My car runs fine for weeks at a time but every so often it will act the ***.

It will start but then immidiately die, and I smell gasoline.
If I hold the gas it will run horribly, backfiring and what not, but if I let off the throttle it will immidiately die.

First things first, I swapped an '85 TPI into my Monte_Carlo_SS.
Secondly I swapped from MAF-to-SD with a 165 ECM.

Third of all, I have a BOSCH external fuel pump, which comes on with the ignition, via a solenoid wired to the battery. It isn't controlled by the computer at all.

I have no idea if I even have a fuel pump relay. Could the computer be not sensing the fuel pump, so not allowing the engine to run, even though it's got plenty of fuel at the rails?
(~45psi)

 

Did you check fuel filter, Afpr, and Injectors? Also Im Probably wrong but i thought ecm 1227165 was for MAF and not SD? I have a 1227165 ecm for my car and i looked up the application and it was for a MAF. If Im wrong sorry for the post.

 

I kept reving it up manually for a couple minutes and finally it would stay running but the idle was crazy loopy.
It would idle down to about 500 like it was going to die but then it would bounce back up to about 1500, then back down, then bounce back up. Somewhat like a "searching" condition.

I have a new Bosch 3 wire heated 02 sensor. I disconnected the signal wire and started it and it ran exactly the same.

The fuel filter is about a year or so old, the fuel pressure regulator is an aftermarket adjustable unit, relatively new also.
I can recheck the ohms on the injectors, I haven't done that lately. I did check them with a diagnostic tool and they were all pulsing correctly.

yeah you're probably right about the ECM I switched 'from' the 165, to an 830 I believe.

 

All vacuum Lines are ok? Did you check the IAC motor?

 

I was just going to suggest the IAC. Vacume lines first. Then, take the IAC motor out of the Throttle body. PLug it in to the addapter. Jump the ALDL a and b to put the car into diagnostic mode. put a plastic bag over the iac motor so the pintle does not jump out. Then, turn the key on. The pintle should extend out all of the way. So you should try and rock the pintle back and forth so it is compressed prior to turning the key on. I did this just a few days ago. My IAC was bad, beyond cleaning. Since I replaced it, it runs like a charm

 

The IAC is new, about a year old from auto-zone.

The vacuum lines look good. I only have 2 vacuum lines to my brake booster and fuel pressure regulator.
Everything else is blocked off.
There is that line that goes from my valve cover to the throttle body too.

 

your iac is a year old. I doubt it is bad, but you should check to make sure it's working, never assume.

 

Ok I pulled my codes (thanks RednGold86Z), and here's what I got;

33, 41, 42, 51.

 

42 is the EST, brown wire you disconnect when setting timing.

33 I think is either the MAF OR MAP sensor

51 and 41 not sure, i'll try and find it in my EFI book

 

I looked in the Thirdgen FAQ and;

code 33 - high voltage (low vacuum) MAP
code 41 - fault at cam sensor OR
cylinder select error OR
tach input error
code 42 - fault at electronic spark timing circuit OR
fault at direct ignition system OR
fault at fuel cutoff relay circuit
code 51 - PROM error

I searched for how to check the MAP voltage, but what about all the other stuff?