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Will a failed RSR cause a lazy fuel pump relay?

I

iHateVolvoPeople

Active member
Joined
Feb 1, 2014
Location
Midwest
SOLVED: a bad 556 ecu was not turning on the pumps and possibly not allowing the radio suppression relay to function either. Symptoms were a crank no start when very cold out. I would notice that the pumps were not priming and it would obviously not start. Swapped in an ECU from my 93 245 and the pumps primed. Car fired right up.



1990 740 na lh2.4.

Car is great when it runs but sometimes on really cold starts (15F today) it’s a crank and no start. I do not hear the fuel pump relay kick on. I removed the fuel pump relay in jumpered it to where both of the fuel pumps work but I was still getting a no start. I am assuming it’s getting fuel at the rail considering almost the entire fuel system is new. Is a bad radio suppression relay a possible cause of a crank no start? Even if the engine is getting fuel maybe the injectors or not firing. I’ve tried to fuel pump relay is but neither seem to be reliably priming and key position to on a regular basis. After everything is warmed up I hear it prime and it starts like normal.
 
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It’s odd that I do not hear the fuel pump relay and fuel pumps prime in key position two. 90 percent of the time they do on this car. I’m wondering if it is a grounding issue that is not allowing them to prime and maybe that could be in relation to the RSR as well.
 
Bad connection at the RSR will cause the injectors to not fire. Cold weather will cause the bad connection to be a worse problem. Fuel pump relay triggers the RSR. Bypassing the fuel pump relay for test purposes requires one connection (30) on end and two connections (87-1, 87-2) at other end of jumper.
 
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The RSR relay provides a constant 12V+ supply to the fuel injectors.
The positive connection on the fuel injectors will be energized whenever the ignition switch is in position 3 and 4.
If the ignition switch is on, the fuel injectors are receiving power.

You can check the RSR relay by simply disconnecting a fuel injector electrical connector and testing for voltage to the injector with the ignition switch turned on.
If you have voltage at the injector, the relay if functioning.

The signal that turns the injector(s) on and off is a negative (ground) signal from the Jetronic Module.
It supplies the ground to the injectors and completes the circuit.
This is a pulse signal that operates all of the injectors together.
All of them open and close together.

You can use spray some starting fluid into the intake to determine if it's a fuel problem that you are having.
If the engine will "hit" on starting fluid, the problem most likely is in the fuel system.
My hunch it your problem is in the ignition system.
When was the last time the engine was tuned? Plugs, wires and distributor cap??

Hope this helps
 
I agree with everything above, but I also gotta chime in. Just because you have voltage at the injectors doesn't mean the RSR is fine. I did have an instance of no start, pumps ran, fuel pressure on spec, spark, compression, power to the injectors. After checking for power I forgot to plug an injector back in, tried it again, lit right off, on 3 holes, ran fine when I plugged the 4th back in. Shut off, wouldn't restart, unhooked a different injector, fired right up. The RSR wasn't able to handle the current needed to start but it was fine once running. The cold would add to that. Simply bypassing the RSR for test purposes only would check for that, but that won't make a difference on starting if the pumps aren't kicking on.

Having said that, no pumps, different scenario. If the FP relay isn't kicking on I'd check power and ground to the ECU and ICU first.
 
I’m just curious why the fuel pump relay isn’t priming the pumps. I think the issue is directly related to that. I’ve tried 2 relays but will try one more. Once i get t running I’m goimg to drive it to a heated garage and look over everything you guys have described. Thanks
 
Well it would not start when I jumped the fuel pump relay to make the pumps run, but I reinstalled another fuel pump relay and got them to prime and then the vehicle started. Does not make any sense to me.
 
2manyturbos said:
It sounds like you have/had a flaky fuel pump relay That would explain why sometimes you hear the pump prime, sometimes you don't.
Click to expand...

Agreed but to me that does not explain why the engine would not run when i made the pumps run manually.

Also After I turn the engine off, I can hear the relay kick the pumps on once or twice for very short amounts of time like it’s spazzing out or something.
 
How did you make the pumps run manually? If you pulled the relay out to do that you cut the power to the ECU and injectors. The fuel pump relay is actually 2 relays packaged together.
 
2manyturbos said:
How did you make the pumps run manually? If you pulled the relay out to do that you cut the power to the ECU and injectors. The fuel pump relay is actually 2 relays packaged together.
Click to expand...

Well that would explain it i guess. I read on here that you could just jump 2 ports in the fuse/relay panel (30 and 87/1???, don?t remeber). I did that and heard both pumps run but still had a crank no start.
 
I just pulled off the RSR connected and half of the bullet connectors stayed in the relay, crumbling plastic and all. Anyone ever replaced these crimped bullet connectors that slide into the main RSR connector? I have a feeling that and possibly a flaky fuel pump relay are the cause of the crank no start. I cleaned the RSR connector with some contact cleaner.
 
PromiseRing said:
I just pulled off the RSR connected and half of the bullet connectors stayed in the relay, crumbling plastic and all. Anyone ever replaced these crimped bullet connectors that slide into the main RSR connector? I have a feeling that and possibly a flaky fuel pump relay are the cause of the crank no start. I cleaned the RSR connector with some contact cleaner.
Click to expand...


I have photos/instructions showing how to jump the fuel pump relay here. A photo always helps: http://www.240turbo.com/volvorelays.html#testingrelays

I can also supply the connector or pigtails to repair/replace the RSR plug if needed: http://www.240turbo.com/blackvinyl.html#sealedbulletplugs
Dave
 
Thanks for the info guys. I’ll get to ordering some new connectors when i get the chance.

It sucks having an intermittent issue because who knows when it’s going to do this next. Maybe cleaning the RSR connectors fixed it, maybe it didn’t.

I’m trying i get the diagnostics box to function properly. No feedback what so ever at port 2. The LED does not faintly illuminate. I think i’ve read that there are no connections in between port two and the ECU. Is this true? In that case if port to is not lighting up but my connection at the box itself is good, then there is either an issue at the connection on the ECU or it is a bad ECU.
 
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