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rsjon
14th January, 2010, 08:05 PM
Hi!
I have a problem with a Merc C200 W202 1998. It has been converted to LPG and will not run on petrol because the long term fuel trims have been learnt while running on gas and when switched to petrol will not run because it is way too lean. Now the battery went flat and when charged it will not run (most of the time) on gas either! Has the ECU lost more base info? Is there a way of resetting the ECU to its' factory setting? Or am I missing something?! :hmpf:

Any info or help would be greatly appreciated.

Thanks, Jon.

Dajan2009
14th January, 2010, 09:44 PM
Hi, Jon. Tell me, have You checked your car with some diagnostic device, Star diagnosis maybe? It seems to me that Your MAF sensor is gone bad, or it is on a half way..:hmpf:. Why? MAF usualy degenerate thru time, and ECU compensate it with long-term adaptation (there are a short and a long term adaptations, both for part and full loads). When your battery had gone flat the adaptations gone to zero, their default value, and now the fuel-air ratio is too lean! Usually the car starts to blow detonations in the intake manifold, doesn't reach full revs, and have very poor trottle response. Are you good at car repair and some electrical theory is familiar to You? If the answer is yes, you can measure the voltages from the MAF sensor and ECU, but if the answer is no, you can try few other things; If the engine revs very poorly, you can unplug the engine with ignition off, start the car, maybe with some throtle, and see how it revs without MAF sensor(but with replacement value from ECU). You can also try an other MAF from other car, it coud be perol or diesel from mercedes, or also from VW like golf or passat, you need only one with this type of connector. The diesel one don't have a integrated temperature sensor for the intake air, but it will do the job for the fuel calculation. If You need something more just ask:santaclaus:
Cheers

rsjon
14th January, 2010, 10:24 PM
Thank you very much for your reply. Originally when I got the car it would start on petrol for a second and then die (initial rich mixture on first start). I managed to get it running by making a series of metal plates with different size holes in them, placed them over the throttle body and gradually made the hole bigger and bigger. I thought that this was making the mixture richer and the car would start and rev, but not tickover. All during this time it ran perfectly on gas.
Now, after the battery ran flat, the same fault is apparent on gas; it initially ran ok for a couple of minutes but then deterorated and now it does what the petrol does. If I plant the accelerator to the floor, it will just about tickover for a short while, both on gas and petrol. I tried disconnecting the MAF and it wouldn't start. Very interesting that you think it could be the MAF; I hadn't really considered it as it ran so well on gas. I am fully conversant with meters etc and have messed with cars for years! Can you then confirm that when the battery goes flat the ecu reverts to its' factory settings?
I do not have a star tester; is that what is needed for the 38 pin diagnostic socket?
Very interesting fault and I will get to the bottom of it!

Thanks again, I am looking forward to hearing your further thoughts!

Jon.:hmpf:

Dajan2009
14th January, 2010, 11:38 PM
Yes, when the battery is flat long enough the ECU looses all adaptations. It has to be more than few minutes, if it stays flat over night it is almost surely done. So, it could be few more things that make the car run realy bad. Just for starting, have You measured the fuel pressure? It have to be 4Bar or 50psi with ignition ON, same at idle with vacuum on fuel regulator blocked. It could also be the throttle body that had loose the learned position, and basicaly it could be defective so the ECU can't learn all by himself a new one. It realy could help if somebody could watch into the ECU for some faults and strange actual values with Star or some other good tester. I know that the engine is dificult to start without MAF for the first time, you need some throttle, but I am also sure that it does not run smooth with MAF plugged on ECU but without intake pipe on throttle body. My logic on this situation is based on the fact that this kind of ECU looses its adapted values when batt goes flat and run worse than before. Cheers

rsjon
15th January, 2010, 08:32 AM
Right, I will investigate and get back to you! I don't think it is the fuel pressure because it is now bad on gas as well. Really I need to find something wrong for both gas and petrol now, whereas before it was only faulty on petrol.

Jon.

rsjon
16th January, 2010, 01:33 PM
OK...got the car going on gas and managed to drive it around and got on the motorway. Drove up and down at various speeds and gradually the engine ran better and better as the ecu relearned its' settings. It is now running fine. Still will not start on petrol though...even with the MAF disconnected. I checked the gas wiring diagrams and found that the MAF is not used on this gas system, so I would suspect the MAF is faulty except for one thing - it will not start even with the MAF disconnected. :banghead:
Maybe there is more than one fault? How do you check the MAF with a DMM? At least I can drive it now!!

Cheers,

Jon.

Dajan2009
16th January, 2010, 11:44 PM
OK, I'm glad the car is getting better.:dancing2:Which kind of MAF do You have, the one with a round connector maybe?

Meat-Head
16th January, 2010, 11:58 PM
Retorical question (not want/expecting an answer)- not subcribed to this thread

Has the petrol tank ALWAYS had 1/4 tank of fuel in it. Fuel pump will sezise if let run dry, yes we all know that petrol has no lubrication properties.

Can you get a diagnostic epquiptment (another new spelling) to read the engine temprature.-no choke?

How does the emulator box work? cut's errectors or fuel pump.

Has petrol pump got a perfect 12+ volts up it's arse?

OFF TOPIC, but not relevant.

If you have a petrol/parrfin engine, what you do is start it on petrol, then change over to parrafin, then at the end of the day, switch back to petrol.

Otherwise it will not start on pure parrafin.

So, before you stop the engine, not that it would matter, switch to petrol and see what happens next start.

rsjon
17th January, 2010, 06:44 PM
Meat Head, thanks for taking the trouble to reply!
Amongst the first things I did were check the fuel pump fuse, relay and replace the fuel pump and filter, all to no avail.
The emulator loops the wiring to the injectors to the emulator box, which simulates the injectors firing and fools the ecu into thinking the injectors are working. If you have multi point gas injection, I believe this system lets the petrol injector pulses run the gas injectors, but I have only got a single gas mixer.
Thanks for your thoughts; I do think the problem is tied up with the ecu trims, but possibly the MAF is faulty (as well?).
Dajan, the MAF has a 5 pin in line plug. Hope this helps.
Jon.

rsjon
4th February, 2010, 03:13 PM
All sorted today! New MAF and it runs perfectly, gas or petrol!

Thanks for all your help.

Jon.

Dajan2009
4th February, 2010, 11:47 PM
Realy good news, I'm glad You did it. Good job rsjon:champions: