RPM relay melted

[Roadster]

She started cutting out yesterday, and upon checking the usual suspects I found one pin on the RPM relay to have begun melting. I'm going to try a new relay, but are there things I should be checking that may be causing extra resistance? I don't want to burn up a new part here. All other relays have been updated and a new fuse block installed last year.

Thanks for any suggestions.

http://img.photobucket.com/albums/v291/generator/IMG_20141221_134758459_zpsfdgh3uei.jpg (http://smg.photobucket.com/user/generator/media/IMG_20141221_134758459_zpsfdgh3uei.jpg.html)

[skill]

What were the symptoms (cutting out) that got you to pin point the Rpm relay be the culprit?

[hmcelraft]

That pin feeds the fuel pump. 87b just above feeds the Lambda and CPR. Fuse 7 feeds the RPM relay at pin 30. You can see the diagram in the Tech manual D:04:06. Numerous issues have been discussed with this circuit. The most common problem I believe is the ground at and in the Inertia Switch. After that the usual focus goes to the No 7 fuse box connection, the RPM relay - poor/failing internal contacts, the fuel pump connections, and finally, the wiring connections going to the fuel pump.

If the motor is "cutting out" that can be caused by a stopping fuel pump due to intermittent power to it. Sluggish or "popping" in the intake can be traced to intermittent or lack of power to the lambda. Your running issues are probably a failed RPM relay based on your picture but, the resistance issue in the circuit will still need fixed eventually if the resistance issue is not within the RPM relay itself.

[David T]

That pin feeds the fuel pump. 87b just above feeds the Lambda and CPR. Fuse 7 feeds the RPM relay at pin 30. You can see the diagram in the Tech manual D:04:06. Numerous issues have been discussed with this circuit. The most common problem I believe is the ground at and in the Inertia Switch. After that the usual focus goes to the No 7 fuse box connection, the RPM relay - poor/failing internal contacts, the fuel pump connections, and finally, the wiring connections going to the fuel pump.

If the motor is "cutting out" that can be caused by a stopping fuel pump due to intermittent power to it. Sluggish or "popping" in the intake can be traced to intermittent or lack of power to the lambda. Your running issues are probably a failed RPM relay based on your picture but, the resistance issue in the circuit will still need fixed eventually if the resistance issue is not within the RPM relay itself.

As mentioned in the quoted post there are a lot of "weak" points that should be checked out. The biggest problem IMHO is when the fuel pump starts to go bad it draws too much current and causes all of the collateral damage to the circuit. Among the reasons the fuel pump fails is wear induced by age and a kinked/collapsed pick-up hose causing the pump to run dry. The pump must always have fuel in it to keep it lubricated and cool.

[Bitsyncmaster]

My guess would be a bad connection on that pin that melted on the connector side. Does your connector show any heat damage? You can also open up the RPM relay and look for damage inside it.

[Roadster]

The connector to the relay shows no melting from the inside like the relay itself does. The fuel pump may be the problem as I have no idea how old it is. The pickup hose and sending unit were replaced this year.

[john 05141]

I had exact the same problem.added an extra ground but that relay gets very hot. I installed Dave's RPM relay and it is muuuuuuuch better.
Jan

[Roadster]

I replaced the RPM relay and it ran fine for about a mile and then began cutting out again just like before. So the melted relay wasn't the problem, probably caused by something else that is the problem. Now I have to find out what would cause that to burn and because it is intermittent it will be difficult to track. I may start with a new fuel pump and work from there. All other relays are new and pickup hose/sending unit replaced last year.

Could the pump intermittently failing and drawing too much power cause that relay to melt without blowing a fuse?

[hmcelraft]

Fuel pumps either work or they don't. They might make a lot of noise but, most of the time, when they go bad the engine stops - period.

I would suspect that you have a problem with the wiring that is causing the RPM relay to burn. You probably found a burned terminal on the RPM relay that has nothing to do with the poor running. The poor running is unlikely to be the fuel pump. You should really analyze the electrics, lambda, fuel metering, etc. rather than throw parts at it. But who knows, maybe you'll get lucky. BTW - The RPM relay you obtained as a replacement is new or otherwise a confirmed good unit? The reason I wonder is - a non functioning lambda can cause poor running if the frequency valve does not get adequate power which is provided through the RPM relay. Check your diagrams - and frequency valve connections.

[Bitsyncmaster]

I agree that the burned contact may just be an older problem. You should measure the current draw of the fuel pump just to make sure it's normal at about 7 amps. If the pump is drawing 15 amps, it still would not blow the 20 amp fuel pump fuse but would indicate a problem with the pump. A nice way to measure currents is to get one of those clamp on (clamps over one wire) meters. That meter lets you measure other high current circuits (like cooling fans) where a normal amp meter is limited to 10 amps.

[Roadster]

BTW - The RPM relay you obtained as a replacement is new or otherwise a confirmed good unit? The reason I wonder is - a non functioning lambda can cause poor running if the frequency valve does not get adequate power which is provided through the RPM relay. Check your diagrams - and frequency valve connections.

The relay is from DMC and the car runs as it should with it for a few minutes or more. I have very little electrical knowledge so this is a tough thing for me to diagnose on my own. I keep checking and cleaning connections and the car runs great for a while and then randomly dies. All other relays are current DMC upgrades when the fuse block was replaced. The only evidence I have is whatever burned the 87 pin and as far as I can tell that only goes to the fuel pump.

I appreciate all the advice of things to check before giving up and towing it 250 miles.

[Bitsyncmaster]

The relay is from DMC and the car runs as it should with it for a few minutes or more. I have very little electrical knowledge so this is a tough thing for me to diagnose on my own. I keep checking and cleaning connections and the car runs great for a while and then randomly dies. All other relays are current DMC upgrades when the fuse block was replaced. The only evidence I have is whatever burned the 87 pin and as far as I can tell that only goes to the fuel pump.

I appreciate all the advice of things to check before giving up and towing it 250 miles.

My guess would be your fuel pump is bad. It's not a bad idea to carry a spare fuel pump when you travel. So even if you replace the pump and still have the problem, you now have your spare pump. I would do testing, electrical and pressures but I have the tools and experience (and a spare pump).

[hmcelraft]

Ok - the engine randomly dies. Does it sputter and die or, die completely all at once - like you turned the key off? The latter would indicate the pump is stopping - may be bad but, it could still be the ground. A common grounding issue is at the Inertia switch (see the attached PDF). You can "exercise" the switch through a few cycles by hand to see if it functions. If the doors were closed and locked, pulling up the plunger would open the doors AND turn off the pump. The recall was for an internal ground issue in the recalled switches. High resistance either melted the switch internals or burned and deformed the connection plugged onto the inertia switch. I would first make sure that the inertia switch is ok and not a recall switch, that the thing functions and, the connections to the switch appear clean an have integrity.

[David T]

Ok - the engine randomly dies. Does it sputter and die or, die completely all at once - like you turned the key off? The latter would indicate the pump is stopping - may be bad but, it could still be the ground. A common grounding issue is at the Inertia switch (see the attached PDF). You can "exercise" the switch through a few cycles by hand to see if it functions. If the doors were closed and locked, pulling up the plunger would open the doors AND turn off the pump. The recall was for an internal ground issue in the recalled switches. High resistance either melted the switch internals or burned and deformed the connection plugged onto the inertia switch. I would first make sure that the inertia switch is ok and not a recall switch, that the thing functions and, the connections to the switch appear clean an have integrity.

If the motor just stops after it has been running for a while it may not be a fuel system problem. A bad impulse coil can let the motor run for about 20 minutes, till it gets warmed up, and then the motor stops. One way to test this is to jumper the RPM relay and inertia switch and make sure the fuel pump is running while trying to restart the motor. Or check for spark.

[Roadster]

Ok - the engine randomly dies. Does it sputter and die or, die completely all at once - like you turned the key off? The latter would indicate the pump is stopping - may be bad but, it could still be the ground. A common grounding issue is at the Inertia switch (see the attached PDF). You can "exercise" the switch through a few cycles by hand to see if it functions. If the doors were closed and locked, pulling up the plunger would open the doors AND turn off the pump. The recall was for an internal ground issue in the recalled switches. High resistance either melted the switch internals or burned and deformed the connection plugged onto the inertia switch. I would first make sure that the inertia switch is ok and not a recall switch, that the thing functions and, the connections to the switch appear clean an have integrity.

I played around with it more this weekend and still made no progress. The engine ran for 30 seconds and then just died, no sputter. Later it ran for several minutes spectacularly and then shut off like the key had been turned.

My inertia switch has been bypassed and is no longer in place due to melting long ago. I've checked every other wire and connection I can think of and everything seems fine. The only thing I noticed is that the fuel pump changes in pitch as it is running, is this normal? I'm ready to throw parts at this thing!

Thanks!

[hmcelraft]

Were you listening to the fuel pump as the car was running - and - was the fuel pump running when it died? If the problem is the fuel pump it should stop and then the engine dies. If the problem is some other issue the engine will die and then the fuel pump stops. This isn't 100%. If the distributor induction pickup is bad the loss of coil RPM could shut the pump off. You may need to jumper the fuel pump to run all the time to verify the status the fuel pump when the engine dies. You can do that at the RPM relay plug.

The change in fuel pump pitch could be just the volts changing as the engine RPM changes via the alternator. It could also indicate a weak connection some where. Did you say you have checked the connections on the fuel pump?

You may want to check out Hervey's parts web pages. His parts web pages are full of help and information.

http://www.specialtauto.com/delorean-parts/electrical.html

[Horsebox]

If the engine will stay running long enough measure

1) system voltage I.e voltage across battery
2) voltage dropped across the pump terminals

The difference between the two numbers is the voltage drop due to wiring and connectors.

The result will tell you whether you need to go through the connections again including the ones inside the tub by the washer bottle.

[David T]

If the engine will stay running long enough measure

1) system voltage I.e voltage across battery
2) voltage dropped across the pump terminals

The difference between the two numbers is the voltage drop due to wiring and connectors.

The result will tell you whether you need to go through the connections again including the ones inside the tub by the washer bottle.

OK, so you say the RPM relay shows signs of overheating, the inertia switch is no longer there because it melted, and the fuel pump changes pitch. Sounds like you need to have someone go over the whole circuit for the fuel pump fixing, replacing, and repairing as they go. As suggested, you should bypass everything and run the pump directly from a power source (only for testing purposes) to see if that is why the motor stops.