cfabe

I'm thinking of making a TPI injector tester that will pulse my injectors so I can test the spray pattern, flow rate, etc. I need to know what the on-time and off-time are that I can run an injector at. For example, maybe its a 5ms on time and 200ms off time at a certian RPM. Thats just a wild as* guess, tho, I'm hoping someone will know for sure, as I dont want to fry these injectors or anything. Also, is it a 12v square pulse that actuates them like i think it should be?

I'll make a schematic of my circuit available when its done.

Thanks

Vader

Cfabe,

The ECM allows a maximum injector pulse rate duty cycle of 80% at WOT. This means 80mS on, 20mS off time (or an equal proportion depending upon engine RPM). Considering that the injectors are pulsed each engine revolution (twice per intake cycle) you can determine the time for one revolution at any given RPM and factor that for the 80% duty cycle to result in the actual "on" time of the injector.

Yes, each bank of injectors (four per side) is powered by a pull-down transistor in the ECM at 12VDC (or more like 13.8 VDC in actual operating conditions). The injectors are actually powered by a 12VDC source from the ignition, and the ECM completes the ground path to operate the injectors. Most ECM output devices are operated in a similar manner. Switching the grounds instead of the power to the output devices results in a lot less inherent "noise" and interference in the ECM. It can make for some confusing circuits for those who don't understand the theory, however.

A 12VDC square wave is the ideal signal, since the injector pintles are designed to be very compliant and have a minimal propagation delay. Actually, you should be using a transistor or digital high-current switch to operate the injectors, since the potential for contact bounce in a mechanical switch can skew the actual operation of the injectors. There is also a potential for some high voltage inductive "kick" resulting from the breaking of a mechanical switch that isn't present in a transistor or digital switch. These high voltage transients could possible damage teh injector coils.

Sounds like an interesting project.

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Later,
Vader
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GMTech

Why don't you just buy the OTC injector tester? Its only like $80. I can be purchased through any OTC jobber, or Snap-On or MAC tool distributers. It has three settings for injector pulse. I think its:

• 1 pulse @ 100ms
• 10 pulses @ 10ms
• 50 pulses @ 2ms

I use mine religously.

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cfabe

Thanks Vader, that was just the information I needed. I'm going to be using a 555 timer driving an output transistor, so I will get a nice square wave as an output. Any idea of the current draw or resistance across the injector coil? I havent gotten mine yet.

The reason I dont "just buy one" is that I'd much rather build it for $2 cost than shell out $80 for it. I've got a tuition payment coming up and money is tight. I'm sure many other people here would do the same if given the plans, which I'll do when I finish it, probably by the end of the week.