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

Hi Samuel,
your car should have a fuel-filter that looks like a box. This should be replaced quite often...
Did you check it?

Regards
Norbert

I tested the MAP sensor (both vacuum and resistance) and it passed ok. I also dis a smoke test for leaks... none was found!

I have not tested the injectors, as it is a pain to remove them from my particular car (Citroen DS). But I would think that if there is a problem with the injectors it would manifest itself at all times, right?

Thank you Norbert,

Yes, I replaced the fuel filter last year, but the fuel pump is original and is now over 51 years old.

What are the options available for a replacement fuel pump?
Best
Samuel

I've been waiting until I get to a computer to properly respond.  Glad to see all the Jetronic interest! The people on this site have been incredibly helpful over the years.

I do not have the expertise of some of those that contribute, but I do have more years than I'd care to mention of trial and error on my 73 450SL.  Some thoughts about recent posts:

• As someone else pointed out, the computer dial only affects idle mixture so if your problem is above idle than it is something else.
• If you've got 51 years on a fuel pump I think it can be honorably discharged by now.  Keeping pressure is different than providing volume.  There is a test somewhere (xx ML in yy seconds) that may help prove if that is not the problem, but if a new fuel pump is available I don't think it would be a bad thing to replace.  That is a poke-and-hope, but I saw significant gains after a fuel pump replace (Bosch fuel pump, but it is a newer flavor....dunno if it will work for the Citroen, but if the JetTronic is the same I would think so?) 
• I've gotten my injectors re-built, but didn't see much of a change.
• I had my entire engine wiring harness re-built and that provided significant improvement.  If the computer is getting bad signals, for whatever reason, then it will respond badly. Dunno if that is an option for you.
• Many of the changes, combined, have significantly improved the operation.  The last time I had it out there was very little bad behavior and the temperature sensor was plugged in.  
• I'm still going to hunt for vacuum leaks.  While the tanks will hold for a while, so my door and trunk locks work now, but that doesn't mean there isn't a leak before the tank(s).
• I still have a horrendous hot-start problem.  It is notorious amongst the older 450's, but mine seems worse that I would expect.  Sometimes, I just leave my hood propped open when I park.
• - I'm still chasing gremlins...but they are smaller.

Hi,

I recommend to keep original Bosch D-Jetronic fuel pump as long as it works and does not leak and of course supply enough fuel. I do that myself. I would not follow our unknown friend x046866x. Please sign by firstname as it is usual here. And if you want to discuss your 450, please open a separate thread and let us not mix this one.

 

Apologies for weird username.  That was a poor choice when I registered and I'm contacting some folks that I hope can help me change that...,or I'll create a new one!

My name is Russell Nile.

The reason I chimed in is because I initiated this thread a while ago and when I received a recent notification I chimed in,  If it deserves to be a separate thread because of the difference in the vehicles then someone in the Citroen space will have to initiate that.  I assumed it came here because of a similar problem, but I am not familiar with the D-Jet used on the other vehicles.

Thanks for your help!

Hi Russell,

thanks for sharing your firstname. I was not aware that it had been your thread before. All I want to hint is that it makes sense to discuss both cars separately.

Actually, since I am the one who posted in response to Russell's post (because it was the same issue be it on another car).

In my mind, it makes sense to group similar problems together, since it is all D jetronic related. But happy to start a new thread if the group feels it is better.

Many thanks
Samuel

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

.

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)?