How to diagnose Fitech units
Hello all,
I'm new to the forum, but I've been running my fitech 600 PA for a few years now. I have it on a 351w with a mild cam, Dart heads, and auto trans. I have been loving how well it has been running the past year.
A few weeks ago, I pulled out onto a main road and it started running rough. As it got progressively worse, I tried a few quick things to diagnose it. I pulled the plugs, and they were gas soaked on cyl's 2,3,5,8 and fouled on the others. Thought maybe I should rule out ignition so I swapped in a spare ignition system. It didn't help, so I looked into my fuel pressure. I put my gauge on the fuel return port and it holds 58psi steady. Then, I looked for a stuck injector by watching the prime shot but they all looked the same. I tried resetting the tune but that just made it really bad now, it just chugs along and runs wildly rich (it chases me out of the garage with tearing eyes, lol).
I guess I need to watch the sensor values now and see what looks broke? Do we have a list of normal ranges? Is this something anyone has seen before and has some pointers on?
Thanks for any help,
copracr
First try to start to start the car and look at the, MAP, AFR values on the handheld. If the MAP value is high ( 90+), you may have a collapsed MAP sensor seal that needs to be trimmed or replaced. There is a procedure here on the form about the MAP seal. If the MAP value is good, than check AFR value.If the AFR is low at idle ( 10- 11.4), it could be a bad O2 sensor casing it to run rich.
It won't idle, but it sits around 90 before firing it up and at 2k rpm, running really choppy. If I goose the throttle it will go down to 60-ish on the way down. Is that normal?
The boost/vacuum is at 3 when it used to be at 10, and the AFR is stuck at 14.7
Quote from copracr on July 3, 2022, 1:44 pmIt won't idle, but it sits around 90 before firing it up and at 2k rpm, running really choppy. If I goose the throttle it will go down to 60-ish on the way down. Is that normal?
The boost/vacuum is at 3 when it used to be at 10, and the AFR is stuck at 14.7
Map is good, as if the MAP seal was bad, it would remain at 90+. When you say AFR is stuck at 14.7, is that at idle? And does AFR change if you press on the gas ? If AFR stays stuck at 14.7 even when pressing the gas pedal, it may be a bad O2 Sensor or check the O2 sensor wire to see if it got too close to the exhaust and melted. If replacing the O2 sensor doesn't help, save your settings to the handheld and load a stock tune file to the ECU and enter all values like it was new to see if it helps. Also check to see if you have any exhaust leaks on the exhaust side where the O2 sensor is installed, as if there is, that will wreak havoc in the ECU changing values as it tries to tune.
A few more questions: 1. Are your using the Fitech to control timing? 2. inTank or external fuel pump and brand of pump. 3. Have you checked fuel pressure with a gauge? 4. Have you checked the fuel filter to see if it's dirty?
If all of the above doesn't help, it may be the ECU being bad as the first gen ECU weren't as reliable as the new gen ECU's and that is a hit a miss scenario as I have the first gen ECU on my fitech and have had no issues for 5 years so far. The difference between 1st and 2nd gen is the 2nd gen has a external fuse box with fuses and the Main and Fuel pump relay, which are replaceable.
You are gonna laugh at me soda.
I figured I'd try a new o2 since it was 5 years or more old at this point. It didn't help at all. I have a GlowShift fuel pressure gauge and it was holding nearly steady, but I got to thinking that it used to be rock solid. I bought some fittings to put a fuel pressure test port on it and sure enough, the fuel pressure was bouncing around.
I had my send and return line ran to the front into an Aeromotive regulator (that was expensive, and it was only there to making swapping back to a carb really easy) and then one feed line to the fitech or carb. I bought some more fittings and line and just eliminated it.
Runs like a champ now, just really rich. I'm hoping the ecm will adjust it out as I drive it.
Thank you for setting my mind on the fuel pressure SodaPop, I really appreciate that.