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1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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428 Posts
Discussion Starter #1
I replaced the fuel filter in my '72 280SEL 4.5 a month or so ago. The next day, I developed a fuel leak on 2 or the hoses from the rail to the injectors. I have now experienced an additional 4 to 5 leaks over the past month. At first I thought the old filter was so plugged, I had more pressure at the rails causing leaks to become apparent. The regulator appeared to be working fine.

I now think the regulator is periodically failing high because the car will leak when started, then not leak if allowed to depressurize and start again.

Any one ever had a regulator fail high intermittently? I can't think what else could be causing the intermittent leaks. It is all new hose (7 BAR) and all new clamps (all 36 of them) and the leaks are all on hose to barb fittings, not in the hose itself.:surrender:
 

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73 280SE 4.5, 71 300SEL, 03 BMW Z4, 72 Fiat 850, 80 Triumph TR7, 85 Porsche 911
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2,280 Posts
When you suspect the regulator fails high, does the engine feel different? Acceleration or idle still ok?
 

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1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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428 Posts
Discussion Starter #3
I do not notice any appreciable change in engine peformance either at idle or at speed. She does idle VERY rich, but then again se is a D-Jet car so that is not that unusual.

When I noticed my first leak, I also noticed the line between the regulator and the pulsation dampener was slightly kinked. I attributed the initial leak to the kink not passing sufficint fuel back to the tank, but that is all fixed and still the phantom leaks about every week or so.
 

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1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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428 Posts
Discussion Starter #4
I finally got the time to replace the fuel pressure regulator with a new one. Solved a few problems and seem to have caused a new one.

The car no longer has intermittent fuel leaks. She starts much better when cold. My fuel efficiency has gone up dramatically. It also seems that I have much less noise from the injectors firing. All good things.

I now have a problem that I suspect is vapor lock. When hot, the car will start, but only with considerable effort and then it runs very rough for a couple of minutes.

Suggestions.
 

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'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
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407 Posts
At first I thought you had an I6 280 with the old style verticle pump.

There is a check valve inside but what style pump do you have?
 

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1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
Joined
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428 Posts
Discussion Starter #7
The car is a 4.5liter V8 with the D-Jet injectio system so it has the small electric rotary pump back by the tank.

I don't think it is a pump issue since it seems to supply plenty of fuel when the car is cold (cold start valve open and running rich) but it could be. It just seems that with the lower pressure in the rails now (with the new regulator) the fuel is being allowed to vaporize when the engine is hot and thus the vapor lock.

It could be I have an injector or the cold start valve leaking slowly which is allowing this to happen. leaking cold start valve is pretty common in the D-Jets I think.

Any ideas?
 

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'13 911 Turbo S, '11 C63 AMG, 944 Turbo Track Car, '68 250SE CONV(2) 72 Unimog 411D, 85 190E 2.3-16
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407 Posts
Do you have the means to check the car's fuel pressure?
 

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1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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428 Posts
Discussion Starter #9
Quick update. I did check the fuel pressure. Holds steady at 30psi when running and is still at about 25 a couple of hours after shutting it off. Does not seem to be the issue.

However, the car has been getting worse. The past week, it still runs great cold, but starting to run rough when hot, so I decided to do more troubleshooting last night.

After an hour of checking everything I could think of, I pulled the cover off the coil. I had put on a new Pertronix ignition about 2 months ago. When I did, I used the crimp on aluminum connectors. Apparently, 2 months of repeated heatig and cooling had caused the aluminum to become loose on the copper strands. One of the connections came off in my hand and the other was not much better. apparently they were making good enough contact when cold, but when it got hot, the aluminum expanded enough to no longer have good contact.

Car ran great this morning. Guess I will redo everything this weekend and return to my standard solder connections. So much for taking the easy way out.

Hopefully this solves the problem. Thanks for the help.
 
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