Can anyone with a Nanocom or similar tell me what these engines display normally for their long term and short term fuel trim?

Can anyone also suggest what the device means by a "positive" trim?

In my mind, a positive trim = Adding fuel, but i'm not convinced thats correct given i've fitted slightly larger injectors yet the trim is jammed at 38.75 and the sensors are stuck around 1v.

Long term trim was showing at -154, which i thaught was way out of whack, so i reset the adaptions. But then it went to -160... surely reset should be 0?!

If you're talking GEMS, and have an early ECU (I forget the part number), then resetting does indeed go to -160... I believe it should work up to around zero, but I'm not 100% on that as mine never ran right with that ECU or one of the newer part numbers (which reset to zero).

The GEMS will not adapt the fuelling if there is 1/4 tank or less. This is to prevent false adaptions due to fuel surge. Large corrections will be held until the tank is properly filled- at least 1/2 tank.
Do you have plenty of fuel in the tank?

Orangebean wrote:

The GEMS will not adapt the fuelling if there is 1/4 tank or less.

So that explains why my short term adaptations never changed from 38.75 since it was run with a clogged petrol injector. I thought it was me doing something wrong! I'll have to try it again now I've got half a tank of cheap Latvian 98 Octane.......

Kind of implies that it'd mess with a sequential lpg system on a GEMS (rare as they are) under the same petrol in the tank condition.
I've only just got my head fully around the intricacies of single point so I could be completely off the mark, but if the trims are locked off when low fuelled, then petrol injector durations will be potentially incorrect. If multipoint ECM gets its lpg injector timings from the petrol injectors and then applies calibration mumbo-jumbo to the duration of the lpg injectors then you'd get messed up mixtures on lpg due to locked off petrol trims.
Happy to be called out on that though! As I said, only just got my head fully around single-point and all I know about multi-point has come from a cursory study of how it works from the web...

If you assume the LPG system was calibrated with the petrol system running properly, then locked off, incorrect, adaptations would certainly screw up an sequential LPG system. All the LPG system calibration does is sets the fiddle factor needed to account for the different fuel at differing revs and loads. It should be set, using gas pressure and nozzle size, so that the LPG injectors need a pulse length of between 1.2 and 1.5 times the petrol injector times. So if at a given revs and load the petrol injectors need to be open for 10mS, the LPG ECU will add 2-5mS to the pulse length to fire the LPG injectors. Even if the LPG map is a little out, the petrol ECU will adjust to compensate. The symptom of this is that it will run rough when switched back to petrol but only until the trims readjust themselves.

If the engine has been running rough for whatever reason (dodgy MAF for instance), the petrol trims will have altered. That will change the injector pulse duration but the LPG map will not have altered, making the LPG mixture incorrect. It'll run rougher on LPG than on petrol as the air/fuel ratio needs to be closer to stoichiometric to burn properly. An engine on petrol will run with the mixture miles out, on LPG and the same amount out, the engine won't even run. Normally it could be run and the trims would adjust and bring everything back to where it should be but if there's not a lot of fuel in the tank, the fuelling adaptations won't self adjust and it'll carry on running rough not matter how long you drive on whichever fuel has incorrect settings.

The GEMS will not adapt the fuelling if there is 1/4 tank or less.

I don't think I've ever had more than a quarter tank in mine, and it seems to adapt the fuelling just fine...

gordonjcp wrote:

I don't think I've ever had more than a quarter tank in mine, and it seems to adapt the fuelling just fine...

Got that info straight from the horses mouth- well Mark Adams actually. I figure that if there's anyone who knows the intricacies of the GEMS ECU as well if not better than the guys that designed it, it's him!

Bloody cars. It wont adapt the LTFT unless its being driven either, and i cant fucking drive it without an MOT. What a stupid arse system.

Why on earth would the LTFT start at -160? That said, it was at -154 when i started, which isnt much better....

I'm still no wiser though, is +38.75 adding fuel or removing it?

As mentioned in the other thread, I fitted some new injectors as i had a feeling the old ones were broken. unfortunately i fked up the measurements, and fitted what are actually 245cc injectors instead of the original 200cc ones. Started the engine after resetting the adaptions and now it wont idle. rev it up, its fine. get it up to 3000rpm or so and the trim moves away from 38.75 and starts dropping down a bit. Drop the RPM's down and it just goes back to +38.75 and the lower the revs the worse it runs. By the time your down at 1000rpm its choking and farting and running like shit. Release the throttle pedal and it dies.

Given the injectors are too large, surely the fuel trim should be fully negative, as it should be trying to reduce the fuel...

Got that info straight from the horses mouth- well Mark Adams actually. I figure that if there's anyone who knows the intricacies of the GEMS ECU as well if not better than the guys that designed it, it's him!

Damn straight. Wouldn't it be good if we could get Mark Adams to join here?

Started the engine after resetting the adaptions and now it wont idle.

That sounds like a borked MAF sensor, if it's a GEMS.

MAF readings seemed perfect, circa 20g/sec at 1000rpm, and 60g/sec at 3000rpm.

I haven't understood one fukking word of this thread lol

Are you using a Nanocom Aragorn?
MAF readings should be in Kg/Hr:
Air mass flow at sea level - Engine fully warm, in neutral gear, with all loads off
At Idle 20 kg/hr ± 3 kg\hr ...............................................................................
At 2500 rev/min 61 kg\hr ± 3 kg\hr ................................................................
I'm guessing you've just scrambled your units otherwise, if your readings are actually grammes per second that equates to:
Idle- 72Kg/Hr
3000= 216Kg/Hr

Aye, if it's 60 grams/sec then it's probably underfuelling a bit. You could try switching to hydrazine ;-)

Current research shows that a Hydrazine/ Methanol mix may be the way to go.....
:-)

yeh sorry, too used to VAG stuff that reports MAF in g/sec.

Readings were from nanocom. 20kg/hr holding the throttle open by enough to keep it at 1000rpm (as it wouldnt actually idle and was really lumpy even at 1000rpm), and 60kg/hr at 3000rpm.