davescustomperformance

I'm having a bit of an issue with my 88 N/A (s4) and something cutting the fuel, atleast to the rear rotor. I have most of the standard mods, including most of the emissions removed, Apexi SAFC-II (where I got the data that I will tell later), and pacesetter header. Most of my other mods seem unrelated to this problem, but if anyone has ideas, i'll list them all. Anyway, I was playing around with my car before I had to go to work today (always the wrong time to do stuff like that) and I decided to make the 5th and 6th port always open. I had done this before with no problems, until today. After I tied wire around them to hold them open, I started it up and it idled fine, which never happened before when I did that, usually is stalls all the time. On my way to work I got on it and at appx 6000 RPM it started bucking violently, backfiring and would not climb any further. Then on my way home I decided to play with it some more and got some info from my gauges. My AFC read 5800-6200RPM, AFL (airflow) 50-52%, Throttle 100%, Knock 0. When it starts this the A/F flickers back and forth from "normal" (where I like to keep it) and the lowest LED on lean. I never saw a single count of knock, nor heard any, the engine runs fine up to the point, and beyond that without being at full throttle. I have an inkling that it may have to do with the air meter, but I haven't found anyone else to have this problem. I know people have these ports open all the time with no problems, as I have had in the past. Also take into account that it acted this way with the MAP sensor plugged in and not plugged it (ofcourse that doesn't mean much since it's N/A, just give a little bit of advance). I have not reset the ECU since opening these ports, and it has been run a lot without them open. since my header only has the O2 sensor reading the rear rotor, I have no idea what the front is going through. I have not yet inspected the manifold or the cylinder valves for the 6-ports, nor have had a chance to read my plugs (which are fairly new NGKs). And most importantly, it is an RX-7, which I'm sure we all know how picky those can be. Any info would be greatly appreciated. my e-mail is dave@davescustomperformance and AOL s/n is darknesshydra
Thanks

SonicRaT

iTrader: (6)

Check the voltage at your fuel pump. When was the last time you changed fuel filters? High RPM hesitations are common on FC's. Here's generally the rule of thumb

Check the TPS and make sure it's highest range isn't out of spec (should be no higher than 6k ohms IIRC).
Replace fuel filter/plugs/wires. Clean the intake filter
Check voltage at the fuel pump
Add/fix up the grounds for the engine (this is the most common solution)

Generally doing those will clear up 90% of the hesitation cases.

davescustomperformance

Sonic
Thanks for the info. Here's what I have so far. I installed a direct power wire to the fuel pump via a relay, the TPS checked a few days ago and was good (since it's a S4, that does mean much), The plugs, wires and fuel filter were replaces about 6000 miles (max) ago when I installed a walbro 255 (yes, from my old DSM). As for grounding I have the stock ground point, 1 to the driver strut tower, 1 to the passenger strut tower, 1 to the front and 1 to the rear rotor housings and one to the rear of the vehicle where my fuel pump is grounded. I have this gut feeling that is has to do with the air meter, because it seemed to be acting up at 50%, not so much at a certain RPM (well, flow and RPM are directly related, just in a weird way here). I hope this helps anyone come up with more ideas.

SonicRaT

iTrader: (6)

Have you checked your fuel pressure regulator? A walbro will kick the **** out of a stock pressure regulator. That pump is some extreme overkill on a non-turbo.

davescustomperformance

That could be an issue. I was planning to turbo it in the near future and am no longer running the stock regulator. The one I'm using is from a 1991 Eagle Talon 4G63T, boost dependent +1/+1. I had to the the rail machined out to accept it, and had to do a little modification to the regulator's bracket, but it fits and seals nicely. I still have the solinoid between the manifold and regulator hooked up. Fuel wise, I also have the pulsation damper removed.

SonicRaT

iTrader: (6)

Have you attempted to pull any codes from the ECU? I get some strange hesitations with my s4 due to a bad thermosensor. Other than that, it seems like you've got all the fixes in place for most causes.

davescustomperformance

I'll have to try that. I really have to do some more research, especially reading the plugs, that tells you a ton. I'm also going to see what happens when I push the meter wide open and what it registers on my afc. I'd run it "4-port" and be happy, but I don't feel it does it justice. I was also kinda curious about how it would feel to have all 6 open when I shot some nitrous into it. I have it jetted @ 37/37 ~900psi n20, 5-7psi fuel (independent pump), it's listed as 50+hp, but i don't have any dyno run to prove it. I know the butt-dyno thinks it's good, but it doesn't spit out numbers. Anyway, a tib bit more info that may be useful. Here is my safcII adjustment with stock injectors @ throttle point HI (set at 90%, still on a S4, so if you press the throttle half way, it thinks you're at 100%) 52000rpm = +6%; 5800rpm - +6%; 6400 - +8%; 7000rpm - +9%; 7600+rpm - +12%. These were all dial in when I was running it 4-port, but it stays about the same (up to where it acts up) on the A/F with the ports open. The variable resistor is maxed for richness, and the idle is set around 1100rpm, unless it's cold, and then the idle is a stall... I might as well just make a page called "How Dave tuned his RX-7" and write out all the specs of everything I've done. Oh well, it happen I guess.

SonicRaT

iTrader: (6)

Holy christ. A N/a should never require you to ADD fuel. The damn things run so rich stock that they require you to remove fuel. Have you had it on a wideband at all? I'd be willing to bet you're running insanely rich with that thing.

davescustomperformance

I have bypassed air, that is why I'm adding fuel. at 800rpm (i think it's still set there) I have +27%, 1400rpm - +13%, that keeps my idle in line most of the time. I will have to look into a wide band (or 2...) and definately 2 EGTs. I guess I'm getting to the point where I need more gauges to go fast, but not in the honda sort of way.

SonicRaT

iTrader: (6)

How do you have it bypassed? This could be confusing the ECU. A wideband or an EGT would really let you know what's going on. I'm assuming you have true dual exhaust, thus why the need for '2' of everything?

davescustomperformance

I have a breather filter behind the surge tank that goes directly to the IAC and that other little annoying valve. As for exhaust, it is a 2-to-1, but it doesn't combine till after the transmission. I feel that it is too far down stream to get a good reading at that point. If I keep it N/A or twin turbo, I'll probably go with an X-pipe idea, if I go single Turbo, I'll just run 3" full turbo back (maybe open dump wastegate for kicks).

davescustomperformance

OK, I was playing around with my air meter today and got a little more info. On the AFCII, when the flap is held the whole way open it reads 68.XX, the last 2 numbers jump around. I put another meter I had laying around into the car, and when I checked it the same way, it gave the same results. At this point I am completely confused.