Only does this in gear its 4.0 petrol auto,car sounds like its backfireing which is why plugs were changed but the problem persists any advice would be welcome

gear box damage is the real problem

When it's in neutral and you hit the gas, does the rpm rise slowly? And if you try to give it too much throttle does it choke and try to die? It sounds like your catalytic converter is partially plugged, or there is some other exhaust restriction. If the check engine light is on, there may be relevant diagnostic codes available, some of the auto parts chains used to read the codes for you for free, but I'm not certain that is still the case.

the gas converter has probably corroded inside and is not working like it should
They do not last forever so I would suggest that you take the vehicle to an accredited gas shop and have the gas section checked out.

If it is back firing through the exhaust, it is not running good because you are putting unburned fuel into the exhaust, bad spark plug or leaking exhaust valve, you need a compression test to start, you may as well change the spark plugs while they are out

try checking all your connections coming out of tranmission. make sure all the plugs are making good a connect. I had same problem. All it was, was a plug not plug in very good.

check the firing order

The problem is that the CNG is not burning. Causing the miss. It is not going to have anything to do with the ignition. Other than maybe spark plugs. You can get a hotter spark plug that will ignite the CNG. If the car runs fine on petrol then the plugs are just not hot enough.

It only has four. Take it to someone that knows how to work on cars and not rip people off

Hello patrick_toal, and thank you for choosing fixya.com. Since you replaced the injectors, it sounds like the timing belt/chain may need replaced. My 87 buick was doing that very thing. Also, have your lifter rods checked. You may have a bent or broken one. You will usually hear a pinging or knocking sound if one is bent or broken, so if your not, than they are probably sitll good, but if your timing belt or chain (whichever is equipped) is wearing out (if chain, the gear is probably wearing out, and if belt, the belt is probably beginning to strip). If this is the issue, then you will want to get it fixed, or it can cause more damage, such as mentioned above, bend or broken rods.

Now, before you do any of that, just in the effort to save you time, and money; change the air filter, and the fuel filter, and if you haven't already, the tranny fluid and oil (the filters for these will be replaced automatically, as they are part of the fluid change process).

Some other things that may cause this are as follows: First however, consider having a diagnostics test done on the car. Go to your (a) mechanic, or a local auto parts store and request (if available) to have a diagnostics test done. It should only take about 5-10 minutes at a auto parts store, and if anything is wrong with the car, the test will reveal such codes for such faults, and they representative will be able to tell you what each code represents and what parts need repaired/replaced.

Other causes:

Fuel Injected Engine:
coil wire/spark plug wires/spark plugs
coil pack(s)/modular <--coil pack(s) will be screwed to modular
fuel filter/air filter
O2 Sensor(s)
Fusable Link(s)


Carburated Engine:
Distributor/Cap/Rotor <-- consider switching to an EFI Distributor as they do not have points
coil wire/coil
spark plugs/wires
fusable link(s)

Also, have the alternator and batter tested for safe measure. Check all fuses. If and when you have a diagnostics test done, write down all the codes and the parts/components for each they represent. Have the codes cleared. Replace parts starting with the least expensive first, and if the issue persists, move up the list.

The above is what I do for all my vechicle. When I first purchase a vehicle, the first thing I do is a complete tune up which includes oil/tranny fluid and filter change, air and fuel filters, new plugs, wires and if carburated, cap and rotor. The chances of the coil pack (if fuel injected) and or modular being faulty are very low, but still possible, so consider them as well.

I hope this information is useful to you, and helps you get your car running smoothly again. I thank you for choosing fixya.com for your car repair solutions. NOTE: If this is a diesel (as diesels have injectors as well) it's best to take it to a diesel mechanic (or if under warranty still, the dealership of purchase, or VW service dealer).

Again, thank you, and please let me know if there is anything I can do to assist you further in getting your car up and running right again.

carsandcomps
Guru
fixya.com

have you checked the fluid level? ther could be several reasons. #1 low fluid level.#2 engine speed sensor.# transmission control module.#4 the solenoids in transmission gummed up or malfuntioning. have these checked out