Slight mis-fire at partial throttle...until I disconnect air temperature sensor

Hi Samuel,

if you and Russell are happy with it, then I am happy too. I was just afraid to mix two quite different cars.

It's all good from my perspective. As long as it is helpful. It's not wrong to have it's own thread with a reference to this too.

Not sure there is a "right" or a "wrong" here.

Thanks again for your input!!

Thanks Dr-DJet

Could you tell me how to measure the volume out of the fuel pump?

Also, as I had mentioned before, with the ignition on only (engine not running) I am getting 22 PSI (about 1.6 bar), but 30 PSI (about 2 bar with engine running).

Should the pressure be about 29.5/30 PSI (~ 2 bar) with ignition only on?

Another experiment today... I plugged the intake air temp wire back in... idle if rough and there is hesitation during acceleration. But if I disconnect the the full-load hose from the full-load switch, idle improves, and there is no hesitation upon acceleration, even with the air temp sensor plugged in.

Since both situations lead to enriching the fuel, I think this conforms my car is running too lean. Now onto more through vacuum leak detection and ???

Many thanks for the valuable information

Samuel

Hi Samuel,

your fuel pump 0 580 463 005 must bring at least 355 cm³ in 30 seconds.measured at return line to tank after pressure regulator. After ignition ON your pump will run for 1 to 2 sec. Pressure may drop to 1,6 bar after it stops.

How I would continue on a DS 23 inj:

• Verify that injectors spray properly and same amount
• Measure resistance of injectors from ECU to GND
• Verify that cold start valve does not inject
• Check manifold for vacuum leaks
• Check pressure switch for full-load for leakage and proper operation
• Verify that no one fiddled with MAP sensor potting

Thank you Dr-DJet

I have done some of these things, but will continue with the check list you proposed.

Will update as I move along with testing.

Best
Samuel

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Hi Russel,

Did you manage to figure out what was/is wrong? I seem to have the exact same issue - namely that my engine runs significantly smoother and with no hesitation during acceleration with the air temp sensor disconnected than if it is connected. My fuel pressure is smack on 2 bar.

/Peter

I'm still tinkering.  I adjusted the MAP sensor to make it more rich (yes, I recorded where it was) and that seems to have addressed the problem, but I dislike my solution.  The MAP was replaced some time ago when the engine was rebuilt, and also tested since then, and the MAP was performing properly.  I will leave the adjustment for a while and if it truly resolves the problem, without adverse effects, then I'll leave it.  I just feel like I'm cheating.....but the last time I drove it everything performed well.

Hi,

I have seen so many detunged MAP sensors during D-Jetronic workshops. It is a bad US habit. And now ti hits me again on EHA in K-Jetronic.

Trouble is to find out whether it was detuned before you got it in your hands.

If memory serves me (and it doesn't always) I think I bought that from Mercedes directly.  The rebuild was in the early 2000's.

That doesn't mean it wasn't mucked with....but I would expect not?

I'll report back after I get a chance to drive it around some more,,,,especially in the heat.

Hi,

As I always write: I do not trust MPS outside the 70s production. I have seen brand new MPS from Mercedes from 2000s that did neither work properly nor could I make them work properly. It was simply scrap as the parts used to assemble it did not match. Poor quality control after serial production in 70s I am afraid.

Hi, yesterday I had the same problem on my BMW 3.0 CSi, and I temporary solved it by disconnecting the air temperature sensor in order to continue my trip. Did anyone (who had this problem) test the coolant temperature sensor? Unfortunately, in theese days I cannot make that simple test.

Could this problem be due to a grounded coolant temperature sensor (0 Ohm between the two pins at any engine coolant temperature)?

A grounded coolant temperature sensor entails a lean air-to-fuel mixture. Could it be roughly compensated by disconnecting the air temperature sensor (which entails a richer mixture)?

I made various tests, including the use of another ECU and another air temperature sensor. All sensors, together with that of engine coolant, seems to work properly within their operative range. With both the ECUs tested I saw the engine working with a lean mixture when the external air temperature raises over 30 °C. The problem is more evident at higher temperatures. In that condition, by disconnecting the air temperature sensor the problem is solved instantly gaining that seems to be (I have not a CO measurement sensor) a perfect drivability, without part-load hesitation and good high revs response.
With both ECUs, the problem seems to reduce gradually up to disappear completely as the external air temperature reduces below 24 °C. In that condition disconnecting the inlet air temperature sensor semms to have not a noticeable effect (sorry, I cannot make a rigorous measurement without having an exhaust gas analyser).

MAP sensor replaced with a new one acquired directly from Bosch some year ago.
TPS sensor renewed/rebuilt with new electrical contact.
Trigger contacts renewed/rebuilt.
New coil, new spark plugs, new cap, new wires etc., new condenser... Dwell and spark advance are ok. Fuel pressure regulator has been tested and it is ok too (2.1-2.2 bar).

Hi,

removing air temp sensor is not a recommended action. Why?

• Air Temp sensor is there to compensate air mass. Cold air has higher mass than hot air. That needs more or less fuel.
• Removing air temp sensor typically increases fuel by 20% in all situations - If you consider fuel a cheap resource you can do that. If not it is a bad idea

I would definitely recommend that you find your engine mechanics, ignition and other D-Jetronic issues instead of doing this kind of bricolage . If you still consider it a good idea, why not remove engine temp sensor? It enriches fuel mixture much more than removing air temp sensor.

My air temperature sensor is working its place and I never considered to disconnect it, with the exception of a brief temporary test.

I wrote that posts just to share my problem, hoping that someone who experienced a similar matter could suggest the way to fix it. It should be clear...

Hi,

then I misunderstood you that you would want to keep that sensor off permanently.