part throttle hesitation

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gazwad
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part throttle hesitation

#1 Post by gazwad » Sun Mar 10, 2019 5:30 pm

i have a 1996 honda stepwagon (b20b engine) fitted with lpg, it has a stag 4 qbox plus ecu but i'm not sure what brand the other components are. It runs perfectly on petrol and almost perfectly on lpg apart from a hesitation at around 2500 rpm on part throttle acceleration when it seems to almost cut out for a second or so, it is worse when cold. i have replaced plugs, lead, dizzy cap and arm as well as the lpg filter and tried some lpg injector cleaner as well. any ideas what could cause it? thanks

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Re: part throttle hesitation

#2 Post by LPGC » Sun Mar 10, 2019 9:09 pm

Plenty ideas!

It's important to get point of gas entry close to inlet ports on most installs but this is particularly important on these engines and even more so on the versions with VVT. On VVT versions I fit singular injectors almost directly onto directional manifold nozzles (pipe between manifold and injectors less than an inch) with the injectors sitting low down between the petrol fuel rail and cam cover. On none VVT versions I've done similar or have fitted straws and an injector rail. Most versions also need a lube distribution spider as incoming air from the throttle body goes way down before coming back up.

Or could be something simple like calibration, QBox seems to be aimed at done in a day installers, it's heavy on the self calibration features. Best to fit fast acting injectors on these motors, we don't know what injectors yours has but given the ECU is Stag I'd guess they're not fast acting. Still dare say I could get it sorted without having to fit new bits (except likely a lube spider if yours doesn't have one and you don't want the engine to suffer valve seat recession) and without having to move things around much.
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Re: part throttle hesitation

#3 Post by gazwad » Mon Mar 11, 2019 7:11 am

That's great information, thanks. I have fitted a valve saver kit although it is just plumbed straight in to the main plenum. It's the non-vvt version but the hoses from injectors to manifold are around 4-5 inches long so I will try shortening them to see if that improves it. I will try and identify the injectors if possible as well

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Re: part throttle hesitation

#4 Post by gazwad » Mon Mar 11, 2019 9:19 pm

i managed to reduce the length of the hose to around 2 - 2.5 inches, and it seems to improved it very slightly but it's still there. I don't think I can make the hose any shorter as there just isn't room to fit the injectors

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Re: part throttle hesitation

#5 Post by gazwad » Mon Mar 11, 2019 9:21 pm

the injectors are 'iniettore inj01' if that helps?

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Re: part throttle hesitation

#6 Post by gazwad » Tue Mar 12, 2019 8:29 am

After a little research it appears these are Egas injectors, does anyone know if they can be stripped and cleaned?
I think i might have an injector issue, I had to remove the inlet manifold a couple of weeks ago and noticed 3 of the lpg nozzles in the inlet trackts were clean and one was dull and slightly crusty, also whilst idling on LPG I put my hand on each of the injectors and could feel a solid ticking from 3 of them but the 4th (same one as the dull nozzle) was a much fainter ticking. could this be due to dirt building up or is it likely the injector is duff?

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Re: part throttle hesitation

#7 Post by Brian_H » Tue Mar 12, 2019 11:15 am

Probably won't be dirt unless there isn't a filter in the line to it (should be a cartridge of some sort). More likely its heavy ends - the greasy/oily bits dissolved in the gas that separate when the gas pressure is reduced. There should also be a second filter somewhere near the entry to the vapouriser - typically on the inlet solenoid, this is usually the one to catch any bits that aren't gas as its the first in line (bits of rust, dirt from filler etc) The second one only really comes in if bits start coming off the diaphragms in the vapouriser.

Cleaning would be a good start, though it might be worth swapping the coils about if they are removable (don't know with Egas) just to rule that out first. If you have any injector cleaner left (assuming this is something like the ic12 stuff) it might help to try and let it soak on that injector if posssible. (reposition the injector block temporally to let it sit on that one if you can, though stripping more likely to be effective if its possible, its not always possible or advisable with some injectors)

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Re: part throttle hesitation

#8 Post by gazwad » Wed Mar 13, 2019 10:34 am

If the injectors can't be stripped or cleaning doesn't fix them I will need to replace them but I can't seem to find these particular ones for sale anywhere. Do all injectors have the same flow rate etc - what replacements are recommended? I think individual injectors with a hose in and out (separate from the rail) as they are now would be best as space is tight, what brands/models are ok? cheers

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Re: part throttle hesitation

#9 Post by LPGC » Wed Mar 13, 2019 11:03 am

Whatever different injectors you fit you'll have to re-calibrate the system. You'd probably need to recalibrate it anyway even if you rebuild your injectors or fit new same model injectors.. particularly if certain supposed self tuning features have been left enabled in your Qbox ECU settings (continuous self tuning on an install with an issue such as failed lambda probe or broken LPG injector soon makes for very incorrect LPG calibration that will not go right again after sorting the issue).

I described (above) where I fit injectors on these engines, it's unlikely your injectors are fitted there because they'll be too large to fit there. MJFX single injectors would be a good bet for you, they'll fit wherever your current injectors are and could be moved to where I described if you wished.
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Re: part throttle hesitation

#10 Post by gazwad » Wed Mar 13, 2019 11:44 am

Thanks, I'll have a look at the calibration. I know the lambda isn't connected to the stag ecu, is this needed for calibration?

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Re: part throttle hesitation

#11 Post by LPGC » Wed Mar 13, 2019 2:52 pm

No you don't need to connect it to the LPG ECU, not even during the initial calibration stage... but if you can't connect to the car's OBD with a scan tool to see lambda readings then connecting to lambda can be useful if only because it allows you to confirm the mixture is correct when the petrol ECU runs open loop mode at high engine load (should be a bit rich under these conditions).

What I was getting at is that if certain aspects of an LPG system's self calibration facilities are left enabled, if there is then a problem with the closed loop functionality of the car and/or a problem with the LPG system, then the self calibration may completely mess up calibration. A broken lambda probe is an example of a problem with closed loop functionality of the car, so if an LPG system is calibrated perfectly but self calibration is left enabled and at some later point the lambda sensor breaks, even if the lambda probe is later fixed and the car runs properly on petrol again it may not run properly on LPG because the LPG calibration has been messed up by self calibration.
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Re: part throttle hesitation

#12 Post by gazwad » Wed Mar 13, 2019 3:43 pm

ah i see, I'll have a look to see if any of the self calibration has been left enabled etc. cheers

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Re: part throttle hesitation

#13 Post by gazwad » Fri Mar 15, 2019 7:18 pm

I stripped the injectors and they were spotless inside, i also managed to reduce the hose length from injector to to manifold to about 35mm. It seems to have improved slightly but the stutter is still there, i think the injectors are fine as the all seem to tap evenly and were in good condition internally. I think the next thing to look at is the calibration, i'm waiting for the cable to come to connect to the laptop then i will see what's what. I've not done anything with calibration before so will have a lot of questions!
Would it be worth replacing the coil? It seems fine on petrol but could it show up a problem on lpg?
also seem to have a problem with the lpg gauge, it reads full all the time, i have re-calibrated as per the instruction on the last fill up but it's not moved and the gauge on the tank has moved to near empty. if the wires to the sender are the wrong way around would this cause it to read full?

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Re: part throttle hesitation

#14 Post by Brian_H » Fri Mar 15, 2019 7:35 pm

Ignition problems are more noticable on LPG than petrol - Usually if your going to notice a problem on a system with a coil pack (as opposed to your seperate coil) it will be noticable at idle, and under accleration. Given yours idles ok, and appears to run ok other than the bit of the range you mention, I'd doubt much is wrong with the coil personally.

The sender does come in different types, wrong way round shouldn't matter as far as i Know, but if you have the wrong type of sensor selected its unlikely to work. Only way to check is with the software - you can also see what reading your getting from the sensor and adjust if its moving as the tank goes down. That said, they aren't the best of things and do go wrong as well. Easily replaced though as long as the screws will come out (won't let the gas out or anything by removing the gauge, its magnetic so you can move the gauge with a screwdriver on the back of the plastic to monitor if its working or not). We don't know if you have a single hole or 4 hole tank, nor which sender you have fitted, the most common is a 0-90ohm sensor, would be helpful to see what the software is set to, and if you can identify it (if its an AEB sensor they have it printed on the casing).

Also - a broken wire to the sensor will cause the reading to stay the same, though the settings will depend what the gauge shows in that case.

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Re: part throttle hesitation

#15 Post by gazwad » Fri Mar 15, 2019 7:40 pm

great thanks, i'll have a look at the software then when the lead arrives

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Re: part throttle hesitation

#16 Post by gazwad » Thu Mar 21, 2019 11:52 am

the lead arrived and i've connected it up for a look, I understand what most of it means but i'm not sure what things should be set at so below are some screenshots of ths software, I have played about with the petrol to gas switch over settings a bit and managed to reduce the stalling when switching over at idle. does any of the calibration look off?
Imagelpg1 by garrywadey, on Flickr
Imagelpg2 by garrywadey, on Flickr
Imagelpg3 by garrywadey, on Flickr
Imagelpg5runpetcold by garrywadey, on Flickr
Imagelpg6runlpgcold by garrywadey, on Flickr
Imagelpg7runlpgcold by garrywadey, on Flickr
Imagelpg8runlpgcold by garrywadey, on Flickr
Imagelpg9runlpgcold by garrywadey, on Flickr
Imagelpg10runlpgcold by garrywadey, on Flickr
Imagelpg11 by garrywadey, on Flickr
Imagelpg12 by garrywadey, on Flickr

gazwad
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Re: part throttle hesitation

#17 Post by gazwad » Thu Mar 21, 2019 12:16 pm

one thing i noticed is the source of rpm signal is set to petrol injectors, should this be set to ignition coil as i know this is wired in to the stag ecu

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Re: part throttle hesitation

#18 Post by Brian_H » Thu Mar 21, 2019 12:32 pm

If its detecting rpm correctly (value in software matches cars dashboard) I'd leave it how it is. I've known it to not work entirely how it should on the coil pickup causing system to switch off when on overrun.

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Re: part throttle hesitation

#19 Post by gazwad » Thu Mar 21, 2019 3:45 pm

ok, yes it seems to read the correct rpm so i'll leave it alone. and suggestions for thing to look at to try and fix the hesitation issue?

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Re: part throttle hesitation

#20 Post by Brian_H » Thu Mar 21, 2019 4:36 pm

Wait and see if Simon replies later on probably your best bet as a first option. Generally you'd monitor the fuel trims (via the normal car obd method) to see if the petrol ecu is adjusting the trims differently on petrol vs gas - if so you have a calibration issue of some sort (can sometimes be as simple as adjustment of the gas ecu by the software, or can be down to altering the reducer pressure or nozzle size when appropriate).

Do you actually have any way to access the obd side of the Honda? Might be a bit more difficult on a vehicle of that age and might be very limited what you can actually see, but if you can see the trims that would give an idea whats going on at that point where you have a problem. Don't know if your particular LPG ecu supports switching individual cylinders between fuels, but that can also allow you to prove if the fault is down to a problem with the a gas injector as well.

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