Preferred way to punch a hole in an exhaust pipe

[MikeInOr]

Plasma cutter. Ok I had to be the smarty pants. Never mind.
Analog EFI should be fun to tinker with- does it use a flap for the air flow meter?

You are thinking of K-Jetronic, which I had in my 1980 Mercedes. The D-Jetronic IS electronically controlled but it used a funky analogue compare and balance circuit instead of a computer to adjust the fuel flow.

Okay, step drill seems the winner. I have a two-flute drill but will see if a single flute is nearby.

Not converting to EFI. The car is D-Jetronic , so it actually is EFI already but thoroughly analog. I am putting in the O2 sensor to monitor and adjust mixture as much as D-Jet will permit.

I have found my Irwin UniBit with only a single flute tends to catch less than a 2 flute step bits... but this may just be me.

Wide band O2 sensor I assume? Which one are you going with? I have a Innovate WideBand O2 in my 1980 Mercedes MegaSquirt install. The first one died and they sent me a warranty replacement... years ago.

 

[AllenV]

You are thinking of K-Jetronic, which I had in my 1980 Mercedes. The D-Jetronic IS electronically controlled but it used a funky analogue compare and balance circuit instead of a computer to adjust the fuel flow.


I have found my Irwin UniBit with only a single flute tends to catch less than a 2 flute step bits... but this may just be me.

Wide band O2 sensor I assume? Which one are you going with? I have an Innovate WideBand O2 in my 1980 Mercedes MegaSquirt install. The first one died and they sent me a warranty replacement... years ago.

I am using an Innovate LM-1 handheld readout with a Bosch wideband sensor. Eventually I plan to switch over to sensor “controller” that will be hidden while displaying on an iPhone. But that won’t do data logging

 

[DannoXYZ]

You will find that LM-1 doesn’t use regulated reference-voltage for analogue input display. Turn on headlights and displayed AFR suddenly changes. Many Porsche engines have been destroyed by using LM-1.

I now prefer only units that are fully digital, sending binary data as output. To display, to datalogger, etc.

 

[AllenV]

You will find that LM-1 doesn’t use regulated reference-voltage for analogue input display. Turn on headlights and displayed AFR suddenly changes. Many Porsche engines have been destroyed by using LM-1.

I now prefer only units that are fully digital, sending binary data as output. To display, to datalogger, etc.

Hey, thanks for bringing this to my attention. A bit of on-line study suggests that folks have encountered ground loops or ground offsets by referencing the LM-1 to battery ground while the PCM, or ECM, has a different chassis ground. This is an important issue, which I won't minimize. BUT, what I am doing is very simple. Building a stand alone circuit of sensors referenced to battery ground. This ought to be fine, but I'll keep an eye out for proper ground management.
On top of that, I doubt D-Jet will let me get anywhere near stoichiometric. Let alone getting a lean mixture. Mercedes/Bosch made it reliable by making it rich. These were pre-oil-crisis times.

 

[DannoXYZ]

Yeah, pretty much ALL factory mappings I've found were pig-rich under WOT. Especially carby engines on motobikes. So rich, they're smoking out tailpipe like diesels! Idle and partial-throttle, much, much better. Rich mixture is safety margin while leaving lots of power on table. Just in case you run into bad petrol out in middle of nowhere on super-hot day. Or your fuel-pump/pressure regulator starts failing, or filtre/injectors start clogging. No major major manufacturer would tune for max-power, just too risky.

What's your goal with this?

 

[AllenV]

What's your goal with this?

No short answer for “what’s my goal”, so indulge me in a bit of bare-bones D-Jet history.

Bosch D-Jetronic is a speed-density system with no means of closed-loop operation. None. It has no O2-sensor and no means to measure the AFR. It was introduced in the late 60s and was used by Mercedes, Porsche (in the 914), VW, Volvo, Jaguar and Saab up to the mid-70s. The Electronic Control Unit, ECU, is an impressive exercise in analog electronics. No integrated circuits, nothing digital. It is a “fuel only” system where ignition and timing are handled by a mechanical distributor and points.

The fuel mixture is set by the injector pulse length and the fuel pressure. A manifold pressure sensor, MPS, senses the manifold vacuum using a metal diaphragm attached to a variable coil (an inductor, L). The ECU uses this L value in an electronic decay circuit to establish a variable vacuum-dependent injector pulse length. (I am skipping several details that aren’t relevant to this discussion. If you want more info, ask and I’ll put up several links.)

Now, Bosch built the MPS to specific parameters and did a final adjustment at the factory using a rather poorly hidden screw which fiddles the pre-load on the diaphragm. The calibration used for this remains a tightly-held secret at Bosch. Of course, mechanics in the field quickly began fiddling the MPS screw and the fuel pressure to make cars run “better” for their customers. This was all done ad-hoc using seat-of-the-pants reconning.

In the present day, MPS’s are aging and most of them have been adjusted for better or worse. Bosch will refurb and calibrate the MPS at significant expense. We think they use the same old calibration stand from the 70s. A couple of clever Mercedes enthusiasts have obtained two “known good” MPS’s and figured out how to adjust the screw on unknown MPS’s to get a reasonable match with the known good ones. This puts the MPS coil setting back to a good value at a particular vacuum level.

I am hoping bolster this with AFR measurements on the road. Thus, with my car ( a 1972 Mercedes 350SL) I am installing an O2 sensor and a vacuum sensor to data log AFR, vacuum, and RPM at various engine loads. After I have this baseline data we’ll remove the MPS to measure and reset the coil. After that, get new data and see what happened.

Beyond that is uncertain. If the mixture is still very rich at all loads and conditions I may tweak the screw in an iterative fashion seeking improvement.

And, for you viewers at home. The only reason I am using an old LM-1 meter is that I bought it in 2006-2007 when I put a blower and bigger injectors on my Tacoma and re-mapped it. Otherwise, I’d definitely use a new meter. I am even using the old laptop running Windows Vista!

 

[AllenV]

step drill arrived. Punched that hole in but-a-moment

 

[DannoXYZ]

No short answer for “what’s my goal”, so indulge me in a bit of bare-bones D-Jet history.

Bosch D-Jetronic is a speed-density system with no means of closed-loop operation. None. It has no O2-sensor and no means to measure the AFR. It was introduced in the late 60s and was used by Mercedes, Porsche (in the 914), VW, Volvo, Jaguar and Saab up to the mid-70s. The Electronic Control Unit, ECU, is an impressive exercise in analog electronics. No integrated circuits, nothing digital. It is a “fuel only” system where ignition and timing are handled by a mechanical distributor and points.

The fuel mixture is set by the injector pulse length and the fuel pressure. A manifold pressure sensor, MPS, senses the manifold vacuum using a metal diaphragm attached to a variable coil (an inductor, L). The ECU uses this L value in an electronic decay circuit to establish a variable vacuum-dependent injector pulse length. (I am skipping several details that aren’t relevant to this discussion. If you want more info, ask and I’ll put up several links.)

Now, Bosch built the MPS to specific parameters and did a final adjustment at the factory using a rather poorly hidden screw which fiddles the pre-load on the diaphragm. The calibration used for this remains a tightly-held secret at Bosch. Of course, mechanics in the field quickly began fiddling the MPS screw and the fuel pressure to make cars run “better” for their customers. This was all done ad-hoc using seat-of-the-pants reconning.

In the present day, MPS’s are aging and most of them have been adjusted for better or worse. Bosch will refurb and calibrate the MPS at significant expense. We think they use the same old calibration stand from the 70s. A couple of clever Mercedes enthusiasts have obtained two “known good” MPS’s and figured out how to adjust the screw on unknown MPS’s to get a reasonable match with the known good ones. This puts the MPS coil setting back to a good value at a particular vacuum level.

I am hoping bolster this with AFR measurements on the road. Thus, with my car ( a 1972 Mercedes 350SL) I am installing an O2 sensor and a vacuum sensor to data log AFR, vacuum, and RPM at various engine loads. After I have this baseline data we’ll remove the MPS to measure and reset the coil. After that, get new data and see what happened.

Beyond that is uncertain. If the mixture is still very rich at all loads and conditions I may tweak the screw in an iterative fashion seeking improvement.

And, for you viewers at home. The only reason I am using an old LM-1 meter is that I bought it in 2006-2007 when I put a blower and bigger injectors on my Tacoma and re-mapped it. Otherwise, I’d definitely use a new meter. I am even using the old laptop running Windows Vista!

Good ideas!!! What I've done along these lines with old Porsches is ditch the MPS altogether. Then use PIC controller taking input from modern piezo MAP-sensor that will simulate output of MPS/AFM/MAF sensors to give true 3D speed-density fuel-mapping based upon MAP x RPM. Once you've gotten MPS's calibration recorded, it's very easy to re-program PIC to whatever output curve you want.



I use fully-digital wideband-O2 that will also datalog additional analog-inputs such as: MPS, MAP-sensor, TPS-position, RPM, vehicle speed, ECT, IAT, etc. Then I just do several runs from idle to redline using 10/25/50/75/100% throttle to get MPS calibration along with MAP, AFR, RPM, etc. to get resultant 3D map of RPMxMPS-to-AFR at various operating zones. Recreate simulated MPS output using MAP-sensor and scale output at various 3D points up or down to adjust AFR. Done! There are actually off-the-shelf products that will do this.



TechEdge/WBo2 - 2Y DIY Wideband Unit
I built several of their early DIY kits 30-yrs ago, can also get modern pre-built ones too. Their tech-docs are incredible with explaining exact how each circuit works.



At some point, I didn't think effort of hacking Jetronic or re-programming Motronic was worth results. So I just ripped them out and installed MoTeC, Electromotive TEC, Haltech, Linksys, etc. programmable EFI systems from scratch. Converted quite a few moto-bikes from carbs to EFI with Microsquirt.... and TURBO!!



For some "stock" racing series where rules required "stock Motronic DME box", I've even stuffed Megasquirt into "stock Motronic DME box" hahhahah!!!!!



Sorry for the spew, just tossing ideas out there that may help.

 

[DannoXYZ]

step drill arrived. Punched that hole in but-a-moment

Awesome job! Very clean!

 

[GrifterGuru]

Awesome job! Very clean!

The true value of a unibit (step drill) can never be fully stated or understood until you have used one or own one.

I have a few of varying sizes both in metric and imperial. I would not be without them.