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Make a Bosch Throttle Body Tester

Bosch throttle body for the Ferrari 360.

 If you've got a Bosch throttle body (series 280 750 ---) on your car, and it isn't a Ferrari 360, then it's likely if anything goes wrong, or is even suspected of being wrong with your throttle body, you'll just replace it. They're inexpensive, typically under $150, and super easy to install.

However, if you have a Ferrari 360 and suspect an issue with your throttle bodies (plural), then you're probably sweating right now. The stock of new OEM throttle bodies (aka holder) has been exhausted for years. There just aren't any more and there will likely never be any more produced. 

Used throttle bodies are generally useless, due to the requirement that both units be matched. Unmatched units, as in one degrading faster than the other, result in trouble codes and limp mode.

Luckily, the same exact innards to the 360's throttle bodies exist on quite a few other cars and these innards can be transplanted into the old 360 throttle body with excellent results.

The Ferrari 360 has some peculiar issues with the throttle body destroying one of the ECU's. These ECU's are no longer available and can be quite expensive to replace. The throttle bodies can destroy the ECU by drawing too much power and melting the H-bridge solder joints in the ECU. In theory, the ECU can be repaired but it's better to catch the problem before that happens and replace the throttle bodies. 

A test to determine how much power is being drawn by the throttle body would determine if it is a danger to the ECU and needs replacing. The total power that a Ferrari 360 ECU can supply before burning out is about six amps. A normal throttle body in good condition draws about one amp. So two, normally operating throttle bodies should draw about two amps. 

Testing a throttle body for amp draw is pretty easy once the details of how they work are laid out. The "280 750" series use two potentiometers to sense the position of the throttle plate and a motor with a PWM (Pulse Width Modulation) power source to move the throttle plate. 

This test is for the motor circuit only. The motor is typically the problem and can be tested using inexpensive parts and a simple setup.

Parts used in this test:

Onyehn PWM DC 10-60V Motor Speed Controller (~$13)
(note: any 12V motor speed controller that uses PWM is adequate)

DC Power supply (10-30V 10A) (~$100 - No longer available)
(Any similar power supply can be used or a 12V battery and clamp ammeter can be substituted)

Test lead banana to socket Pomona Electronics / 4771-36-2 / 4771-36-0 (red ~$12) (black ~$12)
(a male connector can be used too:

Instead of using a dedicated power supply, substitute a 12V battery and a clamp ammeter. A complete connector with pins can be purchased on eBay for less than $15 and can be used instead of the test leads. 

The rest of the parts are standard stuff available anywhere.

Here's the test setup.

The power supply is connected to the PWM controller. The positive (+) output is connected to pin #4 inside of the connector. The negative (ground) output is connected to pin #1. The pins are numbered inside the connector so it's easy to figure out which pins to use. A bit of light helps.

The test measures one thing precisely: the current required to open the throttle plate to full deflection. This is typically the peak power as the throttle body valve is being held closed by a rather strong spring. At full deflection, the spring is at maximum tension, so maximum current is needed to open it all the way.

Another data point is the position of the PWM motor controller knob. A PWM waveform is a square wave that is zero at 0% and high voltage, 12V in this case, at 100%. In between the wave consists of a zero portion and a high portion and the ratio of the two is the percentage.

This wikipedia image explains it nicely.

Since the PWM motor controller isn't "calibrated", we can only guess at what the numbers on the dial mean. A much more accurate way of measuring the duty cycle would be to use an oscilloscope. However, for the purpose of these tests, the knob is good enough.

The knob reading is really only good when testing two throttle bodies, as in the Ferrari 360. Since the two throttle bodies have to be matched to keep from throwing trouble codes, this test can show if there's a relative difference between the two units in regard to duty cycle.

Here's a video showing the test in action.

In the video, the motor controller knob is turned slowly until the throttle plate starts to move. From then on, the knob is turned very slowly since the range of power required to open it all the way should be fairly small. In this case, it was about 1/2 a "number" on the dial. 

One amp is about right for a good condition throttle body. The one in the test video is the Ferrari 360 model (280 750 038) rebuilt with parts from a Porsche model (280 750 474). If the amps are over two, that would concern me enough to rebuild the unit. The motor is completely replaceable using the parts from a Porsche unit.

This test doesn't address problems with the potentiometers. Testing those sensors would require a different and more elaborate test.

For a more indepth look at how a throttle body works and the pin layout, please see this article on the topic: Bosch Throttle Body Woes


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