300E vacum thingy under air manifold?

[biggles_8]

I have got a misfire on No 1 cylinder my 1995 300E diesel (55,000 miles). So I have stripped the top off the engine to get to the injectors.i intend to swap the injector with a known fireing one then if the misfire changes another cylinder i know the injector is duff. When I took the air intake off there is a vacuum unit bolted to the underside of the air intake it has 4 /5 vacuum takeoffs and two electrical plugs on it. On my car the insulation on the wires to this unit have got hard and broken off allowing the wires to touch each other. My question is what is this unit and what is the result from the wires shorting to each other? Apart from the misfire the car works fine although it do lack acceleration.
Also the air inlet has a heavy build up of soot in all the passageways in particular No 1’s ports is this normal? Should I clean it out? Have I got a serious engine fault?

​

 

[Dieselman]

That sounds like the EGR valve control..They won't be working properly if the cables are shorted. best fixed.

 

[biggles_8]

what's the ERG do?

 

[LastMinute]

Impressive mileage for a 12 year-old car.

How do you know it's number 1 that's misfiring?

If you mean item 205 here, it's a vacuum changeover valve - not the EGR valve, which controls how much Exhaust Gas is Recirculated into the intake manifold and is located on the exhaust side of the engine. The changeover valve controls the two flap valves that adjust the air flow through the "variable resonance" intake manifold.

Wiring loom degradation is well-known on these cars. The result of wires shorting can be anything from benign to the loom catching fire. I'd make replacing the damaged wires the first job. Check the rest of the loom while you're in there.

Soot in the intake manifold is to be expected - largely down to Exhaust Gas Recirculation. One port being worse than the others - and a misfire - might indicate a problem with the intake valves for that cylinder. Cleaning out the manifold won't do any harm, but it'll just get dirty again...

 

[biggles_8]

I am sure that No1 is misfiring because when started up from cold all the exhaust outlets get hot but not No1 which stays very cool almost cold.
As far as I understand diesels there are only three things that can stop a cylinder from firing, injector, injector pump and valves by changing the injector I am hoping the I can illuminate one.
Is it remotely possible that the ERG can effect the running of No1 cylinder? So would it be wise to sort out the wires then try the engine again?
There is no blowback from No1 when Running the engine with the inlet manifold off.

The mileage is genuine, as I know the original owner; this MB is my first shame about the rust! I was hoping that we could grow old together

 

[LastMinute]

Is it remotely possible that the ERG can effect the running of No1 cylinder?

In short: no. EGR affects all cylinders the same.

So would it be wise to sort out the wires then try the engine again?

Yes, but malfunctioning valves in the intake manifold would affect all cylinders the same, too.

 

[Dieselman]

So it's either a compression problem, injector problem or fuel pump.
I think you've already done the injector so check the compression and fuel delivery.

My bet says fuel pump. It could be a simple as the rack come loose or the outlet delivery valve stuck.

 

[biggles_8]

So it's either a compression problem, injector problem or fuel pump.
I think you've already done the injector so check the compression and fuel delivery.

My bet says fuel pump. It could be a simple as the rack come loose or the outlet delivery valve stuck.

how do you get to the rack to check & can a stuck delivery valve be unstuck?
if so How?
can the compression be checked though the glow plugs?

the car is booked into a garage on the 14th but i would like to sort this out myself if i can. time is running out

 

[Dieselman]

Remove the pipes from the injectors and crank the engine over. Each delivery pipe should deliver equal quantities.
Best to refit the injectors to create pressure but be careful not to get your hand in the way as the spray can pass through the skin which can be very dangerous.

 

[biggles_8]

Well I have not found the cause of the misfire I have taken apart the injection pump as far as I dare and could not see anything amiss but with no knowledge or information about the pump I think that it is time to let the garage have a go and have now reassembled ready to take to the garage.
THANK YOU all who gave advise if I find out what the fault is I will post as it could help someone else.

 

[biggles_8]

Well I have not found the cause of the misfire I have taken apart the injection pump as far as I dare and could not see anything amiss but with no knowledge or information about the pump I think that it is time to let the garage have a go and have now reassembled ready to take to the garage.
THANK YOU all who gave advise if I find out what the fault is I will post as it could help someone else.

its back from the garage and i am £600 lighter in my pocket it was the injector pump that had an internal leak on 3&6 but it was also not timed right they sent it away to recon the pump and then refitted and retimed the pump, it is now running ok.:bannana: wish i had taken it there first
all this because i let a garage (who has a fool pretending to be a diesel expert working for them work on my car) last year for a fuel leak, so do not take your MB to Prettys garage in Diss Norfolk cos they are c**p