Emulate injectors - how?

Dodge Durango 99 5.9L, converted to run on LPG (single point). When running
on LPG injectors are disconnected to prevent them from working (or rather
the common positive lead is routed thru resistor so that voltage drop on
injectors is insufficient for them to operate), and naturally PCM complains
about open injector circuits. Alldata is pretty vague about P0201-P0208
codes, and only says "if induction kick is not detected PCM will set the
code". Apparently it checks not just for correct resistance but also for the
'inductive kick'.

Anybody knows how to properly emulate injectors on this engine?

Peter

 

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).

 

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

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.

 

Dodge Durango 99 5.9L, converted to run on LPG (single point). When

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

 

just buy an emulator! i know AEB make them for 4, 6 and 8 cylinder
vehicles. wireing it in takes under an hour too

 

just buy an emulator! i know AEB make them for 4, 6 and 8 cylinder

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')

 

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')

 

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

 

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...

 

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.