Thread: installing lpg injectors on intake manifold

thanks for the photos peter. the plumbing for the vapouriser on mine will come from the heater as it currently does. the ecu is on the firewall on that side of the car and so to the vapouriser. the pre heater line you are talking about i will just be blanking off.

am keen to get one of those temp alarms (not just low coolant alert) but have to offload my tdi first.

have you any diagnostics which identify the timing you are running when using lpg? my motor is a high compression too and i found it has to be waaay too advanced to get a ping sound from the engine and the car seems to go better without needing to be near the ping point. i once put electronic ignition on which i controlled from my laptop whilst driving (highly not recommended) where it was quite easy to repeat the ping test. i am curious to see what corrections the ecu is making to the timing on lpg as it is a very different curve to petrol and whether it is able to fully advance under low load to where lpg likes it (i've had no problems winding it up to 16 and 18 degrees at idle) or is it banging up against a configuration parameter which only lets it move x degrees from the standard timing curve?

I'll get the figures as soon as I can.
I am currently overhauling the EAS air block and a few other projects.
I recall seeing 40 - 50 degrees advance on my old GEMS powered P38 at highway speed - petrol powered only.
I think all P38 brought into Australia are low compression - mine is anyway.
Regards
Peter

Well I had quite a bit of trouble getting an airtight valve block, but having finally suceeded I have grabbed some video files of the advance figures at various states for my Bosch Motronic 4.6.

I used the Blackbox solutions MSV2 extreme with its sister windows software.

You may need VLC media player to play the files - but should work on windows media player.
I have attached the following:

1. Idle on petrol
2. Idle on switching to gas - notice the misfires recorded - there is no human detectable stumble by the way -smooth as silk changeover.
3. 50kph on gas
4. Accel from lights to 60kph on gas
5. Hard accel in sport mode from 40kph to 100kph on gas- reaching 4000RPM. At this stage the gas system beeps - assume insufficient gas pressure- bee-uty would know the answer. Notice the advance stabilises at 30 degrees when reaching 100kph.

At a constant 100kph the advance on all 8 cylinders remains at 30 degrees and stayed for the duration of our short observation period. However the ECU should continue to advance the timing in 2 degree increments until knock is reached.

I did have the battery disconnected for several days so I dont know whether these are learned or default values
Hope this helps

Originally Posted by peter51

Hard accel in sport mode from 40kph to 100kph on gas- reaching 4000RPM. At this stage the gas system beeps - assume insufficient gas pressure- bee-uty would know the answer.

If it drops out into petrol mode and stays that way then you are probably right about pressure dropping. If it swaps straight back to petrol on decel it is just programmed to run petrol under high RPM. Quite a common strategy, may be related to max injector speed.

hi peter,

thank you for capturing the data. seems like quite a powerful diagnostics tool. i had to download VLC to get it to play, WMP wouldn't play ball. the under under load concurs with what i found when modifying my advance tables when i had the electronic ignition. i would go no more than 25 degrees. i am a bit surprised it is in the low 30's under steady state driving as i found it was better in the 20's . i assume the knock control is pulling it back from the knock point as expected though i found lpg behaved different to petrol, it was better further away from the knock point whereas petrol is better close to the knock point.

these results also go to once again show the difference in timing curves between petrol and lpg. often people will advance their distributor to say 10 degrees at idle but this is really near the maximum to stop the knocking on petrol. it doesn't achieve the retardation that lpg needs when under load and is probably making it worse as it is advancing the timing curve more (though gives better initial acceleration until the advance goes past the magical 25 degrees). the knock control does not appear to be active at idle based on your results as it shows petrol and lpg at the same advance.

once again, thank you for collecting the data. it is very informative.

if i had the tool (and time) i would like to build a graphical representation of advance as determined by knock versus load (say MAP). even better would be a third set of data being torque, these are 4wd's after all. i have read of the iphone? having an app (possibly on aulro) which was able to calculate torque quite accurately when compared against a dyno.

brett.

Hi guys,

I have an older style Elco system on my 1995 4.6 GEMS Rangie and I'm in the process of converting it over to liquid to allow me to return the air intake system to standard and remove the restrictive in line mixer.

I'm struggling to find anyone that has done a GEMS 4.6 to try and understand where is the best place to mount the gas injector manifolds. My system has 2 x 4 injector manifolds, one for each side, but with the shape of the upper GEMS intake manifold, trying to mount anything on the Pass side of the engine is proving impossible.

I hear all these stories about how the downstream hoses have to be as short as possible and all be equal lengths etc, but how critical is this really?

I may have to mount the injector rails both at the front of the engine and sweep the tubes back to the manifolds which will make the rear most hoses around 400mm long, and curling up 400mm of hose in a pig tail to get to the closest front points seems silly if not totally necessary?

Has anyone done direct injection on a GEMS that could feed back some input here and even post up a picture of your manifold mounting?

I have an injected system on my 4.6 GEMS. I'll get some pics up later today.

Mine is a KME system.

To keep the hoses short, and of equal length, the installer, KLR Automotive, made up two mounting brackets for the injectors which are in two banks of four.

Thanks Ron.

Going to be quite difficult I think. Here's a picture of the gas rail that is in my kit.