I just finished replacing the fuel pump (it was delivering only 4lbs)
and it now is giving me a consistent 10lbs of pressure, and now at
cruising I have no performance problems. I also replaced the cat and
the muffler with a straight pipe and muffler, and am awaiting a
tailpipe I ordered to put on later this week. O2 sensor a foot ahead
of the location of the cat is new-ish.
So now that some of the other problems have been corrected with the
fuel pump, I'm getting a clearer picture of the remaining problem(s).
When I first start it up cold without pressing the pedal, it starts
quickly, but runs rough. After about 10-15 seconds, it smooths out and
runs better - not perfect, but fairly good. I have the feeling it is
running rich though. Lots of smoke from the exhaust initially until it
warms up, heavy fuel smell. And it seems to run fine down the street.
Then, when you stop at a light, the idle is okay for a moment, but
then it often will quickly stumble and stall unless you juice the gas
a little while it idles. This seems to happen when warm or cold.
After it is started and right as the idle smooths out somewhat, the
check-engine light comes on. The code it is throwing is a 33 which my
book says "Mass air flow (MAF) sensor - signal voltage or frequency is
high during engine idle. OR Manifold absolute pressure (MAP) sensor -
signal voltage is high during engine idle. (Note: Engine mis-fire or
unstable idle may cause this code.)"
I'm told I don't have a MAF sensor, so I can rule that out. I replaced
the MAP sensor before I changed the fuel pump, so it's not likely to
be the cause, but I could throw the old one in to see if the problem
changes. My thoughts are maybe fuel injectors or a vacuum leak. A
while back I found a massive vacuum leak at the back of the TB where
it mates to the manifold. I pulled it and re-did the gasket, but maybe
it's returned. Engine has low miles (a replacement) and the truck has
230k miles, and most sensors have been replaced. Any ideas or
suggestions on how to proceed?
Thanks in advance,