s4 cuts out if past 25% throttle
 

Ok so i have an 87 mazda rx7 gtu, 13b 5,000 on rebuild, i removed emmissions via. block off plates, and i removed the secondary butterfly's along with cold start system.
now i drive my car and if i give it more than 25% throttle it cuts out and starts dieing unless i go back to 25% throttle, i do eventually get to speed but it is very annoying speeding up with only 25% throttle being used...

what could this be any help appreciated


~Rian

hi my car did this and it turned out to be the flap in the maf was stuck closed with gummy black stuff. hope this helps

just checked that it functions correctly.

no one to help?

well, when you pull the secondary butterflies you have to be more delicate with your throttle control, because the secondaries are there so that you can floor it and not bog terribly, so when they're removed you can't do that anymore. that might be what you're experiencing, it might not, but I think it's a good guess.

Did you check your tps? After I did the tb mod I had to adjust it.

fc3spro.com has a write-up on how to do it.

so what i can give any more than 25% till after 3k rpms?

Hailers is the expert on RX7 electrical and computer stuff, but from my limited experience and understanding:

s4 TPS isn't a fullrange TPS, and doesn't have much effect on fuel delivery anyway, other than opening the butterflies that allow more air through the vane-MAF which DOES determine the amount of fuel to add.

Since the S4 TPS isn't a fullrange TPS, if you're guessing 25% based on pedal travel, you're probably beyond 100% on the TPS anyway. My bet would be that your secondary injectors aren't coming online, and what you're thinking of as 25% pedal travel has more to do with the 3800 rpm hesitation/brickwall effect.

If it ISN'T that, then I'd have to go with restricted fuel flow, as in bad filter or underdriving fuel pump.

i just bought a fuel pump last week

Check and see if it's starting to bog bad around 3800 rpms...

Not at all. Those secodnary "choke" plates as I call them are there for the safty of the engine while its cold. I believe you wont be able to go past 4000 rpm with those shut. After the engine is warmed up, I forget exactly what temp they open at, they are open all day long. So removing them will not cause any issues at all.

Being at 25% throttle and being at 3800 rpm are completly different times. He can be at 1000 rpm and at 70% throttle. Obveously this is not working for him.


We have a AFM not a MAF (Mass Air Flow) Sensor

Check the AFM (Air Flow Meter). This will happen if the AFM is bad or if the flapper is stuck.

Look in the Fuel and Emmisions Control System of the Factory Service Manual here

The Full FSM is here

That is not what I've heard, and I cut out at 5500RPM versus 6500RPM when it's cold, and my tach may be reading low. If you check the operation of the secondary plates, they simply open along with the primaries, but slower, so as to allow the intake to adjust without choking the motor at any time.

While technically that IS true, as soon as you push the pedal down, at least in MY car, the tach starts to rise - my point isn't that they're the same thing, I'm asking if it's possible that the OP was confused as to whether it was happening only at 25% throttle or at a given RPM, because given the way the system works, 25% throttle in and of itself doesn't mean anything in terms of fuel.

You're getting confused between MAF (Mass Air Flow) and MAP (Manifold Absolute Pressure). An MAF is any sensor that determines the mass or volume of air going into an engine. What the RX7 has is a Vane MAF, a type of Mass Air Flow sensor. You can call it an AFM if you like, but Mazda themselves calls it a MAF when they use it on the B series engines, and the RX7 MAF and B6 engine MAF are interchangable, even down to the connector.

I don't mind being corrected, but it would be nice to be wrong first.

If you'd like to read more about MAF sensors and Vane type MAF sensors, http://en.wikipedia.org/wiki/Mass_airflow_sensor

Oh, and Speed of Life is correct on the secondary throttle plates, they open with a slight delay after the primaries, even when cold, and I've gone beyond 4,000 with them and without them, cold, with no problems.

The secondary throttle plates are to smooth throttle transition, a well trained foot does not need them.

Its definately a fuel issue, if there was anyway for you to tell if it was lean or rich it would help.

What size are the secondary injectors, stock right?

Did you have a working config following the installation of the fuel pump?

thou shalt check thy tps.

Your tach may be reading high. Is this with the "choke plates" closed?

They don't open slower, the open later in the throttle range. At 25% throttle is when they start to open. The bogging is 100% not caused by removing the choke plates. Those plates are completly open when warm so if removing them caused the engine to bog, then your engine would bog with them open while in the TB.

No im not getting confused. AFM and MAF come out with the same answer. How they do it is very different. The voltages are very different as well. you can call it vane-maf but its actually called a Air Flow Meter. It measure air volume instead of air mass. The ECU uses the temp sensor in the AFM and the flap to determin Air Mass, where a MAF can directly measure Air Mass.

Actually he is not, they don't open SLOWER then open later like you said. Im talking about the choke plates not the throttle plates.

Looking up either one goes to the same place because, like I said, they are two names for the same thing. Both are sensors used to determine the amount of air into the engine.

And yes, Speed Of Life IS correct, if you didn't nitpick every damn word in everyone else's sentence. I realized what he meant and gave him a little bit of credit for not being a total idiot. Even if you don't think the rest of us are as smart as you, maybe you could extend some of us the same courtesy? :D

Since you want to press the issue though - Here ya go:

https://www.rx7club.com/attachment.p...1&d=1189812102

http://www.autoshop101.com/forms/h34.pdf

Before saying anything else, remove the TB elbow and look at the secondary throttle plates (not the choke plates). While the engine is off, open the TB very quickly and you will see the secondary plates do not open slowly. They will snap open and snap shut. They open up later in the throttle range, thats it.

The vacuum diaphram for the secondary choke plates usually is bad and doesn't hold much vacuum to close the choke plates as far as they will go. They don't completly block the TB bores. Their is a delay valve used for the choke plates so they open up slowly when cold but while warm they never shut.

Your right, they are both intended to have the same outcome. That artical even states "vane air flow meter". Not a Vane-Maf. Show me where in the FSM or training manual where Mazda states the AFM as being a MAF.

Seems I have confused myself and apologize. Rereading previous posts, SpeedOfLife seems to be talking about the choke plates like I was, yes they do open slowly if there was vacuum applied to them which there only is when the engine is cold .

After the engine is warmed up the choke plates never close so they never have to open.

Like I said above, a lot of times the diaphram can't hold vacuum no more so the choke plates never close to their maximum. When they are closed to their fullest extent, they do not fully close off the 2ndary bores. Driving the car without the airflow running through the 2ndarys when needed, power drops off at around 1800 rpm.

If he was talking about the throttle plates (not the choke plates) then he heard wrong.

And I think you are talking about the Throtte plates and not the choke plates and which if you were talking about the choke plates, you explain the operation slightly different anyways so it would be incorrect.

Seems we are talking about 2 different parts as one.

Same on my car. He specifically said 25% throttle, whether you go over 25%throttle low in the rpms or go over the max able rpm at 25%, there is still a load problem and sounds like a AFM or fuel issue.

Yes it does. If you are at say 1500rpm and you press the throttle to say 20%, there is a certain amount of airflow through the AFM, if you press the throttle to 25%, there will be more airflow through the afm, and if you press the throttle over 25% there will be even more airflow through the AFM at the SAME rpm. So fuel does directly effect this issue.

Hook up a tach to the engine or use the stock tach (which is not vary accurate) and a volt meter to the AFM. Pick a RPM and and quickly go from the RPM/Throttle you are at, to 50% or 65% or 100% or somewhere in between and you will see that at the same rpm, you will have different amounts of airflow through the AFM at the same rpm. Its easier to do this while in 5th gear btw, this way the engine can't rev up right a way.