Engine has started running rough
Situation
I have the FiTech Go Street EFI 400 (30003) installed on a GM 350 crate engine in my 1937 Chev street rod which has started to run rough that I require some guidance to sort out.
Last summer it was running fine though the IAC value was in the 100 – 200 range. Come the fall, the engine started running rough upon initial start up but sorted itself out after 10 – 20 seconds. Unfortunately, this settling out period started growing in length reaching 2 – 3 minutes. We’re now at the point where the engine continues to run rough all the time and I need to feather the gas peddle in order to keep the engine turning over. The engine is behaving as if the fuel mixture is too rich.
So far, I’ve changed the spark plug leads, replaced the O2 sensor and replaced the exhaust collector gasket all with out resolving the problem. I’ve also reloaded the software (default V8 T210A GoEFI 30003) and reset the Learning. I have not modified any of the default settings.
The AFR is around 10.5 while the target is 12.5. The IAC starts off around 200 but reduces to near 125 when at operating temperature.
Questions
Where should I focus on in my trouble shooting?
Out of curiosity, is it possible to operate the FiTech without the O2 sensor, i.e. a default mode?
Out of curiosity, what governs / influences the IAC?
Would my IAC values be impacting the operation/ performance of the FiTech?
Your thoughts would be appreciated.
How old is your FiTech unit? Does it have a external fuse and relay box? I ask because of the firmware version you have. You need to focus on IAC as yours is way out of line. Should be between 3 and 10. Also when you set the IAC make sure you adjust the front and back IAC adjustments screws. Also check for vacuum leaks on the various ports on the EFI unit as it will greatly effect IAC. Especially look at the port you would use for power brakes as it can be tricky to install the vacuum line. I had to remove the EFI unit to properly seat the Vacuum line for the Brake booster. Also check to make sure your timing is set properly as it will greatly effect how the EFI unit runs. I only use GM branded distributors in my car and others I have set-up for, since the 30003 unit doesn't control timing. Too much Chinese made junk being sold now a days.
Thank you for your reply.
I didn't delve into my FiTech history as I don't believe it impacts today's problem but here's a quick synopsis. I purchased the 30003 system back in 2020 and after resolving some electrical issues, finally got it working. Come the summer of 2021 I started encountering heat related issues that ultimately resulted in replacing the ECU assembly with the new design (external fuse/relay box) and the Hand Held Unit. The following year I had to replace the circuit board in the distributor (brand name unit) as it was producing a noisy pulse when hot that the FiTech could not sync off. Last summer was the first fault free season until this issue arose.
My buddy & I worked on the car today, verified we had not vacuum leaks around the intake manifold & throttle body base. We validated the power brake plumbing and check valve - no leaks there and everything is functioning correctly. We readjusted the IAC adjustment screws (yet again), set the CAM to 1, disconnected the vacuum line to the distributor (and capped it off) and set the idle to 800 rpm. The engine now started and idled smoothly on it's own. The IAC (once the engine warmed up) was around 0. The vacuum was -9.8".
Moving forward we plan to connect the distributor to the "un-ported" port and review the engine timing. This will be followed up with test driving over the days to validate operational behaviour at various temperatures.
What brand of distributor are you are using? If it is MSD, replace it as it is now made in China and total junk. I just use a GM branded HEI distributor that I buy from GM. No issues what so ever with that distributor. To prevent heat soak and help keep the EFI unit running cooler, use a non metal spacer under the EFI unit to prevent the EFI unit from absorbing heat from the intake manifold. Makes a HUGH difference. I also use a electric fan with a PWM controller that runs the fan for a few minutes after shutting down the car to prevent heat soak. You would be amazed how high the temperature of the engine gets after you shut it down due to heat soak. Because of your Vacuum you may need to use the CAM 2 setting. Fitech has a video explaining this. You still need to tweak your IAC to run between 3-10. I have had my 30003 unit in my car for 8+ years, with no issues.