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Posted by: saigon71 Jun 8 2019, 05:46 PM

Even in a fine state of tune with no vacuum leaks and the ECU set to full rich, my cars idle would hunt terribly during warm-up (occasionally stalling).

The other problem I have is that on particularly hot days, the car heat-soaks if I shut it down while running an errand. It becomes extreemly difficult to start until it cools off. I'm not talking vapor lock here, definately heat soak.

Last year it left me stranded in a cemetary following a funeral in the blistering sun. Twice, heat soak has caused my car to not start while on a date, which is a little embarrassing in your 40's.

I drive this car a lot and needed to find a permanent solution.

I studied this thread closely:

http://www.914world.com/bbs2/index.php?showtopic=298261

After considering a bunch of alternatives, I felt the best all around fix was indeed a parmanent trim knob in the passenger compartment. Based on the testing and research by PBanders, I only needed to richen the mixture for both problems.

I'm not big on drilling extra holes in my car, so I fabricated a custom bracket that takes the place of one of lower dash washers to mount the potentiometer.

I tested it today. It wasn't hot enough to verify that it will cure the heat soak condition, but it sure worked awesome to smooth out the idle hunt during warmup. I'm pretty sure it will work to get me over the heat soak condion and allow me to start the car as I can instantly add 500 ohms of resistance to the CHT circuit and cause the mixtrue to richen.

I used a 500 ohm pot for this. I'll try a 1,000 ohm pot if the 500 doesn't cure the heat soak problem.

A huge thanks to Pbanders for his research thread listed above.

Posted by: BeatNavy Jun 8 2019, 06:36 PM

Elegant solution, Bob

I have never had the issues to that extent, although I must admit I always brace myself for a potentially difficult start / re-warmup period after getting gas, running a quick errand, etc. Sometimes it's no issue at all, and sometimes it is (although it hasn't left me stranded yet). I have the hi-torque starter now, and that seems to have mitigated hot start issue somewhat. It is really the only thing that still bothers me about D-Jet.

Posted by: worn Jun 8 2019, 07:36 PM

I also have a 2056 with d-jet. Keep me posted.

Posted by: GregAmy Jun 9 2019, 06:59 AM

Watching.

I've had similar issues with cold idle, but not so much the heat soak problem. I've got a couple of settings on the D-Jet ECU idle mixture that I know where to set, but of course when it's set properly for cold start then it runs rich when warmed up (and vice versa).

I've often thought that if we could determine the proper resistance values to accomdate this then the best solution would be a latching relay. Hit the button and the relay closes for a set amount of time (5-10 minutes?) and then automatically opens the circuit. This relay would control both a resistor for the CHT sensor and an electric solenoid AAR valve (seems so silly to me to have to maintain constant power to the AAR after warm up).

So...quite interested in what numbers you come up with.

Posted by: IronHillRestorations Jun 9 2019, 12:37 PM

Nice solution!

It's easy to forget that these cars use an injection system from the 60's that was ahead of it's time. Not perfect, but ahead of it's time

Posted by: JeffBowlsby Jun 9 2019, 02:44 PM

The ECU idle control knob only has effect at idle, because it is switched through the TPS. Off idle it has no effect.

Posted by: GregAmy Jun 9 2019, 05:55 PM

Exactly.

Posted by: McMark Jun 10 2019, 06:53 AM

Did you try the CHT extension? Moves the CHT away from the head so it cools off faster, leading to richer 'hot starts'.

Posted by: TX914 Jun 10 2019, 08:04 AM

Nice! Someone with the requisite skills could probably make and market the complete solution as a kit.

Posted by: saigon71 Jun 10 2019, 10:54 AM

I didn't try the extension. I was trying to wipe out both problems (hot start and severe idle hunt) with a single adjustable fix.

Posted by: jim_hoyland Jun 10 2019, 11:25 AM

I like your bracket solution; how did you make it ?

I need one.......

Posted by: saigon71 Jun 11 2019, 05:39 AM

It's a 1/4" washer tack welded to a strip of 18GA sheet metal. The sheet metal was bent in a vice using a socket for the radius to match the washer. Shot it with semi-gloss black paint.

Posted by: brant Jun 11 2019, 08:56 AM

Agreed, the adjustment knob is idle only and not a tuning knob.

It seems that using a wide band to tune the MPS would provide a better solution
having the correct mixture all of the time and not running the risk of tuning the fuel mixture by seat of the pants or sound.

Posted by: mepstein Jun 11 2019, 09:15 AM

Very clean install -

Posted by: jim_hoyland Jun 11 2019, 09:28 AM

Got it; thank you.

Posted by: ChrisFoley Jun 12 2019, 05:32 AM

A better solution would be to turn the center screw in the MPS diaphragm about one full turn counterclockwise while not allowing the outer screw to turn at all.
In addition to stabilizing the idle and reducing the likelihood of hot start problems it will probably make more power too.