its an intermittent secondary misfire, plugs/wires/coil
"Ted Mittelstaedt" > wrote in message
...
>
> "Janne S Sweden" > wrote in message
> om...
> > Today i discovered that i by pressing the throttle several times could
> > get the car to accelerate fully without bacfiring in the aircleaner.
> > It worked fine several times. If i press the trottle only one time it
> > still backfires.
> >
> > Does that help anyone to get a bright solution to my problem???.
> > Janne S
>
> Hey Janne,
>
> What you have described so far isn't possible. Here's what I'm hearing
> you say:
>
> 1) Backfiring at part throttle, not full throttle.
>
> 2) Ignition system completely checked out with a friend's scope and timing
> is correct and all parts of ignition system have been replaced
>
> 3) Car completely within emissions.
>
> In short, this isn't possible.
>
> So, let's go back to the beginning and start over.
>
> If this was a spark plug/secondary ignition problem (bad coil, crossed
> wires, etc.) then
> the misfiring/backfiring would get worse the higher the rpm.
>
> If this was a spark primary ignition problem (ie: timing) then the friend
> and his scope would have caught it.
>
> If this was a restricted fuel filter or bad fuel pump then the higher the
> rpm the
> worse the problem.
>
> If this was a compression problem it wouldn't be backfiring.
>
> If this was a fuel problem then the emissions would be out of wack.
>
> So I have to conclude that your testing methodology is flawed. If you are
> absolutely
> positively positive that the timing is perfect and the ignition system is
> perfect - which means your friend and his scope tested it out correctly -
> then the problem is in the fuel system,
> specifically the engine is running too lean - which means that the HC
would
> be high and
> the CO way low - which means the emissions would be off.
>
> In short, you cannot have it both ways. You cannot have a perfect
emissions
> report
> AND a perfect checkout with your friend and his scope, and still have this
> problem.
> One of them has to be wrong.
>
> Off the cuff the most likely candidate is bad timing at part throttle, OR
> too lean
> condition at part throttle. However both the timing and the mixture are
> computer
> controlled. There is an old saying with computers, garbage-in,
garbage-out.
> I think
> the likeliest problem here is you have one or more bad sensors feeding
into
> the computer.
>
> The fact as you say that sometimes it runs fine is even more an indication
> that it's
> a sensor-to-computer problem. Maybe a bad sensor that with the vibration
> occasionally "heals"
>
> Some would say that if it's a bad sensor that the computer would set a
code.
> Well I
> have a '95 T&C with a 3.8 and when I bought it 3 years ago used, the EGR
> valve was
> shot, and the van wouldn't pass emissions, and there was NO CODE set.
> PERIOD.
> Replacing the EGR valve dropped the NoX down and it passed emissions. So
> don't
> argue with me and tell me that the computer in these things is smart
enough
> to detect
> if a sensor is shot. I know from experience this is just wishful
thinking.
> Sometimes
> sensors will fail in such a way that the computer cannot figure out that
> they are bad.
> For example, your TPS could have worn out the middle of it's slide and the
> computer
> not know where the throttle is, fuel mix is going to be wrong, then. Car
> computers
> are notorious for saying one part is bad when it's another part entirely.
>
> You say you have already shotgun the ignition system components. Well
fine,
> great,
> quite replacing them. Or better yet keep replacing them and send me your
> old ones
> because they aren't broken.
>
> It's time you put a scan tool on this vehicle, or pay someone to do it.
If
> you really want
> to do it yourself, you can buy an OTC Monitor 4000E off Ebay pretty cheap
> that will do this. You need to scan it and run the engine and make sure
> your actually getting
> valid inputs from all the sensors. You need to check timing with a timing
> light - yes I
> know the factory manual says timing is non-adjustable, but a timing light
> and degree wheel on the crank still work. The cam chain could have jumped
a
> tooth and that is going to
> shift timing out of wack. You need to put a fuel pressure guage on the
fuel
> rail and test that. In short, you are past the stage of being able to fix
> it with a $39.99 on-sale Sears Craftsman wrench set, a Haynes manual, and
a
> bucket of miscellaneous screwdrivers. You are either going to have to go
> out and buy the tools (and documentation, like the Factory Service Manaul)
> to troubleshoot it properly or pay someone who has the tools to do it
> correctly.
>
> Ted
>
>