off idle/acc flat spot

[monaro308]

Hi all,i,ve had the munro at my place for a week since I hardly get a chance to drive it these days.
The last time I did any logging on it was about 2 years ago (building the track car and the mrs passing away)
95% of the time I run it on lpg and I always cold start it on petrol.
Its developed an off idle lean out/flat spot when taking off and the motec PLM shows a lean out whenever I accelerate slowly.
Always noticeable taking off from lights/stop signs etc etc.
I haven't changed or altered anything in the 2 years and it has run fine on the original BLCF and fine with 12P BLCF.
Never really had a chance to continue calibrating it as its run pretty well and then just drive it on lpg (tight arse )
If anyone is bored or has a chance to look at the d/log see if you can spot something.
Never touched anything related to AE
Remember that this is my homemade delco'd 5.0lt red motor with original 4br manifold running 12P with ostrich 2
cheers

run 1 start.xdl

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run 2.xdl

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[Holden202T]

if nothings changed and it didn't have the flat spot before makes me think theres a issue with fuel pressure reg or the pump maybe ?

[VL400]

Or injectors blocked up from a lack of use.

[monaro308]

I'll check them on the weekend and see what may show up.

[hot308vb]

what about "VE learn" leaning the mixtures out??? this same thing happened to my vs clubby a few times so i eventually turned it off. you can tell by unusual spikes in the VE 20-100kpa volumetric efficiency map

[monaro308]

I had a bit of a play on sunday,i disconnected each injector one by one and rpm and exhaust note dropped evenly.
I sprayed brake cleaner around the inlet areas and found a leak at #4 injector lower o ring as the injector angle doesn't look to be seating 100% inline.
The more I sprayed it the better the rough/rich miss became,to the point there was no more "leak" as if the seal swelled from the brake cleaner.
I took the car for a spin and it felt a little better but not 100% although I noticed my wideband showing leaner readouts upto around 2000ish rpms.
Took it out again yesterday and Its back to what it was although no leak at the injector anymore.
I did a fuel pressure test and @idle it showed 260kpa and 320 with the reg vac line disconnected.
260 sounds a little low for me but i'll check the VN specs for a guide.
The fuel did smell stale even though I put in about 30 litres a week ago.
Might have to pull the tank off and drain/clean and check if there is any crud in the tank.

I read conflicting versions that you should run the pump when running on lpg to cool the injectors yet AC delco site for their fuel pumps say.....

"When you change the normal operation of a fuel system to accommodate a LPG / Petrol (dual fuel) vehicle, you are
changing the normal operation of the EFI fuel pump. And if the pump is not turned off when running on LPG resulting
in the fuel being circulated through the fuel system, it will make the pump work harder causing a higher amperage
draw, resulting in a excessive build up of heat, and ultimately failure."

PS hot308 my VE learn is disabled

[Dylan]

Off top of my head, VN fuel pressure is 38 with vac and 43 without vac. In PSI sorry

[HQ355]

Simplest way would be to get rid of the LPG ? If you don't drive it much why bother with it ? I've taken my monaro off LPG now I don't drive it every day, just make sure you keep fresh fuel in it and should be ok

[monaro308]

Thanks Dylan
Those work out to 37.7 and 46 so that sounds ok

The car runs great on lpg and its handy to have it as a back-up if/when the efi side of things play up.
I have been driving it more to work and back as I easily do 750-1000kms a week

If I got rid of the lpg I have achieved nothing as the fault is on the efi/petrol side of things.
Might have to compare to the original 12p bin to see what changes I "may" have done and go from there