Engine Performance problem
1997 GMC Sonoma 4 cyl Two Wheel Drive Manual 155000 miles
as the tittle says. I get a lean code P0171 but only if I use 87 octane.
I verified this by filling the tank 3/4 of the way with 89 and ran it completely (almost of course) out and the CEL never came on.
I then put 87 in it and in just 20 miles, the CEL came back on.
so I put 89 back in, CEL never comes back.
a little background first,
I recently replaced the engine with a rebuilt one.
the old engine spun a rod and aparently had a cracked head.
ok, the CEL was on with the old engine also. I just thought it had something to do with the old worn out engine that was low on compression too.
but it's back on even with a new engine.
I've checked the fuel pressure and it seems fine. It's in the specified PSI ratings.
I also replaced the TPS because it had a glitch when I tested it with a multimeter.
the truck runs fantastic other than a slight hesitation under light throttle opening.
I'm pretty confident I have no vacuum leaks. And the brake power booster holds vacuum. So does the heater control vacuum line.
I also blocked off the EVAP system by unhooking the vacuum line to it and using a new line I zip tied off so it wouldn't leak.
the CEL came on with the evap system problem(which I expected) but the Lean code was also present.
I've also replaced the Coolant Temperature Switch.
(this truck only has this sensor to read the coolant temp)
would a leaking or clogged injector cause this?
I don't have a problem replacing all of the sensors, they are relatively inexpensive. But I'd rather not.
especially since the O2 sensor is pretty stuck. I doubt I'll ever get it out.
have the same problem?
Wednesday, February 18th, 2009 AT 8:08 PM