Hi everybody, my name is Jon and I have 73 mustang convertible with an 89 5.0 bored out to a 306. I just installed a FiTech EFI and fuel command center. The car started great initially but was ideling at about 1500 rpms, I fiddled around with it and had it down to about 800 last night. This morning I started it and the engine is now surging between 1500 and 3000, and IAC is stepping around 150.
Also, I can't get the CPU to save my changes.
Any advice is welcome.
Hi Jon, glad you got it running. Here are some things I learned putting a dual throttle body system on my hemi charger which might help you get it running even better.
The ECU does not save ALL settings from the handheld even if you "sent" them from the handheld until you power off the ECU for about 30 seconds. (Key off, wait for all dashboard values to go blank, then changes are saved)
Cold idle RPM is not necessarily what you set for idle RPM. You can check this by referencing "target" RPM on page 2 or so on the dashboard. It gradually falls to your set RPM as the coolant temperature comes up.
No ECU learning occurs until the coolant temperature reaches 130 degrees.
The ECU requires a minimum of 10 volts. Most B+ circuits on our older cars have a significant voltage drop during starter engagement, down to 6 volts or so. You must grab key on 12v near the ballast resistor, on a circuit that doesn't drop during crank.
I'll agree with the previous poster that the most likely cause of your idle surge is a vacuum leak. I didn't have a vacuum leak before I put the Fitech on, so I disconnected and plugged heater box vacuum controls and hideaway headlights, as well as the brake booster and I STILL had a leak. Found it in a very unlikely place. The Fitech throttle body to intake manifold mounting flange is just a hair less tall than the carburetors I removed. Check the studs in your intake manifold and make sure you are not tightening the throttle bodies to 16 ft lbs against the unthreaded middle of the mounting studs since the Fitech mounting "ears" are less tall than the carb you removed. Put a die and thread the middle of the studs down further, or add a washer at all four corners.
The second slightly less likely reason for RPM surge at idle is a dirty RPM signal to the blue wire on the Fitech ECU. You should, but may not, have a fault code if this condition exists. Route the blue wire as far as possible from coil, spark plug wires and other potential sources of electrical interference.
The ECU is grounded by the engine block. Check and make sure you have a grounding strap block to battery, battery to frame, and block to frame.
Your IAC steps should be 3-10 on a warm engine. These will not be valid until you fix the vacuum leak/dirty RPM signal. Work on that first, then set your IAC.
Hope this helps.