Red 86 rx-7

Ok I have replaced just about every thing under the hood to try and fix my 3800rpm hesitation and hot start problems.new alt,new injectors and seals,new lim and uim gaskets,fuel filter,plugs and wires,o2 sensor,battery,engine and secondary ground.The car has a crappy idel and will not rev without sputtering.The car is a 86na fc.

rhinor61

Parts changing...........humm

How many miles on the engine?
What is the history of the car?
Did it just start crapping out did you buy it this way?

You think about do a compression test of both rotors and see if you lost compression?

Red 86 rx-7

The car has 156000miles oil change every 3000miles I got the car with 96000 miles on it from a old ladie who kept it in a garage for most of it's life.Ran good always started even when hot no 3800 rpm bump.I think most of my problem is bad wiring/grounds the mileage and a vac leak or two.I did a compression test with a piston gauge and got pulses of 30,30,30 both rotors good or bad? I wonder what seals the rods that go into the lim for the 5th and 6th port sleeves?I bet I have a leak there.I used form a gasket to reattach my BAC to the diff chamber.I still have to test my other motor for compression.I'll drop that one in it's a rebuilt with 30,000.I guess get a winter beater and try to store the rex till summer,Right now my rex is not a good daily driver.I just want to get her right Right now.I drove the car last winter and got front ended by the rear end of a snow plow truck.Fuked the front end up! This past summer a lady with a van full of kids with no seat belts on,Stomped on the brakes forcing the honda civic in front of me to stop quick.I slammed his *** end good!So I found a 87 fc n/a parts car and swaped over the hood and bumper assembly.The 86's body other than the front end is fairly clean for a 17year old car.A little rust in the rear wheel area.Rot hole in the front engine compartment under where the battery sits.I mig welded a patch in and covered it over with some dura-glass. Ok long post... shut up dude....

black_sunshine

If you've replaced all that stuff, then I'd look into these things:

The BACV can go bad and when it does, it's a booger to diagnose initally. Use an OHM meter and check the resistance. 10.7 - 12.3 ohms. Apply +12volts and ground to the terminals on the BACV and it should click.

AWS solenoid (same area as the BACV). These sometimes begin to leak. Take it off and blow in one end of it. Shouldn't leak air out. Best way is to suck on it; easier to tell pressure increases versus drop IMHO. It should check out at Apply +12 and ground and it should click. 9.2-11.3 ohms. The Brown/Yellow stripe wire should be ground.

TPS. When these start to go bad, it's really hard to diagnose because they appear to be working correctly. Check the resistance of it between connections A and B. A is the top connector. With the connector facing you, A on top, B is the right-side one, and C is the left-side one. A and B resistance: At idle position 1k. At WOT: 5k-6k. On A and C: Idle position: 5k-6k. WOT: 5k-6k. (This is most likely your culprit).

Generally, how I diagnose a vacuum leak is by capping-off the vacuum sources (except for the boost sensor) and see if there's a difference in idle quality. Cap off the two on the backside of the TB, the one on the driver's side of the plenum, the three on the front of the TB. There's one hose that runs to the lower intake manifold, so make sure to plug that one and the ACV ones, too. Start it up, but don't run it very long without re-connecting the two on the back of the TB and the big one on the front. If it idles WORSE, check and make sure I didn't forget to tell you to plug an important hose (I'm a little sleepy). Plug them back in one-by-one, each time starting it again to see which is the culprit.

The actuator shafts are sealed with a little rubber boot, similar is material to the injector rubber spacers/seals (not the O rings). They get hard and maybe it could cause a vacuum leak; If you wanted to, you could goober the actuator shafts (on the outside) with silicone and see if your idle quality is better.

Make sure to check the water thermo-sensor (around 2.45k at 68d fahrenheight) and the air intake sensor (around 41.5k at 68f).

Your compression SHOULD be around 85psi per face. Much lower than that (around the mid 60's) will cause some idle problems. Since you say you're getting 30 (psi?) on all 6 faces, I presume your gague's reaction time isn't excellent. Put the check-valve back in and see if it goes higher (haven't ever seen an engine run with onlt 30psi yet....).

Hope this helps a little.....

Matt

Project84

120psi on the compression tester is factory specs. 30psi is way too low. An easier way to find a vaccuum leak is to spray something like starting fluid or carb cleaner around all the vaccuum connections and around the intake manifold where it connects to the block while the engine is running. Spray in short burst, do lay on it and drown the engine. If you spray at a connection and the engine RPMs surge up, then you know you found the spot that is leaking. Honestly, if you get 30psi on the compression tester, the engine needs a rebuild because the compression is extremely low.

Red 86 rx-7

Thank you black sunshine for the info thank you also project84.I 'm gonna check the thing you suggested and get back to ya on the results.I have a rebuild kit on it's way this week,Every thing but the Apex seals.I think I have to get them from a dealer.What I want to do is swap motors and rebuild the 86's engine.but not untill I have got all the life out of it first.

Project84

You don't have to get apex seals from a dealer. www.atkinsrotary.com
www.mazdatrix.com
www.rotaryaviation.com
those are a few places that sell them. rotaryaviation has the best price. For $168 you get apex seals and all the apex seal springs. They just introduced these to the market a few months ago. They are supposed to be 700% stronger than the stock mazda seals. If you use new rotor housings, they will give you a lifetime warranty on the seals. Check them out.

Red 86 rx-7

All right I cleaned and tested mt TPS close to perfect results.I installed the TPS went for a rip to warm it up.Readjusted the TPS with the engine hot "two led tester"
I don't know the mm test yet.The car takes off better.Still got the 3800 bump.Still has a ruff idle and dies when you turn the lights or heater on.I noticed that if you advance the throttle slowly the engine surges whoo whoo whoo untill you reach the end of the TPS travel?I got a new transistor from rat shack,I'm gonna try to install that into my spare ecu.To try to fix the bac.I feel like I'm stabbing in the dark all the time with this car.Thanks for the link for apex seals project84 where can I get new rotor housings?I have two engines do I really need new housings?

Project84

If your rotor housing are within specs, then you can reuse them. Its just that the only way rotaryaviation applies the warranty to there apex seals is if you use new housings. I would still use their sells just because they are cheaper than all others.

When you make changes to the TPS, are you putting a jumper wire across the initial set coupler? If not, you will be inducing more problems because the engine will try to use the BAC to compensate against the changes you are making instead of allowing the changes to effect what you want it to effect.

If the car dies under an electrical load, you might want to check the alternator.

The TPS does not travel the same distance as the gas pedal. Once the TPS is at the end of its travel, the ECU considers it wide open throttle.

At 3800 RPMs, two things should happen. The secondary fuel injectors come on, and the auxilary port actuators should be opened up. If the secondary injectors are not comming on, a common cause is the main engine harness ground wire. There is a write up concerning this in the 2nd gen archive. Click here. The auxilary ports on the 86-88 cars are operated by exhaust back pressure. The metal tube coming from the exhaust pipe to the intake should have a smaller rubber tube going to a small metal tube on the intake. You'll see it when you look under there. The small metal tube carries air to the auxilary ports actuators. If the actuators don't hold the vaccuum, they may not open the ports. If they don't open then the extra ports don't allow the extra fuel in thats needed to go zoom zoom. Sorry if I'm explaining this too much, I don't know how much you know about their operation.

Red 86 rx-7

I did not know you had to jumper the coupler to adjust the TPS.I just replaced the alternator and batt.I know about the 5th and 6th ports.I cleaned them and made sure that the actuators are working,By blowing into the line,the actuators opened.I have some wire taps and I have to track down the right wires to tap and ground.Thank you project84

black_sunshine

On the Boost sensor, it's the two wires that become one (my 87 had this; some only have one wire).

Basically, run a ground from the boost sensor to the strut tower. Then, run another ground from the engine (the filler neck has a "blank" untapped hole; I tapped it to run the ground) to the chassis. Run a direct ground of 12ga wire from the battery - terminal to the chassis, then another from the chassis to the leading coil mount to the chassis, and another for the trailing to the chassis.

I also re-grounded and re-wired my fuel pump. I just took a 4-pole solid state relay (2 poles to activate the "switch" and two more for the actual switch) and cut the power wire for the fuel pump. I used that wire to activate the relay. I ran the ground wire of the fuel pump directly to the chassis, and I ran a direct wire from my battery to the relay (switched source). Before I did this, I was seeing 9.8v - 10.7v (9.8 with everything turned on including brake lights at idle) to seeing 12.5v - 14.2v (12.5v with everything turned on including brake lights at idle).

Also, since you're going to be around the fuel pump, it'd be a good idea to take replace the fuel pump's filter, as well as blow the lines out backwards. You may have to undo the main fuel filter (it should have a check-valve, but they don't work most of the time unless it's a liquid). I disconnected mine in the engine bay and blew compressed air through them. Quite a bit of gunk came out (rusty gas tank; I took it out, filled it with gravel, shook the hell out of it, rinsed it very well, and re-installed it. It's easy to do, just time consuming). Make sure to position the lines on the fuel pump so that you don't spray gas all over the inside of your car. Oh, and no open flames.

Now, the method for grounding the ECU and everything I typed for no appearant reason.... https://www.rx7club.com/showthread.p...=ecu+grounding

If this doesn't fix your problem, get a new O2 sensor. If you've still got a problem, either re-solder the ECU (all of the solder joints; there's a lot), or get a replacment if some parts look burnt or otherwise bad. Aside from all that, I'm out of ideas.

Matt