Hesitation on moving off

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Zaphod
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Hesitation on moving off

#1 Post by Zaphod » Tue Apr 30, 2019 11:08 am

I have just fitted my old OMVL Dream XXI system to my 2003 CLK320, and run the calibration software and all seems well, except for one thing, there is a very slight hesitation/delay to moving off, it's not the end of the world, but it is a (very) minor irritation, any ideas how to fix it?
My system consists of , OMVL Dream XXIN with OMVL injectors and a Magic II vaporizer (the last bit is brand new)

Brian_H
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Re: Hesitation on moving off

#2 Post by Brian_H » Tue Apr 30, 2019 4:21 pm

I would guess the first question that will be asked is where you have put the manifold nozzles, and how long are the pipe runs from the injectors to them?

LPGC
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Re: Hesitation on moving off

#3 Post by LPGC » Tue Apr 30, 2019 9:56 pm

As Bri said.

Plus you didn't mention what car the LPG system was installed on before, you may need different injector nozzles and/or different working pressure to the last car.

Or if you made a mistake with wiring / connecting correct plugs to respective LPG injectors you may have it injecting LPG to 2 or more cylinders at the wrong time.

You can't really just rely on autocal, you've also got to do some manual tuning.

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Zaphod
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Re: Hesitation on moving off

#4 Post by Zaphod » Tue May 07, 2019 2:00 pm

Hi, the system was taken off my old CLK320 (W208) the new CLK is a W209 both with the M112 engine. The original Dream XXI vaporizer lost the wired to the temp sensor when I took it off, so the Magic took its place
The inlet manifold was also moved from the old car to the new one, and the nozzles are as close to the end of the tips of the petrol injectors as I could get them, the end of each being within 1 cm of the injector tip itself, off to one side, they are oriented parallel to the center line of the engine. The pipe runs are longer than I would like due to there being very little space for anything! the Injectors themselves are mounted on the outer upper face of the air cleaner housing, about 12" each.

However the hesitation has gone, I found one of the PCV pipes from the throttle body had cracked where it goes into the cam cover. With that replaced it's very nearly perfect.. with one irritating intermittent fault.

When started from very cold, on switchover it misfires a bit and the CEL appears. It does not do this if cold and the ambient temp is warmer. The codes are P0134, P0154, P0300, P0306 and P0305. My feeling is that the changeover temp may be low, as its only done this on cold mornings. On this car the Vaporizer is in series with the heater matrix as it's a constant flow heater, on the previous car it was in parallel. I seem to be getting 330 miles to 65litres of gas with no performance loss that I can tell

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Re: Hesitation on moving off

#5 Post by LPGC » Thu May 09, 2019 9:49 pm

Did you just fit the MJ reducer or fit it, adjust pressure and check calibration?
Codes refer to pre and post cat lambda probe issues (readings) on bank 1, multiple cylinder misfires and misfires on cylinders 5 and 6. So most of these codes point to bank1 fuelling except for the odd misfire codes... I think if you repeated the test you'd probably get different errors codes but all would point to incorrect fuelling particularly when the engine is relatively cool/warming up.
MJ reducer temp sensors respond differently (for temperature) to the OMVL temp sensor that you removed and AEB ECU's (including your OMVL Dream ECU) by default compensate fuelling un-intuitively for reducer temperature besides the intuitive gas vapour temperature compensation... So it only takes a different reducer temp reading to effect fuelling compared to when you had the old reducer fitted. But also if you haven't adjusted reducer pressure to same as the old Dream reducer pressure this could effect fuelling too. The 2 aspects combined could really mess up fuelling during warm up.

Advise checking readings in software and adjusting calibration if necessary.

Also do you know what spec the lambda sensors are on both the W208 and W209? Mercs with the unusual spec 0.8v>1.6v lambda probes tend to steer mixture very slowly at idle especially during the warm up stage, this will have been something Merc thought up to keep a steady engine note (prevent surging etc) to give the impression of smoothness but it doesn't help make LPG calibration for these conditions easy because slightly wrong calibration can lead to poor fuelling and misfires etc.
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Zaphod
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Re: Hesitation on moving off

#6 Post by Zaphod » Fri May 10, 2019 2:22 pm

OK, I will take a look, but IIRC when I ran the calibration software the gas pressure looked very similar to the old system and so left it alone, but ill take that with a pinch of salt.

However what does seem to work is keeping it on petrol till it's slightly warmer and then letting it switch to gas, then its fine. Is it possible that as you say the temp sensor characteristics have changed its trying to switch early? there's not a lot in it, I had found that if I stopped, cleared the codes and restarted it would then swap over just fine after you drove off

One other oddity I have noticed the trip computer MPG readings have not changed, on the old car when on gas they went from slightly optimistic on petrol to ludicrously optimistic on gas.. (reading just over 30mpg avg on petrol to 34avg) but returning 340 miles to a tank. This has been a feature of most of my LPG converted cars with a trip computer, this one however it's unchanged (but slightly more optimistic when on gas as its still giving petrol figures)

Zaphod
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Re: Hesitation on moving off

#7 Post by Zaphod » Wed May 15, 2019 11:47 am

OK I may have this fixed..
There seems to have been air in the cooling system, as when I was looking at it I noticed the level was slightly down in the header tank, pretty sure it was full when I last looked at it after refilling when the vaporizer was plumbed in so maybe some has worked its way out.
Rectifying this seems to have eliminated the fault, I've been keeping an eye on the coolant level and it's not dropped since. However it has not escaped me that the mornings have been marginally warmer. The changeover has become very smooth

Reducer pressure is just above 1 bar which if I remember correctly was about the same as the old OMVL reducer was giving

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