Can anyone tell me where the fuel pump relay is located on my SEC?

Are there any special tools needed to replace both fuel pumps?

On my 500 SEC, it was in the rear of the fuse box.
The big relay that is NOT labeled 'klima'.

In your car it's near the center of the car between the firewalls between the ABS brain and the Klima relay. It'll have Kickdown or the like on it. Maybe 6000RPM min too. Black 1" X2 1/2" by 3" tall approx.

Ok, I replaced the fuel pumps, and am using a known good Fuel pump relay, and it is still doing the same thing!!! :mad: Looks like the mechanic's diagnosis was wrong. UGHHHH!!!!! I did, however replace the OVP with a spare I grabbed at the junkyard, and it made it run quite a bit better, almost driveable, but still not quite "right". There is still a slight loss of power, but when you mash the throttle it takes off like nothing is wrong. I should also mention that it runs perfect, smooth and responsive for about 30 seconds to a minute, then it starts to bog down and run badly.

I had a similar problem and I found it was a cascading effect... I had bad ignition wires that threw off everything I replaced cap, rotor, wires, plugs, and coil, ground wire, and cleaned out the idle air control valve... if you have never done these things it's about time you do and it's not a loss even if this is not the cause. maybe your cold start valve is stuck open... look it's something simple... hopefully

Well the car is back at the mechanic's shop...let's see what he comes up with next! :rolleyes:

Warmup regulator!!!! May be the culprit. The 30 seconds thing sounds like the WUR or the Cold Start injector. The gasket under the Cold start injector my be toast causing it to suck air. How about vacuum lines? Is the EGR hooked up correctly? does the Tempo Vac Valve work? Lots of thing screw up the Idle. If the EGR is actuating at idle it'll run like crap, almost die.

Wife's Maxima had symptoms nearly identical to what you described, particularly the parts about it (1) starting fine and idling fine for a bit and (2) bogging down on accleration. Injectors were replaced, CTS replaced and plugs, wires, distributor/rotor and coil checked out good. Turned out to be MAF sensor.

On mine, a 1987 560SEC, the fuel pump relay is right below the windshield in the middle of the engine compartment.

Got a call back from the mechanic, he replaced the fuel filter, and all is well. Apparently it was clogged to the point where it would no longer flow. He even gave me a demonstration with compressed air, and the filter would barely flow, and lots of dirt and chunks came out of it.

Change your fuel filters people!! :)

fuel flow
 

Did your mech offer any relief for faults misdiagnosed and work/parts done but not needed?

Seems that fuel filter would be the logical place to start rather than last resort.
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BTW, a similar temperature related effect on my 560SL (basically the same engine and control system) was isolated to the engine temperature sensor that inputs to the EZL. Ran good cold then went sour when warmed up.

Well, know he has the peace of mind, knowing that all of those parts have been replaced and are not likely to break anytime soon . . . .

Nope, he even charged me more than he had originally said he would. I ended up paying about $100 for the filter change.

Is it finally running correctly? My US spec 380SE's CSV (Cold start valve) is inop but doesn't hamper the performance, except on start up (you have to give it a bit of gas). Hopefully it's fixed but it does sound like a faulty FD. The same thing happed in my 200TQ just pulling out of the driveway and driving up a hill and all of a sudden no power... Smelled raw fuel and car bucked like a horse...

Makes you wonder how clean that fuel is coming out of the pumps! :eek: