Recently I discovered my car won't go past 60mph if I floor it. It DOES go past 60 if I get there gradually and let the speed build up. If I go to 50 mph and gas it or even put more than half throttle into it, the car seems like is choking for air and feels like when you reach redline BUT the car DOES NOT rev past 4,500. I have an automatic ( kill me). But the engine revs fine to 7 k if I put it in 1 and hauls *** like a mad dog.
I recently replaced the fuel filter with a new one that was about double the size of the tiny one it originally had, interestingly the car ran much better.

Why can't I go past 60!!!

 

There may be a couple of things that could cause your problem. You mentioned changing the fuel filter and it running better. Possible you have fuel delivery problems. Dirt and rust in fuel tank could be restricting fuel flow,examining filter you took off for contamination would be a start. If already discarded,examine the one on car now for evidence of contamination. If filter looks ok,next you'll want to test fuel pump for proper pressure and delivery. Try to rule out fuel supply,fuel pump,carburetor in that order as cause for problem 1st before moving on to other systems.

 

[QE=GSLSEforme;12206622]There may be a couple of things that could cause your problem. You mentioned changing the fuel filter and it running better. Possible you have fuel delivery problems. Dirt and rust in fuel tank could be restricting fuel flow,examining filter you took off for contamination would be a start. If already discarded,examine the one on car now for evidence of contamination. If filter looks ok,next you'll want to test fuel pump for proper pressure and delivery. Try to rule out fuel supply,fuel pump,carburetor in that order as cause for problem 1st before moving on to other systems.[/QUOTE]

​​​​​​​It might be the fuel pump . The old filter is Orange due to age , it didn't clog up , it simply cracked and fell appart in a spectacular gush of gas. New filter looks squeaky clean . My carb looks clean and considering the car starts up on the first turn of the key and idles smoothly at 700 rpm . I doubt the carb is having issues . What I can say is this , when I rev at idle past 5k × and let off the gas I hear loud explosion/ popping noises from the exhaust ( it backfires every blue moon ) . I'm also seeing smoke( steam ) from the Thermal reactor that you nailed down to being a possible intake manifold coolant leak in another post ( thank you for that) , interestingly it's yet to leak again after I tightened a few hoses. My ATF fluid was at L yesterday and I added a quart today . Could that be the issue ? ( the car didint go past 60 prior to the fluid being added In , in fact it shifted way late and supper hard , that was solved easily )

​​​​​​​Edit : maybe the car needs more Trans fluid ? It might not be engaging the final gear

 

It's a 3 sp auto, so you should be able to feel it shift twice once you are moving. If the fluid is low, it would normally hesitate to go at all when you first put it in drive, not have a problem confined to just 3rd gear. Another fault inside the tranny could be preventing it from going into 3rd, if it is not engaging.

I'd start with the fuel system as suggested and I wouldn't automatically rule out the carb just cause it starts and idles smooth. If you rule fuel starvation out, I'm wondering about the exhaust. A restricted exhaust will keep it from reving out, but you say it revs to 7K if you put it into low 1? Does it rev free in neutral too? The popping or backfiring when you chop the throttle is unburnt fuel igniting in the hot exhaust and is another issue. A normal, healthy RX-7 should easily see 100 MPH, even an automatic.

 

Regarding level of fluid in transmission,avoid overfilling in an attempt to cure a possible shifting problem. Fluid should be checked with a warm engine at idle speed in park. On level ground. Observe the full mark on dipstick. Overfilling leads to foaming of fluid,this condition is worse than running it low on atf,can also cause atf to be expelled thru vent tube appearing as a leak. Your transmission has a vacuuum modulator which controls upshift/downshift modes by determining engine load thru vacuum. These can't/don't go out of adjustment,but are known to fail. The diaphragm of the modulator sometimes ruptures/splits and can cause the transmission to shift differently,sometimes too early which could be seen as a bog or lack of power or shift late and hard. A ruptured diaphragm also will allow engine vacuum to pull atf from transmission at a small rate,burning it in the engine which may or may not be seen as smoke from tailpipe. Could be a possible reason for low level of atf in transmission. Modulator is external to rear of transmission and has a metal line with short rubber hose connecting it to modulator. Can be checked by removing hose at modulator,if hose is wet,diaphragm is leaking and should be replaced. If not leaking,start engine and determine there is vacuum available at modulator hose. Feeling for suction on your finger is sufficient to ascertain all is ok & you can cross this off your list of causes....be sure car is supported safely on jackstands before crawling under.

 

IM going to say plugged exhaust.

 

+1 on the modulator, that was my second guess after verifying fuel
delivery. Clogged exhaust is very rare usually.

 

My experience the Rx-7 autos is that they are setup from the factory to shift pretty low in the rev range (about 4,000 / 4,500 RPM). Verify if you are getting 2 upshifts or not. If you only get one, then yes, the the vacuum modulator would be the logical place to focus on. As said above, either the diaphragm itself or the vacuum signal going to it. The low shift RPM sucks for fun, but it also means your engine was probably never over stressed or pushed anywhere near redline. 5 speed manuals can be swapped in fairly easily.

 

I might swap out the trans IF it turns out to be having issues. It's probably the fuel pump going bad. Such a shame considering the car runs great and is highly responsive below 60 mph , im surprised how hard it pulls when i put the trans into low 1 . It's ALMOST as fast as my 73 mach one, but im suspecting that engine is only doing 350 hp. That being said the rx pulls and the Mustang doesn't, it just spins its wheels XD! Sadly I don't have the money to buy a fuel pump ATM . and probably won't have the cash unit late December.

 

Since you have a 1979, it's an easy swap. Just need the following:

1. clutch/brake pedals
2. Clutch box long bolt
3. Master, slave, and hose
4. Trans (1979/1980)
5. Starter
6. Trans cross member
7. Clutch switch on the pedal box
8. Shifter surround
9. Maybe the drive shaft, can't remember on this one.
10. Flywheel - This MUST match the year(s) of the 12A. Here is a good reference https://www.mazdatrix.com/faq/flywheel.htm
11. And of course new new clutch disc/plate throw out bearing.

 

The 215mm flywheel from an 81 or 82 manual tranny car will work too. It bolts right up and is compatible with the SA rotors but is 8lbs or so lighter than the 79/80 flywheel. They have the number 21 cast into the back side and weigh right at 23lbs.

 

+1 on that, I have an 82 flywheel and it feels great.

 

Ok, so back on the fuel pump topic. where is it located? Hopefully not in the fuel tank.

Also, I was reading another post saying the fuel filter is the fuel pump under the car? The filter I swapped out was next to the rat's nest, and it runs gas through it.

 

Under the car just aft of the drivers seat. It has a cover over it. You access the plug by taking out the rear bin.

 

So it's behind the drivers seat ? My car doesn't have any bins behind the seat , it's just carpet . Or are you saying UNDER the car by the driver seat ?

 

The plug that supplies power to the fuel pump is on floor behind driver seat on all 1st gens. On FBs it's under driver side bin. The fuel filter/pump is under car in front of left rear tire. Suggest you investigate/replace that filter and tap removed filter on paper towel to see what comes out-unless you can see it has a bunch of trash in it.

 

The fuel pump is under the car located just aft of the drivers seat. Look under the car.

The plug for the pump is behind the panel that runs behind the seats that has the carpet covering it.

This is the 1980 manual on fuel. Close enough for what you need. It's a good start for reading.

http://www.foxed.ca/rx7manual/manual..._Inlet_Exh.pdf

 

You say you replaced gas filter underhood already. That filter was not oem,Mazda did not put filters in engine compartment in any RX7. That filter likely added to keep trash that got thru oe filter from getting in carb. Have worked on several FBs that had this dual filter arrangement +drivability problems to go with it. In attempting to keep dirt/rust/etc from getting in carb another filter was installed. While this may have helped,it introduced another problem. The load from extra resistance(even with clean filters) of trying to push fuel thru a second filter makes the pump work harder to maintain necessary pressure/volume,sometimes can't and results in hi rpm/speed deficiencies in fuel supply. This is a band aid fix. A few posts back you mentioned replacing filter by carb as it split and sprayed fuel everywhere,also mentioned the condition of it. This type of filter is not meant to be exposed to underhood engine heat(which is what caused it to fail) and is exact reason Mazda did not put one there to start with. Very lucky car didn't burn to the ground,saw one many years ago that was a total loss from this. Recommend after finding out and repairing root problem causing your troubles,you delete the underhood filter.

 

You say you replaced gas filter underhood already. That filter was not oem,Mazda did not put filters in engine compartment in any RX7. That filter likely added to keep trash that got thru oe filter from getting in carb. Have worked on several FBs that had this dual filter arrangement +drivability problems to go with it. In attempting to keep dirt/rust/etc from getting in carb another filter was installed. While this may have helped,it introduced another problem. The load from extra resistance(even with clean filters) of trying to push fuel thru a second filter makes the pump work harder to maintain necessary pressure/volume,sometimes can't and results in hi rpm/speed deficiencies in fuel supply. This is a band aid fix. A few posts back you mentioned replacing filter by carb as it split and sprayed fuel everywhere,also mentioned the condition of it. This type of filter is not meant to be exposed to underhood engine heat(which is what caused it to fail) and is exact reason Mazda did not put one there to start with. Very lucky car didn't burn to the ground,saw one many years ago that was a total loss from this. Recommend after finding out and repairing root problem causing your troubles,you delete the underhood filter.

 

Disregard double post,working from phone not sure how that happened.

 

Thanks for the info! I did mention in another thread/post I WAS lucky as the little ****** exploded in front of my dad who immediately told me to shut the engine off as grass began squirting out all over the place like a sprinkler. If he hadn't been there im 100% sure it would have caught fire. Also, the filter is on the Driver side in between the oil filter/ rats nest, but higher up . not next to the carb.
I had no idea this was a mod, it explains why the cables seem oddly positioned.

So the culprit might be a dirty filter under the OEM pump, right?
I found this picture on here. IS this the correct position ( not my pic)

 

Its close to there but thats a non-OEM pump and filter setup. The filter is usually in a wire holder and is a staight thru filter like this:

 

So I crawled under the car ( didn't lift it,i fit under it) and found the filter. OH GOD, it's orange and black. I have NEVER seen anything that fucked up that still works, it's warped, slugged up at the edges and just nasty. Oh and my car has no rust!

 

Do I need to do anything special while removing the Filter in the bottom? Or do I just release the clamps and put the new one in?

 

Just undo the clamps and pop in the new one. I'd change those lines while I was under there... they look awful crusty.


Change that under hood filter for an all metal filter. Plastic isn't good for under the hood.