Lean Tip-In Lean Stumble and Weak Idle (Possibly Solved)
I recently solved a lean stumble problem and it was a journey to say the least. I wanted to summarize what I found and learned in one place to help future readers and others struggling with these issues.
I have a 30002 EFI 4 600HP purchased approximately 10 years ago as one of the early units. I have never flashed or updated the firmware.
Setup:
- 1972 Oldsmobile Cutlass Convertible.
- Oldsmobile 455 street machine. ~500HP.
- Moderate Cam.
- Tanks-Inc fuel injection ready tank. In-tank Walbro fuel pump. 10micron downstream 250gph fuel filter. Stock Fitech fuel pressure regulator (originally).
- originally THM400, currently 4l80e with Saturday Night special TC.
- MSD ready-to-run distributor.
- Completely custom everything. All wires, fuel lines etc. (Note, Do NOT run aluminum fuel lines!)
- Edelbrock RPM intake manifold (looks identical to stock for an Oldsmobile, but aluminum.)
- Drop base 3" tall round aircleaner. I mention this because I believe the drop base is hurting performance and could be affecting flow pattern into the Fitech. I haven't had a chance to experiment here yet but I've seen tests to suggest this.
Assuming your initial install is done correctly:
- No vacuum leaks
- No exhaust leaks upstream of your O2 sensor.
- Correct fuel supply pressure (Fitech sells a 3bar and 4 bar unit depending on your model.)
- IAC steps between 2-10 etc.
- Clean grounds and power supply. Direct to battery is recommended by Fitech if unsure.
- >10.5 volts to Fitech during cranking. Hard starting could result otherwise.
- Proper AFR setpoints (Default if unsure).
- Note that with 10% ethanol fuel (E10/most pump gas), 14.7 is not stoic. 14.1 is. You probably aren't running as rich as you think you are if your targets are around 14 AFR
- Depending on your vehicle, a relay for your fuel pump, and at least proper gauge for the long distance wire run. I have 10 gauge ran from Fitech to the in-tank pump.
Early Issues
RPM noise code. I swapped to the distributor tach rather than coil negative which resolved this. Wrapping wires in foil, building shields etc made no difference. Make sure you change the setting in the handheld according to your RPM signal source, or you may have a no-start condition. I had this setting revert to factory on me after unplugging the battery for a while, which led to frustrating troubleshooting. This noise code, even though I resolved it, did leave me wondering if it was also my idle issue (it wasn't).
Stall or stumble when shifting to drive or reverse. Overall the car idled like it had a much larger cam than it did, weak and erratic, smelly, with noisy RPM. I thought this was partly due to a tight torque converter on the THM400 and planned to upgrade the transmission anyway so I converted to a 4l80e. This did not resolve or change the issue but I love having my 4l80e!!
Severe lean tip-in, especially after a coast or idle, causing backfire and/or stall. This occurred at pretty much any condition, warm or cold, but was worse with faster stab of the throttle.
Rich and raw gas smell at WOT. I did have some fuel leaks at the top of my Tanks-Inc tank and assumed this was the cause. I finally repaired these leaks and still had a raw gas or fuel smell enter the cabin after a long wide open throttle run, and occasionally while running in the shop. I began suspecting a weak spark at a cylinder or some other issue. The true cause was the fuel pressure regulator as noted below.
Troubleshooting steps in the order I tried them:
Wired fitech hot directly to battery rather than a fused distribution block per tech supports recommendation. Also grounded a throttle body stud directly to battery. Neither made any difference.
I adjusted the accelerator pump settings which did help with the lean tip-in issue, but it did not resolve it. I eventually had all ACCPump settings (fast and regular) and all temps maximized at 100 and STILL had a lean tip-in. I began assuming I had a severe vacuum leak causing this, which I don't. Turn on pro-tuning for additional acc pump settings, including decay and response rate. Accpump settings made no difference to my idle rough running issue though.
Turn off PWM if your fuel pump or relay setup does not support it. I disabled this as Walbro specifically says it's not compatible, however it was not the cause of my issues either.
Trimmed the MAP sensor gasket as indicated here. No improvement in my case but is a good practice based on the number of issues being seen. If your MAP sensor is not fluctuating >10 on normal drives, this could be your issue. I am worried I have damaged my map sensor due to lean popping at this point, however I am not sure how fragile these units are and it seems to be working correctly.
Adjusted Secondary butterflies. Mine had an enormous amount of play in the secondary's, and I was able to turn the rod nut at least 2-3 full turns. I had to readjust my IAC steps after this so it made a difference.
- https://fitechefituning.com/fitech-efi-tuning-forum-2/topic/secondary-adjustment/
- https://fitechefituning.com/fitech-efi-tuning-forum-2/topic/lean-under-minimal-throttle/?part=2
Try changing or verifying your cam settings (1 through 4). Look at your fuel trim adjustments that Fitech is making to see if they are significantly high or low, which indicates you may need to change your cam setting.
Disabled DFCO. This actually did help alot, as based on my logs it seemed my lean stumble was worse after DFCO activated based on the default settings. I turned mine off for the sake of troubleshooting, however the correct solution is to tune DFCO as needed, by adjusting return fuel and cutoff MAP. I have not yet reneabled DFCO but plan to.
Changed throttle body gasket and added a gasket adapter plate (~$5 from Summit). At this point I had had the unit off a number of times and suspected a vacuum leak. This did not solve any issue but was a good practice at this point. Since this was a new motor I also retorqued the intake manifold bolts.
At this point I began suspecting a fuel supply issue. It made no sense to me that I was still have a lean stumble upon acceleration unless I was losing fuel pressure, had a huge vacuum leak somehow, or had a defective unit. I pulled the fuel pressure regulator vacuum line to do a vacuum test and fuel residue dripped onto my finger. BIINGO. I tested the pressure regulator with a handheld vacuum pump and it passed. It held ~25inhg vacuum for over 10 minutes. I can't explain this, however for fuel to leak past the diaphragm it was definitely bad. I suppose this surprised me to learn that a vacuum test alone can't verify if your regulator is good. Upon closer inspection, it is a counterfeit knockoff Bosch unit (made in China) with Bosch's part number. Do not order a replacement from Ebay or Amazon as it will likely be another counterfeit. Summit, Jegs, or a brick and mortar are your way to go, and should say Bosch and made in Germany, Brazil, etc. It may be more expensive but for a reason.
- Replacement 3 bar unit is 280160557
- Replacement 4 bar unit is 280160575 (mine)
I also ordered a new fuel filter since I was suspecting a supply issue, but I do not know if mine was plugged or not. If you are running fuel injection you should have a 10 micron filter downstream of your fuel pump or you are asking for regulator or injector failures.
- TNK-FF-10
Results
After replacing the fuel filter and regulator my car completely transformed from a lean popping and lazy turd, to the street machine it was meant to be. This time I left the vacuum line off of the regulator as I am naturally aspirated and don't need it anyway. I then reset all the learned parameters (change from 0 to 1 in the option in the handheld) and am letting the car re-learn itself. I also reset all accelerator pump fields to 0 (default) to see how it behaves, and tune from there.
My regulator has been bad since day 1, and I have been fighting it with tuning and other adjustments for over 5 years. In hindsight, I recall the fuel pump having to fully prime for 2-3 seconds every time I turned the key, even after having recently driven the car. The stock regulator was not holding pressure as it should.
Install a pressure gauge if you are having issues! for about 50 bucks, these two fittings and gauge let you hook it directly to your Fitech throttle body.
https://fitechefituning.com/fitech-efi-tuning-forum-2/topic/return-line-fitting/
- FIF-60024
- FRA-495005-BL
- AEI-15633
- FRA-492906
Current Status
I drove the car for the first time after resetting the learn parameters today. It now starts almost instantly, where before it would turn over a number of times. It idles stronger and has much more power and response. I have 1inhg more vacuum at idle, and was even able to lower the idle by 50rpm. The exhaust gas at idle is also noticeably cleaner. It is still lean popping with an aggressive stab of the throttle, however it has less than 5 miles on the new tune, when it was 25 degrees F outside on a cold engine, and all accelerator pump settings back to 0 or default. I plan to increase ACCpump 10 at a time after driving ~20 miles on the new tune, and see how it does. I am hopeful my issue is resolved.
If you are having weak idle or lean issues, I hope this helps put some ideas and solutions in one place for you. Happy trails.
Update 1:
I'm up to 30 miles and overall everything is running much better after the regulator swap, however it is still spiking lean at throttle tip in-especially after coast and idle, however I'm only at ACCpump of 10 warmed up. I've increased to 20 and we'll see.
LeftLaneBrain
Glad to read you figured out your issues. I have one of the early Fitech units that had the fuel regulator vacuum port open with no hose. I contacted Fitech and they confirmed that it doesn't do anything for NA engines. However, they noted that it was a safe practice to have the vacuum hose connected to the base plate just in case the regulator fails like in your case. It is safer to have the extra fuel dripping into the manifold than on top of the manifold. This made sense to me so I added the vacuum line, but now I know another point to troubleshoot if I have future problems.
Thanks for the reply Tony. This is a good point. I wonder if another approach would be to hook up a drain line to the regulator that runs below the exhaust manifolds somewhere. In this way you will still see/smell a leak, but solves the fire risk of having a fuel leak on top of the motor. A carb, which could flood or leak and pour fuel all over the engine was one of my main reasons to convert to EFI, so this is a good thought.