stockrex

looks like these guys spent a quite sometime debugging the issue:

http://www.asashop.org/autoinc/april97/techtips.htm

Mazda Flatspot At 3500 To 3800 RPM
by Tom Anderson
The owner of a 1988 Mazda RX-7 had complained about a lack of power
on hard accel. The technician drove it and found that the engine
flattened out about 3500 RPM. When he stepped on it harder, it picked
up again and accelerated at a more normal rate.

The technician had tried the things a good tech would think of on a
multiport injected engine. He swept the throttle position sensor
(TPS) and the vane-type airflow meter on a scope. The patterns looked
perfect with no dropouts or glitches in the voltage sweep. When the
fuel pressure was checked, it stayed right where it should.

He called me looking for ideas. There is a shroud of mystery most
people feel when dealing with rotary engines. I explained to him that
there are four injectors on this engine and they are set up much like
a four-barrel carb, with two primary injectors and two secondary
injectors that just happen to come on at that 3500 RPM mark. The ECU
will cut back the primaries, open the auxiliary port actuators - if
needed, since this is a normally closed port - and begin operating
the secondary injectors.

A check showed the vacuum sensor was OK. (Who knows why Mazda calls
it a booster sensor?) The O2 sensor voltage dropped from .7 volts to
0 volts immediately, the auxiliary port actuators opened and the
secondary injectors began pulsing.

In this case, the ECU was trying to do its job, but the engine just
wasn't getting what it needed. Either the injectors were plugged and
not spraying fuel or they were spraying, but the fuel wasn't getting
to the engine as it should. I advised him to pull out the secondary
injector rail and inspect the mixing plates in the holes below the
injectors. This piece has several holes in it that the fuel has to
spray through to get into the intake runners. The holes were blocked
with a carbon-like substance, so the tech cleaned and reinstalled the
rail. He also checked the injector spray pattern at this time by
securing the injectors in the fuel rail to keep them from popping out
from the fuel pressure. He pressurized the rail and operated the
injectors manually. An injector "pulser" works very nice here. The
injectors sprayed a fine cone pattern.

The reason it drove the way it did was that when the ECU began
operation of the secondary injectors, the fuel hit the plugged mixing
plates and the fuel puddled there. These large drops of fuel weren't
burned in the engine completely so the vehicle lost power. The ECU
received a lean O2 signal from the oxygen sensor. Remember, the O2
sensor measures oxygen, not fuel. Because of the large amount of
oxygen, it brought the primary injectors up again and the power would
improve. The car now runs fine!

RETed

Somehow, I highly doubt clogged air bleed valves are the culprit...

These guys scare me.

Why?&nbsp The secondaries fire only above 3,000RPM+ or so.&nbsp By this time, the air flow is going mighty fast at this RPM.&nbsp I doubt the secondary fuel injectors can fire hard enough to even hit the air bleed valves.&nbsp Regardless, the moderate RPM has enough intake velocity to take any fuel shooting out of the secondary fuel injectors and pass them into the engine.



-Ted

RX7BEAR

Well I have had this damn problem for ever on my 87 GXL and I did everything there was !!!!!!!!!!So I thought !!!!LOL When I did the ATF thing to get some power back I changed the plugs like I was told to do !!! But like a dimb *** I was I forgot to get a new O2 Sensor !!!!! I got a new Bosch from autozone for 35.00 tonight popped it in and bingo it runs nice and smooth again . I realy was surprised about this because I thought it was a electrical problem !!! Im sure it was everything combined but it was the last thing I did that fixed it . THANK GOD

91vert

I don't quite understand exactly what purpose those "mixing plates" are supposed to serve. but I just bought that Bruce Turrnetine video for RX-7 engine removal and replacement and he mentioned a couple of times how important they were in the video. He showed the difference between the different styles that were used and made it a point not to damage them while taking them out and replacing them. He said that they were very important to the proper performance of the engine and to make sure that you didn't forget to put them back in.

What are they supposed to do....atomize the fuel even more than the injector does? To me it seems like they would just disrupt the fuel spray pattern even if they weren't clogged with carbon.

The other question is if you ran some fuel injector cleaner every once in a while and drove it hard enough to bring the secondaries online all the time wouldn't the cleaner blast the carbon off of them?

RETed

They are important for the primaries.&nbsp Due to the low intake velocities and the low "squirt" of fuel during cranking, the air bleed valves help in atomizing the fuel at cranking and idle.&nbsp You really don't need the secondary ones, and they do pose as an intake obstruction.

Every try cranking the engine over with no air bleed valves in the primaries?&nbsp It just won't start...


-Ted

Bambam7

Uhh, my car starts in the first 1/2 second of cranking every time- and I have no air bleeds.
Mine were also clogged completely- but I never had any hesitstion. My guess is the mechanic, in the process of reinstalling the secondary injector rail, improved the ground on it, and fixed the problem indirectly.

Think reinstalling them on the primaries would increase mileage? I get pretty rich running at very low throttle (even before closed loop starts), if I lean it out too much, it runs poorly, but I still have black crabon in the pipes....maybe I should try that....

RETed

I'm surprised it started at all!&nbsp The fuel injectors literally shoot a squirt of fuel when cranking - it's not a spray.&nbsp That can't be good at all for "atomization" if you got no air bleed valves in there.&nbsp Does it run well or stumble a lot?



-Ted

Bambam7

It used too, but I traced that to electrical.
It really runs like a dream... the smoothest engine I've seen in a 7 in a long time!

RX7BEAR

okay now this is strange. My hesitation is back again!!!!!! But only when the car is cold as in hasnt been driven all day . Its at the warm up temp but damn I really dont know what else to do? I did the wire grounding on the engine and pressure sensor / ECU wires/ battery ground/ exhaust ground/ new o2 bosch/ capacitor on the hot wire to my stereo/ its a new battery/new injectors/all the tests on fuel regulator /BAC/solinoids/TPS/is all good. can the ECU have a bad solder on it on the board somewhere? Imean after its been driven a mile or two its fine. Also it dont happen when I floor it just when I slowly tach it up to 4000 then it bucks like a bitch.

NZConvertible

Well there’s a serious mistake right there. Under acceleration, the ECU is in open-loop and completely ignores the O2 sensor. They may have a point about dirty injectors, but there O2 sensor theory is all wrong.

NZConvertible

Probably not. Those injector cleaners are fairly weak and rely on the whole tank being pumped through the injectors. Driving “hard enough to bring the secondaries online all the time” would be a lot harder than you think, and you’d probably be throw in jail for dangerous driving before the injectors are cleaned! Removal and professional cleaning is really the only answer.

HAILERS

91 VERT........ Just put the primaries where the secondaries are and go drive the car. All you have to do is remove the intercooler, intake manifold..........wellllllll, on second thought, forget it. But if you don't have anything to do for two or three hours on a weekend, you might just swap them out.

RX7BEAR

Well its me again !!! I put my old injectors back in from the secondaries and turned my afm sideways and no more hesitation !!!!!!!!!! smooth as a babys *** all the way through.

NZConvertible

Why'd you do that?