Diagnosing D-Jet Problem...solution & update, All of a sudden...loss of power... Options

[MikeInMunich]

Greetings once again from Munich gentlemen! (IMG:style_emoticons/default/bye1.gif)

It started with a thought and no wood to knock on, seriously! (IMG:style_emoticons/default/mad.gif)

I was driving around Munich about 6 weeks ago and thought to myself, this car is running perfectly and needs nothing. What could go wrong? Then literally, less than a few minutes after that, it started. A light hesitation in the lower RPM range. Seemed like the car was choking a bit, or missing on once cylinder.

I was at a D-Jet workshop last year with Dr. D-Jet. See https://oldtimer.tips/de/

Volker is a great guy and knows as much about this system as anybody. He tested the vacuum on my MPS last year and informed me that it was "borderline". So that was the main culprit. I took it out, sent it to him and this year it was indeed worse and thus the main culprit. Volker disassembled it and replaced the copper diaphram. Now it's tight like new. Some may be surprised that this is possible and / or where he got a new diaphram from. He had them manufactured or perhaps, I'm not sure, manufactured them himself. PM me if you want / need one and I'll send you his email address.

So, with my restored MPS I hooked it up and, low and behold, the problem was quite the same, only about 10x worse! (IMG:style_emoticons/default/hissyfit.gif)

Now, with the car immobile and Volker hundreds of km away, I'm practically on my own, with his and your advice, to try to track down the real problem.

Volker thinks that because the MPS was operating sub-optimally previous to my purchase of the car that the mechanic or the P.O. had compensated elsewhere to get the car to run properly and that now that the MPS is sending a different signal to the CPU, things are off.

More info:

Just before the problem started my milage was really bad
The CPU is the correct one for my MPS and working according to specs. Volker tested it.
Engine has about 5,000 miles on it. Was rebuilt and running GREAT.
Fuel pressure was set at 29 psi only about a year ago. I reckon it could have hardly changed on its own since then. (IMG:style_emoticons/default/idea.gif)
The engine was originally a 1,7 but is now 2liters with a “proper FI performance Webcam” (as stated by the mech ic who rebuilt the engine)

No adjustments were made to the FI to get it to run properly. It was running excellentwith a virtually perfect idle when warm and just slightly rough for the first 3 Miles or so.

TPS plate and air temp sensor are new.

What do y'all reckon could be the culprit? What should I be testing?

I'm taking it to a place to tell them what to test, including:

Fuel Pressure
Plugs
Compression
CO value
TPS setting
Timing & dwell
search for Vacuum leaks
grounds
Valve adjustment
Fuel filter
Relais
Injectors...

What else should I have them look for?

Thanks for your input!

With best regards from what was just ranked The Most Livable City in the World by Monocle Magazine,

Mike in Munich

[JeffBowlsby]

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif)

Exactly. Every engine today is unique in its configuration and wear characteristics. the exact fuel requirements for any two 2.0Ls are not alike. On top of that I personally own a few NOS MPS and have characterized many others that...guess what...are calibrated differently.

The best and really only way to get an optimal calibration is by using an exhaust gas analyzer, WB02 meter or Dyno on YOUR ENGINE. Inductance calibrations on the MPS with the Wavetek can only get you close. Using the caliper depth gauge method is also only an estimation because the calibration adjustment parameters are extremely fine for accuracy.

[MikeInMunich]

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif)

Exactly. Every engine today is unique in its configuration and wear characteristics. the exact fuel requirements for any two 2.0Ls are not alike. On top of that I personally own a few NOS MPS and have characterized many others that...guess what...are calibrated differently.

The best and really only way to get an optimal calibration is by using an exhaust gas analyzer, WB02 meter or Dyno on YOUR ENGINE. Inductance calibrations on the MPS with the Wavetek can only get you close. Using the caliper depth gauge method is also only an estimation because the calibration adjustment parameters are extremely fine for accuracy.

Hi Jeff, thanks for chiming in here. I just spoke with George Hussey about sending me a new CHTS and he was nice enough to take some time with me on the phone to discuss the problem. First off, he emphasized the challenges that often occur when changing the CHTS, such as getting the old one out without breaking it, and discouraged me from changing it unless I was sure that the one I have is faulty, which I am not. In fact, I’m pretty sure it’s OK. I will test it again with a multimeter.

But what I’m writing about is how George believes that the problem likely lies elsewhere altogether, like with timing, valve adjustment, dwell, fuel pressure, etc. and not with the MPS. He also said that the MPS adjustment screw is for FINE tuning mixture and that my problem seems way too severe for such fine tuning to be the potential solution, whereby you and Bleyseng seem to emphasize the adjustment of the MPS screw as the primary(?) way to change mixture. I’m not clear on this.

Also, can you offer me some info on what you mentioned about the cold start valve and flow testing? (IMG:style_emoticons/default/confused24.gif) This valve only enriches the mixture while the engine is cold, no?

After we’ve ruled out all of the usual suspects, as mentioned above, if the problem persists and I’m hooked up to a CO / AFR sensor and can see if the car is running too lean or too rich, how should / can the mixture be adjusted? Primarily with the MPS screw? How else?

George also said that a camshaft can make a big difference, but the simple fact that the engine is 2.0 liter instead of 1.7 shouldn’t / doesn’t / in his experience has never been a problem. This is a far cry from Dr. D-Jet´s opinion on exactly that point and I’d say George has far more experience with the D Jet on 914s than Dr. D-Jet does. (IMG:style_emoticons/default/idea.gif)

Thanks again for your input. Hope to read a reply from you again.

Mike