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-   -   FAQ Faults & Tips for factory Volvo Bifuel LPG / CNG (

CNGBiFuel Apr 29th, 2018 20:51

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P80 pre 1999 have their ECU 4/74 as this piccy.
They also have a fault code system outside of ODB 24/97. Translated from German, this gets lumpy.

CNGBiFuel May 3rd, 2018 13:25

2 Attachment(s)
Doing this bit-by-bit, I was going to cover the wiring and which relays fire what, and the wiring diagrams, but as I said it's all in German, and it'll take me a while to copy and translate. I've tried English, not mentioning the war, then shouting louder. Then ever louder... in English. Hasn't worked so far.

I should detail the differences between LPG & CNG with respect to Necam.

Stepper motors do not change, however the distributor is 'Green' label in regard to CNG and 'Red' for LPG. The outer casting is identical. What changes is the cylinder barrel, see piccy. CNG has wider 'V' slots.You will see these 'V' slots when you look down the barrel.

CNG is on the left in the piccy, LPG in the middle and on the right. Shown with a stepper motor missing and a blanking-plate in its place, ignore the middle dizzy. It's a spare for use in stepper rebuilds only.

CNGBiFuel May 4th, 2018 11:28

2 Attachment(s)
Differences between LPG & CNG with respect to Necam.

After the high-pressure regulator these systems are much the same. It's only the minor ignition and burn characteristics of the two fuels that makes for minor cahnges. Save for ECU differnces to account for this, with the aforementioned exception, mechanically they are identical.

There is an earlier type of vaporiser. I've put the later vapouriser on an early car simply because I had it to hand. To further comfuse, early vapourisers in CNG have Red stickerage.

CNGBiFuel May 9th, 2018 23:32

1 Attachment(s)
Essentials: Put a Heatsink on your Stepper
Here's another essential trick. Those of you that have read my replies to threads know I got into Necam systems by accident. I have an electronics background, and when my system went lumpy, I started to look around for info. I found zilch. So I got the stuff onto my workbench.

Whilst I'll always kow-tow to 'classicswede' on this forum for his vastly greater knowledge over the wider sphere, my little kingdom has become these systems. Whereas most LPG/CNG pros just component swap, I get my hands dirty with the sparky bits.

Now, if you've been following the plot so far, you'll know the stepper-motors cook and once fried, give up the ghost. There's a Triac in there that is borderline for the job, and heat finishes this component. I'll say it again, you have got to move the dizzy & stepper assembly, else if you don't, it'll cook.

But, here's the thing, and with the aid of a digital IR Thermometer, I've only nailed this down in the last 18 months.

What the IR Thermometer told me, is, you still need to fit a heatsink...


CNGBiFuel Jun 19th, 2018 12:45

I've been away from this thread, got a bit of time a few more pointers...

A digression, whilst I remember... Another point about moving your Dizzy & Stepper
Vaporiser to distributor if I recall is 16mm hose.
Distributor to injectors x 5 is 8mm hose.

I covered before but in more detail... These hoses carry low pressure gas. Ahem, bits of orange BBQ hose will work for a short while. Then they will perish. Not intended for use in a hot oily engine bay environment. Use the correct rubbery hose, marked for LPG/CNG to E67 standards. Else, make your will out to me.

I can't remember why, but there's a good reason why you won't be using fuel hose either. I thinks its porous (at molecular level) to gas, but don't quote me. In short, hose is not hose. Anything will not do.

Propane & CNG eats radiator/heater/water hose, before you ask.

CNGBiFuel Jun 19th, 2018 13:13

4 Attachment(s)
How the Steppers Got its Heatsink
Oh best beloved your stepper needs a heatsink. We shall begin.

See the piccy. You are lucky. My background is electronics so I was aware small motor can sizes are to one industry standard. Our friends with Radio Control cars, boats, and aircraft have come to our rescue. Their DC motors have the same can-size as a Necam stepper motor. See? I said you were lucky.

Dirt cheap, you'd be a fool not to fit one. You want a 540.
But again, pulling from my background, I suggest you bring heatsink-paste to the party. Used on heatsinks in your laptop etc, heatsink paste gives a vastly improved surface-areas to the bond. The fan you hear on your laptop will be blowing over the heatsink. This heatsink will be fixed to the processor-chip using a paste. Also dirt-cheap, this paste can be used to glue the heatsink to your stepper. Electronics must be kept cool. Borrow this lesson from the electronics industry.

These heatsinks are almost always Chinese made, hence the colours of these things are definitely last season, but this is no concours-parade. I repeat, I would advise you follow what one of customers did, fit the heatsink, and get your old vacuum-cleaner hose force-cooling the stepper by letting it act as a scoop fitted somewhere in the grill. Hence a nice cool stepper.

Heatsink paste/grease
You'll find these pastes easily enough. See pix, you need the tiniest squirt. You'll do the whole job for under 10 (Euro15). Far cheaper than a cooked steppper.

CNGBiFuel Jun 19th, 2018 13:36

A word of Warning

Do NOT fit a heatsink if you do not intend to move your stepper. Failure to heed my advice and all the heatsink will do is help to cook the stepper. How so, you ask? Leaving your stepper in the heat source, my tests have shown the heatsink actually makes the situation worse! It cools where the air around it is cooler, yet heats where the air is hotter.

You want to move your stepper, but then I already said that.


CNGBiFuel Jun 20th, 2018 13:45

I'm adding bits to this as I find time. Please don't post until I'm complete.


CNGBiFuel Aug 3rd, 2018 22:58

The best method yet, to get to your Stepper?
3 Attachment(s)
Removing your Stepper. The best method yet?

Over the ripped knuckles school of stepper removal others say they use, there's this. I run a P80. Not owning a P2 means I have little chance to really look at the later cars.

On 2002 models removal of the fan is very simple. A few plugs, and two fixings at the top and the fan slides out. See the pics, I now pass this on... 'Tis far easier than the method given to me as best by many of you.

This should really be at the start of this thread. I would move it if I could. Sorry, I'm not the Modmin here.


CNGBiFuel Aug 4th, 2018 23:20

Software glitches

These cars are getting old. Sometimes you'll get poor earthing and software glitches. This will cause no-start conditions,. Leave your battery disconnected for at least 15 mins, and whilst you wait, run an extra wire to ground from your distributor.


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