Hi guys!

I'm hoping you can help me solve a long-term misfire mystery with my 2003 Dakota 4.7 V8 AWD?

A bit of background on my truck and me. I'm British, living in France, my truck is a Canadian one, imported first to Belgium, then to France. It's been converted to dual-fuel petrol/LPG with an Italian "Stargas" system. (this is important regarding my misfire in that it both complicates and clarifies things).

So, for quite a while now my truck has been showing the amber check engine light. It's perfectly driveable, I use it everyday as I am renovating houses for a living but it does misfire. It seems most likely to happen either if I do a lot of short stop-start journeys, or if I cruise around a city for a while at lowish speeds, then accelerate onto a main road.

I try to run on LPG most of the time as it's much cheaper, but as is usual with LPG, a misfire is much more severe when running on that fuel. When it gets bad I switch back to petrol/(gas?). The misfire can still be felt as it's slightly stuttery to drive (but not massively so as when it's happening on LPG).

The fact it happens on both fuels makes me think the LPG system is not the issue. The engine does throw out a lot of OBD codes (which i'll note down this weekend and post here). They mostly indicated lean fuel mix and/or a leak in the charcoal filter system. I and several mechanics have checked all the lines going to and from the charcoal filter, no leaks are evident. If I block the exhaust pipe the engine dies, so an air leak seems unlikely.

I took it to the local JEEP dealer for examination (Dakota never sold here, but it's the same engine as used in the Grand Cherokee so it was not alien to them). They could find no fault, cleared the codes and sent me on my way (350 euros lighter). Within half a day the engine light was back on and misfire was evident again.

I have already replaced the spark plugs and iginition coils (the old spark plugs showed signs of lean fuel via white traces) but it hasn't helped this time (it did on my old Dakota 3.7 V6). I changed the TPS due to another issue recently aswell and the air filter is new.

I'm at a loss. As I said I'll post all the OBD codes this weekend, but any advice and suggestions would be very welcome. There are very few places here who will look at an American truck. I want my Dakota to run perfectly again! :-)

Thanks!

 

Ok i've had a chance do read the codes via the OBD (it's actually throwing out less codes than the last time I looked). They are...

P0420 - Powertrain
Catalyst System Efficiency Below Threshold (Bank 1).

P0456 - Powertrain
Evaporative Emission Control System Leak Detected (very small leak, check fuel cap, piping, etc).

P0440 - Powertrain
Evaporative Emission Control System.

I'll take a closer look at the fuel cap tomorrow and I have the opportunity to use a friends vehicle lift at the weekends. Any ideas or well known failures I should be looking out for? Indeed, are these codes likely the cause a misfire?

Any advice welcomed!

 

I don't think you will get the help you need on this forum we don't deal with these kinds of fuel or fuel systems you in Europe do. Some Dakotas may run on natural gas these are usually City or County Government vehicles.


I don't speak for everyone so I may be wrong wait and see someone may reply.


Good luck

 

Hi thanks for the reply. I don't think the LPG system is the culprit, it misifres on both fuels (it's just more noticeable on LPG). That also makes me think I could rule out injector or fuel pump issues, as both fuels use their own injectors/pumps.

Driving the truck around yesterday, it really does seem to become more noticeable as the day goes on, after many start/stops and when the engine is well warmed through. The other thing that usually triggers it is after a burst of hard acceleration (say to pass another vehicle or climb a long hill). Once I ease off the throttle it starts to cough.

My next course of action is to do the obvious thing of replacing the fuel cap and reinspecting the tubes around the charcoal filter.

I noticed when filling up yesterday there is no vacuum when I remove the fuel cap, is this normal for a Dakota? All vehicles are different, I remember my various old Mercedes made a real whoosh sound as you removed the fuel cap and the pressure equalised, but on the Dodge, nothing...

 

Your e-vap system shouldn't cause any missfire.
As my dakota has an Evap leak no missfire from it. I would
maybe replace your O2 sensor if it's bad that could cause your missfire.
Do you get the code for what cylinder is missfireing?