cnowalk
Geologist
Since I bought my 1998 C1500 5.7L last summer, I've been trying to fix what I think is a random miss that is most noticeable while cruising between 45-50 mph. Most of the time the miss will occur, while other times the truck runs and drives perfectly.
It's been a while since I had codes checked, but at the time this is what it had:
- P0102 MAF low voltage input
- P0103 MAF circuit high
- P0113 intake air temp circuit high input
- P0118 engine coolant temp sensor high input
- P0300 random miss
- P0420 cat deficiency bank 1
- P0430 cat deficiency bank 2
The cat codes are no surprise as the previous owner cut out the cats and welded in pipe in an effort to make the (true dual) exhaust louder (he also pulled the bulb for the SES light). It's a bit loud for my taste but that's another story. I'm not sure where to start with those high/low codes, but it would be nice to get those sorted out too.
So far I have made these repairs:
- NGK V-Power spark plugs (gapped correctly out of the box, but I double checked them)
- Summit spark plug wires
- AC Delco cap
- AC Delco rotor
- AC Delco Fuel Filter
- Cleaned MAF sensor
- Upper/lower intake gaskets
- Delphi ignition coil
Prior to my ownership, the MPFI upgrade was performed, and it is a Delphi unit.
Drove the truck quite a bit yesterday, and as usual it did it's stumble/miss around 45-50 mph, even after a long drive at highway speeds. The stumble/miss occurs at the 45-50 mph cruising speed and can be felt, as well as shown as slight fluttering on the tach. When driving slower or faster than this range, the truck drives nice and smooth.
Today I decided to do a fuel pressure test. On the way to the auto parts store, the truck drove perfectly and did not miss at all.
Results:
Key on engine off: 54 psi
Idle: 47-48 psi
2500 rpm: 46 psi
Acceleration: 54 psi
Cruising speed: 48 psi
Key off after drive: 56 psi
The truck drove perfectly fine during the test (of course), and the fuel pressure remained constant for over 5 minutes after turning off the engine.
I'm not sure this is related, but occasionally I'll get a hard start when the engine is hot, but I'm wondering if that is more of a starter issue as it cranks, stops, then starts cranking again and starts, as long as you keep holding the key. The truck will always start, but sometimes it starts pretty hard. I have a new in box AC Delco starter, I just haven't had a chance to put it in, or on the off chance its another issue.
This is a bunch of text, but hopefully I've provided enough information for someone to point me in the right direction. Thanks in advance!
It's been a while since I had codes checked, but at the time this is what it had:
- P0102 MAF low voltage input
- P0103 MAF circuit high
- P0113 intake air temp circuit high input
- P0118 engine coolant temp sensor high input
- P0300 random miss
- P0420 cat deficiency bank 1
- P0430 cat deficiency bank 2
The cat codes are no surprise as the previous owner cut out the cats and welded in pipe in an effort to make the (true dual) exhaust louder (he also pulled the bulb for the SES light). It's a bit loud for my taste but that's another story. I'm not sure where to start with those high/low codes, but it would be nice to get those sorted out too.
So far I have made these repairs:
- NGK V-Power spark plugs (gapped correctly out of the box, but I double checked them)
- Summit spark plug wires
- AC Delco cap
- AC Delco rotor
- AC Delco Fuel Filter
- Cleaned MAF sensor
- Upper/lower intake gaskets
- Delphi ignition coil
Prior to my ownership, the MPFI upgrade was performed, and it is a Delphi unit.
Drove the truck quite a bit yesterday, and as usual it did it's stumble/miss around 45-50 mph, even after a long drive at highway speeds. The stumble/miss occurs at the 45-50 mph cruising speed and can be felt, as well as shown as slight fluttering on the tach. When driving slower or faster than this range, the truck drives nice and smooth.
Today I decided to do a fuel pressure test. On the way to the auto parts store, the truck drove perfectly and did not miss at all.
Results:
Key on engine off: 54 psi
Idle: 47-48 psi
2500 rpm: 46 psi
Acceleration: 54 psi
Cruising speed: 48 psi
Key off after drive: 56 psi
The truck drove perfectly fine during the test (of course), and the fuel pressure remained constant for over 5 minutes after turning off the engine.
I'm not sure this is related, but occasionally I'll get a hard start when the engine is hot, but I'm wondering if that is more of a starter issue as it cranks, stops, then starts cranking again and starts, as long as you keep holding the key. The truck will always start, but sometimes it starts pretty hard. I have a new in box AC Delco starter, I just haven't had a chance to put it in, or on the off chance its another issue.
This is a bunch of text, but hopefully I've provided enough information for someone to point me in the right direction. Thanks in advance!
