Rich running 280SE 3.5

Hello, I emailed this morning regarding my rich running 280SE 3.5.
You suggested that I should try the leak test on the MAP sensor. I have done this now and it looks very good, also all the resistance readings are within tolerance. I think the sensor is quiet new relative to the car, I attached some pictures. The number on the rivet is 963, is that 1996 March?
I also have a spare ECU which I tried some time ago but I might try it again tomorrow if I get a chance and take some measurements. Another symptom of my problem is extremely rich running when cold. I replaced both temperature sensors some time ago but no improvement. To improve the cold start mixture I put a 4.7K resistor in parallel with the coolant temp sensor which works well for the moment until I get the full solution. I work with electronics but of course I don't have your extensive resources, knowledge or the necessary data. Another problem is the drive signal for the fuel pump relay stopped working. I have a temporary bypass on the relay.
Jim.

Hello Jim,

with your vacuum leak and resistance test of MAP sensor I also believe it to be 99% okay. And yes 963 id 1996 March. So it was sawpped once.

How did you measure sensors? Directly at sensor or at ECU connector with ECU removed? Later method is the right one to be on the safe side with wriing harness issues. Do I read it correctly that you only have trouble when cold starting? If so, please remove cold start valve from fuel ring line and insert a manometer instead. Now please focus on:

• Does it stop your problems? Then check cold start valve and thermo time switch
• If not, how quickly does fuel pressure drop from 2.0 Bar when you switch off engine? And do we have constantly 2,0 Bar while car is running?

I just measured at the sensors but disconnecting and re-connecting the sensors makes a difference to the running so they are connecting to the ECU. I will test at the edge connector of the ECU and I will let you know the result. The problem is present hot or cold but really rich when cold, spluttering and rough idle. I tried isolating the cold start valve some time ago but that was not the problem.
Fuel pressure is constant 2 bar while running, after engine is switched off the pressure slowly drops to I think about 1 bar and stays there for a long time (it was some time ago I tested that) I fitted a new pressure regulator and damper a few years ago. The fuel pump looks fairly fresh too maybe about 10 years old.

Hi Dr D-Jet, I spent a few hours at it today and got some good results. The Temperature sensor connections were all good, tested from the ECU connector.
I tested the fuel pressure again, it is a steady 2 Bar when running but now it drops at a constant rate to zero over a period of about one minute. Last time I tested it would hold a pressure of about one bar for a long time. The check valve must be leaking a bit. My pump is the original Bosch type with the 3 hose connectors.
I had another look at the start valve and all was good there.
Recently I had installed my spare MAP sensor in the car trying to diagnose the rich running problem so I did a leak test on it and it failed, it is the same part number but with the screws instead of rivets. It is always a great feeling when you find something wrong. I just put the newer one back in place and it is idling pretty good. I will take it for a test drive later.
I think I may have some wiring loom problems. When I put everything back together one cylinder was missing, after disturbing all the connectors all was good again. I think some of the spade terminals are loose so I need to remove them from their plastic housings and tighten them with a pliers. That will take some time but not today.

Jim

Hi Jim,

well sounds like good progress. Vacuum leakage of 0 280 100 012 is unfortunately very common. That is why I manufactured my own diaphrgams just for that failure. However the fuel pressure dop is bad news. It can be the fuel pump valve or it can be an injector plus of course the pressure regulator. Build up pressure without starting engine and then close fuel supply hose into ring line. If pressure still drops qucikly it is an injector or pressure regulator. If not, you know where to search. Opening the valve is unfortunately very tricky on those 3 connector fuel pumps. But with your phenomena I suspect it is a leaking injector.

Some good news Dr D-Jet,
Today I installed a fuel line check valve to see where the pressure leak was. It must be the check valve in the pump so the injectors and the regulator are not leaking. Here is the valve I used:

I had installed it before to see if I could fix the warm start vaporisation problem but it didn't help so I had removed it about a year ago.
Now with this valve installed again the pressure drops to about 1.5 bar after about 15 minutes and it takes about 3 hours to drop to 1 bar. If the fuel delivery of the pump is within spec I suppose it is ok to use this external valve.
I have some spare used pumps but they have been on the shelf a long time, one is the original 3 flange type and the other is a 2 flange, part No: 0580464005. The 2 flange pump is nice and quiet running and was not used much, is this a 3 bar pump and compatible with the D-Jet?
Thanks for all the help and advice.

Jim