I have a 88 560sl. Been driving it for months now and it runs good.

Then last week something changed. I was driving and turned the radio off for a phone call. After turning it on again, it stopped playing, but the display was on. And I could not turn it off or change any setting on it.
Two days after that the battery seem to be dead. I charged it, and the car started, but with lots of trouble. Like it wasn't getting fuel. After it did start, the radio went back to normal. But the Idle is like 1600 in nutral and 1000 in gear. This Idle seems to occur after the car is well and warm, and cold starts are very hard. Also, my antilock light stays on since this started. My battery is at about 12 volts with the key off and 13.5 running so the alternator seems to put out.

I have read a few things on the board and have changed my fuel filter just to make sure. I tried testing the OVP relay and I think it passed.

I would like to run the diagnostic codes. I have a Bosch Injection book that tells me to start the test at the fuel relays. It just doesn't say where the relay is.
Can someone tell me where the fuel relay is in an 88 560sl?
Is there some good documents I can get on runing the codes and tests?

Can someone recomend were I can get fittings/guage for fuel presure tests? I have a GM/Ford style EFI guage.

Any suggestions on what to eliminate, and in what order?

The car just ran so good before this, and it survived Katrina.

Thanks in advance.

Dave

sounds a lot like a failed/failing OVP.

__________________
1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

I found the problem. After testing the OVP Relay and finding it worked.
I checked the wiring running to the relay. It has 4 wires. One is a ground, One is hot with key on (activates relay). One is Hot all the time.
And the last is fed power when the relay is activated. Actually it feed to the Idle control relay up under the dash. You will find an orange lead going to the OVP relays plug which is the Hot all the time lead. You can unplug and test it. And that was my issue. I was not getting any power to this (hot all the time) lead. So my relay was activating but had no power to pass onto the Idle Control. Turns out this orange feeder wire comes from a small lead attached to the plus terminal on the battery.
I tested it 5 times and finally found that with a test light on the lead at the relay, I could shake the small wire (actually the bolt in the battery clamp was corroded) and see the light go on and off.
A dead give away for OVP and or power to it issue is High Idle and antilock (Breaks) light staying on. With no OPV functions, the injection system goes into manual mode and has no Idle control, thus idles high.

Thanks to mbtechman for his help on the wiring.

If you are having this high idle and you thing your relay is bad, (check the fuse on top the relay first). You can, pull the relay out, run a hot wire to the wire in the relay plug(should be pin 87 on the relay, lower right corner.) and your idle should return to normal instantly, proving that the relay is not feeding power to the idle control system. If this works, you either have a faulty relay, or you have a wiring issue like I did.

In the 88 the OVP relay is just above the fuse block in the right kick pannel.
Its the one with a fuse stuck in the top of it.

Good luck....