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Volvo V70 BiFuel CNG strange"Push/pulls"

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Old Jul 6th, 2021, 20:51   #1
Andrioman
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Default Volvo V70 BiFuel CNG strange"Push/pulls"

Greetings!
I own Volvo V70 2.4 BiFuel CNG 2006 automatic. I have it for almost 5 years now and overall I am extremely happy with the car!
However, I have a problem for some time and for 2 months now I have not been able to find out what is happening.
My car push/pulls(I'm not sure how to describe it) hard when I drive it out of town, especially after 80km/h, but the strange thing is that on the highway at speeds above 120km/h there are no problems. However, I don't think that the problem is related to a specific speed, because at a lower speed (for example 60km/h), but uphill it still does it. The problem only exists when I drive it on methane CNG! When I switch to petrol, it continues to do so, but after about 3-4 km of driving, the problem disappears and if I drive it only on petrol, it does not reappear at all, but if I switch it to methane again, it starts push/pulling again. It is interesting that in my city I drive it absolutely normally on methane, without troubles (but I do not exceed 60km/h).
The things I have done so far, but without any difference in the performance of the engine are:
1) Almost complete prevention of the evaporator and the Distributor (I already know it by heart, because over the years I have learned how to fix it myself). I have replaced the o-rings of the evaporator, as well as the membrane I ordered from Poland - complete repair kit ...
I also cleaned the Distributor (according to instructions from this forum) and re-soldered the solders on the stepper motor, because I had troubles 2 years ago...

2) I replaced the spark plugs with original ones - no change ..., then I ordered iridium ones, which are still on the car, but again without any difference in the performance of the bike.

3) I bought a brand new original Bosch coil (my original ones are Bosch) and tested it out of town on all 5 cylinders, but again without any difference ...

A mechanic told me that it could possibly be from the lambda probe (Oxygen sensor)and that it should be tested, but if it is the probe, shouldn't it also cause me a problem on gasoline?

Is there a colleague who has encountered a similar problem?
Or someone with an idea of ​​what it could be?

Thank you in advance!

Last edited by Andrioman; Jul 6th, 2021 at 20:54.
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Old Jul 25th, 2021, 15:44   #2
CNGBiFuel
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I realise English is not your first language... yet sorry, I'm not really sure I understand what you mean by push/pull?

Does it falter, stop firing, run rough. Normally I'd point you to coils or narrowing the plug-gaps. Gas likes good ignition, and narrower plug-gaps. 0.7mm for me. You say you've done that?

I'd be rid of the iridium. Standard plugs set 0.7mm is best.
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Old Jul 27th, 2021, 06:38   #3
Andrioman
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Thanks for your opinion! Sorry for my English, I just didn't know how to describe it, but yes, the engine was running rough at high load...
I found the problem! I thought that the iridium spark plugs are a better choice and that's why I bought Denso iridium plugs, but it turned out, that I just needed standard Volvo spark slugs for my car.
Now everything is OK!
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Old Jul 27th, 2021, 07:05   #4
Laird Scooby
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I'm glad you found the problem and it was one of the items i was going to suggest - the plugs. Iridium plugs are all very well on engines originally designed to run on them but regardless of fuel, tend not to give improvements on other engines.

Second thing i was going to suggest was the fuel mixture which is where your meachinc was in the right area too. If the mileage on the car is more than 100k miles (160000km) and the Lambda sensor has not been changed yet, i would do it as preventive maintenance - their service life is ~100k miles (160000km) or 10 years.

Petrol is easier to ignite than CNG/methane or LPG so two things come into play here - the engine is more tolerant of minor mixture differences on petrol and secondly, the spark has to be more precise on gas (any gas) so both of these scenarios point to Lambda sensor and plugs.

With your plugs, i'd suggest using Volvo or NGK standard plugs but decrease the gap by 0.1mm and change them when it starts to misfire (your push/pull - it "holds back" as a result of the misfire) for new plugs, again with the gap set 0.1mm smaller.

Lambda sensor, if it's never been changed and your car has more than 160000km, renew it. When you do, reset the fuel ECU fuel trims to standard, they will have wandered from original to cope with the older sensor so they need resetting to factory so they have a clean base to relearn from.

I hope that translates for you, good luck with it!
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Old Aug 4th, 2021, 13:11   #5
Andrioman
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Thanks a lot for the info! I'll do what you suggest! I just don't know how to decrease the gap of my spark plugs, because the original plugs are with 3 pints(terminals), and the core in the middle, the terminals are not on top of the core(sorry if I don't explain it well!). Maybe I should buy plugs with just one terminal?
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Old Aug 4th, 2021, 13:19   #6
Laird Scooby
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Generally speaking, single earth electrode plugs are easier to adjust than multi-electrode plugs.

The three legs/terminals are the earth electrodes so from the point of view of being able to adjust the gap, i'd suggest you follow your idea and get single earth electrode plugs.

Unless it's a high performance engine with trick valve geometry and other things, there is little benefit in running plugs with multiple earth electrodes and the benefits won't outweight the extra cost. Same goes for Iridium plugs, usually many times the cost of the standard version and while they are capable of lasting longer, it's still usually cheaper to run standard plugs and change them more often.
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Old Aug 7th, 2021, 21:33   #7
CNGBiFuel
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Quote:
Same goes for Iridium plugs, usually many times the cost of the standard version and while they are capable of lasting longer, it's still usually cheaper to run standard plugs and change them more often.
Agreed. Buy right and five NGK on eBay, cost a tenner a set delivered. At that price, who would care? I run them to over 25K, but reallly I should change more.

As I said, on CNG set to 0.7mm, mine doesn't like 0.8mm, my coils might be getting tired. On 0.8mm it runs fluffy under load.

Petrol is 0.8mm stock, but petrol isn't that fussy.
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