My jeep is slow

geordi · **Posted:** Sun Feb 14, 2010 4:02 pm

Some new information on this for everyone:

Just for giggles today, I pulled it out of it's little hole in the airbox and poked at the Mercedes Logo sensor with an ohm meter. I got NADA for a reply from it. infinite resistance, across all three pins. I could only try two at a time obviously, but even a transistor will show SOMETHING across it's pins when testing resistance.

This... Was like I wasn't touching anything at all. I find it interesting that there are 3 pins however. If this is a pressure sensor, would it need a third pin to supply a tiny heating element, like an oxygen sensor or a MAF? I'm wondering if this thing is totally dead, with not reading anything.

My original plan was to try jumping a resistor across the wires to duplicate the voltage drop the computer is looking for, for a default pressure of 1000 mbar or so. But without being able to detect the stock resistance of this sensor, I don't know which wires to jump, or IF that would even work. So instead, I just cleaned it with a liberal application of contact cleaner again, and left it outside the airbox.

Interestingly enough, when trying to reconnect the plug, the stupid thing was actually resisting being shoved together. Like there was a little rubber pad between the two connectors. I had to put a decent amount of pressure onto it to get it to seat, and use the clip to actually hold it in place. Weird, it didn't do that before.

nstg8r · **Posted:** Mon Feb 15, 2010 8:04 pm

Does anyone know what the internal resistance is on the PCM for voltage sensing circuits. This would help in finding out what resistance is needed to fool the PCM.
this little tid bit of info would help me out with a project of mine too.

geordi · **Posted:** Tue Feb 16, 2010 2:40 am

Doing some searching online, the numbers printed on the little sensor come back to an IMPEX part - A Mercedes MAP sensor. So our fun little engines have a second MAP sensor, which is measuring the static airbox pressure.

The trick will be figuring out the proper pressure (and voltage) to feed to the computer. I'd think that telling it a high air pressure would make it believe a higher oxygen content of the boosted air... Hence injecting more fuel. But the problem I've been having of overfueling due to this thing... Makes me think I should be telling it a moderately low pressure.

Decisions decisions. :banghead:

MrMopar64 · **Posted:** Tue Feb 16, 2010 2:02 pm

In a perfect world, that sensor would be used to detect a dirty air filter. However, it's just used for a plausibility check. It's not so much of reading a static value (say 1000mbar) but it needs to read "similar" to the Boost Pressure Sensor at certain conditions. The only real fix would be to 1] fix the wiring (if the connector isn't good any more), 2] replace the sensor, or 3] find someone who could disable the diagnostic for it.

geordi · **Posted:** Tue Feb 16, 2010 3:50 pm

I'm with you on #1 and #2... Wiring isn't busted (at least near the connector it looks undamaged) and I'm already making arrangements to get another sensor.

But #3 would be the best option, for all of us. GDE? Can this be disabled in your programming? I am getting to the point where I can TELL when it is working properly... Even without my laptop connected. Now that I just recently found the power supply for the laptop, I'm going to see if that is one of the sensors that the AutoEnginuty can monitor, and actually get some data from it.

Driving home last night, just normal driving, the engine was commanded into 70mph limp mode 3 times without anything approaching a WOT or idle event. So without further investigation, I am forced to conclude that the sensor's data is being checked at more than idle events.

It would make sense if the plausibility was being checked at idle against the turbo MAP, b/c off idle, boost is changing the numbers. BUT, isn't it possible that the computer's air map includes a calculation for air volume based on the static air pressure AND the incoming air volume, that it can correlate against the boost MAP? If the math doesn't fit the range... Limp. Since I have already replaced the boost MAP with no effect, that is working properly. I haven't replaced the MAF sensor... But with it unplugged, the performance still suffers randomly. With this Mercedes MAP unplugged... Performance is markedly better, but I am limited to 40mph limp mode.

Logically, that thing has to be passing SOMETHING to the ECU during driving, which annoyed it into the 70mph limp mode last night. The unpredictability of the CRD feeling "heavy" under the same amount of throttle agrees.

Unless of course... Something ELSE that doesn't fail bad enough to throw a code has failed. It wouldn't surprise me. :banghead:

geordi · **Posted:** Fri Feb 19, 2010 5:31 pm

Bump for new info!

Ok, I've got my replacement SECONDARY Map sensor (Stupid Mopar) and I have both the Chrysler Part Number for the Mercedes Logo Sensor (Keyword salting) and the Mercedes part number.

The Chrysler part number is: 05101120AB which is a superceded number from something older.
The Mercedes number is 005-153-50-28 which is the number printed on the stupid sensor.

Now, about operation. I put it in, and DO have better performance now, BUT it is still doing it's drag-the-performance-while-smoking gag... But to a much lesser percentage. The CRD feels a LOT "lighter" with just this little thing replaced. So it matters for FAR more than just at idle.

I strongly suspect that the MAF will result in similar results, when I replace that. I'm going to give a try just unplugging it, and see what that does, but I'm not holding my breath that this problem will go away.

On the plus side, I FINALLY was able to video the CRD's performing this nonsense last night, while driving up a long hill.

With my foot PLANTED on the floor, I was at 3800 rpm steady, 17psi of boost, 60mph... So basically limp mode. BUT here is the weird thing: EXACTLY at the top of the hill, it would "release" and rocket ahead.

Thoughts about this? It is repeatable, it has done it for the last few nights consistently in exactly the same spot. The fact that it releases at the top of the hill... Why so specific?

My jeep is slow

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