4.5 fuel "flooding" issues - Mercedes-Benz Forum

 
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post #1 of 4 (permalink) Old 09-27-2012, 11:41 AM Thread Starter
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4.5 fuel "flooding" issues

After returning from a lengthy deployment, I took my 280SE 4.5 out of storage (dad) and intended to use it as my transport to a new job. It ran so poorly that I ended up having the thing delivered to me. After working out all the bugs, one remains:

After a good run of 20 mins or so, I'll park the car for the same period of time, and when trying to start it again, the thing barely starts (a "no start while hot" condition"). If the car had carbs, I'd say it was flooded. This was abnormal from when I left it with dad.

Research suggests the injector seals were bad, but I replaced those about 5000 miles ago and they generally don't get rusty. More research suggested that the check valve in the fuel pump was bad, allowing gas to flow back to the tank, further allowing vapor in the lines to form.

Some background to this was that dad let it sit for so long that the fuel pump rusted, as did the tank. I boiled out the tank and the fuel pump was taken off the car, ran backward with some WD40 in it, and all the rust was blown out. I disconnected the cold start valve, but without effect.

Question: will a shot check valve in the fuel pump cause my symptoms? And if so, where is this thing located? Internal to the pump?
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post #2 of 4 (permalink) Old 09-28-2012, 02:38 PM
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Hey Grubester, I am by no means an expert on mechanical things but my 4.5 in my finnie is doing exactly the same thing. The MB workshop reckoned that it was not holding fuel pressure, and the way I wired it up, the car does not do that little 2 second burst with the fuel pump when you turn the key on. They put a new accumulator on (or so I am told - I had better check) but it still does it. I pulled the pump-filter-accumulator assembly off a W126, so I don't know where a D-Jet 4.5 one is. Is it that thing behind the engine on the firewall?

The current work-around is they got a brake light switch and wired it into the fuel pump relay and located it discretely under the dash. So when the car is hot, I give it a 3 second burst on the fuel pump and the car starts.

I also have a couple of dodgy injectors that are dribbling a bit, and there is an air leak in the intake manifold system somewhere (despite all new rubber joiners). So there are a few thigns to suss out. My mechanic mate is coming over this morning so I was goign to pick his brains about it all. Will report back on any new theories!

Good luck,
Drew
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post #3 of 4 (permalink) Old 09-28-2012, 08:20 PM
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Hi!

These are known for hot start issues. Your first thought was right, losing fuel pressure and vapor lock. Investigate the check valve in the fuel pump line, and the filter and accumulator, then go into the engine and start checking the fuel pressure regulator setup.

I can tell you that if you had rust in your fuel system on a 4.5, you really should go though everything, take out the injectors and clean them, replace all fuel lines as necessary etc.

when you turn the key on, wait for the pump to do it's 2 sec. burst before turning to start. This pause actually will help sometimes. Or you can wire a pushbutton into the cold start injector as drew has, and use that when hot starting. there was a running change during manufacture that always energized the CSI when starting.

good luck!
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post #4 of 4 (permalink) Old 10-01-2012, 05:53 AM Thread Starter
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Hmmmm, all good ideas. I'm not too awfully worried about the injectors - all replaced about 5000 miles ago also. I'd like to check out the check valve but don't know its location. Is it part of the fuel pump?
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