Test Jigs and Equipment for the 944S, part one.

In order to effectively troubleshoot an issue, you not only have to take a logical and methodical approach, you also have to be able to physically connect test equipment to discover what is and what isn't working. And if you can't do that, correctly finding the fault is made way more difficult that it has to be. So with that in mind, I'd like to show you some of the special test leads, equipment and other tools I've built, adapted, or otherwise found to be useful while troubleshooting and working on Gretchen.

 

What, Who?

I've never really mentioned what my background is in any of my blog posts until now. I studied Electronics Engineering Technology after high school, and have mainly worked on analog electronics with a sprinkling of digital over the past 40 years. Understanding how to analyze a system as a whole and applying generic troubleshooting techniques that could be applied to any system played a big part in a quality Electronics education back then. In addition to this, I started wrenching on cars and engines at about 12 years of age. At that time I also avidly read my brother's Hot Rod and Car Craft magazines, and the Petersen "How To Hotrod your..." books. . I loved the way the articles were written and illustrated, the way the words flowed, such interesting ideas and information, it was so much more enjoyable and felt so much more worthwhile to learn this way than anything at school! I do my best to emulate that same writing style in my blog here.

In this two or three part blog article I'm not going to get very deep into any actual test and troubleshooting procedures. My intent is to focus on how to reliably connect the test equipment to the test points you need to access in order to troubleshoot, and show some of the equipment I use and have put together for myself.

For more detail on actual troubleshooting, Youtube has some excellent material on automotive testing and troubleshooting. I highly recommend watching Scanner Danner's videos if you want to learn how to do it well. For an automotive guy with no real electronics post secondary education, he's got a really solid grasp of the electronic principles involved in the automotive field and he's a gifted instructor.

944-specific test leads and adapters

JPT signal tap/adapter leads

JPT stands for "Junior Power Timer". Despite the odd name, these connectors were designed with automotive applications in mind. In fact, while searching the internet for more information on the origin of this connector family, the word "Automotive" almost always appeared in the search result's description. JPT connectors are used all over the place in European (Bosch Jetronic/Motronic) engine bays of the 70's - 90's to connect devices such as sensors and fuel injectors to the DME. Because of the nature of their design and also the weatherproofing techniques of the time (the wires are often encapsulated with a rubbery, tape-like substance where they exit the back of the connector underneath the rubber boots), it's quite difficult to back-probe or otherwise access the conductors for testing, especially while they're plugged in with the engine running or the key on. And that's when a lot of the most useful tests are run. But with some spare JPT terminals, wire, regular heat shrink tubing (not the thick marine kind with glue in it, just normal electronic heat shrink tubing) and a quality open-barrel crimp tool, you can make individual jumpers with an accessible test point on them, and just plug them in-line to whatever you want to test. So if you need to observe the AFM signal, fuel injection voltage and pulse signals, ISV voltage and drive signal, or whatever, no problem. Used with the Porsche wiring diagrams, a multimeter or an oscilloscope, these test jumpers are the backbone of my testing setup.

These fuel injector connector boots, and the wires themselves, are as hard as a rock, and there's sealing goop inside there. How are you going to back-probe the injector in a case like this? The answer is to make yourself some tap jumpers!

These simple jumpers are made with 22 AWG wire and JPT terminals. Each one has a lead-out wire (tap) at the female end which is used to connect to the test equipment. That point is tinned with a small solder ball so the alligator clip doesn't slip off. The wires are inserted between the device you want to test/measure and its JPT connector, allowing you to test while the circuit is powered and/or the engine is running. Being individual wires, you can easily test 2, 3, 4 or 5 pole connectors with these.

These 2-pin adapters work the same as the single wire jumper taps, but with the connector bodies added to make connections quick and easy. I use these on fuel injectors, knock sensors, and the ISV.

Here a 2-pin JPT tap/jumper is being used to test a knock sensor. The red and black alligator clips are connected to the oscilloscope's input, the large clip to the engine block is the oscilloscope ground. Knock sensors are passive devices, requiring no power to generate a signal, so the signal wire to the DME (beige cable foreground) wasn't connected and the key was off. To perform the test, tap lightly on the sensor with a wrench, and its output waveform should appear on the screen of the oscilloscope, as shown below. If there's no waveform, the sensor is defective. If you're unfamiliar with what an oscilloscope is or does, it simply gives you a graph of voltage vs. time. Voltage is the vertical axis, time is the horizontal axis.

This is the waveform from the knock sensor test shown above. This is a typical voltage waveform generated by a properly working knock sensor. The peak voltage shown is 6V (2V per division), the middle line is 0V (ground). The blue vertical cursors can be used to help measure the frequency of the ringing waveform - about 5Khz is shown here.

Where to buy JPT parts

The online Porsche parts stores that you're buying your parts from will typically rape you for these connectors and pins. You could just order them from an electronics supplier like Digi-Key and pay reasonable prices for these things. For example, contact pins are available in many different wire gauge sizes, and available contact materials range from tinned zinc to gold, all under $1.00 each. 17-20 AWG gold sockets are $0.37 in single quantities as of this writing.

How to find them in the Digi-Key website? It's pretty easy once you understand how they categorize everything. From the Digi-Key website, search for Junior Power Timer, and then look in the "Contacts and Housings" categories that show up.

The crimper I use is available from Amazon.com here. You can make crimps with this tool that are very close to the quality of a professional production crimp machine.

O2 sensor tap adapter

The O2 sensor plug is also pretty difficult to back-probe, so I made an inline adapter for it. I used an old O2 sensor connector with some wire still attached, and soldered short pieces of 14 AWG solid copper (house) wire to the other end to make the male pins. It installs in between the two halves of the O2 sensor plug connection at the back of the fuel rail. Now I can test the O2 sensor heater current draw or voltage (white wires). By disconnecting the O2 sensor signal (black wire) to the DME I can force the engine into open loop and run any open loop tests I want. The fuel pump also uses this style connector, so this cable can be used to check fuel pump voltage and voltage drop, current draw (with an amp clamp), and even pump armature winding issues, current waveforms, and pump rpm if you use it with an oscilloscope.

Attach a high input resistance multimeter (like a Fluke DMM) or an oscilloscope to this O2 sensor tap adapter to check and monitor O2 sensor function. In most 944's you could set a ballpark idle mixture by monitoring the output voltage of the O2 sensor while adjusting the air bypass screw on the AFM (this is not possible on the 944S; its DME version ML2.1 uses adaptive idle mixture control).

DME relay jumper

This is a pretty simple one that almost everybody has seen. This jumper wire allows you to control the fuel pump for fuel system testing, pumping out your fuel tank, etc. It has a male spade terminal on each end and goes from terminal 30 to terminal 87b of the DME relay socket. I made identifying marks with a silver Sharpie on my CE panel to identify the correct terminals. This makes it a snap to pull the relay to test and not have to guess which terminals to use. If you want to also turn on the DME, add a second wire /spade terminal to also connect terminal 87 to the other two. The 2-wire arrangement is typically used to rule out the DME relay if it was suspected of being defective. I don't recommend this test; there are better ways to test the DME relay, like plugging in a spare. I just use the two terminal version.

Fuel pump test jumper. Note the silver Sharpie marks on the CE panel used to indicate the two terminals for the fuel pump, #30 and #87b.

Electronic Test Equipment

Fuel Injector / ISV tester

This is just a modification to a small test signal generator I had built years ago for electronics work. Basically, I added an injector driver transistor to the output of a square wave generator.

This setup was a primitive attempt at fuel injector cleaning. Don't waste your time trying to clean injectors like this, it didn't achieve anything!

I needed something to pulse the fuel injectors while I applied a vacuum to the injector outlet with a Mighty-Vac; this sucked carb cleaner through the inlet in an early attempt at injector cleaning (as it turned out, this didn't accomplish anything significant at all). Nevertheless, the injector driver/pulse circuit worked just fine to pulse the injectors, and has also been useful in testing the ISV when I suspected it might have been sticking - by setting it to about 25 Hz, and slowly increasing the signal amplitude, I could hear and feel the armature vibrating back and forth and lightly bottoming out on the stops, confirming that it was working and was definitely not sticking. I don't use this device much any more, but it was very handy when I needed it. If anyone wants the schematic diagram for this, leave a comment!

Hantek 1008C Oscilloscope

In my electronics lab I have some pretty nice HP and Tektronix oscilloscopes, but in the garage I use a super el-cheapo Hantek oscilloscope. I think I paid less than $100.00 for it brand new. I definitely don't recommend this or any Hantek scope to anyone. I went the cheap route and regret it, and I also let the 8-channel feature blind me. In actual use I've never needed more than four channels. Also, the more channels you use on a low-end digital instrument like this, the less available bandwidth there is; your ability to measure fast or high frequency events accurately goes right down. The only reason I get by with the Hantek is that with over 40 years of professional electronics experience, I can tell when it's giving me nonsense and when it's showing me plausible information. I use it with an old HP laptop that grudgingly runs Windows 10. Anyone looking to get themselves a "budget" oscilloscope would be way better off saving up a bit more money and getting a two-channel Picoscope instead. They're way more trustworthy and won't give you the headaches that the Hantek will. Pico's have better, more usable features, way better PC software, and from what I've heard, far better support too. It's real test equipment, not wanna-be test equipment. Hantek support is literally non-existent; no exaggeration. I will be ditching the Hantek in favor of a Pico at some point in the near future.

With all that Hantek bashing out of the way, an oscilloscope is a super-useful tool once you learn to interpret the waveforms, as the screen shots below will hopefully illustrate.

Hantek 1008C automotive oscilloscope used with an old HP/Compaq 6910 laptop. Not a recommended setup by any means!

 

Injector voltage and current waveform, showing the injector on-time (the negative-most/lowest portion of yellow voltage trace, about 2.9 ms), injector pintle opening (kink on rising portion of blue current trace) and closing (hump on falling portion of yellow voltage trace, and peak injector current (topmost limit of blue trace, 1.6A).

This is an excellent secondary ignition waveform (yellow trace), showing coil saturation time (dwell, first step ) of about 1.8 ms, spark plug firing voltage (the peak), spark plug burn time (second step, also about 1.8 ms), and coil reserve energy decay. Channel two (blue trace) was connected to battery ground and is displaying ground noise.

This waveform (yellow trace) displays a lean misfire. Compare it to the screen shot above and you'll notice a difference in the firing voltage (height of the vertical line), and the upward slope of the burn line, a dead giveaway of a lean misfire condition. Also note the reserve energy oscillations at the end of the event are missing, because this time the coil used all its energy to fire the plug, but no mixture was ignited (too lean).

 

Idle Control Valve voltage (yellow) and current (blue) waveforms. On-screen measurement display for Duty Cycle (% on-time) and rms current is turned on. As power consumers such as defroster and AC are turned on or off you'll see the duty cycle change as the DME adjusts it to keep the idle speed constant. This in turn allows more or less air to enter the intake manifold.

Pressure Transducer

I picked up this pressure transducer on eBay, and have only played around with it a little bit, and not on the engine yet. When paired with an oscilloscope, you can do all kinds of really advanced testing. You can view intake manifold vacuum/pressure variations in real time with the engine running. You can take out a spark plug, put the transducer in there, and view real time cylinder pressure cycles while the engine is running on the other three cylinders for an accurate picture of valve timing events, valve sealing, and cylinder pressure. It's awesome, Google "in-cylinder pressure testing" some time. You can also observe stuff like turbo boost pressure curves and a host of other pressure or vacuum related tests with one of these and a scope.

This is an absolute pressure transducer; it's used along with the oscilloscope to display pressure variations on the oscilloscope screen. You can display vacuum signal changes, manifold vacuum, cylinder pressures (cranking or with engine running), or any other pressure/vacuum variations you can connect it to. It must be powered with about 12V to operate. The third wire is the output signal and connects to the oscilloscope input.

Digital Volt-Ohm Meter (DVOM)/ Multimeter

My multimeter is a Fluke 87 that's about 30 years old. It's a testament to the idea that if you get yourself the best test equipment you can afford, and take care of it, it'll take care of you. This meter has never needed service, is very accurate and totally reliable, a real piece of quality test equipment. For automotive current measurements I use an inexpensive Hantek (sigh!) amp clamp with it. It's accurate enough for what I want and actually works OK for the money.

Boresope

I also have a cheap USB borescope I got from Amazon. I think it cost about $15.00. The picture quality is only fair, and there are lots of times when I wish I had a better one. So far I've used it to see inside the cylinders (couldn't see much), down the exhaust collectors to check the cat condition (couldn't see anything), behind the head looking for an oil leak (couldn't find it) etc. In all honesty I have to say that it hasn't really helped at all to have it. I'm still hopeful that it'll prove itself useful one day. I hook it up to the ancient HP/Win10 laptop to use it. If I had a better, higher resolution one I'm sure it would be a  super helpful tool to have. You definitely get what you pay for with these things.

I hope this first part of the Test Jigs and Equipment series got you thinking about your diagnostic tool set. I included the good tools with the duds to show that often it is worth it to pay for the more expensive option. But sometimes the cheaper option works too. 

Next time I'll show a few tools I've made, as well as some standard automotive test tools that everyone who wants to work on engines and cars in general should have in their toolbox. Thanks for stopping by!