Emulate injectors - how?

Why don't you just disconnect the fuel pump and let the injectors operate normally.

I'm not sure that'd be wise. Many injector designs depend on fuel flow to cool the solenoid windings (i.e., to prevent them overheating and cooking).

I'm not sure it's a good idea, too. Fuel pumps are designed to work continuously, and disconnecting it could be yet another reason for CEL to come on.

Peter

If it were me, I'd probably just ignore the check-engine light :-)

But I wonder if you could wind a set of 8 iron-core electromagnets to be the same inductance as a fuel injector, and then have the LPG system cut over to the bank of "dummy" injectors. The fact that they don't have a moving pintle might affect the waveform a bit, but I bet it wouldn't be enough to trip the computer. It would add a lot of complexity since you would have to put in 8 relays to switch over from the real injectors to the dummies, intstead of a single relay to cut in the resistor on the common side.

While it is possible that the fuel injectors may overheat, the CEL will not be set by the fuel pump being disconnected.

I've considered that ;-) However this way I may miss other reasons CEL is on

I don't know what is the injector inductance. Alldata only specifies resistance of 12 ohms

Yep, 8 relays it is. I've considered it, but this would mean ungainly bundle of wires, relays and coils of unknown inductance (or injectors from junkyard). Are there relays that will switch 4/8 separate circuits?

Peter

Fairly pricey. A good 4-cyl emulator with coils instead of resistors will cost about 70$ (equivalent of). Do you know where in EU I can mail-order them for less?

Peter

Far better get another set of injectors, use the same connectors, neat job. If you want to cool them use water and a small circulation pump and a small heatsink (aluminium box). When I have developed ECUs it's always been better to use real loads. Wire wound resistors do not give the same load characteristics. Happy tinkering.

I know nothing of LPG conversions (but I do know something about back-EMF/inductive kick). I guess I'm left wondering how someone doing the conversion knew enough about putting in the resistors to fool the computer but didn't know that the lack of inductive kick would create a computer problem (i.e., didn't know enough to do a totally successful real-world conversion).

But I guess that doesn't help you. I hope someone presents you with the answer (which it would seem would be simple and off-the-shelf rather than you having to re-invent the wheel so-to-speak).

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Peter wrote:

That's what I'm talkin' 'bout when I posted "I hope someone presents you with the answer (which it would seem would be simple and off-the-shelf rather than you having to re-invent the wheel so-to-speak)".

By the time you got thru buying parts and taking the time to wire up and debug your "one-of-a-kind" design, you'd wish you had chosen the simple off-the-shelf solution. Of course, nothing wrong with trying to find a better price.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

In message , TBone writes

There may be a fuel pressure sensor which would be triggered IIRC late Volvo's have one. Incidentally my fuel pump does not run continuously. There is a pressure switch on the rail which controls it. If you listen you can hear the pump start up then after a few seconds switch off when first switching on the ignition. I run my LR 4.0 litre V8 with injectors running and pump off and have done so for 50k+ miles. Switch back to petrol and absolutely no problem. We did this on the advice of a technical consultant in this field who advised us that these injectors do not rely on petrol for any form of cooling or lubrication. However I don't recall whether he was actually referring to "all" injectors.

That there is an Engineering Truth. Bill, did I ever tell you about the turn signals on the UM Solar Car of '99?

You're sure you're not seeing a fuel pressure regulator?

That's how most all electric pumps are set up -- most systems don't toggle the pump with any kind of a pressure switch, though. The momentary pump run upon switching the ignition on is just the prime pulse. Usually just a plain old temp/time pump duration lookup in the ECM, or even just a fixed-time momentary run.

DS

On or around Thu, 02 Jun 2005 20:06:19 GMT, "TBone" enlightened us thusly:

I've heard warnings against firing electronic injectors with no fuel, as well.

you need an injector emulator. I don't know where you get one, but there are such things as many of the more modern cars need 'em.

'course, if the computer is putting a warning light on, you could just remove the bulb...

On or around Thu, 2 Jun 2005 23:49:10 +0100, hugh enlightened us thusly:

however, my 3.5 hotwire which may not be the same system runs the pump initially when you switch on as you describe, and then stops, but AIUI this is because it detects no ignition activity, but when you turn the engine the pump starts again and appears to run continuously thereafter.

On mine, again, I have 2 relays which interrupt the injector supply to each bank; these have a wiring loom with 4 sockets and 4 plugs; you unplug the injector plug from the injector and plug it into the socket instead, then plug the other end of the wiring onto the injector. They have a delay on switch-off which allows the LPG to get through from the mixer.

They are just electric solenoids... Perhaps a bunch of similar current draw relays switching nothing in particular?

I don't recall ever hearing it. Lay it on me!

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Depends on the vehicle in question. Most fuel pumps run continuously and pressure regulation is done by releasing fuel from the rail back to the fuel tank. Some late model vehicles simply moved this regulation fuction back to the fuel pump itself, but it still runs continuously. I dont' know about your specific vehicle, but on the ones I'm familiar with, the only reason that the fuel pump shuts off a few seconds after turning on the key is because the auto shut-down system isn't detecting ignition pulses and kills the fuel pump. As soon as you start cranking the engine, the fuel pump comes back on and (on these vehicles) STAYS on.