So yes, I rebuilt the engine and everything and finally today got it started. However it won't idle, it just shuts off, and it has a low rpm stumble, probably missed something somewhere and not everything is hooked up, so yea I'll have to work out a few kinks.

But I have a quick question about the BAC. With the key in the on position my BAC is continuously cycling on and off, very rapidly. And I had my friend cover the BAC inlet while cranking and running, and apparently there is vacuum at all times, it never closes. Is that right or is something wrong?

 

Have you checked any intake leaks that can cause the engine to die?. Also when you step on the gas, does the engine die or does stay on?. Give us a little more info on your ride? TII or N/A year etc..

 

As far as info on the car.

'88 N/A
All emissions have been removed
Streetporting with TII Housings
and I don't know what else will help

Basically it starts up and shoots to about 3k then drops, if i keep the throttle open just slightly it will stay on with an up and down idle. Let the throttle go it dies. It has no problem revving up to about 4k (that's all I've revved it to so don't know if it'll go higher, don't want to try right now, it's a fresh rebuild)

There does not seem to be any vacuum leaks, all the unused vacuum nipples have been blocked off. So far I have the pressure/boost sens. that's mounted near the passenger strut connected to vacuum, along with the fuel pressure regulator, and cruise control (yes i have cruise control connected, I left it cause I always liked having the comfort of it on long drives), and the OMP injectors that split off that 1-4 vacuum splitter, and that's all i can think of right now.

Does it matter if i just leave the BAC to suck in air from atmosphere or does it have to be connected to the intake before the throttle?

I've tried adjusting the CAS and that only helps marginally. Also, if it makes a difference, I used vaseline as an assembly lube, which by now most of it has burned out. Sparks good, there's fuel, intake vacuum is good, exhaust is definitely not plugged cause i only have the headers installed right now.

Any ideas why it won't hold idle? or is there something else I should check?

 

I am pretty sure that it shouldn't continuously cycle like that at any time. I have no idea whether it should have vacuum at idle or not. How are you testing for vacuum? Is there nothing coving the hole? If so, then that could be your vacuum leak.
Also, have you set your timing? I see that you adjusted that CAS, but have you tried re-stabbing it? A timing gun might be a good investment as well. I think they are only 40 bucks or so for the basic model (all we need).

Also, if it is a really fresh rebuild then that could be why. It takes a bit for everything to seat in and get good compression, especially with used housings.

 

Is this what your car is doing on the tach .. and does it sound like this? I have the same exact problem as you .. and I think it may be the primaries being stuck or leaky ... let me know cause I sure as hell would like to get my car running right lol Anything above 3500 it seems to be fine.

 

Sideways7, I have tried retiming it a few times and that doesn't seem to be the problem. And about the rebuilds taking time to settle in, what if the housings are new, which mine are, will it still take a bit of time to settle in?

Hurleysurf24 that's pretty much how mine is running too. But I don't think my primaries are leaking cause the air/fuel mixture burning out the exhaust isn't rich at all.

 

I have been told that it can take some time for things to settle in. Everything I've read says that it will run rough for a while, but I have no first hand experience to base that on. What seals did you use, BTW?

 

All the internal seals are OEM Mazda. That's what the guys at Mazdatrix recommended, so i went by their word.

 

Maybe you just need to adjust your throttle cable...it's always the little things that are overlooked...

 

It cycles! It's a solenoid that's either open or closed, and to get somewhere in between, it cycles open and closed quickly, varying its on and off time (PWM).

 

Thanks for the info stevej88na.

Dsmrx7, i tried that and it'll stay on, but only because i over-adjusted on purpose so the throttle is slightly more open, but i figure that shouldn't be it.

But on the bright side, I started the car up again and ran it at about 2k rpm for a while and it's slowly beginning to hold about 500 rpm idle for a few seconds then dies. So I figure the seals and such need to be seated after running for a bit, but does anyone know if that's even right, needing to be run for a bit to seat in order to even hold idle? I mean the engine started up on the first try after the rebuild, no long cranking it just wouldn't hold idle, and now ever so slowly it is holding. And yes I do know about the driving for a few hundred if not a thousand in order to get ideal compression and running, but my question is the idling part.

 

https://www.rx7club.com/forum/showth...ght=photobucket

http://www.wankel.net/~krwright/fil.../parts_manuals/

http://wombat.sevarg.net/RX7/RX-7_Training_Manuals/

http://www.cochran-racing.com/FSM/index.html

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Go to the link with WOMBAT in the link and download it. Download the FUEL AND EMISSIONS section and lookup BAC. It's described there.

On startup the BAC goes full open as long as the key is to START. Once started it has a continuous Duty Cycle i.e. on/off, on/off etc. A real little buzzer to help maintain idle speed.

Just realize the BAC by itself cannot/willnot/ ain't gonna do the whole job of IDLE MAINTAINER. The engine should be able to idle with the plug off the BAC alltogether.

Since your's is a non turbo and a series four, and you looked to make sure there are no vacuum leaks and all the small vacuum lines are where they're supposed to be going and not on some place they don't belong, then look to the variable resistor for some help.

Next time the engine is HOT, and won't idle, turn the variable resistor clockwise (richer idle) and see if that helps or hurts the non existent idle. Maybe even turn it anti clockwise (leaner) and see if that happens.

We assume the timing was set with a timing light and the rpms were below 1000 rpm for sure when that was done (if it was above then the timing is not set right). We also assume the TPS was set to output one volt dc with a HOT engine.

We also assume the two small vacuum lines on the front of the dynamic chamber are not crossed up (makes for a crummy idle if crossed).

I'd say that with new housings and how it started right up after the rebuild, that the idle should be there after running the engine after an hour FOR SURE. New housings are GOOD things.

Try the variable resistor thing for sure after the engine warms up to HOT.