In the past week and a half my car has had a slight backfire 3 different times. It is just like a small pop not anything super loud. Does this mean it is running too rich? I have a cel from the egr bypass so I can't tell you if it has a new code, the key dance doesn't work for my 98. The backfire happened twice when first starting the car and once when taking off after idle at a drive through. Is this backfire or just carbon being blown out? If it is a cause of it running too rich will an afc fix the prob and if so what is the best for its price. Keep in mind I do plan to go turbo before too long so I would like one with boost control if possible. The egr has been bypassed for months, the only thing I have changed shortly before this began was the plug wires which I don't think should have any bareing on my situation. I have had the rpms bounce to 2k every time I come to a stop but it quickly returns to about 900 as soon as the car is completely stopped. It always idles at 900. This has been going on since I had the tb bored and the mani p&p. I have reset the computer and checked for leaks every possible place around the tb and intake mani with no luck. Other than these minor annoyances the car runs outstanding. Anybody that can please help. TIA

98 RS/Evo exhaust/gutted cat/p&p int. mani/bypassed egr/57mm TB/custom CAI/ngk plugs/AFX udp/fu,ru Stb/Magnacore 8.5 wires

Hello is anybody out there???


98 RS/Evo exhaust/gutted cat/p&p int. mani/bypassed egr/57mm TB/custom CAI/ngk plugs/AFX udp/fu,ru Stb/Magnacore 8.5 wires

maybe check the gap on the plugs?

The plugs were properly gapped at the time I put them in(3000 miles ago). Could the gap change that fast?

98 RS/Evo exhaust/gutted cat/p&p int. mani/bypassed egr/57mm TB/custom CAI/ngk plugs/AFX udp/fu,ru Stb/Magnacore 8.5 wires

Any other suggestions PLEASE!!!

What method are you using in checking your intake manifold for leaks? Since you mentioned just having it ported and polished and reinstalled it, there in may lie a problem. Especially if you say idle jumps to 2K initially after coming to a complete stop, thats usually indicative of an intake leak.


Patrick
STAR Stage 5

I have checked for leaks by visually checking to make sure all the gaskets were properly in place and double checked to make sure all mounting bolts and nuts were tight. If there is a better way of doing this please let me know. This couldn't cause the backfire could it? by the way thanks for the reply.

There are a couple of other ways I've used in the past.
You can hook up an air compressor to the TB by fabbing-up any simple plastic piece, to serve as a makeshift plug onto the TB, and run a nipple off of it to the air compressor hose. With the engine off, and TB butterfly fully open, run the compressor and listen for leaks.
If that's not feasible, you can also take a spray bottle with soapy water, run the engine and spray the soap-water around any mating surfaces and gasket areas and look to see any uneven movement. I've seen on some 4G63 guys even having leaks around the injector seats so spray around those too.

Since you already ruled-out any ignition problems, generally then backfires are predominantly caused by leaks in the exhaust system. Usually it would happen as you decelerate and come off the throttle. Left-over gas runs into the exhaust system and, when it would just get blown-out the tailpipe, now mixes with leaked air into the exhaust and creates a perfect a/f ratio to ignite again from the high temps.......... BUT since you mentioned this happened when accelerating from idle, I'd be under the impression it has something to do with your intake and the ECU not getting the proper vacuum reading.

Of course it could simply be a bad A/F meter as well. If its been awhile since you replaced it, invest in a new one. And see where it goes from there.

Patrick
STAR Stage 5

I'll try the a/f meter and soap/water mixture we use to use that method at the ship yard, I havent worked there for a long time and had forgotten all about it. Thanks for the help

98 RS/Evo exhaust/gutted cat/p&p int. mani/bypassed egr/57mm TB/custom CAI/ngk plugs/AFX udp/fu,ru Stb/Magnacore 8.5 wires

My car used to backfire real bad from being out of time cause the cam gears were tuned too radical, now its not as bad but backfires cause the DFI is running pretty rich...