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Car Forum / Mercedes-Benz Cars / June 2006300E Flooding Out when running
I know I posted here several times before...I have replaced many parts to this car and still cant figure out why the car keeps flooding out on me. I am 100% sure it is flooding out after a few minutes of running. The car is fine on a cold start but cuts out after a few minutes. When the OVP relay is DCd the car runs o.k. when warmed up. I installed a new fuel pump relay, fuel pump check valves, fuel accumulator, fuel pressure regulator, the OVP relay is pretty new, cap , totor, plugs, wires, o2 sensor, catalyitc converter... The old cat had 2 precats on it, this one only has the one cat in the middle, doe sthis make any difference? I appreciate all the help, I am on a fixed income in school and need this car to run....-chuck, nj "When the OVP relay is DCd the car runs o.k. when warmed up." So you can drive it some distance, say 10 miles, w/o the OVP relay in place? If so, why not buy a new OVP relay? I can go forever with the car after the initial warm up and its ok... You think the relay could go bad that quick? I mean parts to go bad sometimes... But when I stick the relay in the ABS light goes off...as when I pop the relay out the ABS light comes on... Unless only part of the relay is operating..-cg Sorry for not responding further to the previous posting. The fuel pressure (=mixture) is primarily controlled by the fuel distributor. It works in a way that the air mass sensor (the moving plate under air filter) controls the position of a plunger inside the fuel distributor, which again determines the fuel pressure to the injectors. The mixture is adjusted by the screw inside the tube, which leads to the top of the air filter. The pressure is then fine adjusted by the fuel pressure regulator (EHA) through the incection computer. If overvoltage occurs, the fuse in the OVP relay will blow and thereby disconnect the power supply to the injection and ABS computers. When the injection computer has no power, the injection system works without fine adjustment of the pressure. Taking out OVP relay will simply remove power supply likewise. Since the engine runs fine without the OVP relay, you can conclude that the basic system works and has almost correct mixture. Since you see a difference with the OVP relay in place, you can also conclude that something is changing the pressure. That has to be the injection computer, which again means that it does get power supply through the OVP relay (which is then not the fault). But apparently it gradually increases the pressure until the engine finally drowns. This indicates to me that the computer does not get correct feedback from the oxygen sensor (it should indicate too rich mixture, whereby the computer should reduce the fuel pressure). So check again the oxygen sensor and its connections. Other inputs to the computer are: - coolant temperature sensor - EGR temperature sensor (if fitted) - idle switch - start signal (crank) - speed - rpm - airflow (potentiometer mesuring the sensor plate position) - altitude correction (if fitted) - reference resistor (under sealed cap) All these inputs are used to preset the fuel pressure fine adjustment. But at the end of the day the oxygen sensor will measure whether the combustion is correct and make the computer fine adjust accordingly. Therefor the major suspect is the oxygen sensor measuring incorrectly or not being connected correctly. Alternatively it could be the fuel pressure regulator not acting correctly according to its control signals. Or the computer is failing. That's an excellent and thoughtful analysis. Hi T.G. Thanks. You might remember that I tried for months to sort out a no-start problem, which in the end turned out to be a fault in the EHA. That forced me to go deeply into the matter. And then a past as radar/computer engineer becomes handy. You are always also helpfull with good advices in the group. I wish that more would share their knowledge this way. So you guys are saying that the oxygen sensor is bad> Should I just replace it?-cg So you guys are saying that the oxygen sensor is bad> Should I just replace it?-cg Thanks for the response... I am going to check the o2 sensor and its connections... Do u thinkl the computer is bad? But if it was bad , how can the car run so well for a few minutes with the OVP connected....-cg monmouth county nj I don't know the algorithm of the computer and cannot say for sure whether it does not control correctly. But normally a computer of this kind works or it doesn't. Of course there could be an error in the input circuits for sensors or in the output circuits, but I would rather suspect the sensors/actuators and their wiring prior to the computer itself. You are right that something seems to work, since the engine runs for a couple of minutes before overflooding. So, the EHA (fuel pressure regulator) seems to gruadually increase the fuel pressure, either because the computer tells it to or because it doesn't care about the computer control. I believe because the computer tells. The oxygen sensor should then tell the computer to reduce the pressure. Apparently this doesn't happen, and instead it gradually increases the pressure. So it seems that it always get information of too lean mixture. I don't know why it happens gradually (as I say, I don't know the computer algorithm), but I know that the oxygen sensor needs to warm up before it gives the correct signal, and I assume that the computer initially works without this input and acts purely on the basis of all the other inputs (which then seem to be OK) and gradually take the erroneous oxygen sensor input into account. That would explain the behavior. Becomes too theoretical ? Perhaps someone with experience with faults in oxygen sensors would tell. Anyway, good luck. Certainly theoretical, but a very interesting, elegant analysis. And it is impressive to see how you people help in this way for no other reason than you like to. MMansilla > I don't know the algorithm of the computer and cannot say for sure > whether it does not control correctly. But normally a computer of this [quoted text clipped - 26 lines] > > Anyway, good luck. http://en.wikipedia.org/wiki/Oxygen_sensor#Operation_of_the_probe This interesting article states that the O2 sensor puts out .2V lean and .8V rich. I believe the computer uses a "map" algorithm to adjust the motor's controls. I believe this motor's O2 inputs are stuck. It runs well cold, because it's running rich, but as it warms up its air fuel ratio should be made leaner (to about 14.7 (parts air) to 1 (part fuel)). That's NOT happening and the motor is "flooding". Suggest you do a Google search for "oxygen sensors" and see if the various sellers provide further information on O2 malfunctions. http://auto.howstuffworks.com/car-computer2.htm This page describes the conversion of analogic signals to digital ones. I don't know if this 300E has one of these or where it is if installed. However, given the car's once reversed polarity the converter possibility is something to explore if the O2 sensor(s) are found to be OK. The analog to digital converter (and vice versa) is part of the computer. Right, if the oxygen sensor wires were reversed in polarity when you replaced the sensor, this would act the same way. Hello again...What does one mean by the wires being reversed? And the whole analong-digital thing means?- thanks--charlie Chuck, Read the citations I posted, it's explained there. Tom Jens, Its worse than reversion the O2 sensor wires, someone installed the car's battery and reversed the polarity! Chuck has been struggling for months to get this car to run properly - it did seem to be OK for a brief time. The problem has now been narrowed down to cold start is OK but the motor "floods" as it warms up - BUT, if the over voltage relay is removed (crippling the electronic fuel injection) the engine runs OK (on the mechanical fuel injection). So the puzzle is to figure out what Chuck must do so it starts and runs on the electronic fuel injection system - as it should. Tom After the jumper cables were reversed, thr OVP fuse went...so i replaced the OVP relay...After I did that, everything was fine; from October to January 3....I was drivign the car, the check engine light appeared ...the nexrt day the car cut and and was flooded. It has been repeating the same process, running fine cold until warmed up. Could the cars on board computer have gone bad? If that were the case, wouldn't it of gone bad the day or day after the cables were crossed? How could it of ran so well for 3 months?- chuck I would suspect the OVP relay has failed. Hi Tom Oh, I wasn't aware of that story. When two batteries with opposite polarity are connected, the one with most power will "win" with some amount. I assume that Chucks battery was the weak one, and that some negative voltage has been applied to the car then. The zener diode in the OVP then acts as a normal diode, which effectively would limit the negative voltage to the computer circuits to approxemately 0,7 volts and then blow the OVP fuse. The fuse blew indeed and served its purpose (and maybe the diode broke too). The computer (and sensors around it which are in fact supplied with power by the computer) apparently survived, and according to Chucks description it functioned well for some months afterwards. It is possible that something was harmed and finally broke down after that long period, but that would be very rare. So, I suggest to see the problem separately from the story. I will certainly not rule out the OVP relay as the source of the problem. I just can't see how it would give symptoms as described (but sometimes the explanation is first found, when the prove appears), unless poor connections in the OVP relay (which have been seen before) cause a drop in the voltage supplied to the computer, which could then cause the computer to function incorrectly. So Chuck: You can check the voltage output of the relay (pin 2... circuit 87E), or just try to replace it. And by the way, the "Check engine" light came on. This i driven by the computer, so the computer must work in general. SO your saying I should replace the OVP relay? Could it of gone bad? Bear in mind that I replaced the OVP a week after the cables were cross connected, and all was well...-chuck What I say is, that technically seen I would first replace the the oxygen sensor again, as this is a most probable cause of the problem. Then I say, that the OVP relay is not impossible to cause the problem, and you could chance to replace that first (it costs only half, but in the end, it may have cost you one and a half). You never know how long time things last. Both items will normally have a very long lifetime, but if something is wrong with them, the fault will typically appear in the beginning of their lifecycle (if it is a new origininal item, warranty should cover). You can also try to troubleshoot (if you have the means) by measuring the the oxygen sensor signal at the input to the computer. When engine is running correctly, the voltage should fluctuate between 0,2 and 0,8 volts. In your case the voltage should go towards 0,8 volts to indicate too rich mixture: - If so, you should suspect the EHA or the wiring to it. - If not (the voltage is near 0 volts), you shold suspect the oxygen sensor or the wiring (short circuit or open) to it. The above assumes that supply voltages to the computer are OK (through the OVP relay). To measure inputs/outputs of the computer, you can take the computer out of its case, put it on so it is isolated from chassis (on a piece of cardboard) and reconnect the cable. The pins from the plug can be measured at the printed circuit board. The oxygen sensor input is pin 8. Be careful not to harm the computer. What I say is, that technically seen I would first replace the the oxygen sensor again, as this is a most probable cause of the problem. Then I say, that the OVP relay is not impossible to cause the problem, and you could chance to replace that first (it costs only half, but in the end, it may have cost you one and a half). You never know how long time things last. Both items will normally have a very long lifetime, but if something is wrong with them, the fault will typically appear in the beginning of their lifecycle (if it is a new origininal item, warranty should cover). You can also try to troubleshoot (if you have the means) by measuring the the oxygen sensor signal at the input to the computer. When engine is running correctly, the voltage should fluctuate between 0,2 and 0,8 volts. In your case the voltage should go towards 0,8 volts to indicate too rich mixture: - If so, you should suspect the EHA or the wiring to it. - If not (the voltage is near 0 volts), you shold suspect the oxygen sensor or the wiring (short circuit or open) to it. The above assumes that supply voltages to the computer are OK (through the OVP relay). To measure inputs/outputs of the computer, you can take the computer out of its case, put it on so it is isolated from chassis (on a piece of cardboard) and reconnect the cable. The pins from the plug can be measured at the printed circuit board. The oxygen sensor input is pin 8. Be careful not to harm the computer. > SO your saying I should replace the OVP relay? Could it of gone bad? Bear > in mind that I replaced the OVP a week after the cables were cross > connected, and all was well...-chuck What code is the MIL showing on read out? ie what code does the check engine light throw? O2 sensor perhaps? O sensor Sounds like it could be the ticket to me. DON"T JUST THROW PARTS AT IT! Figure it out for pete's sake. Sorry for the shouting. Marty Yes, you can find several articles about how lamda probes work. In normal operation its output would fluctuate between 0,2 and 0.8 volts. I have seen in the postings that some people adjust the mechanical mixture screw (as mentioned earlier) by monitoring the duty cycle of this fluctuation. I am not sure whether that is such a good idea (with reference to how it works with and without power to the computer). However, I was more thinking whether someone had experience with the behavior of engines using this injection system (CIS-E) when the oxygen sensor is defective. Have you looked into the engine temperature sensor. the signal from this sensor should (via the ECU) progressivly reduce the amount of fuel fed to the cylinders as the engine temperature increases johnaglover@Xbtinternet.com Please remove the X for email. >I don't know the algorithm of the computer and cannot say for sure > whether it does not control correctly. But normally a computer of this [quoted text clipped - 26 lines] > > Anyway, good luck. The computer can operate in open loop mode (disregarding O2 sensor) or in closed loop mode (using O2 sensor signal). The computer will enter closed loop mode when O2 sensor is ready. The sensor is considered ready, when the voltage increases towards 0,8 volts. When approaching 0,8 volts, the computer will compensate by reducing fuel pressure, until the signal approaches 0,2 volts, after which it will increase the pressure again. When everything works the voltage will fluctuate between the two values. Any steady voltage will be considered as a fault. All other signals (temperature, air mass etc.) are used to provide correct mixture in open loop mode and to bias the mixture in closed loop mode. It is correct, that the increasing temperature basically should reduce the mixture, but once in closed loop mode, the operation of the O2 sensor will compensate for errors in the temperature signal. If the computer never enters close loop mode (due to defective O2 sensor for instance) and the temperature sensor is wrong, this may lead to the current symptoms. Then we are talking about two simultaneous faults, which of course is absolutely possible. |
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