coachhick
Newbie
I have a 1997 Crew Cab K3500 454 Vortec with an NV4500 and 4.56's and 148k miles. My dream truck - go figure! I owned it for 77 days in 2020, but sold it to a buddy after multiple random issues. A month ago, he sold it back to me. He had just put $3,200 into the front end and got it back running like garbage. He replaced the mass airflow sensor then decided he was done with it. I have read and read and read over these forums the last month and your old threads have been great help SO FAR, but I'm not sure where to go next with it. Here's the skinny:
- Running lean - fuel pressure gauge showed 15 psi
- I replaced fuel pressure regulator (twice - Delphi fpr10021 the 2nd time) , fuel pump, fuel filter
Was running MUCH better, but had a high idle. Fuel trims were within range at idle and speed, but when clutching to slow she would hang around 2,500 rpm at idle until you shut her down. While looking for the problem, I found the most incredible crankcase vacuum that I'd ever seen (pulled the air filter, took off oil fill cap, took out PCV valve, took off the pass side valve cover vent, plugged the air intake..... and it was still running...)
- replaced lower intake gaskets with a MAHLE set
- replaced spark plug wires, dist cap, rotor from Summit since I was under the plenum AGAIN
- replaced thermostat, flushed, new coolant
She still has a high idle, BUT fuel trims now creep and once they reach 50% & 25%, she purrs like a kitten. You clutch from highway speeds and she idles high until the trims get back high and she settles down. (odd how I had a high idle previously but the fuel trims read normal) - - - fuel trims at highway speed are good
BUT ALSO, now I have what feels like a miss in the lower rpm range..... like the truck bucks/vibrates like I've slung a tire weight but you can tell it's short on power when it's doing it (tach dances when this is happening). You get it wound up in the rpm range and its smooth as silk.
No misfire codes, only codes are IAC higher idle than expected and another lean code
I checked fuel pressure today - 58 psi key on, 50 psi idling - 55+ when you romp on it - PPPO installed new AC Delco injectors in 2019 (less than 10k miles ago)
Where do I go? What do I look for next?
- Running lean - fuel pressure gauge showed 15 psi
- I replaced fuel pressure regulator (twice - Delphi fpr10021 the 2nd time) , fuel pump, fuel filter
Was running MUCH better, but had a high idle. Fuel trims were within range at idle and speed, but when clutching to slow she would hang around 2,500 rpm at idle until you shut her down. While looking for the problem, I found the most incredible crankcase vacuum that I'd ever seen (pulled the air filter, took off oil fill cap, took out PCV valve, took off the pass side valve cover vent, plugged the air intake..... and it was still running...)
- replaced lower intake gaskets with a MAHLE set
- replaced spark plug wires, dist cap, rotor from Summit since I was under the plenum AGAIN
- replaced thermostat, flushed, new coolant
She still has a high idle, BUT fuel trims now creep and once they reach 50% & 25%, she purrs like a kitten. You clutch from highway speeds and she idles high until the trims get back high and she settles down. (odd how I had a high idle previously but the fuel trims read normal) - - - fuel trims at highway speed are good
BUT ALSO, now I have what feels like a miss in the lower rpm range..... like the truck bucks/vibrates like I've slung a tire weight but you can tell it's short on power when it's doing it (tach dances when this is happening). You get it wound up in the rpm range and its smooth as silk.
No misfire codes, only codes are IAC higher idle than expected and another lean code
I checked fuel pressure today - 58 psi key on, 50 psi idling - 55+ when you romp on it - PPPO installed new AC Delco injectors in 2019 (less than 10k miles ago)
Where do I go? What do I look for next?
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