hello,

been working on this on and off for months and am stumped.

changed the intake gaskets on my 2000 5.7. now it runs rough and i keep getting p303 code, misfire cylinder 3
have replaced, cap, dis', plugs, wires,
time and again adjusted the dis' to get it running better, but can't,
checked for vacume leak, done a compression test( all good)


The van is duel fuel...Propane gas and petrol. so it can't be anything to do with the fuel injection side of things as it has 2 seperate fuel sytems and the problem happens on both.

I'm in the U.K and nobody knows anything about these vans or has the diagnostic equipment to work on them. ANY help would be massively appreciated!

thanks

 

Use your timing light as an engine analyzer. Clip on each plug wire with the engine idling. The light should flash steady. Any cylinder that does not flash steady has a problem.

Also use a pair of vice grips to try closing off vacuum lines one at a time.

 

Pull #3 plug, it is sootie if it is misfiring. It could be a stuck injector.

 

When you checked for vacuum leaks did you check only hose fittings/lines or did you also check around the ports and the ends of the intake manifold? If you didn't check the manifold you can use a portable propane torch and a length of fuel line to check it. Slip the hose over the end of the torch, turn on the propane then (with engine idling) run the end of the hose around the entire base of the manifold. If the rpm rises the area you are pointed at is where your leak is. Pay close attention around #3 port. You can also use it to double check your hoses, fittings, pcv grommet, etc.

 

Just to add, those hoses are more than likley 12+ years old. I'd still suggest pulling #3 plug, that will tell you whats going on. It could certainly be coincedental this happened after the intake gasket replacement.