cylinder head temp sensor, what the brain thinks Options

[worn]

Well, I have been tweaking the MPS. I still am having low torque below 2,000 rpm, making smooth transitions to speed a bit more dramatic than I would like. I think that the cam may be playing a role here that I may never tune out completely. Now over 2,000 is another story (IMG:style_emoticons/default/laugh.gif) (IMG:style_emoticons/default/w00t.gif)

The point of this post is that if you are fooling around and the cylinder head temperature lead (I think it is Temp I) comes undone, the brain sees infinite resistance. It therefore, on a warm summer evening, thinks the motor is frozen cold and dumps in fuel. It won't start. You have spark, you have fuel, but the thing is flooded to the gills. Nooo, its EFI! Yep, flooded. (IMG:style_emoticons/default/hissyfit.gif)

So I started thinking that a spare might be in order since no start can mean travel by foot - or used to before cell phones. An alternative would be alligator clips to simply ground the lead. That way the brain would think the engine was hot and you could limp home. My list of spares on a trip away from home is growing.

[lsintampa]

May be why some go to carbs.

Once something with FI starts acting up, it can be frustrating.

My BMW 635 had all sorts of mysteries - finally sold it. Doing a carb conversion on the 635 would have been nothing I'd want to A) do or B) take on.

Not the same with the teener though.

[stugray]

Worn,

My recent experience says you are correct. Short the lead to ground.

I had thought that I could use the stock CHT to tell how my car was running with carbs.
However with the stock CHT sensor I chose, the resistance goes to zero at about 280 deg. F.

Not too useful except to tell you the engine is warm enough, does nothing to help determine if it is too hot.

That might not be true with all CHTs as Brant points out, there are at least three different sensors.
The ones I got are known as 2252 type. That means they read 2252 Ohms at 25deg. C and approach a short at about 150 C.

Stu

[Cap'n Krusty]

Well, I have been tweaking the MPS. I still am having low torque below 2,000 rpm, making smooth transitions to speed a bit more dramatic than I would like. I think that the cam may be playing a role here that I may never tune out completely. Now over 2,000 is another story (IMG:style_emoticons/default/laugh.gif) (IMG:style_emoticons/default/w00t.gif)

The point of this post is that if you are fooling around and the cylinder head temperature lead (I think it is Temp I) comes undone, the brain sees infinite resistance. It therefore, on a warm summer evening, thinks the motor is frozen cold and dumps in fuel. It won't start. You have spark, you have fuel, but the thing is flooded to the gills. Nooo, its EFI! Yep, flooded. (IMG:style_emoticons/default/hissyfit.gif)

So I started thinking that a spare might be in order since no start can mean travel by foot - or used to before cell phones. An alternative would be alligator clips to simply ground the lead. That way the brain would think the engine was hot and you could limp home. My list of spares on a trip away from home is growing.

The ECU needs, no MUST, see a ground at the CHT wire. No ground, no start, no run.

As for the camshaft, I'm guessing you are talking about a profile other than stock. IME, and I've been working on 914s for 40 years, you're NEVER going to get acceptable low end performance or idle with virtually any aftermarket grind. Early on, I worked with the guy who developed the first (and probably the best) aftermarket diagnostic machines as well as another guy who was the first person in the US to rework MPSs, and they couldn't get past the vacuum signal problem.

Times have changed, but D-jet hasn't. Same old analog system, pretty limited by hardware and the basic design.

The Cap'n

[worn]

The ECU needs, no MUST, see a ground at the CHT wire. No ground, no start, no run.

As for the camshaft, I'm guessing you are talking about a profile other than stock. IME, and I've been working on 914s for 40 years, you're NEVER going to get acceptable low end performance or idle with virtually any aftermarket grind. Early on, I worked with the guy who developed the first (and probably the best) aftermarket diagnostic machines as well as another guy who was the first person in the US to rework MPSs, and they couldn't get past the vacuum signal problem.

Times have changed, but D-jet hasn't. Same old analog system, pretty limited by hardware and the basic design.

The Cap'n

Well, thanks Capn'. Yeah. The big problem happened early when I didn't make sure the spade plug was in tight. Then go pull the MPS for a little tweak and sleeve catches.

Yeah, it is a webcam 73 + 2.5 degrees. I like it, and I had a hunch it would not have the low rev torque. That isn't what they are supposed to do. Still, I have gotten it better and better with timing and air fuel. It is a real comfort to hear your opinion because it will allow me to quit beating a dead horse that much sooner.

[worn]

As for the camshaft, I'm guessing you are talking about a profile other than stock. IME, and I've been working on 914s for 40 years, you're NEVER going to get acceptable low end performance or idle with virtually any aftermarket grind. Early on, I worked with the guy who developed the first (and probably the best) aftermarket diagnostic machines as well as another guy who was the first person in the US to rework MPSs, and they couldn't get past the vacuum signal problem.

Times have changed, but D-jet hasn't. Same old analog system, pretty limited by hardware and the basic design.

The Cap'n

Forgot to ask. What is the best source of a "stock" grind cam? Is the only route regrinding?

[stugray]

Forgot to ask. What is the best source of a "stock" grind cam? Is the only route regrinding?

I have a stock cam with matching lifters I would sell.
I could provide pictures, but to my untrained eye, it looks likely it was hardly used.

Stu

[Cap'n Krusty]

Webcam has been selling that grind for as long as I can remember, and their sales people ALWAYS say their engineers say it'll work just fine with D-jet. They lie. Hey, their lips are moving ....................

They also offer a stock grind. If you use their camshafts, you MUST use their lifters! Ask me how I know ............... Not really, I don't want to relive the pain. Again.

The Cap'n

[green914]

May be why some go to carbs.

Once something with FI starts acting up, it can be frustrating.

My BMW 635 had all sorts of mysteries - finally sold it. Doing a carb conversion on the 635 would have been nothing I'd want to A) do or B) take on.

Not the same with the teener though.

I went to carbs on my 2.0, and think that I should go back to the FI. It always started easier, got many more MPG, and (IMG:style_emoticons/default/driving.gif) run better under most conditions.

[worn]

Webcam has been selling that grind for as long as I can remember, and their sales people ALWAYS say their engineers say it'll work just fine with D-jet. They lie. Hey, their lips are moving ....................

They also offer a stock grind. If you use their camshafts, you MUST use their lifters! Ask me how I know ............... Not really, I don't want to relive the pain. Again.

The Cap'n

Yeah, we'll I am ok with the cam, but the engine coming out is begging to be rebuilt. What source would you suggest for a stock grind Cap'n?

[ThinAir]

FWIW, I'm running an Elgin 330-1 cam in an otherwise stock 2.0L. This was recommended to me back in the days of the "you have to buy ceramic lifters" era (which turned out to actually be a problem with webcam cores). I've been running this cam for about 10 years.

About a year ago, my injector points went bad, and somehow in the process of swapping distributors I ended up with some low idle issues. I ended up putting in a 300 ohm HTS resistor instead of the stock 270 ohm. I got the idea from some threads about getting the smoothest possible idle. I think my basic problem was that the TPS was not properly calibrated and that it was running rich. Changing the resistor actually made the low idle problem worse by making it richer. After setting the TPS, I adjusted the ECU leaner & leaner until it idled smooth.

I've never had an issue with the 330-1 and stock FI, but with this combination it is idling better than it ever has and it transitions from very smoothly from idle to accelerate. It's kind of counter-intuitive to do one thing to make it run rich, and another to lean it out, but it seems to be working. I haven't run a full tank of fuel yet to check mileage so the jury is still out as to whether I'll go back to the 270 ohm.

[ThinAir]

Update: I just did the first fill-up after making these changes. Normally I get 22 mpg max for around-town driving. This time I got 25.22 mpg. I'm a happy camper! (IMG:style_emoticons/default/driving.gif)

[Retread]

Update: I just did the first fill-up after making these changes. Normally I get 22 mpg max for around-town driving. This time I got 25.22 mpg. I'm a happy camper! (IMG:style_emoticons/default/driving.gif)

I have used DEMA ELGIN's "improved: stock profile non numerous D-jet engines. depending on the age and condition of the injection components, the setup has been from easy to moderately challenging. Never an surmountable hill to climb.

[r_towle]

Ask SLITS nicely if he has the 411 VW mps unit he could sell you.
It does not have the lower end diaphragm, so you can use camshafts that are a bit more aggresive.

Btdt, tuned two large motors with it, works fine and a ton simpler to setup, just one adjustment.

You will need an O2 sensor and some AFM gauge to read it..

Drive, adjust, drive adjust...
Take about 30 minute of tuning in all types of driving types to get it as close to right as you will ever get it...

Djet is really n a finely tuned system, it batch fires when it wants, not when the motor is really in need of fuel, so don't attempt to shoot for perfect, shoot for perfectly drivable.


rich

[Tom]

The CHT is TS2 and contrary to what The Cap'n said, the ECU does not require a ground on that wire. Not sure what he was thinking there. Instead, it needs a variable resistance of between 2500 ohms (cold) to less than 100 ohms (hot) to ground. That is what the CHT (TS2) provides when it is working correctly. You could carry a 150 ohm resister and a jumper wire and limp home OK if the TS2 failed when driving and the engine is warm. Just jumper the ECU wire to the 150 ohm resistor and jumper the other end of the resistor to ground. A pot with values of 0 -3k would work also. That way you could set the pot to 2500 ohms when the engine is cold and after warming the engine up, turn it to less than 100 ohms. I had discussed the hot-no-start due to excessively rich mixture syndrome with Paul Anders some years back and he said at the time he was thinking of putting in a pot in parallel to adjust his mixture for different situations.
Tom