300E Flooding Out when running

"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.

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

That's an excellent and thoughtful analysis.

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.

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.

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

"Jens" escribió en el mensaje news: snipped-for-privacy@i39g2000cwa.googlegroups.com...

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.

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.

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

snipped-for-privacy@Xbtinternet.com Please remove the X for email.

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.

So you guys are saying that the oxygen sensor is bad> Should I just replace it?-cg

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.

So you guys are saying that the oxygen sensor is bad> Should I just replace it?-cg

Hello again...What does one mean by the wires being reversed? And the whole analong-digital thing means?- thanks--charlie

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

Chuck,

Read the citations I posted, it's explained there.

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