GM-GMC: 1996 chev express 305 2500 van, natural gas conversion, intake manifold gasket

Question
Van has 200,000km had a natural gas conversion when i bought at 47k.  now disconnected.  for most of its life it has periodically backfired thru air intake system.  it will not take fuel.  when you give it gas it bogs right out, back off and boot it several times, it clears eventually and then runs generally fine.  computer corroded and changed, fuel pressure tested and ok.  would not start a few weeks ago. i changed cap and rotor and it ran perfectly for 1 drive cycle & then back to the bogging again.  wires and plugs have been changed.  intake manifold gasket finally changed about a year ago and it worked perfectly for 4 days before check engine lite started again. i had changed the tps recently but no joy.  hope there's enough info, thanks

Answer
When you had the natural ga conversation kit on the van , What did you do to the exhaust system , if anything ?

What did you do to the engine , That made it run the best for the longest amount of time ?Ask yourself and go back :


It sounds like you have tried alot of things .

These were band aids that you put on your van for a temp fix , every time .
Usually , when you backfire , It is a sign of exhaust restriction of some  type , or timing , or vacuum .. sensors along with the computers are funny things . They can give you numerous codes and running conditions.

May i suggest the following :

Check the exhaust : If it starts to backfire : disconnect exhaust before the catalytic converter. This will elimanate any restriction issues you might have ,
By having the natural gas then gas this might have  clogged the  converter.

Timing : Check you timing : make sure that the proper timing is set.
Double check your . You might have to retard your timing , to accomadate for the backfire .Pull your number 1 plug and put a piece of paper and check for TDC ( Top Dead Center )

Check for spark :On each individual spark plug wire :

Last Resort !
If the check engine light is on take a tester and get a code reading on what the problem may be . You can borrow these testers sometimes at auto parts stores