+25% LTFTs

[onspeed]

97 Surburban, 198k, replaced heads with stock L31's recently due to a crack, did full tune up at the same time. All filters, fluids, spark plug, distributor, rotor, wires, etc. I'm getting +20%-25% (25% is the max for LTFT) about everywhere for both banks. I checked for vacuum leaks and didn't find anything. I think fuel pressure was fine as well, 60-65 PSI when cranking IIRC, could be mistaken on that number, but I remember it was within spec. New fuel pressure regulator, the fuel spider is still the old poppet style. O2 sensors oscilliate normally.

Any suggestions on what to look for? Fueling issue or unmetered air? I sprayed carb cleaner around the intake and etc and couldn't find any leaks. Both banks are within a few % in terms of fuel trim, so its something that's effecting all cylinders.

 

[michael hurd]

Did the distributor get set correctly with a tool that shows timing offset? I would also clean your mass airflow sensor if you haven't already. You may also have a vacuum leak at the bottom of the manifold, at the bottom of the port, IE: internally. Try re-torquing the lower intake manifold and see if that helps.

 

[onspeed]

Did the distributor get set correctly with a tool that shows timing offset? I would also clean your mass airflow sensor if you haven't already. You may also have a vacuum leak at the bottom of the manifold, at the bottom of the port, IE: internally. Try re-torquing the lower intake manifold and see if that helps.

Did not get the distributor reset correctly. I told myself I'd get it done but forgot. Would being off a few degrees timing cause such a swing in fueling though?

MAF is clean

 

[onspeed]

called around today, apparently most of the stealerships in the area don't work on our "old" cars anymore. Found a GMC dealer that does, got an appt to get the distributor set. Gotta love 1hr labor for a 5 minutes job, a few more times and I might as well buy the autoxray scanner that reads the PID.

Update - got timing offset done. Was only out by -13 deg. No change on fuel trims.