Diagnosing an intermittent D-Jet problem..., Hesitation under load at 2800 RPM but only when cold... Options

[MikeInMunich]

Hi again from Munich!

Here are the details. But please see update from Feb. 5th below!

I have a D-Jetronic intake. Under load and at about 2800 RPM Im experiencing an intermittent hesitation. Yesterday my son and I took the car out for a drive from Munich, towards Innsbruck and back and we ran into a bit of rain coming along the Aachensee (lake), and this hesitation got worse. Then I remembered the only other time I've had this car out with 100% humidity and that it wasn't running well on that day either, so this is apparently a clue.

So what can this be? And why does it happen at all, even when it's not raining, albeit not as noticeably? Is there a cure?

Experts / senior gurus out there, thank you for your time and sharing your knowledge and experience, in advance!

With kind regards,

Mike in Munich
(IMG:style_emoticons/default/smilie_flagge6.gif)

[pbanders]

Hi again from Munich!

Here are the details.

I have a D-Jetronic intake. When the car is warm, and I'm in say 3rd gear at about 2800 RPM there is a slight, intermittent hesitation. Yesterday my son and I took the car out for a drive from Munich, towards Innsbruck and back and we ran into a bit of rain coming along the Aachensee (lake), and this hesitation got worse. Then I remembered the only other time I've had this car out with 100% humidity and that it wasn't running well on that day either, so this is apparently a clue.

So what can this be? And why does it happen at all, even when it's not raining, albeit not as noticeably? Is there a cure?

Experts / senior gurus out there, thank you for your time and sharing your knowledge and experience, in advance!

With kind regards,

Mike in Munich
(IMG:style_emoticons/default/smilie_flagge6.gif)

We just had a discussion among us so-called "D-Jet experts" as to how many of us have had a similar problem with hesitation or skipping that we eventually traced to the cylinder head temperature (CHT) sensor. The problem is caused by not getting the female spade connector (the part attached to the sensor) to correctly slide on to the male spade connector (inside the plastic housing, connected to the wiring harness). What happens instead is that the female spade connector ends up being jammed between the plastic housing and the male spade connector, and the intermittent loss of contact (due to road vibration) causes the car to hesitate or skip.

While this may not be the problem in your case, it's very easy to check and is worth doing before you go chasing other solutions.

If it's not the CHT, as others have mentioned, it might be the TPS, where the wiper track is worn and causes extra or dropped injection pulses. I'd also suggest a full evaluation of your ignition system, with special attention to the points plate. Make sure that it's moving smoothly and evenly so that your mechanical and vacuum adv/ret are working properly. Check rotor, cap, and wires. Pull the plugs and check condition and gapping. Set timing and dwell. Verify strong spark at the plugs.

[socal1200r]

We just had a discussion among us so-called "D-Jet experts" as to how many of us have had a similar problem with hesitation or skipping that we eventually traced to the cylinder head temperature (CHT) sensor. The problem is caused by not getting the female spade connector (the part attached to the sensor) to correctly slide on to the male spade connector (inside the plastic housing, connected to the wiring harness). What happens instead is that the female spade connector ends up being jammed between the plastic housing and the male spade connector, and the intermittent loss of contact (due to road vibration) causes the car to hesitate or skip.

While this may not be the problem in your case, it's very easy to check and is worth doing before you go chasing other solutions.

If it's not the CHT, as others have mentioned, it might be the TPS, where the wiper track is worn and causes extra or dropped injection pulses. I'd also suggest a full evaluation of your ignition system, with special attention to the points plate. Make sure that it's moving smoothly and evenly so that your mechanical and vacuum adv/ret are working properly. Check rotor, cap, and wires. Pull the plugs and check condition and gapping. Set timing and dwell. Verify strong spark at the plugs.

So where is this CHT sensor on the 1.7 engine? This sounds like a simple enough thing to check, since I have the same "bucking" symptoms at the same rpm range. I'm not driving the car anymore until I get this problem solved. Otherwise, I'll drive it to the shop and drop it off.

Thanks!