First off this is a fun thread as we already found and fixed the problem. But it is too strange not to share and ask what would you guess? Call it a test question. So lets have some fun with it.
1991 R/V burb 350 runs better with alt disconnected. Friend who helps keep Patch running had the fellow down the street ask for a hand on this.
Back story is the TB was rebuilt and it's running rich. Code for MAP sensor. They found MAP sensor plugged into wrong port on TBI unit after replacing it and connector. I had suggested they figure out why it's not reading intake vacuum it should via hose leak intake leak whatever - believe the computer for a second. And probe the sensor for voltage to make sure the computer is telling the truth.
MAP sensor code cleared up. Suggest it came up due to troubleshooting, pulling the TB to check gaskets and putting it back wrong, as it ran fine till it didn't.
Still running rich and bad. Turn headlights on and it runs better, but still smells rich. Disconnect the alternator and it runs way better. Turn blower on high and it runs better. (Note AC compressor disconnected as it runs all the time.) Plug in AC compressor and same result is turn on blower and now compressor and it runs better. Wire or control head messed up, but, this isn't the cause of the engine running bad.
Grounds replaced to make sure including new battery cable and 'big 3' ground strap put on. No change. Alternator replaced no change.
I arrive just as they are scratching heads over new alternator not fixing it. Sounds like it's running underwater knock and rich smell. Disconnect alternator and idle speed goes up, sounds better, but still has rich smell. Richer than the "cold start mode".
Wow. I really didn't believe them.
TBI rebuilt, New stock AC Delco injectors, TBI spacer, 18 LB spring, better fuel pump, and fuel pressure gauge on TBI. 383 stoker. Different intake, aluminum, EGR pipe plugged and missing (not added back since intake manifold swap). No updated PROM. Ran fine like this till suddenly it didn't. Of course EGR code, but, not code present at this time.
My first thought would be clogged/melted cats from running rich, but, no power loss at high RPM.
We muck around getting a Snap On Scanner working as the cigarette lighter isn't working.
We read the data - no codes. O2 has cross counts.
Shouldn't be as it should be pegged rich.
Oh, it's in Open Loop! Not reading the O2 sensor, but, computer is telling us a lie. It's telling us what it's using, table data, not what the sensor is really reading. Was warned about this in the past.
MAP appears to be reading properly. TPS appears to be working properly from scanner data.
Timing checks out.
Pull the air cleaner and inspect the injectors and regulator for leaks. None.
Go back to stock regulator spring setting of 12 PSI. No change - still runs rich. No fuel leaks period.
Engine at idle and point timing light at injectors. No drips and patterns look good.
No intake leaks. TBI gaskets ok.
IAC motor swapped out - both functional.
Here is a hint - the electrical load change is a big clue.
Second hint: fuel is ok.
1991 R/V burb 350 runs better with alt disconnected. Friend who helps keep Patch running had the fellow down the street ask for a hand on this.
Back story is the TB was rebuilt and it's running rich. Code for MAP sensor. They found MAP sensor plugged into wrong port on TBI unit after replacing it and connector. I had suggested they figure out why it's not reading intake vacuum it should via hose leak intake leak whatever - believe the computer for a second. And probe the sensor for voltage to make sure the computer is telling the truth.
MAP sensor code cleared up. Suggest it came up due to troubleshooting, pulling the TB to check gaskets and putting it back wrong, as it ran fine till it didn't.
Still running rich and bad. Turn headlights on and it runs better, but still smells rich. Disconnect the alternator and it runs way better. Turn blower on high and it runs better. (Note AC compressor disconnected as it runs all the time.) Plug in AC compressor and same result is turn on blower and now compressor and it runs better. Wire or control head messed up, but, this isn't the cause of the engine running bad.
Grounds replaced to make sure including new battery cable and 'big 3' ground strap put on. No change. Alternator replaced no change.
I arrive just as they are scratching heads over new alternator not fixing it. Sounds like it's running underwater knock and rich smell. Disconnect alternator and idle speed goes up, sounds better, but still has rich smell. Richer than the "cold start mode".
Wow. I really didn't believe them.
TBI rebuilt, New stock AC Delco injectors, TBI spacer, 18 LB spring, better fuel pump, and fuel pressure gauge on TBI. 383 stoker. Different intake, aluminum, EGR pipe plugged and missing (not added back since intake manifold swap). No updated PROM. Ran fine like this till suddenly it didn't. Of course EGR code, but, not code present at this time.
My first thought would be clogged/melted cats from running rich, but, no power loss at high RPM.
We muck around getting a Snap On Scanner working as the cigarette lighter isn't working.
We read the data - no codes. O2 has cross counts.
Shouldn't be as it should be pegged rich.
Oh, it's in Open Loop! Not reading the O2 sensor, but, computer is telling us a lie. It's telling us what it's using, table data, not what the sensor is really reading. Was warned about this in the past.
MAP appears to be reading properly. TPS appears to be working properly from scanner data.
Timing checks out.
Pull the air cleaner and inspect the injectors and regulator for leaks. None.
Go back to stock regulator spring setting of 12 PSI. No change - still runs rich. No fuel leaks period.
Engine at idle and point timing light at injectors. No drips and patterns look good.
No intake leaks. TBI gaskets ok.
IAC motor swapped out - both functional.
Here is a hint - the electrical load change is a big clue.
Second hint: fuel is ok.
Injector pattern literally starts pissing fuel and spray nearly stops. We are all in slight shock. I am surprised the engine even ran at all. Way back in the rusty memory one of my instructors mentioned snap testing the injector pattern with a timing light as idle wasn't a complete picture. Never thought I would ever see it. So here is to instructors/teachers being useful. 
