LPG injection, AFR goes pisrich on first cold start

[kikkegek]

hello guys,

I havent been around for a while, because I have been mostly on the MSEXTRA forum getting my Megasquirt system up and running:

This is the link to my tuning story so far:
https://www.msextra.com/forums/viewtopi ... 31&t=74475

I upload updates there whenever I have made progress.

Some info on my setup:
GMC C15 Suburban, see projectpage in my signature
engine: 454 Chevy Big Block low compression about 8:1
single fuel: only LPG injection
ECU: Megasquirt MS3X (see tune in attachments)
Reducer: Tomasetto AT13XP set at 150 kPa gas pressure (rail pressure - MAP)
Injectors: Valtek 30 BFC, 3 Ohm, drilled to 2.65mm (need to increase that, because I have 100% dutycycle at 4500 rpm)
Peak&Hold boards (4A/1A) from SECU-3.org
I have extra sensors for LPG connected in one integrated unit:
- gas pressure (mpxh6400a)
- gas temperature (10 kOhm NTC)
- external MAP sensor (mpxh6400a)
Ignition is:
FAST dual sync distributor for crank and cam signal
8x LS D585 coils at 3.5ms dwell


I have been chasing a weird cold start problem that started after I made a long trip of 2hours (long for my standards) to our holiday destination.
Car ran fine the whole trip. no problems.
Then after sitting for 5 days I tried to start it. started. ran fine for 10seconds and then it started going rich....psrich..AFR dropped below 10 and then it started misfiring and eventually stalled.
damnit...
It had been a cold night and it was close to freezing that morning.
I have cranked the car at lower temperatures and hev never had this problem before. So I figured must be a hardware problem. I have since then:
- replaced the reducer
- replaced the injectors (from GIAC to Valtek)
- repaced the single coil to 8 LS coils for better spark
- replaced the plug wires
- replaced the sparkplugs (it had #2 Delcos that were way too cold for this setup, now has the stock RT45TS)

and above 10C it seems fine.
But tried a cold start at 5C 2 days ago and again it went pisrich within 10-15s and allmost stalled. And it sounds like its misfiring. Runs really rough. like its working hard.

I now catch it by adjusting the WUE (warm up enrichtment) by hand. Usually Ill have to pull 15-30% fuel to keep the AFR between 13-15. Then when the engine gets to about 25-30C its gone and never returns untill the nex morning cold start after sitting a while.

Its driving me nuts, cause I cant seem to pinpoint what might be causing this.

So all ideas are welcome.

topic where I uploaded loads of log files and tunes about the rich start problem:
https://www.msextra.com/forums/viewtopi ... 49#p570549

[storm]

Without looking at your logs, I haven't got an MSMLV installation ATM, I'd suggest you permanently change your WUE at temps you have the issue at. I'd also check and make sure you haven't got VE Analyse live working during warm up. I'll try to take a look at your logs over the weekend.

[kikkegek]

Without looking at your logs, I haven't got an MSMLV installation ATM, I'd suggest you permanently change your WUE at temps you have the issue at. I'd also check and make sure you haven't got VE Analyse live working during warm up. I'll try to take a look at your logs over the weekend.

Hi and thanks Storm:
- I cant use WUE for that, cause it only seems to happen when LPG temp and/or coolant temp is below 10C. And when its say 5C I need to pull about 30% fuel untill it reaches about 30C coolant temp. But when my coioland and LPG are both 10C or higher on the first cold start it dont ened to pull fuel from 10-30C coolant. see the problem..Something Im considering, is enabeling the wideband control earlier. Now I waite untill the engine is 30C and then enable wideband control. but I could see if enableing it immediately after starting would help catching this odd behavior and keep the engine running

- I have VE analyse on a conditional setting where it will only do its magic when the coolant is above 70C and LPG gas temperature is between 40 and 55C.

Im curious though if you can find any clues in my tune or log files. would really appreciate it if youd take a look.

[storm]

Interesting logs. do you have a copy of your tune file for each of the logs you have listed in that thread?
I am thinking along the same theory as the person who mad the next post in your thread. I think you have clashing settings or maybe even a problem with the coolant flow to your regulator and associated sensor.

[kikkegek]

its always the same tune. The only thing Ill do it try and catch the rich mixture using WUE numbers manually.

I cant upload it here. So I added it to my latest post on the MSEXTRA topic I shared in the intital post.

[storm]

Ok got it, will look at it and see if I notice anything.

Are you using WUE Analyse?

[kikkegek]

Ok got it, will look at it and see if I notice anything.

Are you using WUE Analyse?

No I heard it sucks. Never used it

[storm]

Ok got it, will look at it and see if I notice anything.

Are you using WUE Analyse?

No I heard it sucks. Never used it

Create a backup of everything you currently have so you can revert if required and then give WUE Analyse a go. I've just got home from work and won't get a chance to look at your bin for a few hours.

[kikkegek]

Ok got it, will look at it and see if I notice anything.

Are you using WUE Analyse?

No I heard it sucks. Never used it

Create a backup of everything you currently have so you can revert if required and then give WUE Analyse a go. I've just got home from work and won't get a chance to look at your bin for a few hours.

I'd rather not. Everything is based on gasoline and LPG is such a weird different fuel. I havent heard anything good about it for LPG. You?

[storm]

ok it's up to you. I've heard it is useful and even though it was initially designed for liquid fuels if the settings are correct it should work for gaseous fuels as well.

I've just spent the last hour looking at your msq file. Here's some things I've noticed which you may want to look at and/or explain why you have them set the way you do.
1. Your barometric correction setting is set to 100% everywhere. Cold air has a lower barometric pressure than warm/hot air. Barometric pressure has an effect on fuel requirements.
2. Fuel pump and pressure control, how did you come to the pressure settings you have listed here? You have your sensor inputs listed but if the pressures are incorrect this may lead to instability issues.
3. Temperature adjustment primary fuel, how dd you come to the settings you have here? We know LPG starts to boil at -40 but what pressure is it at at each temp and how much more or less fuel do you need at each temp/pressure?
4. Generic sensor inputs. You've got your extra LPG specific sensors listed which is excellent but, again, how did you come to the settings you have listed? Is the pressure of the LPG at the injectors equivalent to a generic MAP sensor?
5. Put your AFR and VE tables up side by side and take a look at them in table view and then in 3D view. The AFR table is relatively smooth but the VE table isn't. This says to me there is something going wrong somewhere, especially if you are using Autotune for the regular VE table. If you haven't done it already I would Autotune my VE table from idle through to about 3000 rpm just free revving with no load. Get as much done as low in the kpa scale (e.g. 25-50 kpa) as you can. This will give you your base settings for regular idle through to fast idle and cruise rpm. Do you have a dash mounted throttle adjuster (I do in my Toyota Troopcarrier and its great for fine adjustment of throttle opening). Note the RPM and kpa for each so when you are happy with them you can work outward from those points adding or deducting fuel, based on temp corrections and barometric corrections, when you adjust cold start. Remember we need to know the affect of temp on gas pressure as well as barometric pressure so we can adjust the cold start fuelling accordingly.

My gut feeling is there is a slight issue with some settings that are working against you at low temperatures. I'd be inclined to start with the sensor settings making sure they are correct. I'd then move onto the fuel pressure and fuel temperature settings and then barometric correction settings. Then do the no load free revving autotune from idle to 3000 rpm and work my way from there. Any questions just ask and well see what we can work out.

[kikkegek]

thank you for your time. Here's my reply to your fedback point by pint.

ok it's up to you. I've heard it is useful and even though it was initially designed for liquid fuels if the settings are correct it should work for gaseous fuels as well.

I've just spent the last hour looking at your msq file. Here's some things I've noticed which you may want to look at and/or explain why you have them set the way you do.
1. Your barometric correction setting is set to 100% everywhere. Cold air has a lower barometric pressure than warm/hot air. Barometric pressure has an effect on fuel requirements.

I have not set any barometric correction yet.

2. Fuel pump and pressure control, how did you come to the pressure settings you have listed here? You have your sensor inputs listed but if the pressures are incorrect this may lead to instability issues.

I got the baseline from a buddy in schotland. He calculated the values. I zeroed out the middle to ease the correction a little but ouside that middle part is works really well when rail pressure varies.

3. Temperature adjustment primary fuel, how dd you come to the settings you have here? We know LPG starts to boil at -40 but what pressure is it at at each temp and how much more or less fuel do you need at each temp/pressure?

2 friends that have been driving for a while on single fuel found them by hand. You don change the fuel table (hat was established at operating temperature) and then just change the temp correction as the engine and thus lpg temperature
warms up to keep a steady AFR. at cruise and idle I have allmost zero wideband correction, because these are set pretty well. And my LPG temp goes from 5 tot sometimes 65C and during highway driving it will cool down to usually 40C.

4. Generic sensor inputs. You've got your extra LPG specific sensors listed which is excellent but, again, how did you come to the settings you have listed? Is the pressure of the LPG at the injectors equivalent to a generic MAP sensor?

Bench tested them before isntalling on the car and they are spot on.

5. Put your AFR and VE tables up side by side and take a look at them in table view and then in 3D view. The AFR table is relatively smooth but the VE table isn't. This says to me there is something going wrong somewhere, especially if you are using Autotune for the regular VE table. If you haven't done it already I would Autotune my VE table from idle through to about 3000 rpm just free revving with no load. Get as much done as low in the kpa scale (e.g. 25-50 kpa) as you can. This will give you your base settings for regular idle through to fast idle and cruise rpm. Do you have a dash mounted throttle adjuster (I do in my Toyota Troopcarrier and its great for fine adjustment of throttle opening). Note the RPM and kpa for each so when you are happy with them you can work outward from those points adding or deducting fuel, based on temp corrections and barometric corrections, when you adjust cold start. Remember we need to know the affect of temp on gas pressure as well as barometric pressure so we can adjust the cold start fuelling accordingly.

I have VE analyse always on when I have the laptop with me. I only let it adjust fuel levels when coolant is over 70C and when LPG temperature is between 40-55C. Otherwise there is too much fuel temp correction and no use to adjust fuel levels.

My gut feeling is there is a slight issue with some settings that are working against you at low temperatures. I'd be inclined to start with the sensor settings making sure they are correct. I'd then move onto the fuel pressure and fuel temperature settings and then barometric correction settings. Then do the no load free revving autotune from idle to 3000 rpm and work my way from there. Any questions just ask and well see what we can work out.

I made my basic tune exactly like that:
1. all corrections OFF, no wideband, except for fuel temp. You can not warm up an LPG injection engine without some fuel temp correction as you can see from my log files.
2. start car, keep it running and get a base tune with in the lower values using VE analyse.
3. Then start dialing in the correction:
a. fuel temp
b. WUE
c. wideband

The thing I can get my head around is that when it was -5C it warmed up just fine to operating temp not going rich or doing anything funny.
I only currently have it when LPG temp is around 5-10C and not always as bad.
When lpg temp is over 10C it seems to be gone

[storm]

Sounds good, I'm just trying to figure out how you got to the point you are at now.

It seems to me there are 2 possibilities causing this issue. 1 is mechanical the other is a setting. You may be getting, and I think this is highly unlikely, highly condensed fuel coming through at start up/warm up. If this is the case I'd be trying a booster pump on the coolant line that feeds the regulator and have it operating as soon as the key is switched on/run. This will give priority to the regulator for coolant flow ensuring that during cranking the coolant is flowing through the regulator and all liquid LPG is regulated equally.

Having said that I am still leaning towards a setting in your tune. The reason why I am leaning towards this is because you have said it only occurs at certain temps. A 5 degree difference isn't all that much and having seen the logs I can see the change in AFRs is dramatic after you get past the extremely rich condition.