LPG injection for cars without electronic fuel injection

[willholman]

Hi. For some years I ran a 1971 Merc 280SE on LPG. It had a Romano RIS system fitted by a chap called Jess Court down in Kent (he's now moved to France and doesn't work with LPG anymore). Obviously the old Merc didn't have EFI but Jess still managed to get the Romano injection system running and as far as I cn remember, the only thing he had to add was a switch on the throttle so the system knew when the throttle was opened. This wasn't a throttle pot, just a simple open or shut switch that told the RIS ECU when the car was off idle. It ran brilliantly and I did many miles in it, before taking it off the road to restore it and fit a later Merc 5.6 V8 to it.

I did label all the LPG loom wires when I took it apart using masking tape and ballpoint pen - not a system I recommend as the ink on the tape that hasn't crumbled away during the work (which took several years longer than planned) is unreadable.

Does anyone know how Jess might have wired up the Romano RIS system to work without any electronic petrol injectors to piggyback from? And are there any other LPG injection systems that can run without a petrol ECU?

Thanks

Will.

[mat_fenwick]

Hi Will (enjoy the mag!) It's something that's come up before - if you have time to read through this thread it may be of interest. There is an installer (Simon at LPGC) at the end who claims to have developed a standalone system. I think some (all?) of the early gas injection systems had their own map rather than slaving off the host ECU so this may be the case for yours. With it being a 6 cylinder gas ECU it may well have the potential to fire 8 injectors anyway.

EDIT - just found this thread with the same claim.

[rossko]

The old RIS would have probably been wired up with the "petrol injector" blue/yellow signal wire to something like an ignition pulse, so as to trigger LPG cycles. It's be smart to have some kind of filter to deal with possible spikes from an ignition trigger.

[willholman]

Evening Gents. Yes - that sounds right. I'm certain the system used a connection from the ignition coil. Thanks. Any ideas about the throttle switch though? I assume that normally the system would connect to the car's throttle pot? If so, I'll mount one - it won't be much harder than mounting a throttle switch and would presumably work better.

Any idea where I can get a wiring diagram for the old Romano RIS system?

[rossko]

It'll be as per OMVL Dream 21-C, take care to choose the correct sub-version (probably the type with MAP sensor onboard the ECU)
http://www.fesautogas.co.uk/download.htm

[willholman]

Thanks Rossko - so the Romano is a rebadged OMVL Dream 21 C then?

I still have the ECU so can probably use it. But the injectors had started playing up. Is there any reason why I couldn't use better ones with it - say Prins type ones?

[rossko]

so the Romano is a rebadged OMVL Dream 21 C then?

Not quite, AEB manufactured the ECUs and wiring looms and supplied to several 'customer' system builders, with tailored software.

I still have the ECU so can probably use it. But the injectors had started playing up. Is there any reason why I couldn't use better ones with it - say Prins type ones?

Yes, it will blow up. The injector drive circuits in the ECU are only useable with old-tech high impedance injectors. Before it fries itself, it won't work very well either - the firmware is expecting injectors with a particular dynamic performance (open-close times etc.) and won't work properly with other types.

Frankly if the injectors are goosed, the reducer is probably past it too, and it wouldn't be worth salvaging. Except ... there are no modern standalone systems off the shelf.
Barring one of the posters here, who says theirs will do it.

[willholman]

Yes - I'd replace the reducer anyway. It's the ECU I want to use - simply because it will work without piggybacking.

What other old style injectors could I use? Or are the Romano ones rebuildable?

[tommo2009]

just be a bit careful with the TPS switch, the signal is usually a 5v signal not 12v. I simple potential divider circuit wired up to give you around 5V is simple enough.

[rossko]

The early romano injectors risk losing factory setup if stripped. I do not know if they can be re-rubbered, in the absence of proper kits.
Other brand injectors of similar vintage stand a good chance of being workable. Unlike some early injection systems, I do not think this one offers an option for still-available Matrix types.
I do not know of any supplier of high impedance injectors, having struggled to find any new-old-stock for odd repairs.

[Gilbertd]

Sounds like this may be another application for a second injector driver stage. Use the ECU output to drive a high impedance load to switch a transistor capable of supplying the current required by a low impedance injector. Then you'd need to find a modern low impedance injector that has similar characteristics to the older Romano injectors.

[willholman]

Is there a box available that converts a high impedance output to a low impedance one then? I was thinking of using Keihin orange dot injectors.

[Gilbertd]

Not off the shelf as far as I know but it's a pretty simple bit of electronics. Use the ECU output to turn on a transistor which is used to drive the injectors. What you need to do though is find out how close the Keihin injectors are to the Romano ones in terms of opening and closing times otherwise you may find that although they work your mixer is miles out.

[rossko]

It is not as simple as a high-current follower; to drive low impedance injectors without frying them, or having them hang open at closing time, requires a peak-and-hold type driver.

Commercial product (intended for updating petrol ECU to peak-n-hold)
http://www.aemelectronics.com/engine-ma ... module-17/
Only 300 dollars

The ECU firmware would know nothing about the fast response of modern injectors, and try to do its thing assuming the injectors are still old slow-response types. This might not make much difference if you mapped it as carefully as you can; or it might make it rough and unworkable at idle speeds, I really wouldn't like to guess.

[woody]

You have the old injectors meaure the resistance , anything under 6 ohms is low impedence,1.2 to 2 ohms is perfect and any make injectors will work.


woody

[tommo2009]

didn't earlier rover v8's use a low impedance injector with a resistor pack

[willholman]

I'm pretty sure I measured them in the past and they were 3Ω.

[marek]

Dear Will,
you can easily build your own peak and hold driver board based around the LM1949 chip - if you are handy with a soldering iron, or you can buy ready made modules quite cheaply from Jean Belanger who posts on the Megasquirt forum bulletin board (msextra.com).

All petrol injectors work on a 4:1 ratio between peak and hold current (typically 4amps to open the injector and 1 amp to keep it open), but Keihin are 4 amps to open and 1.5amps to keep open. Fortunately, Keihins are rated at up to 6 amps peak current, so the conventional petrol injector circuit using the ubiquitous LM1949 can be used with one alteration to bump up the peak current so that the hold current is high enough - the two are tied together.

LM1949 can be purchased on the net from China very cheaply. Pay by credit card and delivered in about three days.

kind regards
Marek

[Martec]

Hi Will,

David Hampshire of CANEMS has built an ECU for his brothers car (Capri with a vauxhall 3 ltr V6) that controls petrol EFI and LPG, set up from the laptop. I've driven the car and it went very well.

Brian

[willholman]

Hi Brian

Yes, I spoke to David at the Autosport Show a while back and we talked about LPG. It would be reasonably simple to set up an aftermarket ECU (Emerald, Megasquirt, Canems or whatever) to run an LPG system and I certainly haven't discounted the idea. But it would mean getting the car's front pulley off and fitting a toothed wheel. Probably a cam sensor to. I was hoping to avoid that but we'll see.