87GTR

iTrader: (61)

I have been building a compression tester on and off again. I got the parts a few years just got around to putting them together.

It uses the following parts.

usb data-logger DI-148U Starter Kit http://www.dataq.com/products/startkit/di148.htm
pressure sensor MSI pressure transducer 0 - 5 volt 250psi MSI 2000204
http://search.digikey.com/scripts/Dk...6259&k=2000204
extension hose kit. KD Tooks part# KD 2992 http://www.mytoolstore.com/kd/kdengi14.html

The data logger has software that can record the wave form out put by the 0 ~ 5 volt pressure sensor.

it has 8 input channels so you could datalog more things if you wanted to

Here is a prototype picture. I'm going to redo the wires and build a harness with connectors with strain relief and mount the data-logger in a small box add, also a inline fuse on the power

The software they give you is really basic. it plots a graph of the 8 data channels. you can record it and playback old logs.
maybe someone could write a better user interface and do the conversion from 0-5 volts to PSI or what ever measurement units Mazda uses.
To make it easier to read the output.

Go48

iTrader: (7)

Experimentation with this arrangement early on in our development cycle, showed that with the hose in the system, the readings were about 10% too low, probably due to the inability of the very-short-duration compression pulse to fully charge the internal volume of the hose. We developed a different approach as you will see at our web site (http://RotaryDiagnostics.com).

RotaryEvolution

iTrader: (30)

IMO, unless it logs RPMs then the typical piston compression testers give accurate enough of a reading(it just relies on a strong cranking RPM signal to be fairly accurate since reading the tach at those RPMs isn't a good indicator of true engine speed).

Go48

iTrader: (7)

With this system, the engine cranking speed during the test can easily be computed from the recorded data using the time track.

Pele

iTrader: (28)

Something smaller and with a display would be better...
I don't like carrying around a laptop when checking out engines.

I typically use the compression tester in a carport, on the side of the road, in someone's garage, in a parking lot (at a meet) or at the scrapyard... I usually am shopping for or selling (or helping a friend buy or sell) an engine or complete car... Or diagnosing a problem vehicle for someone.

It's why I liked the TwistedRotors model. It's about the size of a pack of cigarettes, completely self contained... It fits in my pocket or toolbox and it doesn't have a bunch of connections or buttons to get greasy and dirty.
Reads PSI, gives last three readings, and calculates RPM.

When doing a compression test, I'm not sure what else I'd want to datalog since it only takes a few minutes (Including removal and replacement of plugs) and the engine will not be running at that time; It'll only be turning a couple revolutions. Bam, get numbers, reassemble, and put the tester away.



However, for other diagnosis, I'd think a multichannel datalogger would be absolutely awesome...

Four channels, one for each injector (Pulsewidth)
Four channels for inductive voltage pickup on plug wires
A channel each for O2 sensor, MAP, TPS, AFM, Coolant temp
(That's thirteen channels, though I doubt I'd ever run all at once.)

Enough harness pigtails so that you can plug it into the car's factory harness at one end and into the component under test at the other end... Then just throw the laptop in the passenger seat and go for a drive to watch the drivability problems show up...

SpeedOfLife

iTrader: (16)

very interesting, subscribed

87GTR

iTrader: (61)

wow very nice man! I agree the hose is not a good idea too, it is better to move the transducer as near to the compression chamber as you can.


you can calculate rpm over a given time by using the pulses

SpeedOfLife

iTrader: (16)

Any update on this?