running lean

[90gmc3500]

1990 gmc 3500 454 over 300k has been rebld 100k ago...computer tells me left bank running lean.I have put new injecters new plugs,wires,rotor and cap and coil,now,, when on the freeway the check engine light comes on and still says left bank lean..help what's the fix..timing is set to factory specs 4*btdc

[aflesch]

Check your fuel pressure. Could be the pump starting to go or the filter could be clogged.

[90gmc3500]

fuel pressure is fine,both fuel filter and fuel pump are new

[8.1HD/ALLISON]

Have you checked for intake leaks? Also check for any exhaust leaks between the block and the 1st o2 sensor. That could cause lean code also. Could also be o2 sensor related.

[kmborland]

Have the same problem with my tbi 350 in my 95 k2500. I have new (year old now) coil, cap, rotor, wires, plugs and a rebuilt tbi. Change the filter every 15000 miles and have been running 89* fuel in it the past few months. I think for my truck it is the header gaskets. I noticed one day that the header bolts where backing out so I tightened them but still get the SES light on any highway trip over 10-12 miles. I plan on replacing the header gaskets during the being of spring before my trip to GA. After that, only thing left to do is check fuel pressure again, see where its at, then replace the fuel pump.