Backfiring/Timing Issue
 

So I've been doing some more work on the rx7 this weekend. I finally got my RB header in only to realize the damn thing is about 4 inches too short to bolt up to the stock cat... Damn them. Anyways, I've got that taken care of for the time being but my new issue is with the timing and a backfiring issue. It used to be that it backfired on startup and that was about it.

Now it seems that the backfiring is occurring more frequently and I have a feeling it has to do with the timing. Pulled out a timing light, lined up the yellow mark on the pulley to the marker on the engine, pulled the CAS and lined up the upper most circle to the mark on the CAS housing, and checked that the inside part of the CAS was set to around 8 and 2 oclock. Everything seemed perfect until I threw the timing light on...

When looking at it, it seems to be quite a bit off, probably 40 - 60 degrees ATDC and adjusting the CAS doesn't even allow me to see the marks on the pulley, regardless of the direction it's turned. I did ground the test connector before doing any adjustments. So any help on fixing this would be greatly appreciated.

-Jon

I'm surprised it runs with that much retard.

I don't ground any test connectors when checking timing.

Set your engine at leading timing mark.
Pull CAS
Line up notch and divot on CAS
Carefully stab CAS
Start engine and check timing

Takes less than 5 minutes. Should be no need to open the top of the CAS.

So I fixed the timing as best I could. Timing seems to be on when the idle is proper so that seems good. Now my issue is fixing the idle(which has been my biggest problem from the beginning). I can get it to idle around 900-1000 but it's still jumpy and backfires when I let off the accelerator, so now I'm at a loss.

Sounds like you have a vacuum leak that is sucking in unmetered air, the easiest way to check this is to get some starter fluid and spray it around your throttle body/vacuum lines/intake, could be one or a combination. The extra air isn't being registered by the ecu , thats what's causing it to backfire.

If your rpms go up when you're spraying the starter fluid, that means you have a vacuum leak, youll need to figure out what it is and fix whatever is causing it. (gaskets/capped off vacuum lines/vacuum lines themself), also you can check the bolts and retighten them incase any could be loose anywhere.

Another thing it could be is your throttle position sensor is bad, or not set right, if it's not working it will cause lots of backfiring on deceleration.

The only other thing that will cause a jumpy idle is if you have a streetport, removed 5/6 ports. (assuming you have an na for removed 5/6 ports)

what happened to the tube that ran to the cat.?

The Anti Afterburn Valve in the ACV also prevents backfiring from occuring upon deceleration.

There was no tube that ran to the cat previously... When I bought the car it had a Corksport header on it. When I got in the RB header I realized it was about 4 inches too short to bolt up to the old cat properly. Right now I've got a fabbed up pipe that connects the cat to the header.

Another question I have, and I know it's been discussed many times over but it seems to be too difficult for my understanding... >.> On an s5 na engine, is the TPS adjustment screw the small flat head screw with the 8mm nut around it, or the flathead screw with the sping on it that controls the throttle?

Spring!!!!!!!!!!!

What's the other one with the nut on it? The throttle stop screw? Btw just an update, rechecked the timing, seems to be dead on. Drove her around a bit, everything seemed to be super smooth. Did backfire a few times during the drive and a couple when I got back and sat at idle. RPMs are a bit bouncy(around 750-900, although I've heard that maybe from the port?) But the backfires are still worrying me... From everything I've heard backfires are the death of the engine.

On a completely unrelated note, it does leak oil... quite profusely, but I haven't been able to pinpoint the place it leaks from. For reference, I have to put a qt of oil in every 3 weeks or so, which is only about 250 miles. Any ideas, or should I just poke around till I find the leak?

Rotaries are built to burn oil while they run, so you're burning and leaking it at the same time, as far as the backfiring it's probably because you're running really rich, it's not so much of a bad thing as you probably think it is, at least from my knowledge...there are some rotaries with high hp that backfire and shoot out flames.

I could be wrong though, someone else with more knowledge on the subject could give more input, but in any case backfiring isn't what is will mess up your engine, its detonation inside that engine that will, and i really dont think the chances of your engine backfiring back into the engine are very good, but i could be wrong.

If you are referring to the item in post #15 in the following link then that is the secondary throttle stop screw which is not to be messed with.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/engine-stalls-out-any-thoughts-1003065/

Are you familar w/how to set the TPS? It has a Green/Red wire that is to be set to 1 volt w/key to on and the engine as warm as possible. And again, if the Anti Afterburn Valve is not working properly then there will be backfiring when decelerating and this is the only reason why this component is there.

Alright, the lever that rests on the screw is indeed level, so nothing should be amiss there. So basically attach a meter to the green/red and check that it's at 1 volt? Np, I'll get on that tomorrow and report my findings. As for the Anti Afterburn Valve, how can I test that to make sure nothing is wrong with it?

Remember, the car needs to be as warm as it can get for taking the reading beforehand will provide you with a faulty reading.

The easiest way to check the valve would be to disconnect the hose to the air pump and with the engine idling place your hand over the open end of the hose and the idle should not change. If the idle dropped for example then there is a decent chance that the valve is faulty. There is also a test in the fSM that you could look over, and not sure if it is the same as test as just described.

In looking over the FSM, you disconnect the same hose and increase the idle speed to 3000 rpm and then quickly let off of the throttle and air should be sucked into the hose for a few seconds.

I refuse to troubleshoot past this.

If you were 40deg ATDC, STOP! FIX YOUR TIMING before doing anything else. "as best as I could" isn't good enough. Get your timing SPOT-ON, then move on and set your TPS.

timing has been fixed... It is now matching with the marks, so it is SPOT-ON.

Ok, now check/test/reset the TPS.

Still haven't had the time to adjustthe TPS yet, will definately do it after work today. A new update for today, car is now ONLY backfiring at idle. Also, how do I go about adjusting the fuel/air ratio so it doesn't run as rich at idle? And could that cause a jumpy idle?

You can't adjust the ratio on an S5 and I believe the car is supposed to run rich at idle. And does the idle jump only when the engine is cold or at any time? Focus on the TPS for now and see how that plays out.

The idle is jumpy hot or cold. It's not nearly as bad as it was at one point but it's still not smooth. If there's any information that I can provide (pics, mods, video, etc) that might help out I'd be more than glad to provide it.

The TPS is your best bet in an attempt to rectify your problem.

So I finally got to mess with the TPS, however I'm getting some funny readings... I used Aarons method, disconnected the TPS and checked resistance. With my meter set to 20k, I measured 4.5 ohm... Something definitely is off here.

That would be 4500 ohms and not 4.5 ohms. And just set it to 1 volt as suggested.

Trying this again, give me 5. lol

Okay took a bit longer than expected, I wanted to go out and get her warmed up again just to make sure. So after testing again, I can't get the readings to under 2.5k without completely removing the screw...

May have been reading/doing something wrong there... When reading further down the post someone mentioned the wires are green and black, not the two I was using... So after using those 2 connectors, mind you they are both the furthest to the right when the connector is facing upwards. One on top of the other, adjusted to exactly 1k. This about right?