I recently replaced the engine in a 1984 manual shift RX-7. I first went to the salvage yard to find an engine that had good enough seals to run. Once I knew the engine had enough compression I replaced the original one showing 180K miles. The engine ran fine for aprox. 2 weeks then started loising power, especially in the high RPM range. As a matter of fact, it with no load on the engine, will not rev past 6,000 rpm- even with the throttle held wide open. I have tried several tests to determine what could be the cause, but with no solution! I feel that it could be timing related-if timing is not advancing...
..who knows. I've been working on this car for 2 weeks now so I guess i'm ready for some help. I found you guys forum on the net & just thought I'd give you a try.
thanks for any help or ideas any of you may have to offer and I'll keep you posted on what I've already tried & what I will try. Thanks again!

 

I had a similar problem with my old '81 13B GSL.
It was a couple of things. The Alternator was weak, and not driving the coils properly. I replaced the alternator and it didn't improve much. Finally, when I checked the coils, the trailing one was literally dust.
It was an electrical nightmare, but was resolved with new coils and new battery.

Check your coils, alternator, & battery.
Then check your fuel filter,as it may be clogged and bogging you down.

Good luck

 

Thanks, I'll try testing the coils(something I haven't done yet) Do you know witch coil is Leading & witch is Trailing? None of my manuals designate the difference & someone may have switched the coil wires in the past.

 

Either or a combination of your Air exhaust or intake system, Fuel system and ignition system are going to turn out to be the problem.

If it's a US spec car, is your cat plugged?
Is your intake snorkle blocked or air filter blocked/old or just ugly?
Are your secondaries opening in the carb? choke stuck open/closed?
Are you getting enough fuel? Fuel pump dead or dieing?
Too much fuel? are your jets messed up? fuel pump too strong?
Fuel filter clogged?
Old fuel lines are collapsing/dripping?
Coils are burnt out?
Ignition Wires are bad, plugs are bad?
Plugs are loose - wires are loose?
Exhaust Manifold loose?
Distributor on backwards?
Is it a points ignition? Are they worn out?
Battery hosed/ugly and alternator on the fritz?
Air pollution vacuum hose got a hole in it? or loose?

Good hunting!

 

Checked the cat, ran without air breather, secondaries opening & choke operating properly, checked fuel cut-off valve & all lines, did fuel pressure check, fuel filter fine, new fuel lines- when engine was replaced, wires& plugs are new as well, Elec. Ignition appears to be fine other than coil check, Battery & Alternator-check good, haven't found any vacuum problems as of yet-but feel that could be a possibility as well as solenoid valve problems causing the timing not to advance as it should-not for sure though. Thanks for any thoughts on this matter. I'm getting frustrated with the car (to say the least) & I don't want to carry it to the Mazda dealer because I know their equiptment & training deal generally with new Mazda's as well as $$$.

 

Does it start and idle ok?

If it does that blows my apex seal theory..

Trailing coil on my 85 is towards the front of the car closest to the bumper.

 

At high RPM with the throttle open the vacuum advance doesn't matter. The mechanical advance will advance it 12.5* by about 2,000 RPM. As your two timing marks are at 0* and 20*ATDC you can estimate if it is good at higher RPM with a timing light. But you could disconnect the vacuum lines and it wouldn't change anything.
With everything you've checked, I'd be looking for a coil to swap with the existing ones one at a time and see.

-John.

 

Well folks, seems like I've tried it all...
...and still no good! I can can probably give you guys a better idea of exactly what the car is doing (or I should say, not doing!) The car will idle just fine & will rev with no load on the engine up to aprox. 5800 rpm (where as normally it would pin the tach at 8K). When you drive the car it starts out fine in 1st gear, but when you reach aprox. 2800-3200 rpm the engine acts like it has no more power to give. In other words you're lucky to reach 45 mph! I have seen it act as if wanted to run better at times and may even run a little better than it did before I started replacing every part on the car. The diagnosis may be something very simple that I've overlooked, or yet extremely technical. Who knows?
I even replaced the entire carb today (boy was that a bitch!) & both coils I had in another RX-7. Maybe you guys can help, if not, I guess it's Mazda Service time. Thanks again!

 

I'd stay away from Mazda dealerships. Try to see if there's a rotary mechanic somewhere in your area if it comes to that.

 

Well...
Only a couple of things left, that I can think of.

How did you check the cat? Did you disconnect it and run the engine? They usually clog up slowly but maybe something came apart inside.

You haven't mentioned if you have checked the compression since it started acting up?

-John.

 

Are you positive you have the plug wires going to the right places? By the way, how do you know the secondaries are opening? You say the car will not rev past 5800 rpm with the car parked? When you replaced the carb did you make sure those little screens are clean where the fuel lines enter the carb. The shutter valve ok? Distributor in good shape, cap, rotor, etc.
Throttle cable adjusted properly? Definitely make sure that is done right, or it can't rev.
let us know,
hanman

 

You never know what someone else might've done with an engine before you got it. Is it possible the distributer was removed, and not replaced properly? It could be one gear tooth off.
I would try changing the timing really drastically just to see if that makes a difference.

 

Do any of you guys know how to or if it is even possible to self-test the compression on a rotary engine? The dealer says they get $75.00 to do a compression check that may be my only option.

 

There is a quick and easy way to tell definitely whether you have done something serious like popped a seal. You may want to do this first for peace of mind. It goes like this:

Pull all the spark plugs out and disconnect the wires from the coils so you don't have any power running through the ignition system. Now let the starter turn the engine over. You should hear three loud and distinct "pffftt" sounds coming from the spark plug holes everytime the motor turns over. They should all sound exactly the same. Now, if you get something else, like 2 strong pulses and then a weak one, you know you have a problem. Assuming this test goes well, you can rest assured that your compression is fine and something else is the matter.

As for my 2 cents, I wonder if your secondaries are frozen in the closed position? As well, I would make damn sure that your whole ignition system is good. Check even the simplest stuff. Maybe swap in someone else's distributor if you can.

Maybe you should try to find a really knowledgeable rotary shop in your area, or else someone who really knows their RX-7's and would be willing to help you. Good luck!

 

CORRECTION

The compression test advice I posted above is slightly incorrect. Only pull the plugs out for one rotor a time (ie. 2 plugs). Do the test, then repeat for the next rotor.
The big thing to make sure of is that the power to the system is disconnected, so you don't start the car on 1 rotor lol.

Sorry guys, it's winter time and I haven't worked on my car in a while.

 

If you want a relatively accurate compression test you can use a conventional compression tester. Heres the process.
Disable the fuel system, pull the fusible link, plug the fuel lines whatever. You don't want fuel into the chambers when you are turning the engine over.

Pull all of the plug wires.
Pull the trailing (top) plugs from both rotors.
Screw in the compression tester in the top hole of the front rotor. Hold the release "pin" in on the tester, this will allow the pressure to immediately release on each compression "stroke".
Have someone hold the gas pedal to the floor and turn the car over while you watch the gauge. You should see the needle on the gauge start "bumping" up and down. After watching you can see the three compression cycles. They should all be fairly consistent and not too low.
Repeat the process with the rear rotor.
Also, the car needs a fully charged battery and good starter. It needs to rotate around 250 rpm to get a decent reading.
hanman

 

Did compression self-test, appears to to be fine. Still not sure what cause is...
Deceided to send to Mazda dealer - there are qualified mechanics in my area but they do not have the the tools or knowledge a Mazda master mechanic has. So, I guess I'll have to bite the bullet (so to speak) & let someone else take a look at the problem. Thanks for everyone's help & I'll let you guys know what I find out!

 

Watch it! Mazda 'master mechanics' often run and hide when they hear the word 'rotary'... just search the forum for horror stories. You'd be far better to find a reputable specialty RX-7 shop in your area. Even they're not real close to you, a lot of the time it's worth it.

 

I had a similar problem with a previous car although it wasn't a RX-7 its worth a look. Would idle fine but once in gear unless I started off real slow it would die. Turned out it was the distributor cap. The contacts were corroded and all I was getting was a weak spark. New cap cured it. Just my 2 cents

 

outrun,
Did you try the ATF trick?

What were your comp readings when you did the test? Anything below 60 is not too good, you want to be around 80 for all three pulses on both rotors. How much difference was there between the front comp and the rear comp?

 

Hey dont mean to be a a$$ hole or anything but I had a problem like that in my car... just got done takeing out the plus to check them and guess what... ran like crappp I reall didnt notice at first but when I started to get into the upper rpm's it relised it wasnt my imagination... change the plug wires... mabey the dirty litle piston fairy messed up one of your sparkplug wires... its woth a shot...

 

Just for the record...
ALWAYS, and I mean ALWAYS never forget the most basic simple process of troubleshooting. I took the car to the local Mazda dealership, and yes turns out their "master mechanic" has 17 years experience in rotary engines. So, to make a long story short 4 days and only $65.00 latter here was the verdict :
THE DAMN INTAKE MANIFOLD GASKET HAD A SMALL HOLE IN IT, DRAWING AIR, THEREFORE NOT ALLOWING THE ENGINE TO REV PAST 3K RPM!!!!!!!
Never thought of that, did we? I feel like an idiot, but at least I know now. Thanks again for everyone's ideas and make sure this thread is placed in the archives for future reference to this problem.


Outrun

 

[QUOTE=outrun;482465]I recently replaced the engine in a 1984 manual shift RX-7. I first went to the salvage yard to find an engine that had good enough seals to run. Once I knew the engine had enough compression I replaced the original one showing 180K miles. The engine ran fine for aprox. 2 weeks then started loising power, especially in the high RPM range. As a matter of fact, it with no load on the engine, will not rev past 6,000 rpm- even with the throttle held wide open. I have tried several tests to determine what could be the cause, but with no solution! I feel that it could be timing related-if timing is not advancing...
..who knows. I've been working on this car for 2 weeks now so I guess i'm ready for some help. I found you guys forum on the net & just thought I'd give you a try.
thanks for any help or ideas any of you may have to offer and I'll keep you posted on what I've already tried & what I will try. Thanks again![/Q



are you shifting the car gear correctly?

 

I am currently experiencing loss of power from around 5500 rpm and up. The car boggs out and back fires, ive been reading on here looks like a fuel delivery issue. I replaced my fuel filter still had the same problem. After I replaced the filter I let the car sit for like 2 weeks. When I went to look at it the new filter was looking brown and rusty. Someone told me this can be due to the premix. Ended up dropping the tank and it look good. My friend that owned the car before me had serviced it a couple of months before I picked it up from him. I am going to try blowing air thru the fuel lines and also replace the fuel pump and all rubber hoses. Hopefully that helps me get my rx7 back up to 8500 rpm I also ended up buying a new bypass vent valve, thought mine as well replace it also.