Impco accel Hesitation, poor idle when warm VY Commodore

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wilsom4
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Impco accel Hesitation, poor idle when warm VY Commodore

Post by wilsom4 » Wed Jul 03, 2019 9:04 pm

Hi all,
Help needed with my Factory fitted dual fuel VY commodore.
Used to run beautifully, and suddently started this mess of symptons, the odd backfire, (backfire now stopped after all my mucking around, but all other symtops remain), and is now beyond my knowledge to T/Shoot what is in fact a fairly basic system.
Its got an impco E type regulator, impco 225 mixer with no adjustments, & has a vacumm FCV closed loop system, all factory installed.
I'm at my witts end after spending hours on T/Shooting & replacements parts, trying to fix following alot of "good advice" but no luck curing the problem.
I'm in NZ and we have next to no decent LPG shops around, certainly no-one with as much knowlege or interst in T/Shooting, so hence hoping you guys and gals can help.
Very poor info to be found anywhere on the internet about these factory fit impco systems, especially the electronic control of the FCV.
Parts currenty inspected or replaced as follows (in no particualr order);
Fully Cleaned & Rebuilt pressure regulator with new kit
New FCV vacumn valve
New vacummn pipes everywhere
New coil packs, plugs, leads (in case of electrical issue)
New MAF assembly (in case of backfire damage)
Mixer inspected, no diapghram damage visible, reassembled with no parts replaced (could it still be the mixer?)
Cooling sytem thoughouly checks (definatley not icing up, regualtor nice and hot, & no air bubles in lines)
Symptoms:
- Worse when warm
- Poor starting on LPG
- once warm cannot accelerate, hesitates badly or dies altogether, possible to limp along with little or no throttle if on the flat
- much worse under load,
- Rough idle
- Running very rich (o2 sensor >1000 mv)
- occasionally throwing a check engine R/H O2 sensor fault on LPG - no other fault codes
I suspect its the closed loop not working correctly, and not adjusting the vacumn to the regulator properly, hence no/little cutback of fuel. (I changed the FCV for this reason - no change)
As I understand it, the factory Vy only uses the R/H O2 sensor on LPG (OBD reader confirms both o2 sensors good on petrol, switch to LPG & left sensor says "unavailable") this O2 reading is then used to modulate the FCV to reduce or increase vacumn to the regualator to keep the O2 reading s correct, hence richening or leaning out the LPG supply
I know after market Impco systems have a "command electronic controller" or similar, which would have been my next item to replace, but I cannot find any bolt on controller anywhere on my car, or under the dash etc, and now suspect Holden have programed its controll into the factory PCM / ECU.
Does anyone know if this is true? or where I can find the controller on a factor VY?
Any ideas or suggestion welcome!
Thansk in advance

storm
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Re: Impco accel Hesitation, poor idle when warm VY Commodore

Post by storm » Thu Jul 04, 2019 6:12 am

A couple of things strike me with this.
1. Your O2 reading is not right full rich should be approx 900 not >1000.
2. Not wanting to idle and getting worse when warm are an indication of a vacuum leak. Backfires tend to blow holes (small and large alike) in the intake tubing. If you have replaced the MAF due to concern about backfire damage you should probably change the intake pipe from the TB right through to the MAF. I had this exact same issue with my VS although it has GRA system on it. I now have stainless steel exhaust pipe with flexible turbo tube and hose clamps from the TB through to the air cleaner air box.
3. Further to the vacuum leak idea there are vacuum ports on the back of the manifold. When these things backfire they can, and sometimes do, blow the hoses off the manifold.
4. The O2 sensor fault code is common, Ecotec's are great engines but they were designed to run EFI not mixer/carb type LPG systems. LPG doesn't fill the manifold fully and some cylinders actually run lean. On my car this happens mostly about 1500-1800 RPM which equates to approx 60-80 KMH in 3rd and 4th (Automatic trans). In your case the PCM makes the mixture richer to compensate for the uneven distribution.
5. Check the vapour hose from the regulator/convertor to the mixer. Ecotecs aren't a smooth engine and these hoses sometimes split on or near the hose clamp due to vibration and movement.
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Steptoe
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Re: Impco accel Hesitation, poor idle when warm VY Commodore

Post by Steptoe » Thu Jul 04, 2019 5:16 pm

Had a similar issue on my Camaro yrs ago...
Chased my butt around everything..until found a very old post here from yrs ago by CH..

this sort of nailed it for me which was consistent after replacing / servicing everything else

Symptoms:
- Worse when warm
- Poor starting on LPG
- once warm cannot accelerate, hesitates badly or dies altogether, possible to limp along with little or no throttle if on the flat
- much worse under load,
- Rough idle
- Running very rich (o2 sensor >1000 mv)


Turned out to be a worn piston/ bore in the mixer...it only takes a couple thou of ". was slightly worn oval.
Replaced the mixer and all good for another near 100K miles.

Another issue I did have a few yrs before, similar...I had replaced the lpg hose between the regulator and mixer, a few yrs previously. Was marked and meant to be the correct grade hose for LPG....
The inside layer had deteriorated causing a bit to come adrift. When under loads, the flow would pull it down and cause a restriction..
This I also chased for ages, and only found by accident. I was just in the process of removing and stripping everything thing down in frustration .. it was my wife who happened to pick the hose up, and happened to stick her fingers up and found the loose flap inside..against the wall.

Personally I am pretty sure it is worn mixer. Mine had done around 150K/175K miles from a lowish milage 2nd hand yrs before.
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jono
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Re: Impco accel Hesitation, poor idle when warm VY Commodore

Post by jono » Tue Jul 09, 2019 9:49 am

For diagnostic purposes I would try a clean air diaphragm and temporarily disable the FCV stuff. This stuff forces the mixer to work in reverse to the way it was meant to. I am tinkering with a unit by Peel that allows mixer to work as it should but more on it later when I have sorted it's demons. Changes of operation regarding temperature. O2 sensors are service item and may need to be renewed but if on petrol runs sweet, should be good for gas but gas can be a little more sensitive. I hate FCV stuff

wilsom4
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Re: Impco accel Hesitation, poor idle when warm VY Commodore

Post by wilsom4 » Wed Jul 17, 2019 9:19 pm

Hi all
thanks for all your tips/suggestions.
I thought i solved it after pulling the mixer appart again to check for wear, but this time noticed a small crack in the mixer diaphram centre aluminium piece thingy that the mixer spring goes onto.
Changed the diaphram assy, expecting all to be well.
NOT.
definately runs much smoother now than before, but i still get the hesitation under load or acceleration.
I read somewhere about an adjustment on impco E type reg on the vacum filter thingy which can cause this, but cannot seem to find that post.
Anyone know what i'm referng to and how to test/adjust?

C3H8
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Re: Impco accel Hesitation, poor idle when warm VY Commodore

Post by C3H8 » Sun Jul 21, 2019 1:39 am

I'm pretty sure your referring to a check valve IMPCO designed back in the 90's. The tiny airbleed orifice in the fuel control fitting is too small to allow rapid movement of the secondary diaphragm and this caused a hesitation. IMPCO made a spring loaded check valve to allow control under most circumstances but during quick acceleration the check valve is supposed to open. If I am picturing the correct check valve there is a small allen screw on one end of it. All you have to do is use a volt meter on the Fuel control solenoid by attaching one lead to each wire and then turn the allen key CC until the solenoid duty cycle goes to 100% or about 14 volts. At this point the check valve is letting air into the regulator secondary unchecked. Now turn the allen screw clockwise until the duty cycle begins to drop and the voltage shows readings between 3 and 7 volts. The voltage will vary. Now rev the engine to about 2500 RPM and watch the volt meter. It should stay between the 3 to 7 volt area. Go test the vehicle and see if the hesitation is still there.

An alternate way is using the seat of your pants. Find a lonely stretch of road. Acelerate where the hesitation happens. Back out the allen screw one turn and repeat acel. Keep doin it until hesitation disappears.

jono
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Re: Impco accel Hesitation, poor idle when warm VY Commodore

Post by jono » Tue Jul 23, 2019 8:58 am

It sounds like the hesitation on take off is a lean fuel mixture. A tailpipe analyser can work that out. Maybe if you can get an O2 reader off front most oxygen sensor might also tell a story

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Steptoe
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Re: Impco accel Hesitation, poor idle when warm VY Commodore

Post by Steptoe » Tue Jul 23, 2019 6:05 pm

I have 02 sensors and An Innovate data monitor...which showed a very high momentary high 02 level.

I thought i solved it after pulling the mixer appart again to check for wear,

How did you "check" I missed any signs with a visual check. It only became apartment when physically measured. I rem at the time, was taken back at how such little wear effected such a hesitation.

The 90s set up C3H4 is mentioning .. is that the old lean burn EC1 (think was called), cover on the front of the E ?
I messed with mine for a long time.. once set up good, reliable , but every now and then would mess up.
Have to be very careful when adjusting one of the screws (under the brass cover screw) as it is only into a bit of soft board.. mess that that up and you will never get it right.
The long allen key adjustment on the side.. between good and not good is as fine as 1/8 to 1/16 of a turn..from memory mine was 8 or 11 turns out (??)

In the end remove/ swap out for std cover...IMPCO obsoleted that for good reason.
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wilsom4
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Re: Impco accel Hesitation, poor idle when warm VY Commodore

Post by wilsom4 » Tue Jul 23, 2019 6:52 pm

thanks Steptoe & C3H8
I never measured the Mixer, just visually inspected with no evidence of wear anywhere, do you have a link to any measurement to check?
When I found the cracked aluminium centre on the diaphram, I was sure that would have been the root cause, but although this cetainly helped the idle, still wont accelerate, basically I can idle it upto speed, and limp along, but it dies under anything but very fine acceleration, hence digging deeper to see what controls the power increase side of things.
I'm yet to get a chance to play with the allen key on the vent, i'm now supicious this may be blocked or failing, which could have cause d the initial backfire to damage my diaphram.
You mention a replacement cover on the E to modify this regulator, do you have any details what part number this might be to purcahase? and does this then remove the Feed back loop to the FCV, or does it still have a duel vacumm port?
Regards

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Steptoe
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Re: Impco accel Hesitation, poor idle when warm VY Commodore

Post by Steptoe » Tue Jul 23, 2019 7:21 pm

do you have a link to any measurement to check?

I mentioned before that C3H4 was very helpful in sorting this out.. and from memory the cover as well.

It is all documented in older posts here.. we could be talking 10 or 12 yrs back now.

From memory I simply changed/ swapped the EC1 cover with a std cover.
Edit: I may have had to change the colour of the spring???
I assume u have taken the cover off before?
If not.. after removing the screws, take your time.. real slow.. like really slow lifting the cover and diaphragm/ gasket without damage.. a little kero helps here.
When reassemble parts like this a thin smear of oil or light grease will prevent gaskets sticking in the future.
When you do check the lever height (and that has to be spot on) and make sure it is connected under the flap when re assemble.
Also a build up of wax crap inside can cause these sorts of problems... espec if the unit is mounted without the outlet pointing downwards... Cleans out with kero and turps.

Im saying a lot of "remember"
I sold the camaro (and all the other classic vintage cars) last yr, after near 40yrs daily driving over 300,000 miles and most on LPG.
I had not needed to do anything on the car for maybe the last 10 plus yrs... We sold up out land bank in the city, down sized to a small rural town, retired and spend a lot of time out in our boat fishing...
I may pop my head into these older forums once in a while, if using tools its to build a new on suite, and kitchenette, landscape in the new house. The closest I get to grease and oil or car now is maintenance on the outboard boat and trailer.

These forums have been around for a very long time, and some of the most experienced and knowledgeable around the world.
And it is all been logged in these forums
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