I've been struggeling with the same problem for the past two months. I cant figure out why I cant get a solid idle, and why I get so much backfire when I'm revving it past 6k... .... I've tried everything I know, checked for vaccume leaks, adjusted TPS to 1 ohm, replaced spark plugs, spark plug wires, adjusted timing, new oxegen sensor, new fuel injectors, new fuel pump, new fuel filter. it's got no smog equipment, no cat, 3" piping, block of plates on bac and acv, removed cold start and did throttle body mod. It's and 88 Turbo II with good compression. I knew it would be loud and rough but I dont think it should back fire so much while I'm revving it up.
has anyone had this problem, and have an idea of whats causing it

thanks
jaycob

 

Modded rotaries will backfire. You will learn to love it.

Sometimes a vaccum leak is very hard to find. The only way to garantee that you dont' have any vaccum leaks is to tear the engine down and rebuild it. You might try running new vaccum hoses.

I'm pretty sure the TB mod might cause your idle to suck. Then again I'm not 100% sure. I will let someone else who has done the TB mod tell you for sure.

The removal of the BAC and ACV could be the source of your problem. The BAC adjusts the idle when an electircal load is added to the system. It is controlled by the ECU.

You might try running codes for your car. This requires making a code checker but it isn't too hard I don't think. I have a S5 so I couldn't tell you for sure.

Try this out:
http://www.fc3spro.com/TECH/HOWTO/ER...KI/zerror.html

 

well I know they backfire when you let of the gas, but I've never had one backfire like that on the up revv, I mean it sounds like a machine gun. almost like the timing starts to retard at 6k rpm. I'm familiar with rx7 backfire, but then again this is the first Turbo II I've owned. Oh yeah and It dose have an MSD Box, do Those ever go bad?

 

I didn't think the BAC OR ACV Would affect anything cause it has no AC/PS Or smog equip. I was under the impression that the BAC Was an idle compensator for when accessories are turned on, and the vehicle receives a load. I didn’t think it would mess up the idle all together. And the ACV was just taking up space since there are no cats or smog pump.

 

You're not going to get a solid idle easily with no BAC. It's purpose in life is to basically regulate idle. Any small change in engine load (ie. more electrical load on the alternator) can effect the idle. So need to either put the BAC back on (really there's absolutely no reason to remove it in the first place) or crank the idle to 1000 RPM or so to compensate.

I hope you set your TPS to 1K ohm, not 1 ohm.

I have seen several MSD boxes fail, especially if they are hard mounted to the car. Vibrations can kill them easily. To troubleshoot, just remove the MSD box from the circuit.

Is it actually a backfire, or does it feel like you're hitting a wall? If it's a "wall" feeling, it may be fuel cut.

 

well thats what I wanted to do in the first place set it like 1000 rpms or so, but It wont even idle smooth there. the MSD box is mounted on the firewall near the windsheild wiper motors. so it is hard mounted, I'll have to look at it some more and see if I can figure out how it was wired in. it was on the car when I bought it.
well I don’t know if I would call it a wall, it doesn’t stop revving it just seems like it has a harder time. It sounds like it's firing way retarded, or it's choking for fuel

 

I need to hook my boost gauge cause I can hear the BOV Leaking, I need to see if theres a Boost drop Off at 6k

 

I did the TB mod on my GXL at the same time as my S5 intake swap and now my idle sucks as well. I know I have no vacuum leaks, my injectors just came back from a cleansing (I've tried it with a different set as well) and everything is adjusted to spec.

I still have the BAC installed but I think I might need to adjust the little screw on the front because the S5 BAC puts out more air then the S4 (I reused my BAC) which might be causing it not to regulate properly.

I'd put the BAC back on again and see how it runs, because weven with my S4 intake disconnecting it would cause a stumbling idle. I don't think the BAC will effect your backfiring problem though.

 

I had a simular problen on a s4 engine NA. You did things to improve to breathing of the engine by removing the cats. Did you also install a K&N air filter? If you did your a/f ratio may be off. You can remove the air flow meters cover and adjust it. Just be sure to mark it before tampering with it. Also check solomiata.com for more airflow meter tips. Theres also a metal plug cover over a screw that helps adjust the idle on the air flowe meter that you need to drill out to see the screw. Again check solomiata. I would also double check your timing to be thourough. Nailpolish works great for marking the airflow meter spring wheel. Hope I helped.

 

Is there a difference betwean a NA Airflow meter, and a Turbo II airflow meter. cause the Airflow meter on it is off of an NA Rx7?

 

use a SAFC and vacuum gauge to get a good idle wtihout BAC
mine is 750 steady - and barely drops with lights on... jerking my wheel around with the powersteering is naother story, and i dont ahve ac

as for backfiring on reving up - only time tha thappened to me was hwen it was rich... way too rich

 

yeah when I 720cc on my secondaries it did it all throughout the power band, it got alot better when I put the 550cc injectors back on but now it dose it once I hit 6k rpms

 

Dose anybody know if a leaking BOV would affect anything other then losing power?

 

A leaking BOV is a huge vacuum leak.