedyplay]

Your 930 has a dual fuel pump relay setup, so it's possible for the car to start and run with only one relay functioning. However, this can cause issues like engine starvation at high RPM.
To test the relay's current flow, you'll need a multimeter with an amp clamp or an inline amp meter. Measure the current draw of the fuel pump while the engine is running.