Stussy

I have a 1987 S4 TII. I have weird problems with AFR running lean on low throttle. Below are YouTube videos of each of the problems I am about to address, and I will have a description on each of them, followed by a summary and relevant information at the end. Grab some popcorn, may be a long read. Any insight is greatly appreciated.

• AFR at startup

This is my AFR on startup, it never used to do this. It does this on a cold start (shown here) and a hot start. During the hot start, it does the exact same thing, but seems like it is flooded instead. When it warms up the car idles at 1000-1100, except when the volts drop to below 13, then it idles at 850, and sometimes dies off. It will not idle with the lights on. I have a new AFR sensor installed as the last one went bad for some reason, only 1200 miles on the new engine, and previous sensor. It starts at 14.7, then goes down to the actual AFR value. Is the car running lean right away at start up?

• RPM while pressing brake

Dont know if this is an issue or not, but the RPMS go up while pressing the brake. Is this a sign of a vacuum leak?

• Lean on first gear low load acceleration

This is the biggest issue, and the one that scares me the most, it may be tied into the next video also. This is the most obvious in first gear. I know the AFR values are hard to see, but trust me. At idle I get about 11 AFR, while pulling away it ends up at around 14 AFR, but then sometimes it goes to 16 or 17, and I can feel a buck, and a loss of power. It can also happen if I am moving slow in first gear, then slowly speed up. This is only when boost is NOT applied, when it is applied, it runs well. The next point will elaborate a protentional cause of the issue.

• Bouncing AFR at certain throttle point

This is a strange problem that has pretty much always happened. My throttle pedal seems to have two positions (I think they all do). The first portion is easier to press, and doesn't activate boost. The second portion is the after the first, is harder to press, and is where the power comes into play. When I am in the second position, the AFRs are fine, as I am boosting and getting good fuel, rich if anything. The first position is strange. There seems to be a certain load point that makes the AFR bounce from 14-16. The car does feel a little different, and kind of jerks just a little bit (may be placebo). If I back off the throttle just a hair, the AFR stays steady somewhere in the 12 or 13 range. I mean steady, doesn't jump around at all. I just adjusted the TPS using the ohm method, and had a reading of 1.02 Ohms. I figured that was good enough, I also slowly actuated the TPS to make sure there wasn't any dead zones. There was no bad spots in the TPS. This issue will happen in every gear, and Im wondering if it contributes to my issue of lean on low load acceleration. If I mash the throttle, there is no issue. The issue mainly happens when it seems like I am right on the verge of going from throttle position one to throttle position two (easy and hard).

• Forum post kind of like my problem but has no solution.

This is something I found with close to the same issue (I think)
https://www.rx7club.com/2nd-generati...-889547/page4/



MOD LIST

• Fuel
  • Walbro 255 Pump, new sock
  • Rewired fuel pump to relay, 12V
  • New Hard fuel lines, OEM size, to fuel filter
  • New OEM fuel filter (I premix 0.5oz per gallon)
  • Parallel fuel system
  • Aeromotive FPR at 40 PSI
  • New 550 CC primary injectors
  • New 720 CC Secondary injectors
  • Have a small fuel leak, think it is out of the gas tank, doesnt pool up on the ground
• Engine Control
  • Cleaned all the grounds
  • Going to be adding DC Power alternator soon
  • RTEK 1.7 ECU
  • APEXI NEO piggyback (I turned off the fuel map, and the same thing happens)
• Other related mods
  • Ported Wastegate
  • Emissions delete
  • Racing Beat Rev TII exhaust
  • Stock airbox
  • Stock engine port
  • Rust for weight reduction

Other Information
Tps/Timing
As mentioned before, I have set the TPS and insured there are no dead zones. My timing could be slightly off, as I was not able to get the car to idle down to 850 at the time of setting it, but it is in the exact same spot as when the engine was removed before rebuild.
Rich at WOT
The car runs very rich at WOT, lower than 10 AFR, and the car is hesitant, I tuned this out with the Apexi NEO, and it runs better at WOT,
2 stage throttle pedal thing
Just for future reference, what is this called, where it is lighter to press at first, then gets a bit harder. Anyway, my car does it, hope its normal.
Vacuum issue
I recently hooked up a smoke tester and fixed any vacuum leaks I had, the main one was because I forgot to i install the diffuser under the injectors. These issues were happening before this.
Other notes
The low load lean condition may have started happening at the same time my AFR gauge started acting weird on startup. I can also hear my fuel pump. If this issue is caused by my filter or pump, why would I be rich at WOT?

Overall, Im confused and annoyed. The car runs well with decent power, these are just the only issues that dont make it run perfect (Except my diff that has slop, but that's for another story)





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Stussy

No thoughts? The car is still going to 17 afr under light load, sometimes bucking like a ****. Tested the afm, turned out good.

WondrousBread

I think (regarding the strange pedal feel) that what you're describing is the secondary butterflies. Unlike most cars the Rx7 has a primary butterfly that cracks open first, then two secondary butterflies that open when you press the pedal further. At WOT they are all completely open. So this is not unusual per se.

Regarding the AFRs, I feel like the TPS is the likely candidate since it seems to be load-related. I know you have adjusted with the resistance method, have you tried the voltage method?

Personally the two-lamp method has always given me the most reliable results, but that requires a bit more setup.

Stussy

Thanks for the response! I’ll try a different method, and make sure the butterfly’s are clean.

WondrousBread

Even with the butterflies clean, the feeling is normal. Certainly not a bad idea to make sure they're operating smoothly though.

Since you have the S-AFC, can't you just add fuel at the appropriate areas of the map to fix the lean condition? At least as a temporary solution for safety.