Misfiring at low rpms when running on LPG.

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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Fri Nov 23, 2012 6:36 am

Polini? Very Happy I think no, Polini is a make of cylinders and power parts for moped and motorcycles.

My LPG kit is made by Landi srl, it is a LSI model, similar to the Landi Renzo Omegas, but with different injectors (mine are Matrix, the Omegas have MED injectors).

There are other makes, in UK from the photo I seen, there are ots of Prins systems.

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Re: Misfiring at low rpms when running on LPG.

Post by elfin girl on Fri Nov 23, 2012 6:29 pm

Mines prins don't know if its factory fitted or after market tho, was all working fine till I noticed the leak now the switch is disconnected since I had the dash off
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Re: Misfiring at low rpms when running on LPG.

Post by PFM on Fri Nov 23, 2012 6:57 pm

IIRC, a dealer told me that the conversions were carried out in (or near) Southampton after the vehicles arrived in the UK - these were the official 'factory' versions for us, and qualified for some discount or incentive.

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Re: Misfiring at low rpms when running on LPG.

Post by HighlyJetted on Fri Nov 23, 2012 7:58 pm

Prins! That's the one. The bodged on aftermarket "factory" conversion Smile
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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Sat Nov 24, 2012 4:07 pm

daisydon wrote:Mines prins don't know if its factory fitted or after market tho, was all working fine till I noticed the leak now the switch is disconnected since I had the dash off

Your is a 1.0 or a 1.3?

Is an injected or it has the gas/air mixer?

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Re: Misfiring at low rpms when running on LPG.

Post by HighlyJetted on Sat Nov 24, 2012 7:17 pm

Its the same as mine from the pictures she's shown me, a prins diahatsu dealer bought as new one. They have a gas/air mixer in the air inlet before the throttle body. Crude but seems to work ok. It's a 1.3 petrol one. I think all the dealer bought LPG hijets were the 1.3 model ones - but I could be wrong. All my dealers sales brochures only offer the 1.3 lpg one.


Last edited by HighlyJetted on Sat Nov 24, 2012 9:51 pm; edited 1 time in total
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Re: Misfiring at low rpms when running on LPG.

Post by elfin girl on Sat Nov 24, 2012 8:00 pm

yep, 1.3 petrol with the lpg added
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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Sun Nov 25, 2012 10:11 am

I don't like the system with mixer because the A/F ratio becomes often inaccurate during the different driving conditions...
Prins have the cut-off?
I think it is good for engines pre euro2, but from Euro 2 the anti pollution system needs a precise dosed injection.
Furthermore engines with the mixer systems have a higher fuel consumption and generally a higher power loss.
That is wht I bought an injected system...If I had higher fuel consumption and less power than now, mine probably runs backwards Razz

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Re: Misfiring at low rpms when running on LPG.

Post by elfin girl on Sun Nov 25, 2012 4:08 pm

Can't say I'd noticed Difference in power between petrol and LPG but then it doesn't go that fast anyway!
I have noticed it drives much smoother and quiter on LPG, gear changing is much smoother on LPG too, no idea why ????
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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Sun Nov 25, 2012 4:34 pm

I don't have idea for the gear changing, probably it is a placebo effect because of the smoother running of the engine.
Engine runs smoother because LPG burns slowly than gasoline.

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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Fri Dec 21, 2012 10:15 am

Yesterday I done a full check up.
I changed engine oil and oil and air filters, and spark plugs, claimeda as LPG spark plugs...Beru UXF79.

Also I added a "ceramic" additive that I used some years ago on my first car with good results.

I must drive for at least 20km to mix the additive with engine oil, then I started to a 25-30km trip in my zone.

With that spark plugs engine works badly on LPG, i have severe misfiring under 2500rpm and some misfiring up to 3000rpm.

Now I re-installed the old NGK.

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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Sun Jan 20, 2013 12:16 pm

Last week I tried to re-gap the Beru spark plugs at 0.7mm.
Engine works very bad, so I tried to put on it the Bosch one that I tried in last months (before the ECU reset and installation of the AEB emulator), I set the gap at 0.6mm...the engine works perfectly, but it seems to be lightly "slower" during acceleration.

I think it is only an impression.

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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Wed Feb 13, 2013 1:14 pm

In last weeks I had some problems with it.

It seems we have a bad LPG in fuel stations last time, because not only me, but even my parents and some friends noticed some irregularities driving on LPG.


My problem was that during deceleration, the LPG ECU shut off the LPG valve on the tank, but accelerating engine re-starts working on LPG.

Then, I go to the LPG installer, we take a look for errors in the LPG ECU and we found that there was too high pressure after the pressure reductor in some circumstances.
Then he reset the errors, and tried to put on the ECU a new map.
The new map fails, then next day I return to him and he put on the ecu the old program.

Then, the engine restarts to work badly at low RPMS...and every day it is worse!

Initially, last year, he suggest me to check and change the spark plug wires.

Today I do the check with my tester, and I found that the 1st cylinder wire was broken.
Then, I call to piaggio to know how much they want for the wires, and they want 100€...

I can't find one make that do the HT cables for hijet/porter, then I tried to find some adaptable one from my spare part shop.

I found some 8mm silicone cables that fit on it, for 20€, and I put it on.
And I had about no changes...
I checked the spark plug, all OK.

Then I decided to run for some kmeters, to try to reset carburation with new cables, and it seems to work better...but not at the same low rpm.

The only one cable I don't check is the one between coil and distributor...
I must check also this one.

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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Fri Feb 15, 2013 7:23 pm

Yesterday I went to the LPG installer to ask him what to do to correct the problems.

He simply put off the LPG filter (I have a decantation filter like THIS), cleaned it and filled with Motul brake cleaner... Very Happy

Turned on the engine on petrol, then passing to LPG for a second, engine choked and then passing to petrol, and so forth until the engine runs on LPG, then he gave it some acceleration, and the engine is running perfectly... Very Happy

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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Mon Apr 08, 2013 7:21 pm

In last month problem reappears.
I'm angry, because engine starts to run badly even at constant speed...
Then we tried to check the LPG map, and we find there are some wrong "correctors" (?i don't know their name in english, we have a chart on the PC that shows the parameters of the correction of the A/F ratio compared to gasoline map, in its fields there are a number, a percentage of modification of the A/F between LPG and gasoline, called "correttore" in italian).
Then we eliminated the "gasoline contribution" (contributo benzina in italian, at high loads the ECU sprays some gasoline with LPG to reach the A/F ratio and to cool the exhaust gases) and activated the auto adaptivity.
Then engine runs a lot better.

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Re: Misfiring at low rpms when running on LPG.

Post by HighlyJetted on Mon Apr 08, 2013 8:27 pm

El_Ventu wrote:In last month problem reappears.
I'm angry, because engine starts to run badly even at constant speed...
Then we tried to check the LPG map, and we find there are some wrong "correctors" (?i don't know their name in english, we have a chart on the PC that shows the parameters of the correction of the A/F ratio compared to gasoline map, in its fields there are a number, a percentage of modification of the A/F between LPG and gasoline, called "correttore" in italian).
Then we eliminated the "gasoline contribution" (contributo benzina in italian, at high loads the ECU sprays some gasoline with LPG to reach the A/F ratio and to cool the exhaust gases) and activated the auto adaptivity.
Then engine runs a lot better.

I think I understand exactly what you have done, your description is great.

It sounds like quite a comprehensive LPG management system you have on your hijet from the options you write about.

Hopefully the "auto adaptivity" or as I'd call it "closed loop" routines will tune your LPG map to run even better than ever, using your lambda sensor to guide the mapping of LPG.

The "gasoline contribution" method seems a bit pointless, it should be able to run 100% on LPG really.

I wish you the very best of luck with getting rid of this misfire. Our Prins LPG systems are very crude but work great.
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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Mon Apr 08, 2013 11:13 pm

HighlyJetted wrote:
El_Ventu wrote:In last month problem reappears.
I'm angry, because engine starts to run badly even at constant speed...
Then we tried to check the LPG map, and we find there are some wrong "correctors" (?i don't know their name in english, we have a chart on the PC that shows the parameters of the correction of the A/F ratio compared to gasoline map, in its fields there are a number, a percentage of modification of the A/F between LPG and gasoline, called "correttore" in italian).
Then we eliminated the "gasoline contribution" (contributo benzina in italian, at high loads the ECU sprays some gasoline with LPG to reach the A/F ratio and to cool the exhaust gases) and activated the auto adaptivity.
Then engine runs a lot better.

I think I understand exactly what you have done, your description is great.

It sounds like quite a comprehensive LPG management system you have on your hijet from the options you write about.

Hopefully the "auto adaptivity" or as I'd call it "closed loop" routines will tune your LPG map to run even better than ever, using your lambda sensor to guide the mapping of LPG.

The "gasoline contribution" method seems a bit pointless, it should be able to run 100% on LPG really.

I wish you the very best of luck with getting rid of this misfire. Our Prins LPG systems are very crude but work great.
The Landi (a common AEB control if I'm right) ECU for injected systems is so complex.
It allows to run the engine with the lowest fuel consumption, but is difficult to tune.
For some recent cars they send to the installer a pre bench-tuned ECU, but for the Hijet they haven't one...probabily because Hijets runs fine on the single-point systems, and they're used primarily for working purposes.

The "gasoline contribution" helps to save the exhaust valves from seat recession, but probabily our old injectors aren't too fast, and they sprays too much fuel, then I have the problem.
It's an useful possibility in my opinion, on our engines...

I must check the valve play soon to see if there are differencies between using it with the gasoline contribution or not...

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Re: Misfiring at low rpms when running on LPG.

Post by HighlyJetted on Mon Apr 08, 2013 11:31 pm

The hijet I have just replaced the head gasket on is an LPG vehicle,

And on inspection of the valves they were in fantastic condition. They have just been vacuum tested and gave very good consistent readings.

As for seat wear, the valve lash before adjustment was typical for a 80k mile petrol vehicle.

I can only think the valve seats and valves are of good quality material.

Recently I have been working on an Opel ecotec engine, and from speaking to Opel fanatics they tell me they are prone to valve seat failure - and this on petrol. I wonder how many owners and garages blame LPG for Opel valve damage which was just a material issue.


The Denso injector type found in our Hijets are still used in production cars recently manufactured. I would be most likely blame the setup/tuning of the Landi LPG ecu. Maybe the injector specification has not been correctly defined in the Landi ECU.

So on your setup, do you have an extra set of injectors? How is the LPG injected into the engine exactly?
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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Tue Apr 09, 2013 7:49 pm

HighlyJetted wrote:The hijet I have just replaced the head gasket on is an LPG vehicle,

And on inspection of the valves they were in fantastic condition. They have just been vacuum tested and gave very good consistent readings.

As for seat wear, the valve lash before adjustment was typical for a 80k mile petrol vehicle.

I can only think the valve seats and valves are of good quality material.

Recently I have been working on an Opel ecotec engine, and from speaking to Opel fanatics they tell me they are prone to valve seat failure - and this on petrol. I wonder how many owners and garages blame LPG for Opel valve damage which was just a material issue.


The Denso injector type found in our Hijets are still used in production cars recently manufactured. I would be most likely blame the setup/tuning of the Landi LPG ecu. Maybe the injector specification has not been correctly defined in the Landi ECU.

So on your setup, do you have an extra set of injectors? How is the LPG injected into the engine exactly?
I'm happy if our valve seats are hard and good for LPG operation, teoretically it haven't problems (there are a lot of 1.0 and 1.3 engines fitted with LPG systems, and searching on the web I never heard of problems).

Ecotec are known for problems,I think because of the huge amounts of EGR on these engines, and then for slower combustion (with less NOx) and higher exhaust temperatures...and probabily because of seats materials.

I re-installed windows on my old girlfriend's PC oday, in next days my installer give me the ECU software and an old cable to allow me to try to fine-tune my system... Smile

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Re: Misfiring at low rpms when running on LPG.

Post by HighlyJetted on Tue Apr 09, 2013 7:51 pm

El_Ventu wrote:I re-installed windows on my old girlfriend's PC today, in next days my installer give me the ECU software and an old cable to allow me to try to fine-tune my system... Smile

cheers That's awesome, get playing
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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Tue Apr 09, 2013 8:21 pm

Very Happy
I'm curious to see what I can do with it...

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Re: Misfiring at low rpms when running on LPG.

Post by HighlyJetted on Tue Apr 09, 2013 8:32 pm

Will it let you map for positive pressure situations - e.g. on boost?! Wink
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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Tue Apr 09, 2013 9:50 pm

I don't know, maybe yes, because the ECU has his own MAP... Very Happy

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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Tue Apr 09, 2013 9:51 pm

I downloaded the english manual for setting the LPG ECU, you can find it on emule, or I can send it to you if you give me your E-Mail.

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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Sat Apr 20, 2013 3:37 pm

Yesterday I started playing with the LPG ECU.
I corrected some points on the map, to see where you have the problem you simply watch where the indicator is.

On the X axis here are the rpm, on the Y the injection time difference between the base (gasoline time) and the LPG time.

This is the installer map.


Then, starting from low rpm giving some throttle(40-100%), I had misfire between 1000and 2000rpm.

The indicator (the red ball, that becomes blue running on LPG) goes between 4.50 and 12ms in the 1000-1500 and 1500-2000rpm interval,when I had misfiring.

It seems to be too rich at my ear, and i'm not wrong.
Then I corrected the map, to reduce LPG injection time.



No more misfiring... Very Happy

Then, what's the zone of the map where I had irregularity at constant speed?

Running between 60 and 85km/h (my normal speed) the indicator stays between 2000 and 4500rpm and 6 to 10ms.
Then I tried to give more LPG, after a million of trials, I have my corrected map!
This morning i connected the oxigen sensor to the LPG ECU (not required, because the ECU works basically on the gasoline map, also corrected by the lambda factor), and it seems it is damaged...
I read casual voltage even at constant speed on the PC.
I need to try it with a decent multimeter, because my old Fluke was damaged, and now I have a cheap and slower one...it seems the sensor is working with the multimeter, but I think the PC reading is more precise... Very Happy

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Re: Misfiring at low rpms when running on LPG.

Post by HighlyJetted on Wed May 22, 2013 5:46 pm

I must of missed this post a while back.

I think this is great that you can alter the mapping of your LPG ecu, with time and playing you should be able to get it really good.

If you do not have a lambda sensor connected or working - the first thing I would do is get it replaced and connected. Having the feedback from the lambda sensor will really help you meet your Air/Fuel ratio targets.

I have experimented with lambda sensors alot over the years - make sure you buy a good one like a Denso, the cheap ones are very poor and do not last very long and give poor readings. I also not very keen on Bosch lambda sensors.
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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Wed May 22, 2013 6:53 pm

After the first trials, I connected and changed the old lambda sensor with an NTK one.
Then I ran the "auto mapping" utility on the ECU program.

The new map is a lot leaner than the old one, probabily because of the corrected gasoline map by the new lambda.

At now I solved about all the problems, engine runs good and EGT was lower than before of about 40°C.

The misfiring problem is so reduced, but dont'disappear.
Randomly it have misfiring at low rpm, but it seems a thing correlated to the engine temperature.
I want to fine tune the map, because there are some "correctors", not only correlated to the gasoline injection time, but even to water and LPG temperature.

I also solved a problem in the connection between intake manifold and LPG evaporator, the tube was cracked on the evaporator conection and evaporator pressure don't follow correctly the intake manifold pressure, and also in the intake enters some "false" air.

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Re: Misfiring at low rpms when running on LPG.

Post by HighlyJetted on Wed May 22, 2013 7:05 pm

Does the LPG ecu use the original Daihatsu MAP and TPS sensors?

Are they calibrated correctly in the LPG ecu?
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Re: Misfiring at low rpms when running on LPG.

Post by El_Ventu on Wed May 22, 2013 7:21 pm

No, LPG ecu use his own MAP, and it dont require TPS sensor, I think because the basical data for LPG was the petrol injection timing.

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Re: Misfiring at low rpms when running on LPG.

Post by HighlyJetted on Wed May 22, 2013 9:07 pm

Being an odd guy I have just read into you system with an english manual I found here:- http://plimont.com/softwareLSIOne.pdf

Just an idea, but your low RPM misfiring could be cause maybe by these bits - "Tip in adjustment" or "Injector Sequence"





The ecu appears to auto scan for the injector sequence, but the manual says some stuff about advancing or retarding the sequence. At high rpms, the sequence timing has less effect, where at low engine speeds it can cause issues.

As for tip in, the reason most ECU's have both a TPS and map, is because MAP reading go unstable during tip in. Your LPG ecu has the "Tip in" modifiers to help this situation.
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