Rough start after cranking
 

A month ago I installed a MS3 PnP Pro on my otherwise stock 97 with 60,000 miles. I spent a couple weeks tuning and getting things dialed in, things were running pretty well. A couple of weeks ago I installed FlowForce 640cc injectors - everything is mostly dialed in, however I have been experiencing issues with starting now that were not present before with stock injectors.

Issue 1: On cold starts after sitting for a day or so, the first start is very rough - a bit longer cranking time and very rough/hesitation after the engine starts to catch. As soon as the engine catches and switches over from "crank" to "run", it shudders as it climbs in RPM. A couple of times it died and was not able to fully catch.

Issue 2: After the engine catches and starts running, the rpm rises based on the Idle Cranking duty setting on the IAC, the car switches over to closed loop idle, and the rpm begins to fall towards target set by the CL Idle curve. As it approaches the set point after tapering off, the RPMs rise back up away from the set point before eventually settling back down. I'm not sure what is causing this oscillation, it seems to only be a problem on startup. Occasionally, the engine will also stutter as it approaches the target RPM, but not every time. You can see the general behavior and stutter in the attached log from ~12s to 14s on the first start.

My primary issue is the rough start after the engine "catches". The rpm oscillation after entering closed loop idle is typically less bothersome but still annoying. I attached a .msl and .msq.

Additional notes and things I tried since switching injectors:

• Adjusted Dead Time curve per specs on FlowForce's website, 3Bar fuel pressure
• Adjusted small pulsewidth curve per FlowForce specs
• Adjusted required fuel; technically I should have been around 4.94 based on injector scaling, but I bumped it up to 5.40 after the first start as it seemed closer based on my current VE settings. Wondering if this is causing an issue - I understand required fuel to be the "base" used in the fueling calculations, but I also think cranking pw is calculated purely as a percent of required fuel? This would mean cranking would be a bit richer if I didn't adjust cranking PW after installing injectors.
• I tried making changes to Priming PW and Cranking PW, I have not noticed any major difference in how the car starts. Again, the problem doesn't seem to be in the cranking phase, it seems to be in the early running phase.. might be wrong thinking.
  • This only really happens after the car has been sitting for 8+ hours, so it's been hard to test. It starts nice after the initial hard start.
• I got my battery tested, just because. Looked A-OK.
• Ordered a new fuel filter - need it anyway, haven't installed it yet, don't see this helping.
• Read lots of posts and googled for similar issues, really hoping noob isn't being noob here... :bang:

You shouldn't make up for untuned sections by adjusting the req fuel. You should just tune what is needed to make it run right. Other calculations may be off as a result.

Regarding issue 1, have you employed the WUE autotune feature in Tuner Studio? You made no mention of it.

BEFORE using it, fix your req fuel and get your idle cells properly set for AFRs to match your targets on a hot engine. Make sure the hot idle is relatively stable. Then run WUE autotune next time the engine is completely cold. You may want to fine tune it again later after a good cold snap but it will help immensely during warmup in the meantime.

I target WUE to phase out by reaching 100% about 10 degrees below my thermostat opening temp so it doesn't accidentally come into play during normal operation. Everyone has their own preferences.

I guess I should clarify - my VE table was pretty good before switching injectors. I tuned for a couple of weeks on the street on stock injectors, learning megasquirt. I was happy with my AFRs in cruise, wot, etc. Generally everything was okay, and the car started nicely. My goal was to get everything pretty close before swapping injectors so I wouldn't need any serious changes after the swap.

My understanding is req fuel is used in the fueling calculations as a base number and it is somewhat arbitrary if your other settings are set correctly. My AFRs driving around town and under load are good throughout the RPM range. I could bump my Required Fueling down to the "calculated" value, but in theory I will have to scale my whole VE table accordingly to maintain AFRs where they are. My understanding is the VE table is referenced after the car is started which is where my issue was. Correct me if my understanding here is wrong.


My idle is very smooth. I idle at around 14.4, seems to be where the car is happiest. Hot idle is rock solid. I am using WUE, you can see my settings in the tune I posted. My AFRs are high 12's low 13's while the car warms up to about 180F CLT.

I have done some more troubleshooting and I am beginning to think I need additional fuel. I have played with upping ASE in the cells 90F and below, it seems to be getting a bit better with ASE up in the 70's, but still not perfect. Does this seem high? Maybe I should be upping the WUE as well. Either way, the car seems to want quite a bit more fuel at the very early stages of switching from Crank to Start.

I attached another log where you can see the car die after "starting". I then started it again, it started right up, with just a slight stutter on start. This seems to be the general trend: If the car doesn't start the first time, it'll start right up the second time.

Did you ever get this sorted? I'm seeing the exact same issue.