Confirmation on bad RPM relay?

[ifelder]

Last weekend I replaced the following

Distributor Cap/Rotor
Spark Plugs & Wires
Fuel Lines & Hardware
Ignition Coil
Vacuum Hoses
Air Filter

When I had it all put back together (Less the airbox), the car won't start. It cranks but will not turn over.

I pulled a plug wire and checked that I had a blue spark with an old plug. I checked my inertia switch and it hasn't been triggered. I poured over fuel diagrams and spark plug schematics and am pretty confident everything is plumbed and wired properly. I spent some time making sure I had the Distributor cap on correctly by orienting the notch and making sure it wouldn't rotate once latched down.

If i put the pedal to the floor, it will turn over and rev up high while the exhaust is quite smokey.

Tonight I made a jumper and jumped the Fuel pump on the RPM relay socket, after a few cranks it fired right up and seemed to idle normally.

Does this verify that my RPM relay is bad and I need a replacement? Are there any other failure modes that jumping the relay fix as well? I'm pretty sure I shouldn't be driving around on a jumped RPM relay so I guess i'm grounded until I order a replacement. Since its already Friday night my chances of getting a relay this weekend are pretty low so I figured I'd bounce my issue here to make sure I'm not neglecting to try any other solutions before ordering a replacement (and possibly a spare).

Alternatively, is it possible to repair a bad RPM relay?

Thanks,

Ian

[DMCMW Dave]

Last weekend I replaced the following



Tonight I made a jumper and jumped the Fuel pump on the RPM relay socket, after a few cranks it fired right up and seemed to idle normally.

Does this verify that my RPM relay is bad and I need a replacement? Are there any other failure modes that jumping the relay fix as well? I'm pretty sure I shouldn't be driving around on a jumped RPM relay so I guess i'm grounded until I order a replacement. Since its already Friday night my chances of getting a relay this weekend are pretty low so I figured I'd bounce my issue here to make sure I'm not neglecting to try any other solutions before ordering a replacement (and possibly a spare).

Alternatively, is it possible to repair a bad RPM relay?

Thanks,

Ian

Did you jump both sides of the RPM relay, i.e. brown to yellow/red AND to white/purple? If so, the FI part is probably bad. You can try opening it up and cleaning the relay contacts and/or resoldering the relay to the circuit board.

You are correct, you can't leave the jumper there for a couple of reasons. First, with the jumper in the FI system and fuel pump will run all the time, even with the key off. Second, the purpose of the RPM relay is really to shut off the fuel pump when the engine stalls. That's a safety issue.

Carrying a spare is a good idea. This is a common failure part.

[ifelder]

Did you jump both sides of the RPM relay, i.e. brown to yellow/red AND to white/purple? If so, the FI part is probably bad. You can try opening it up and cleaning the relay contacts and/or resoldering the relay to the circuit board.

You are correct, you can't leave the jumper there for a couple of reasons. First, with the jumper in the FI system and fuel pump will run all the time, even with the key off. Second, the purpose of the RPM relay is really to shut off the fuel pump when the engine stalls. That's a safety issue.

Carrying a spare is a good idea. This is a common failure part.

I jumped Pins 30 & 87 on the RPM relay Socket. I'd have to go back down and look to see the color codes. If this is only jumping 'one side' does this tell me my Fuel pump is OK?

[DMCMW Dave]

I jumped Pins 30 & 87 on the RPM relay Socket. I'd have to go back down and look to see the color codes. If this is only jumping 'one side' does this tell me my Fuel pump is OK?

It's odd that only jumping the fuel pump would make it run better. That could mean that the pump is fine and something is wrong with the lambda system, and by running the fuel pump only it is running better without the lambda control. If this is the case the fuel pump is good, the RPM relay is good, and you are looking for something else. Possibly O2 sensor, base adjustment, frequency valve etc.

How did the car run before you changed all that other stuff?

[ifelder]

It's odd that only jumping the fuel pump would make it run better. That could mean that the pump is fine and something is wrong with the lambda system, and by running the fuel pump only it is running better without the lambda control. If this is the case the fuel pump is good, the RPM relay is good, and you are looking for something else. Possibly O2 sensor, base adjustment, frequency valve etc.

How did the car run before you changed all that other stuff?

Car was running great before changing everything. I thought I had problems with my lambda system that were causing an idle hunt, but tracked down the issue to an unpluged vacuum advance solenoid. Once I plugged the advance back in, I readjusted the CO and it was running great. Only then did I plug the O2 sensor back in and found that I didn't have any idle issues and thought that my lambda system was running fine.

Only when the car was running well for nearly a month did I had the confidence to replace my hoses thinking I would't be complicating any issues.

I just tried jumping Brown to Yellow/Red and heard the FV buzz in the engine bay. When I jump Brown to White/Purple I can hear the fuel pump run. With the RPM relay installed, I think I should hear the fuel pump run for a few seconds with the key in RUN but I don't hear it but I may not be close enough to hear the fuel pump when in the driver seat.

Jumping the fuel pump makes the car run, but not perfectly. My understanding is the RPM relay runs the fuel pump to prime the system, then once the engine has started the RPM pulse keeps the fuel pump alive, so like you said, if the engine stalls the Relay doesn't receive the pulse and it kills the fuel pump.

So jumping just the Brown to White/purple should run the fuel pump but effectively keep the lambda system OFF, and the FV does not buzz but the engine idles. Unplugging the jumper kills the fuel pump and the engine starves as expected.

[DMCMW Dave]

Yes, you understand the operation correctly. So what you appear to be seeing is that it runs better with the lambda system turned off. This is typically quite a bit richer than with the lambda on, open loop or not. That would imply to me that you have a vacuum leak somewhere and by disabling the lambda system you are feeding it enough extra fuel to smooth it out. Does it seem to idle too fast when you run it like that?

My guess is that the RPM relay is fine and you are masking a different problem by turning off the lambda. Recheck the hose routing against the diagram, check your base timing again, etc.

[Bitsyncmaster]

How did you adjust the mixture?

Most people think you adjust it for the smoothest idle.......Wrong. Doing that will most likely run the engine very rich and make starting the engine very hard.

You need to adjust the mixture with a meter (dwell or duty-cycle) to get the Lambda system centered on a warmed up engine. When you do that, the mixture should be good for starting and warming up the engine.

[ifelder]

How did you adjust the mixture?

Most people think you adjust it for the smoothest idle.......Wrong. Doing that will most likely run the engine very rich and make starting the engine very hard.

You need to adjust the mixture with a meter (dwell or duty-cycle) to get the Lambda system centered on a warmed up engine. When you do that, the mixture should be good for starting and warming up the engine.

I had originally tuned it 'by ear' because I didn't have the o2 sensor connected so my dwell signal was useless. When I hooked the o2 back up I attached a dwell meter and was able to better adjust my tuning.

Is it possible to jump the fuel pump and FV (brown to yellow/red AND white/purple) and test my dwell again. Its possible I fixed, or added, another vacuum leak when I replaced all my hoses and now my CO is out of wack.

Does jumping these pins setup the lambda system to run in a fashion that would prohibit me from properly tuning the dwell?

Last night I opened the RPM relay case and couldnt identify any weak solder joints. The relay coil seed like it was moving freely and the spring return was functional. I plugged the relay in without the case and suspended it in the air so nothing shorted and turned the key to RUN. The relay did not move at all in RUN, but when I went to crank the engine the relay kicked over. From my examination of the circuit, the relay was connecting ground to 87 & 87a (Fuel and FV). Does this test tell me that the relay is at least partly functioning since it does tick over but might still have some problem because it does not prime the fuel pump in the RUN key position.

[DMCMW Dave]

"Priming the pump" function is not universal. If the relay closes when you turn the key to "start" it is functioning normally.

[ifelder]

"Priming the pump" function is not universal. If the relay closes when you turn the key to "start" it is functioning normally.

OK! That is a good sign that I don't need to scramble to order a new relay.

So does jumping the FV and fuel pump put my engine in a normal enough condition to check the dwell and adjust the CO? I have double checked my vacuum hose routing, save for the 3 connections on the Y pipe under the intake manifold, but am fairly confident those are OK.

Or is jumping the FV going to put my electrics the same state the RPM relay does and I might not get it to start. Is the better approach to lean out the CO (counter clock) till I can get it started on the RPM, then retune?

[Bitsyncmaster]

OK! That is a good sign that I don't need to scramble to order a new relay.

So does jumping the FV and fuel pump put my engine in a normal enough condition to check the dwell and adjust the CO? I have double checked my vacuum hose routing, save for the 3 connections on the Y pipe under the intake manifold, but am fairly confident those are OK.

Or is jumping the FV going to put my electrics the same state the RPM relay does and I might not get it to start. Is the better approach to lean out the CO (counter clock) till I can get it started on the RPM, then retune?

Making a three way jumper so the brown connects to white/purple and the double yellow/red wires would run the engine normally as if the RPM relay was doing those connections. Yes you can do all your adjustments with that three way jumper. You can even drive the car that way but you have to remove the jumper after you shut the car off. Like Dave S said, pump will not shut off if your engine stalls.

[ifelder]

Making a three way jumper so the brown connects to white/purple and the double yellow/red wires would run the engine normally as if the RPM relay was doing those connections. Yes you can do all your adjustments with that three way jumper. You can even drive the car that way but you have to remove the jumper after you shut the car off. Like Dave S said, pump will not shut off if your engine stalls.

So i just went and adjusted the CO lean (Counter clockwise, by quite a few turns) and managed to get it to fire up and idle with the RPM relay installed. It's still pretty smokey exhaust but that may be leftover fuel from mucking around last night.

the FV was buzzing so I hooked up a dwell meter to the Orange diagnostic plug and a ground and the needle remained centered, once the engine had heated up it the dwell needle dropped to the left and didn't bounce around. I think I need to drive it around to get it cleared out and then readjust everything.

Could this large adjustment required to get it to idle be an indication that I have a vacuum leak NOW and am compensating, or that HAD one and it was tuned rich to compensate. I'm having a hard time wrapping my head around the relationship between a vacuum leak and the CO adjust position rich or lean.

I just don't wanna take it out of the garage if I should tear down the intake manifold again and sort out a potential vacuum leak as I don't want to tune it with one.

[Bitsyncmaster]

If your Lambda system is working correctly, the reading should be bouncing around 30 to 40 degrees of dwell on the four cylinder scale (engine is warmed up).

It typically takes only a 1/4 turn of the mixture screw to go from minimum (dwell 10 deg) to maximum (dwell 80 deg).

[ifelder]

So i just went and adjusted the CO lean (Counter clockwise, by quite a few turns) and managed to get it to fire up and idle with the RPM relay installed. It's still pretty smokey exhaust but that may be leftover fuel from mucking around last night.

the FV was buzzing so I hooked up a dwell meter to the Orange diagnostic plug and a ground and the needle remained centered, once the engine had heated up it the dwell needle dropped to the left and didn't bounce around. I think I need to drive it around to get it cleared out and then readjust everything.

Could this large adjustment required to get it to idle be an indication that I have a vacuum leak NOW and am compensating, or that HAD one and it was tuned rich to compensate. I'm having a hard time wrapping my head around the relationship between a vacuum leak and the CO adjust position rich or lean.

I just don't wanna take it out of the garage if I should tear down the intake manifold again and sort out a potential vacuum leak as I don't want to tune it with one.


So I'm a bit embarrassed but I think I've sorted it out.....

I just drove it around the block and it was dying when I clutched. In had this same problem earlier this summer and remedied it by replacing my WUR. This caused me to train my eyes on the WUR and realized it had a BLUE plug on it.... Meaning in had the CSV plug swapped with the WUR!!!

Switching them back caused it to fire right up!

So I guess the WUR power was running to the CSV and dumping fuel causing my rich condition. Going to retune the CO with my dwell meter now and see if I've sorted it out.

Could I have caused any damage by having these plugs swapped?

[DMCMW Dave]

Probably fouled the O2 sensor. It's cheap, change it.

If you can't get the dwell reading to change with the adjustment, that's the indication that it's fouled. If you can get the dwell to bounce around 45, you may have dodged a bulled for now. If the dwell stays at 45 no matter what you do, the sensor is dead.


Sent from phone

[ifelder]

Probably fouled the O2 sensor. It's cheap, change it.

If you can't get the dwell reading to change with the adjustment, that's the indication that it's fouled. If you can get the dwell to bounce around 45, you may have dodged a bulled for now. If the dwell stays at 45 no matter what you do, the sensor is dead.


Sent from phone

OK. I have a spare o2 sensor already. My oil smells a bit Gassy so I'm gonna change it. I probably dumped a bunch of gas into it with my dumb mistake.

Thanks Dave and Dave for all your feedback last night and this morning. Nice feeling to diagnose and fix an issue even if it was my fault.

[DMCMW Dave]

OK. I have a spare o2 sensor already. My oil smells a bit Gassy so I'm gonna change it. I probably dumped a bunch of gas into it with my dumb mistake.

Thanks Dave and Dave for all your feedback last night and this morning. Nice feeling to diagnose and fix an issue even if it was my fault.

Good call on the oil change. We've had cars in here with gallons of gas in the oil. Really rough on cams and bearings.