I was just reading this before and someone mentioned that it's a blocked catalytic converter. I have got the same problem with my 2003 H2. It's got about 120 km on it and starts misfiring and running really rough. I have replaced the leads, ignition packs and spark plugs look fine. I have replaced 4 injectors and I'm yet to do the other 4 but it has made no difference up until now.. is it the catalytic converter that is the issue?

 

Check the pressure in the exhaust pipe between the head and the cat, should be below 1.5 psi at or around 2000 rpms, the lower the better. Is the MIL flashing at or around 50 mph?

Neal

 

Thanks for getting back to me Niel!
How would you measure that? Serew in a meter on say bank 1 sensor 1 measure pressure. Then put back o2 sensor back and check it at bank 1 sensor 2? I have had the engine light come on and once even flash when it started to run rough but flashiflashing went away when it started to come good.

 

Yes, or you can have another bung welded to the pipe and put the gauge there for the test. With the 02 out it will likely set a MIL so you may have to have it cleared after testing.

The flashing light usually means the ECM thinks the engine is running very rich, enough to cause damage to the cats.

Neal

 

I actually have read that if the h2s run rough and misfire (po300) they will run rich. I'm going to get the remaining 4 injectors replaced as I only replaced the 4 on the American passengers side as I didn't want to remove the fuel lines myself next week when I get a service done. That will mean that it has new leads, ignition packs and injectors. I pulled out the spark plugs and the had bosh iridium plugs in the block which seamed ok. Think I should replace them as it's done 120,000 kilometres (74k miles approx) or do you think the wouldn't be original plugs and should be right? I have cleaned the mass flow air sensor when I washed and re-oiled my DNA air filter but may do it again. I also might look for any leaks in the intake pipe. That vacuum GM gauge with the green and red indicator has seen better days.. Ahhhh who bloody knows. I just want the big fulla running right again so I can be seen out in public again with out being in shame of the way it's running 😂