So while trying to make the car actually run, i pulled all the LPG pipework out the engine bay.

The injectors were originally mounted above the exhaust manifolds which was stupid, so on reassembly i remounted them off the plenum.

The pipework from the evaporator was strange so i removed all that and want to re-do it properly. there was also no filter.

So i currently have this:

Originally there was two short pipes off each side of the evaporator, each running to a Y connector. One branch of the Y went to a gas rail, and the other linked to the other Y.

I understand i should have a filter, and i've discovered filters with two inlets:

http://www.lpgshop.co.uk/lpg-filter-h-inlet-2x12mm-outlet-2x12mm/

So instead of all the messing with Y pieces, can i just run the two evaporator outputs into that, and then run the outputs from that directly to each gas rail?

Don't see why not as long as all 4 connections are link internally. The idea of the two Y pieces is to balance the pressures from the two sides of the reducer. Effectively it is two in one housing and if they were kept so one outlet fed one injector bank and the other fed the other, any difference in pressure would cause one or other bank to be out.

yeh i guessed it was pressure equalisation.

I will fire an email to lpgshop and ask them if they're connected internally.

There is no internal pressure balancing on your Bigas double reducer.
2 In 2 out filters can be used for pressure balancing. Your Bigas setup will use 10mm vapour pipe, though, not 12mm. 12mm is the standard size for filters etc..

Highly likely that your Bigas injectors are worn. Valtek type30 are a good match provided nozzle sizes on Bigas are 2.5mm or less. Don't strip your Bigas injectors to measure nozzle size, on those injectors the degree of nozzle tightening affects injector response and rails are calibrated at Bigas, removing the nozzles ruins the injectors.

Not sure if LPGshop will know much about the Bigas twin reducer, very likely they would phone me to ask anything they didn't know about it.

TinleyTech was the long time importer of that reducer, and injectors.

Simon

Thanks for the info. They do an 11mm filter instead of 12, so i guess i'll get one of those and hope the pipes squeeze on!

I was actually already thinking about the possibility the injectors were iffy. Also have been run without filter might have clogged them up etc?

There was a note from the last LPG service about "fluttering" injectors on one bank, which seems to have been fobbed off with "ignore until it gets worse". Interestingly its the same bank that was fouling plugs on petrol so maybe more going on than meets the eye.

Is there an easy way to check nozzle size? I will have a look thru the installation paperwork and see if its mentioned in there.

Had a look at the bigas rails last night.

Both had "3.0" stamped on the underside. I'm not sure if that suggests they're running 3.0mm nozzles, or is something else?

Yes it will mean 3mm nozzles.

In which case you could still fit Valtek type 30 rails but would need to increase reducer pressure and do a full recalibration. There are two allen sockets, one on each side of the reducer, alternate adjusting them in turn while watching pressure readings in software because you want them both to be fairly equally matched. If pressure from the individual reducers isn't well matched what happens is one reducer does all the work until it can flow no more (when you put your foot down) and then actual pressure suddenly falls to the setting of the lower pressure reducer.

The V30s are still a decent bet for a cheap no hassle fix because they're available with outlets to suit 4mm pipe (Bigas has 4mm outlets) and have very similar open/close time characteristics to Bigas. If your Bigas injectors had 2.5 stamped on them you could probably have got away with doing a straight swap without even connecting a computer and it would run at least as well as with the old injectors. .

Not all types of Bigas injector are available anymore (I still have some working ones of each type but they're old), the V30s are a better match for your Bigas injectors than the newer type Bigas injectors. New type Bigas are £100+vat for 4, you need 8, V30s are £35 including VAT for 4 but you will need to add a combined inline temp sensor / pressure T (easily fitted into piping) which is about £10 and will need the interface to recalibrate.

Simon

Thanks.

I guess i'll pipe up the existing ones and see what happens.

I presume the computer software and leads are readily available? How would i know what i'd need the reducer pressure to be at?

The new petrol injectors i fitted probably have a slightly different flow rate anyway (they're bosch Gen3's from a 1.4L K series), so the LPG calibration might well need a tweak regardless.

With the injectors you've got I'd expect optimal pressure to be between 1 bar and 1.1 bar, but the installer probably left pressure set at the Bigas standard of 1.2 bar.

3mm Nozzles will flow 1.44x as much gas as 2.5 nozzles, since even V30 injectors will be working within spec at 4.5ms I would set pressure at 1..6 bar and adjust from there if necessary... but 1.6bar will work and the Bigas twin reducer will go to above that pressure.

Calibration will need a tweak anyway following fitting different LPG injectors, especially of a different type with a smaller nozzle size. If you left the old LPG injectors in place and they were working OK, fuel trims while running on LPG wouldn't be effected by changing petrol injectors - though it is possible to cause problems if fuel trims are very different when running on LPG versus running on petrol. I've never tried to look up info on specs of P38 injectors versus K series injectors, they'd have to be a fair match for petrol trims to be anything like correct when running on petrol and tbh I think they won't be that far wrong.

Simon

Thanks, thats helpful. So essentially, raising the gas pressure from 1.2 to 1.6 to compensate for the smaller injector nozzle.

yeh i think they're both nominally "200cc" injectors, which is why they're sold as a replacement/upgrade for the GEMS ones.

When i last checked the long term fuel trims it was sitting at -10 on both banks. I've done a few more miles since then though, so i'll recheck at some point and see if its stayed there. If its sticking around -10 then it suggests the new ones are a wee bit larger.

When i got it, the engine would barely run. I've replaced the MAF, both lambdas and the fuel injectors and finally have an engine that mostly works as it should on petrol. Hence now looking to get the LPG back up and running.

Once i get the LPG back online, i can compare the trims between gas and petrol and see if they look sane. If they're miles out or uneven between banks i guess thats a sign that the injectors are needing replaced? At least these V30's are nice and cheap. I may well just replace them anyway, but a few other bits need fixing first!

Yeh, in simple terms the higher pressure compensates for smaller nozzles, if you look at it in a bit more detail it should change the shape of the map in the low load area more than the high load area - but would have been best to re-calibrate anyway when fitting new injectors.

Simon

Ok so managed to get the pipes connected up today and try things out.

Using nanocom, i started the engine on petrol and viewed the long term trim, which was showing as -35.

I started the engine on petrol and let it warm up, and the short term trims were fairly low. bank 1 was oscillating around zero, the other a little more negative, say -5 to -1 sorta range. I'd say the trims looked fine, while on petrol.

Then i switched over to gas.

After it stalling the first time (empty pipes i presume?) i restarted and switched over again and this time it switched fine. But the engine note immediately changed and there was a pronounced vibration and roughness from the engine. The fuel trims also seemed to swing in opposite directions. Bank 1 went from oscillating around 0 upto maybe +15-17ish. Bank 2 seemed to get more negative, but only a little bit.

So clearly something aint right, and given its different from one bank to the other i presume we can say its probably an injector issue? If it was system calibration then it would affect the whole engine the same way right?

Is there any other diagnostics i should look at, or should i just bite the bullet and buy some new injectors?

Possible you have a dodgy injector, in which case would most likely be on bank1, but neither is by any means certain.

I suppose you could do the stethoscope test, bit of narrow pipe in ear while holding open end to each LPG injector in turn, see if any injector(s) make a different noise to the majority of injectors, not a conclusive test but can give some insights about condition of injectors. / Swap injectors on sides of the engine, see if what's happening with trims now goes the opposite way after moving them.

Simon

Quick one. I'm going to order a pair of the valtek rails and the diagnostic cable.

But before i do, am i going to have to pull the manifold off again and replace the nozzle things, or can i retain the bigas nozzle things and just swap the injector rail out?

Yes, the nozzles are just something to attach the hose to, the ones that set the size are in the injectors.

phew thats good then :)

Had that bloody manifold far too many times already!

If you are going to change the hose, which is a good idea while you are at it, be careful when you pull the hose off. It can go brittle with age and it's possible to snap the brass spud off. Your best bet it to slit it lengthwise with a Stanley knife so it comes off easier.

I've replaced all the pipework already, did when i had the manifold off as some of the hoses looked a bit worn out. :)

Your Bigas injectors will use 4mm internal diameter pipe, V30s usually come with the nozzles to suit the same diameter pipe but can come with nozzles to suit 6mm internal diameter pipe - make sure you stipulate V30s with nozzles to suit 4mm internal diameter pipe and 10mm gas inlets when ordering. Also order a combined inline gas temp sensor / pressure take off like this (http://www.lpgshop.co.uk/12mm-omvl-inline-temperature-sensor-with-pressure-out/). This is listed as 12mm but is more like 11mm and most 10mm pipes will fit, but ask if they can sell you a 10mm one instead before buying. Tinleytech is more likely to be able to supply a 10mm one.

There is another way of going about it - buy V30s with 12mm inlets, use 12mm pipe, use a 2 entry 2 outlet 11mm pipe fitting filter. 10mm pipe then runs between reducer outlets and filter, 11mm pipe between filter and injectors.

4mm Pipe, similar electrical properties, similar injector response and similar physical dimensions were reasons I suggested the V30s.

Simon

Thanks.

I've got 10mm hose from the evaporator to the filter already. Its an 11mm filter, and i've got 11mm hose from there to the rails. I guess the 11mm hose will stretch onto the 12mm barb just fine, so i'll get the 12mm rails and T piece thing.

The LPGShop Valtek rails appear to have 5mm hose outlets, i'll email them and see if they can swap them for 4mm, but again i suspect the 4mm hose will squeeze on.

Will report back once the stuff arrives!
Cheers