96 Chevy 5.7 running rough

[Jbarry14]

I am having lots of problems getting my 1996 chevy 3500 with the 5.7 running correctly.

About 4 months ago the truck started to run rough. I found out I had low fuel pressure, and that the fuel pressure would drop off almost instantly once the key was shut off. I replaced the fuel pump with a Delphi brand pump. And I also replaced the fuel filter.

After the fuel pump change, the truck still ran rough. So I brought it to a mechanic to diagnose. They did a fog test and made sure I had no vacuum leaks. They also said my sensors were working correctly. Then they put a camera down and saw that a few of my injectors were not working correctly. My LTFTs were basically pegged. So I parked the truck for a while and just this last week I replaced the Injectors with standard brand MPFI. While I was in there, I saw that my plastic distributor was cracked, so I also replaced the distributor with an aluminum body, changed out my plugs and wires too.

After changing the spider injectors, FPR, distributor, cap, rotor, and plugs. The truck is still running rough and throttle response is horrible. I did check the CMP with my scan tool and it is set at 0° when the truck was above 1000rpm. At idle my LTFT bank 1 is at 25%, bank 2 is at 20%. At about 1200rpm bank 1 and bank 2 are around 18%. it says my air fuel ratio is 14.7:1. Seems very lean.

I am just not sure where else to look. The truck is not throwing any codes, but i have not driven it more than around the block a couple times. Does anyone have suggestions on where I can start troubleshooting?

 

[Schurkey]

Connect a scan tool, look for misfire counts on the individual cylinders. Verify ignition coil output with a spark-tester calibrated for HEI. Distributor cap problems seem epidemic with Vortec caps. Cranking compression test of all eight cylinders, looking for problem children.

Consider clearing the fuel trims, and letting the computer re-learn what's correct. It probably learned "bad habits" when the original spider injectors failed.

If the computer is adding 25% more fuel, I'd be re-checking the fuel pressure, and considering whether the O2 sensors are old enough to vote. O2 sensors get lazy with age/mileage. A hidden vacuum leak seems possible, too. Are the IAC counts showing extra air getting in? Faulty brake booster? Faulty PCV valve? Cracked intake manifold? Faulty lower intake gaskets? I assume the upper intake gasket is new with the electronic injector replacement.

In short, there's LOTS of potential problems, you're going to have to narrow-down the possibilities.

 

[Jbarry14]

Connect a scan tool, look for misfire counts on the individual cylinders. Verify ignition coil output with a spark-tester calibrated for HEI. Distributor cap problems seem epidemic with Vortec caps. Cranking compression test of all eight cylinders, looking for problem children.

Consider clearing the fuel trims, and letting the computer re-learn what's correct. It probably learned "bad habits" when the original spider injectors failed.

If the computer is adding 25% more fuel, I'd be re-checking the fuel pressure, and considering whether the O2 sensors are old enough to vote. O2 sensors get lazy with age/mileage. A hidden vacuum leak seems possible, too. Are the IAC counts showing extra air getting in? Faulty brake booster? Faulty PCV valve? Cracked intake manifold? Faulty lower intake gaskets? I assume the upper intake gasket is new with the electronic injector replacement.

In short, there's LOTS of potential problems, you're going to have to narrow-down the possibilities.

Thanks for your reply.

My scan tool has not been showing any misfire counts. I have only driven it a short distance though. I did just install a brand new distributor, distributor cap, rotor, plugs and wires. I will need to check the ignition coil output.

How do I go about clearing the fuel trims? I have not been able to find much online.

Last night I replaced the coolant temp sensor, EGR valve, and all O2 Sensors. I had some of these parts laying around, so I thought I would just replace them. What was interesting was when I replaced the O2 sensors, the fuel trims seemed to go to more normal numbers and the truck started running better. But, within a few minutes or so, the fuel trims went back up to 20+% and started running worse.

I have been looking all over for a vacuum leak with no luck. A few months ago, when I had the truck diagnosed by a shop, they did a fog test and told me I had no vacuum leaks. Tonight I will be testing compression and fuel pressure. I have an IAC at home that I will replace too.

Anything else I could test or look for?