OVP Relay - Mercedes-Benz Forum
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post #1 of 14 (permalink) Old 04-16-2019, 06:25 PM Thread Starter
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OVP Relay

Hello, I'm attempting to change the OVP relay in search of a solution for a cold start issue. Is there a trick to the connector on the bottom of the relay or is it just that hard to pull off? The car is a 1990 560SEL.
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post #2 of 14 (permalink) Old 04-16-2019, 06:36 PM
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Iím assuming youíve already checked the fuse in the relay. The connector just pulls off.
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post #3 of 14 (permalink) Old 04-16-2019, 06:36 PM
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Quote:
Originally Posted by sbpsu354 View Post
Hello, I'm attempting to change the OVP relay in search of a solution for a cold start issue. Is there a trick to the connector on the bottom of the relay or is it just that hard to pull off? The car is a 1990 560SEL.
When I replaced the OVP on my 1989 300se I had to pull really hard to remove it from the connector on the bottom. For me it is held in place in a plastic bracket that the two tabs of the OVP slide into. After I slid it out of those brackets, I firmly held on the plug and pulled the OVP out. I was chasing a cold start issue too, but the new OVP didn't make a difference.
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post #4 of 14 (permalink) Old 04-16-2019, 07:16 PM Thread Starter
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Thanks! Yes, I checked the fuses as those were easier to pull. The OVP relay actually looks recent, so I’m betting it’s not the issue either. I popped in a new fuel pump relay and found new old stock of the cold start injector. The orig cold start injector mounting screws were barely finger tight, so i know I had a vacuum leak. The new injector didn’t help, so fuel pressure is likely my next stop
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post #5 of 14 (permalink) Old 04-17-2019, 05:30 AM
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Yes a fuel pressure test will be revealing. I usually just remove the fitting on the CSV and hook up the guage there, that's much easier than pulling the air cleaner housing off, because the cold starter injector is right there. One other thing the correct fuel pump relay also has a roll in energizing that injector.
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post #6 of 14 (permalink) Old 04-17-2019, 06:36 AM
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If I may ask, what is your cold start issue exactly?
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post #7 of 14 (permalink) Old 04-17-2019, 06:47 AM
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i changed mine a week ago, i bought it from the dealership, i was reading on the overload relay, Kent Bergsma from mercedessource said if your car has one of these one fuse black relay, consider changing it immediately with the new updated part "red with 2 fuses".attached the difference between the new one vs the old one.
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post #8 of 14 (permalink) Old 04-17-2019, 11:21 PM Thread Starter
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Thanks for the pics. My OVP Relay is the new style with dual 10 amp fuses. The primary challenge I face with the car is just the cold start. The engine turns over fine, but needs to crank for 10 seconds or so before it catches. Sometime it stumbles for a few seconds then smooths out while other times it’s pretty smooth once it catches. If I let it idle for 30 seconds or so and shut it back off, it’ll fire right back up like a new car. I can run into the store and come back out an hour later and the car starts fine. Overnight, back to extended cranking. It’s never stalled. The only other challenge with the car seems to be electrical and likely bad grounds, but I welcome input. When cranking the starter, the speedometer needle can jump around. At night with the lights on, the 2 turn signal indicators in the cluster glow constantly like they’re partially on. The blinker indicators work when I use the turn signal, but they’re dim. I’ve bought the tools to pull the cluster and clean contacts, but I’m focused on the starting issue. The selling dealer is said to have replaced the fuel pumps and filters as well as plugs, cap, and rotor. I also believe they replaced the Plastic device on the side of the fuel distributor. The EHA device if I’m not mistaken. I’ve replaced the plugs to be sure they’re non resistor. I’ve replaced the fuses with the copper ones, and recently replaced the coolant temp sensor for the cold start valve, the cold start valve with NOS, and the fuel pump relay. I have a new OVP relay as mentioned above, but the fuses on the existing are fine, and the new one looks just like the one in the car which isn’t original. I’ve got new injectors and new cups, seals, etc, so they may be next. Amy help is greatly appreciated
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post #9 of 14 (permalink) Old 04-18-2019, 07:30 AM
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Originally Posted by sbpsu354 View Post
Thanks for the pics. My OVP Relay is the new style with dual 10 amp fuses. The primary challenge I face with the car is just the cold start. The engine turns over fine, but needs to crank for 10 seconds or so before it catches. Sometime it stumbles for a few seconds then smooths out while other times itís pretty smooth once it catches. If I let it idle for 30 seconds or so and shut it back off, itíll fire right back up like a new car. I can run into the store and come back out an hour later and the car starts fine. Overnight, back to extended cranking. Itís never stalled. The only other challenge with the car seems to be electrical and likely bad grounds, but I welcome input. When cranking the starter, the speedometer needle can jump around. At night with the lights on, the 2 turn signal indicators in the cluster glow constantly like theyíre partially on. The blinker indicators work when I use the turn signal, but theyíre dim. Iíve bought the tools to pull the cluster and clean contacts, but Iím focused on the starting issue. The selling dealer is said to have replaced the fuel pumps and filters as well as plugs, cap, and rotor. I also believe they replaced the Plastic device on the side of the fuel distributor. The EHA device if Iím not mistaken. Iíve replaced the plugs to be sure theyíre non resistor. Iíve replaced the fuses with the copper ones, and recently replaced the coolant temp sensor for the cold start valve, the cold start valve with NOS, and the fuel pump relay. I have a new OVP relay as mentioned above, but the fuses on the existing are fine, and the new one looks just like the one in the car which isnít original. Iíve got new injectors and new cups, seals, etc, so they may be next. Amy help is greatly appreciated
From the sounds of it a lot of things have been changed, but I have not seen any vacuum components.

I had an issue on my 300se where I would try to start the car and I would crank for 10 seconds, like you, and sometimes it would idle rough for a few minutes and then smooth out, or when it was really cold out it would start right up. Sometimes I had to give it gas to keep it running. At the same time, when warm I had no problems. I ended up doing a smoke test and found that the gasket below the throttle was causing a large vacuum leak. On the 300se that happens to be below the CIS fuel distributor boot and hence below the air flow potentionmeter (which I believe meters the air that is going to the intake). I replaced that gasket, among other rubber components I had to take off in the process because I believed them to be original to the car and the car starts much better and runs fine when started.

I would try to do a smoke test, and if you don't have a smoke machine people on the forum suggest brake cleaner, carb cleaner or propane. All have their advantages and disadvantages. Do a search in the forum to see what others do and which you would feel comfortable with.

Hope this helps!
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post #10 of 14 (permalink) Old 04-18-2019, 10:14 AM
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i agree with you 100%, check my thread about smoke test using cheap pump from harbor freight and $3 cigar from local grocery store, also check my other thread to replace the boot underneath the meter, when i did smoke test it was leaking also.



Quote:
Originally Posted by 89benz300se View Post
From the sounds of it a lot of things have been changed, but I have not seen any vacuum components.

I had an issue on my 300se where I would try to start the car and I would crank for 10 seconds, like you, and sometimes it would idle rough for a few minutes and then smooth out, or when it was really cold out it would start right up. Sometimes I had to give it gas to keep it running. At the same time, when warm I had no problems. I ended up doing a smoke test and found that the gasket below the throttle was causing a large vacuum leak. On the 300se that happens to be below the CIS fuel distributor boot and hence below the air flow potentionmeter (which I believe meters the air that is going to the intake). I replaced that gasket, among other rubber components I had to take off in the process because I believed them to be original to the car and the car starts much better and runs fine when started.

I would try to do a smoke test, and if you don't have a smoke machine people on the forum suggest brake cleaner, carb cleaner or propane. All have their advantages and disadvantages. Do a search in the forum to see what others do and which you would feel comfortable with.

Hope this helps!
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