300Tdi Fueling and EGTs

Red90 said:

Cutting the wire will make zero difference.... ....You will read within a few degrees 100% of the time.

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^ ^ ^ I've been inclined to believe this version of things, I just know so little of this stuff that when the original instructions say NOT TO CUT, I tend to go with what they say. HOWEVER, since to pull apart my dash and extract the coil, and get it all back together again really will mean a lot of work (and I'm afraid it will damage the plastic pieces) I think I will try it like this: The original VDO wires have a set of connecter loops at the sensor end. Once you've strung it through the bulkhead, this is how you actually connect the last 12" of wire and sensor probe to the main 10 feet of wire. I can't see how it would hurt to use the new sensor probe, 12" of wire, connect to the main VDO line at that point. In the end I might have a centimeter of difference, but virtually the same connection.

That said, my plan right now is to get the blanking plate tapped, or replaced. Reinstall my current sensor to it's maximum depth -- I think I can get another 1/2 inch at least, if I tap the bung correctly. Test to see if I notice a difference, and I watch it close enough that I can tell the difference between the types of fuel I'm using, so I should be able to tell if extending the probe shows quicker and more accurate results.

You should not really, though, have a wiring connection in the engine bay unless it is a proper thermocouple junction. All connections should be in the interior, as close to the gauge as possible if you are using "regular" wire and regular connectors.

Except that's where the factory wire connection is. You can see it here, and that it is not far from the probe. Not sure how to do it, I just know that I can't think of why it couldn't be done. You can also see why if I can't even thread that NPT fitting more than halfway, I barely have any of the probe going into the manifold, let alone the exhaust stream 3" away.

OK, so after all that, I'm back to where I started. Just like five or six other projects I've done on this thing...

But I did manage to bore out a bit more, and thread a bit deeper, so that the original probe is extended another 1/4-1/3 of an inch.

I think I've been getting what you might call accurate readings, but only once the entire area is warmed up, but I know I've been getting slow response on the readings. My hope is that I will see generally the same temps (I go up the same exact hill at the same exact speed every day) but that I will maybe see that needle move a little quicker. I'm still planning on getting a new probe, but that might have to wait now...... ...since the truck won't start....

May have missed it, did you post a picture of your probe install ? The plate is angled and if you go straight into the plate the probe will actually touch the casting inside and not be in the airstream as required. Trucks that are poorly tuned will have slow pyrometer movement.

There is nothing wrong with the VDO thermocouple length. I have them installed in two of my personal trucks and have installed dozens for others. All read correctly, it is perfect for the application. We drill and tap the plate and thread the thermocouple directly into the plate, ie we dont use the weld on bung.

Uncle Douglas said:

I may have missed it, did you post a picture of your probe install ? The plate is angled and if you go straight into the plate the probe will actually touch the casting inside and not be in the airstream as required.

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post #8 with all those fittings the probe isn't in the exhaust stream

Yeah, that's not going to work. Buy a new plate and ditch the bung and the fitting threaded into the bung. Thread the couple directly into the plate.

Got the angle right though !

What fitting do I use to thread the probe in besides the 1/4 NPT? Or are you saying to use the NPT directly into the plate?

Otherwise, I get what you mean, and I did eek out another 1/4+ inch by rethreading last night.

I took a blank plate and a weldable bung into a machine shop and had them machine and weld it:


EGT Probe by Chris, on Flickr

Yes, that's what I have, but I don't have the long probe. So imagine a probe that is only 1/2 that length.

By the way, is the black tube on the right from your intake filter? I don't need a snorkel right now, but I would love to be able to pipe the intake to the wing-top vent. Parts?

Reviving this thread because the other thread threatened to veer into it.


Chris, how did you know which probe to get, and where did you get it from?
Javelindave, when you have installed the longer Auber probe, what did you do with the extra length? Right now, my VDO wire is coiled behind the dash.


I'm about to order this, and since I don't want any more extra new parts in my garage that can't be returned, I hope this is right: https://www.auberins.com/index.php?main_page=product_info&cPath=5_22&products_id=145


With the 1/4 NPT, which is the the tap I used for the plate.

That is the correct Auberins probe.
As for the extra cable I wrapped it up with a few zip ties behind the dash. Others have shortened the cable and claim to have no issues. What you do is your call on.

I'm just worried about having the "double" extra long wire! I may call them to make the order tomorrow, and ask about getting a shorter wire.


Thanks.

The length of the wire makes no difference.

I managed to use a new flat EGR blanks to drill and tap the fitting. Doing it all by hand, I didn?t quite get it ?centered? or at the right ?angle? but it is pretty close. The result is that the probe gets in about 1/2 inch more. This does not get it into the stream. A drive seems to show that the needle is reacting a tiny bit faster, and since it climbed faster, the temps may have been showing slightly higher by about 50-100 degrees. But even while accelerating through 60 mph on a 1/2 mike long hill, I only saw about 850 degrees.

The photos show before and after.

Sincerely doubt you have a "stream" issue

FWIW returned a customer truck to him yesterday after a clutch job. Truck has a vdo pyrometer (weld on bung used), fitted by someone else. I was seeing 1100-1200 degree's pulling Blue Ridge mountain grades in 5th yesterday. Ambient temp was 90, coolant temp 190-200. Tires 265/75/16, 1.4 tcase, roof rack wind resistance, road speed 70-75 mph as best I could maintain it.
I've done nothing to tune that truck.

Yeah.... so I have no clue what is wrong.

Tuning. Fuel. Timing. Boost.