gigabot

So I bought my 90 NA a year ago. The compression numbers at the time were basically 6-6-6 and 7-7-7 with even bounces on all rotors on the Mazda meter. The idle sucked however, and the RX-7 shop I was taking it to told me it was due to low compression (they recommended at least 7s on both rotors). I didn't quite know what to think of that, given that the FSM shows minimum spec at sea level of even 6s. Long story short, over the last year I have replaced all the plugs, the fuel filter, the TPS, the computer, the AFM, the Alternator, tested the BAC using the technique in the FSM (passed), adjusted the TPS about a half a million times, reran grounds in the engine, checked for vacuum leaks, and after all that the idle is still really weak. Basically, if I have the A/C on and hit the brakes the car will stall nearly every time.

I've since moved to Denver and out of frustration took it to the local rotary shop to either fix the problem or rebuild the engine. First they retested the engine with the Mazda meter and found the exact same compression numbers as before. They told me that in their opinion these numbers are excellent for this altitude (which is true according to the specs in the FSM) and that some adjustment was all that should be needed. Lots of adjustment later and the problem hasn't really improved.

Ultimately, I guess my question to the group is should I rebuild, or given my compression numbers is the problem likely something else and I'm just going to waste money on a rebuild when it might not fix this problem? Any other suggestions? I think I've read every thread on troubleshooting idle problems on this forum, but can't figure out what else to try.

iceblue

Allot of people recommend 7s. I say your compression is in spec and all is good. If you want to rebuild for a fresh motor and porting go ahead. Just for the idle issue I do not feel it is your problem.

Now id idles perfect all day without AC? It works using your power steering? What are you idling at? 750rpm? It drop maybe 200rpm when you move the steering wheel? Can you explain how you use your cars equipments like AC and how the RPMs react?

This should be a idle control issue or electrical. Is your BACV cleaned well? The wires look good? The grounds are proper and cleaned? Check your timing. You have no vacuum leaks?

I have no idle control components on my car or emissions, I kept all luxury’s AC PS so on. I bumped my idle to 1.1k using the fast idle cam screw on the TB. Runs perfect.

gigabot

I wouldn't say it idles perfect without A/C on, but it doesn't stall unless you turn on A/C AND are braking to a stop (which I'm guessing is about peak load the accessories can put on the engine). The idle is not rock steady at all. It normally hovers around 750, but is very variable depending on what loads are on (brakes, lights on, A/C on, etc.) -- sometimes higher (as much as 1200 RPM), sometimes lower (as low as 5-600 RPM). For instance, if I turn on the A/C at a dead stop without the brake depressed, the RPMs will increase to as much as 1200 RPM. As soon as I depress the brake, the idle drops dramatically and comes near to stalling or stalls. If I'm turning at slow speeds while idling (like parallel parking) it will sometimes stall as well.

When I took the BAC off to test it, I cleaned with carb cleaner as well. I'm thinking about just replacing it completely though, to eliminate the possibility that it is intermittently not working. Wiring all looks good and I reran grounds using the method outlined on the Rotary Resurrection site. Timing is good and no vacuum leaks that I or the shop I took it to could find. A lot of the vacuum hoses were replaced when I had to replace the OMP lines.

Can't really ditch emissions around here, but removing the idle stuff completely is an interesting thought. I've tried bumping my idle speed up before and it just seems to make the idle worse. Then in addition to the stalls I get pulsing and just overall idle weirdness (stop at a light and it pulses betwen 1100-1300, stop at the next light and it settles down to 800, etc).

iceblue

Lets check our coils are good. Then plugs and wires. If you have the ability check your fuel pressure at the rail and clean the injectors ither yourself "it helps" or have them pro done for like $50. After this time the motor realy should make it idle properly atleast under no load idle. Good time to do a lube check and check all oils are nice clean and not burned or varnished or gummy. If you want to make it easy to work with the emissions and vacuum lines, you can do the VAC rack removal and you can allso remove all them silinoids at this time. If you have a S5 keep the VDI silinoid. If you want and you are under the UIM you can go ahead and remove the AWS cold start system and PCV if you want. I sugest remove the rack because it helps you understand evrything under there, you clean up the maze and makes it easier to work on. People may disagree this is up to you.

Check the coils -

Specifications
General
Coil resistance 0.2 to 1 ohm
Crank angle sensor resistance
Between terminals G1 and G2 110 to 210ohms
Between terminals Ne1 and Ne2 110 to 210 ohms

Torque specifications
Crank angle sensor locknuts 69.6 to 96 in-lbs

Ignition system
The ignition system includes the ignitions switch, the battery, the crank angle sensor, the leading and trailing side coil/igniters, the primary (low voltage) and secondary (high voltage) wiring circuits, the spark plugs and the spark plug wires.
When working on the ignition system, take the following precautions:
a) If the engine wont start, don’t keep the ignition switch on for more than 10 seconds.
b) Never allow an ignition coil terminal to contact ground. Grounding the ignition coil can damage the igniter and/or the coil itself.
c) Don’t disconnect the battery when the engine is running.
d) Make sure the igniter is properly grounded.

Ignition Check
1 Attach an inductive timing light to each plug wire, one at a time and crank the engine.
A) If the light flashes, voltage is reaching the plugs.
B) If the light does not flash, proceed to the next step.
2 Inspect the spark plug wire(s), and spark plug(s).
3 If the engine still wont start, check the coil/igniter assemblies.

Leading Coil Check
1 Detach the cable from the negative battery terminal.
2 Detach the high tension leads from the coil Note that the leads are marked (white dot on high tension terminal No. 1 and white band on leading high tension lead No. 1) If the leads on your vehicle are not marked, be sure that you mark them to prevent incorrect reassembly.
3 Remove the plastic cover from the primary terminals of the coil.
4 Using an ohmmeter, measure the resistance between the primary terminals of the coil and compare you measurement to the value (specifications listed).
5 If the indicated resistance is not as specified, replace the leading coil.

Trailing Coil Check
1 Detach the cable from the negative battery terminal.
2 Remove the plastic cover from the primary terminal.
3 Detach the high-tension leads; the leads should be marked (a white dot on the N0 .1 high tension lead). If they’re not marked on your vehicle, be sure that you mark hem to insure proper reassembly.
4 Using and ohmmeter, measure the resistance between the primary terminals and compare your measurements with the value listed in specifications.
5 Repeat this procedure for the other trailing coil.
6 If the indicated resistance of either unit is not within specifications, replace it.

Igniter
1 Testing the igniter assemblies requires special equipment and is therefore beyond the scope of the home mechanic. Take the vehicle to a dealer service department or other qualified repair shop to have the igniters checked.



Here is a VAC rack thread that may help you.
https://www.rx7club.com/showthread.p...c+rack+removal
https://www.rx7club.com/showthread.p...c+rack+removal
https://www.rx7club.com/showthread.p...c+rack+removal

Good luck any more help just ask.

iceblue

The stalling on brakes. I say VAC leak. All the brakes will do is pull some vacuum. If it dies there is more then likely a leak. Sounds allso like uour idle controlls "BACV" are not keeping up or tuned wrong.

gigabot

Thanks much for the suggestions iceblue. That gives me some more stuff to look into over the weekend. I'll follow-up post if I find anything.

RETed

Watch out when other people are doing compression tests...
Ask them the right questions to make SURE they are doing it RIGHT.
- 1 spark plug from both front AND rear rotors are pulled
- throttle is at WOT
- battery is fully charged; compresion specs are at 200 - 250RPM (I think?)
- test must be done on warmed-up engine

Sometimes people forget to pull both spark plugs and / or prop open the throttle - this WILL cause lower readings.


-Ted