97 silverado L31 cylinder 3 issues p0303

[mrvsfriend]

https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-engine-control-module-ecm

#2 reads:
Engine Stalling or Misfiring
Erratic engine behavior may also indicate a bad or failing ECM. A faulty computer may cause the vehicle to intermittently stall or misfire. The symptoms might come and go and not appear to have any sort of pattern to their frequency or severity.

Thought this was interesting, could be your problem.

 

[Dewman67]

Pretty much, what I have been thinking. If anyone thinks this may be there problem. There ecu's on ebay for under $100 that are programed for your truck. If you don't want to upgrade to the 411.

 

[jaywestfall]

Very interested as well. I'm having the exact issues (254k mi) but P0301, cylinder 1 misfire. I have a brand new gm performance L31 engine, changed plugs, wires, cap, rotor, rotor gear, timing re-set, new coil, cleaned injectors and manifolds, swapped plugs and wires around (P0301 stays). Just started getting another code for o2 sensor in addition to the misfire. The misfire comes and goes... the black box hadnt even crossed my mind.

Looking forward to what the shop tells you.

Very interested as well. I'm having the exact issues (254k mi) but P0301, cylinder 1 misfire. I have a brand new gm performance L31 engine, changed plugs, wires, cap, rotor, rotor gear, timing re-set, new coil, cleaned injectors and manifolds, swapped plugs and wires around (P0301 stays). Just started getting another code for o2 sensor in addition to the misfire. The misfire comes and goes... the black box hadnt even crossed my mind.

Looking forward to what the shop tells you.

How long ago did you buy your L31? I need to buy one soon.

 

[Dewman67]

I bought my 97 around 2010. It ran good for a year or so, then started the missfire issue. My last trip to the salvage yard, there was alot of them out there. If your not looking to rebuild, then I'd look for one with low miles.

 

[mrvsfriend]

How long ago did you buy your L31? I need to buy one soon.

The L31 in my truck is maybe 8 months old, I've put less than 2000 miles on it. I went with Jeg's gmperformance 350 vortec.

 

[mrvsfriend]

I just asked about a new reprogrammed ECU and I was told that the 305 knock module was different from the 350, is that true?

 

[Supercharged111]

I just asked about a new reprogrammed ECU and I was told that the 305 knock module was different from the 350, is that true?

I could see the knock sensor or calibration being different, but these PCMs don't have knock modules. That was an LT1 thing

 

[Unssafe]

hey now,

i dropped off my truck and let them know the problem was intermittent and the service adviser was saying no problem. well, they got to it a day later and said they wanted to start doing major surgery at $150. or so an hour. this was at a local chevy dealership and they didn't care to work with me or not. so i went and got it and they didn't charge me anything. that was 2 or 3 weeks ago and i have just been driving it. when i started this thread the truck was shaking and smoking and the smoke smelled like gas. as i drove it, it started getting better and as of a few days ago it has been running great. no codes, no smoking. i am almost positive this is computer related issue. what are some good options on computers or ecu or what chevy calls them for when this comes back.
thanks for all the replys

 

[Schurkey]

as of a few days ago it has been running great. no codes, no smoking.

Why are you dicking with it?

Runs great = leave it alone.

If it stops running great, connect a fuel pressure gauge, a scan tool, and perhaps a compression tester. Find out what's REALLY wrong.