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)

[TheCabinetmaker]

First suspect would be the tps adjustment. Usually causes a miss at steady cruise. Caused by a worn circuit board inside unit. Sometimes they are just dirty and need cleaning.

[EdwardBlume]

Dads car had the same kind of RPM hesitation back in the 80s. It was the head temp sensor on a 2.0L.

[MikeInMunich]

Thanks, I'll check that out. Good tip.

[MikeInMunich]

(IMG:style_emoticons/default/beerchug.gif)

[MikeInMunich]

Hmmm. A mechanic had checked that here just a few weeks ago. Should be OK, unless it's worn, which is also a possibility. Thanks for the tip!

[914_teener]

Mike.....

Here would be my thoughts and in this order.

Check fuel pressure.
Fuel additive to take out water from fuel.
Fuel filter or kinked fuel line
Condensation in the distributor....spray a little WD40....the wonder spray inside..clean the dizzy plate.
Bad CHT connection....check wire for nicks and or body for oxidation check values warm....ohms.
Dirty or worn TPS.

[MikeInMunich]

Mike.....

Here would be my thoughts and in this order.

Check fuel pressure.
Fuel additive to take out water from fuel.
Fuel filter or kinked fuel line
Condensation in the distributor....spray a little WD40....the wonder spray inside..clean the dizzy plate.
Bad CHT connection....check wire for nicks and or body for oxidation check values warm....ohms.
Dirty or worn TPS.

Thanks!
FP = 29 psi

Will look into CHTS and see if an additive for H2O in fuel may help. Fuel lines and filter are new, but will have a look there as well.

Seems like the TPS parts are NLA... Any info on this?

M.i.M.

[914_teener]

mark at 914 rubber sells the boards...IIRC

That.s last on the list.

[MikeInMunich]

mark at 914 rubber sells the boards...IIRC

That.s last on the list.

Just sent Davesprinkle a message. If he can't help, I'll get in touch with Mark. Thanks!

[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.

[Dave_Darling]

Worth double-checking all the electrical connections.

--DD

[MikeInMunich]

Mike.....

Here would be my thoughts and in this order.

Check fuel pressure.
Fuel additive to take out water from fuel.
Fuel filter or kinked fuel line
Condensation in the distributor....spray a little WD40....the wonder spray inside..clean the dizzy plate.
Bad CHT connection....check wire for nicks and or body for oxidation check values warm....ohms.
Dirty or worn TPS.

Question!

When checking the resistance at the CHTS, what should it be, and sorry, but exactly where am I to connect the Ohm meter to when testing? (IMG:style_emoticons/default/confused24.gif) When it's attached to the ECU, the plug isn't accessible, or is it?

Thanks!

M.i.M.

[BeatNavy]

First of all, I agree with DD - check your electrical connections and your charging system. I had a very slight hiccup at 3k RPM a few weeks ago that I think was slightly faulty connections at the common ground point (3 point ground at back of case). If those are not secure, you'll get fuel delivery interruption issues.

To check the CHT do several tests in whatever order makes sense to you:

1. Visually inspect the actual connection - check the lead to make sure it's connected securely connected to the wiring harness and that the connection isn't grounding out against case or other things around it (where the lead and wiring harness connect should be protected with plastic connector). Inspect the entire length of the wiring harness to ECU to make sure it's not kinked or breaking. If the connection is intermittently open, as with a failing wire, you may get symptoms like you're describing. Keep in mind the CHT lead may be wonky at the base, where you can't see it unless you remove the whole sensor, which can be a little tricky.

2. Disconnect CHT lead at wiring harness, and with Ohmmeter, check resistance from CHT lead to ground (e.g., negative battery terminal). When engine is cold, at ambient temp (e.g., 60 degrees), you should get in the neighborhood of 1500 to >2K ohms. With engine warm, you should get around or <200 ohms (check Anders's site for more info and specs: http://members.rennlist.com/pbanders/djetparts.htm). If you don't get acceptable readings, CHT sensor is bad.

3. Reconnect the lead to wiring harness. Disconnect ECU connector (25 pole plastic connector). Check continuity from Pin 23 in connector to ground. You should get the same readings as #2 above. May want to move harness around a bit while doing this to see if you have an intermittent break in the connection somewhere.

Others may have more/better info, but again, this is a good reference: http://members.rennlist.com/pbanders/djetparts.htm

[MikeInMunich]

Checked the CHTS connection...seemed to be OK, BUT, after that, my idle changed upward significantly! I turned it back down with the idle screw. With the AAR shut completely the idle was over 1600 and was previously about 900. So, apparently the CHTS wasn't working and now is?? What do you think about this new symptom?

As for the "hesitation", I can at least confirm that it's not definitely still there. Seems like it MIGHT be better.

M.i.M.

[BeatNavy]

Checked the CHTS connection...seemed to be OK, BUT, after that, my idle changed upward significantly! I turned it back down with the idle screw. With the AAR shut completely the idle was over 1600 and was previously about 900. So, apparently the CHTS wasn't working and now is?? What do you think about this new symptom?

I don't think that had anything to do with the CHT. It sounds like you disconnected a vacuum line in the process.

I guess you could say the CHT (and CHT "circuit") has three modes (basically): working, intermittently failing, and failed. When it's failed, or during those times when it is intermittently failing, due to a broken/breaking wire or flaky connection, the engine dies. It super-enrichens to the mixture to the point where the engine floods. If the connection is "restored" quickly enough, the car may not fully quit but "buck," I suppose, during that episode. That's it.

As for the "hesitation", I can at least confirm that it's not definitely still there. Seems like it MIGHT be better.

Wait...what? (IMG:style_emoticons/default/confused24.gif)

I'm guessing CHT may not be your problem...

[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!

[BeatNavy]

There's a hole in the engine tin next where the #3 spark plug wire goes. There's a one wire lead coming out of it. That lead is part of the CHT, although you probably can't see the sensor itself (as it's under the tin). You need a deepwell 13mm socket to get it out, and you have to bunch up the lead inside the socket.

The CHT has a profound impact on mixture to the point that if the circuit is open the engine won't start or will die almost immediately (and won't start again until cold). I can see the "bucking" thing being possible with a sketchy CHT connection, but I'm also a fan of what I think are more likely suspects, like FI grounds, ignition connections, etc., etc.

[MikeInMunich]

[/quote]
I don't think that had anything to do with the CHT. It sounds like you disconnected a vacuum line in the process
[/quote]

OK, apparently you must be right about the vacuum leak. I'll have a look for it tomorrow and report back. I'm starting to think the problem may be the TPS. I ordered the repair kit for it today and it'll be put in next week. I will report back results.

Thanks for your time and advice!

Mike

[MikeInMunich]

Tested CHTS, <300 Ohms when warm. Approx. 2000 when cool. So that seems to be working OK.

Found one hose at the pass. side of the engine on the corner of the fan shroud which had come off. Capping it didn't seem to change the idle much at all, so not sure if that was the reason why the idle had gone up so high or not.

Waiting for TPS rebuild kit from Dave Sprinkle, which will be installed next week. I'm hopeful that this will solve the issue. Will report.