I have a 96 gmc sierra with 4.3 V6. At first truck idled normally but bogged down when accelerating, sometimes would shut off. Borrowed a maf sensor from a buddy and is driveable now and made a big difference but if i get on it from a stop it's sluggish at first. If i gradually get into it, it drives good. Now im getting some long term fuel trims that are off big time. On LONGFT1 and LONGFT2 im getting between 16 and 25 which points to a vacuum leak. I made a homemade smoke machine and im not getting any leaks. Ive searched up and down using a flashlight and all... ...What else could cause the LONGFT's to be off like that? Fuel pump is new and has the right pressure. Any ideas anyone?
Goofy fuel trims don't "point to a vacuum leak". At least, they don't point ONLY to a vacuum leak.Aint the brake booster, just checked and made no difference. Any ideas anyone?
Low fuel pressure, failed "spider" injectors, defective O2 sensor(s), could all cause this problem.
Connect a scan tool, look for issues in the data stream. Verify that there's no misfire.
What do you consider "right pressure" for the fuel system? Will it maintain that pressure under heavy load?