S15 Issues

[S15 Powered]

I finally got to drive my car today after the SR20 swap and it feels awesome... except for one thing. Sometimes, when I rev above about 3k and shift gears, the car backfires. I'm taking it back to the shop that did the work and having them fix it, but I was just curious as to what the problem is. I'm thinking the timing is off, but I could be wrong. Anyone got any ideas?

[Bill Roberts]

This is my vibe, take it with a grain of salt.

Performance engines will always backfire with post detonation in the exaust if their is unspent fuel vapor in the exaust system.

Their is a lot of fuel flow going on and if you are backing off of the normal burn by driving "outside the curve of the engine" the left over vapor has to explode somewhere.

Try running it kinda hard through the gears.


When I let off the gas with mine, I get continuious back pops through the exaust systewm winding down and I have a good tuned black top.


I suppose that your exaust system is getting "broken in"


Run it and report back in 3 days...if it is a loud under hood type of pop, yes, check the valve lash and the timing curve and the default idle timing VS 2500RPM timing non-loaded and look at the curve shift.

It is common to experience pre detonantion and post detonation during a new engine.


I actually feel that minor popping is normal...loud bangs are not...at all.


Full under the hood bangs are cause for concern.

[elevator]

Absolutely right! That is why you see flames come out the exhausts on high performance cars.

[S15 Powered]

I drove the car again last night and I was wrong in my original post. It's actually shifting BELOW 3k that makes it backfire. When I push the car rather hard, it sounds perfectly fine. I'm planning on taking it to the shop today and I'll let you guys know what was up when I get back.

[drift freaq]

well folks , it all depends on if his engine is stock or he has bolt on mods. basically stock SR's are not prone to excessive backfiring which is what it sounds like he has . I think he might need to do some tuning to it. Also is the car running rich? What kind of fuel pump are you running? If your running a stock fuel pump please please please do yourself a favor and put in a hight pressure one.
Stock KA fuel pumps were designed for 270 injectors not 370(stock SR injectors) . We would have to have more details on the swap but yes the best thing to do is take it back to the shop that swapped it for you and have them tune it.
Oh yeah folks any shop thats worth its weight in SR swaps will know how to tune the engine good. If they do not you do not want them doing your swap. Lack of SR tuning knowledge translates to lack of doing SR installs on a regular basis.

[Bbandit]

the most simplest problem i can think of is the timing... retarded timing will cause backfires as some fuel went in to the turbo and creates a combustion by itself in the turbine .. and later being pushed out to the exhaust creating that popping backfire sound

[S15 Powered]

Well, I went back to the shop and they told me that it is probably the timing and they're gonna adjust it. But they also told me that since I'm running no cat, the backfiring may not go away completely. As far as tuning SR's, I had enough trouble finding a shop that would even touch an S15 and the guy that did the wiring had to be flown in from out of town. I think I'm gonna wait til I'm back in San Diego and take it to Jim Wolfe for tuning.

[theronin]

Backfiring is JdM TyTe, just watch 2F2F makes your car faster

[drift freaq]

when your back in San Diego you should take it by McKinny Motorsports . they are good with SR's and RB's