Hesitation at low throttle
 

Hi All,
I' m just getting my car running after years in storage. I remember having some issues before putting the car in storage 7 years ago and this issue seems vaguely familiar but I can't remember in detail.

At low throttle conditions I'm getting a severe sputtering/hesitation/stumble/misfire/bucking, Not sure what the best terminology is. But as soon as I get off throttle on light load (starting from a stop or cruising at a stead 50 or 70km/hr) the car falls on its face. It feels like the car isn't combusting consistently like its misfiring when I'm at these throttle conditions. I have a power FC with a single turbo (EFR 8374)I did the tuning myself, I was learning tuning before the car was put away for storage. Because of this I don't have alot of confidence in the tuning but I know I definitely had the car running without this issue sometime prior to storage, I'm not sure If i changed something just before putting the car into storage or if this is in fact a new issue.
I've got a power fc master and I was going to get FC tweak to assist with tuning now but with this hesitation/misfire issue as bad as it is It almost impossible to drive the car enough to get any of the logs needed to start tuning.

My fuel pump failed during storage and I have just installed a new walbro 350 fuel pump. I have a fuel pressure gauge and a wideband. During the hesitation range my AFR's shoot up into the area of 19-22, so I'm going very lean during the period for some reason. If I throttle up enough the AFR's drop back to 12-14 and the car runs normally. the car also idles fine. My fuel pressure is stead through this period which should eliminate fuel pump and fuel filter as causes (the pressure sensor is at the fuel rails). The injectors are stock 550 primaries with 1680 secondary's. If there was injector issues I would think that the car either wouldn't idle or it would have issues at higher rpm/ loads with the secondary's online. I can monitor the TPS signal on the fc master and the signal is moving smoothly with throttle application, which should remove the TPS as an issue.

I've found some similar threads online but I feel like I've eliminated the common issues. I'm starting to lean towards the fact that something may just be seriously wrong with the tuning. I'm thinking I'll get FC tweak pro and just start a tune from scratch using that. I'm open to any other potential causes that I should be looking at.

Have you ruled out fouled plugs?
What coils are you running?

The change since it was running well was fuel related, and storage. So, I would also pay close attention to those variables.

Can you save your tune, and start over with a fresh base tune and see if low throttle drivability is improved? Obviously stay out of boost, but the base tuning with stock sized injectors should run just fine in low load conditions.

I haven't changed plugs recently and I'm still running stock coils.
I would think if either were an issue it wouldn't just be so consistent at one spot in its range.

That's essentially my plan at this point. I think that is the fastest way to rule out tuning as the root cause.

Fantastic troubleshooting.... truly excellent.

based on your description, i would say your problem is one of 3 things: throttle body adjustment, tip in tune related or a fueling issue.

For the throttle body, there is a thread here that explains how to essentially reset it with all the screws and stuff. The upper twin blades can be set in a way that will give something like what you're describing but not quite. It's worth the check either way

"Tip in" tuning related issue is what I think is most likely. The base settings in the power fc basically force exactly what you're describing but not the degree you're describing it. There is for sure an underlying issue but it can be tuned out which I don't recommend. Fc tweak will fix this issue automatically.

A fueling issue is also likely. The fuel filter can and does have a greater impact on things than most attribute to it. If you haven't, the jp3 relocation kit should be a standard service upgrade for all FDs. It's worth the effort. In addition, your upgraded fuel pump could be installed "wrong".

We have a video on our YouTube page on how to properly install an upgraded pump and most importantly WHY to install that way. Finally, the primary injectors themselves could also be the pproblem. They do fail in a variety of ways and of that variety, a partial failure is possible.

I don't mind sending you a map with the tip in setting corrected but I think it would be best to go through the process first. Unless there are sections of your map in the tps vs x tables that have been touched then your issue is an actual issue and not solely tune related. can you upload the map you're using? I can take a look anyway

I tried to find a thread with info on how to reset the throttle body but I wasn't finding a good thread. I found some pointing to "chuck Westbrooks pfc notes" as the best resource. I found a second thread that then lead me to ask arghx from the forum to get into a google group where these notes are now stored but with no answer so far. I most likely messed with the throttle body so resetting it would be good. All I did this time was adjust the idle screw up to raise the idle a bit, this does mean my TPS is slightly open from the base setting, not sure if resetting the TPS to this is a good idea.
I know I had never really had any success setting the idle settings with the pfc in the past so I would like to reset the throttle body and get this working for once.

Right after getting the car running now, before I touched anything, the idle was at about 550 rpm and it wasn't the most stable. I just adjusted it up to 800 while cold and it was steady. Once warm the idle raised to 1000rpm or so without any adjustment. I haven't messed with it much yet but would like to figure this out as well so that it is stead and the same at both temperatures if possible. pretty much everything that made sense to delete was deleted in the past I believe, the ICV is still there but I want to test the function of it, as I'm not sure if it is doing anything.



I ordered the walbro 350 from Banzai Racing, it came with everything and was a pretty straight forward and simple install. I'm still using the stock wiring minus the lead in the fuel tank that I had to splice during the pump install.
The fuel filter was on my to do list. I was thinking about an aftermarket options either radium or the injector dynamic filter with jp3 kit. but I wanted to do more stuff at the same time over the winter so haven't touched or ordered parts yet. I figured since the fuel pressure is steady at the rail that the filter was unlikely to be a problem, if there was a restriction enough to cause issues IO imagine a fuel pressure drop would be observed.


I'll have to find your channel and take a look. I may have a second set of primary injectors I think but they would have just sat out of a car for the last ten years or so. they might be a possible troubleshooting step to try as well.


I appreciate any help. As I'm just getting back into the RX7 hobby I've forgotten nearly all the detailed stuff about tuning and I've been lacking the time to do the research to get back into it. Any and all help is appreciated. I've attached my tune.

That map is a disaster waiting to happen. Fuel corrections are all over the place. You have removed low load fuel all the way up to 3600 RPM, then over in INJ adjust it is done again. I would suggest changing all those low load negative adjustments back to 1.00 and see if your tip in goes away. Car needs a proper tune.

You also have O2 feedback turned on as well as sequential turbos

I'm gonna blame younger me and call him an idiot. So best path forward is to start from scratch.

INJ adjust is a wholesale change that is accessible with the commander for quick on the fly adjustments., Your map has major adjustments at all RPM intervals. I always have all those settings at 100.

The correction screen is where tuning with a laptop is done and when it is complete, it should be recalculated to the base map so that the ECU doesn't need to pull from 2 screens to run the car.

I'll have to do some digging, as of now this largely sounds like a different language to me. I'll do some research to see if I can figure the basics out again. But I will likely largely rely on FC Tweak pro and the FC master to do the initial tuning for me. If/when I get into heavier mods and higher boost levels I'll have to maybe look at different options.

Are we assuming the car is not trying to run on 7 year old gas?

I did drain and fill the car with fresh fuel and premix. a few days before starting I injected two stroke in all the rotor faces through the spark plug to allow it to sink in. vacuum at idle is around 20".
So i don't think its a fuel quality or engine compression issue.

Did you look for corrosion residue in the fuel tank, that may be getting sucked up against the fuel "sock".

I didn't do a thorough inspection but I didn't see any during the pump replacement. I didn't think to take an in depth look. If I have a fuel restriction I would think the fuel rail pressure would drop as a result though, and the fuel starvation wouldn't be so consistent at the same low part throttle spot.

perhaps also check the fuel pump resistor, if that has not already been mentioned.

So on the drive home today I turned off the sequential turbo setting and the O2 feedback setting that Banzai noted was on when it definitely should not have been.

My stumbling/missfire was completely gone on the drive home.

I'm assuming it is likely more the o2 feedback setting.
The new version of the fc master has the wide and signal connected through the factory O2 signal wire into the eco.
my guess is that the power fc was seeing the wideband signal and was likely trying to cut fuel to “correct” my afr ratio in the cruise area of the map. So with the fc master connected in this configuration it is likely extra important to make sure the o2 feedback is off.

tomorrow I might do a short test where I turn the o2 feedback back on just to confirm.

I did confirm on my drive in this morning that the O2 feedback was the cause of the issue.
my guess is that previous to the fc master install (7 years ago when it was last running) I had the o2 feedback not turned off, but since the stock narrowband was disconnected the power fc wasn't seeing any signal and so the O2 feedback was not actually affecting anything.
With the fc master version 2 the aftermarket wideband is connected to the stock narrowband ecu connection. So now the power fc was seeing a voltage signal and was trying to correct the AFR's but obviously would never be able to.
My PSb-1 has a voltage output from 0V = 7.35 AFR to 5V = 22.39 AFR, and the google AI over view says "A rich mixture will show a higher voltage (around 0.8–0.9V), while a lean mixture will result in a lower voltage (0.3V or less)" for the stock narrowband.

I also think I was a bit confused as well as I had believed I had turned the o2 feedback off previously as it was a requirement for starting the auto tuning on the FC Master. I've since learned that when changing the setting in the FC master that there is a "send" button to change the setting in the power fc. I was only changing the setting then exiting the menu and I didn't see the send button.

Nice job on the easy solution to the poor running condition. Great diagnosis and investigation.

Curious how you end up liking the PFC master. I'm still on the fence about going that route since my car is basically bolt-ons, but i did see a good improvement with the FC tweak.

It is Banzai. You’re welcome 😂

My bad, caught it in time to edit my error. Thanks again for taking the time to look through my map and help me find the issue.