S4 backfire & blue smoke
 

I got an '86 with 105k miles. Not sure of the trim level as it's been repainted. Just picked it up yesterday. It revs good, idles okay (550-650, but never stalls), and seems like an all-around sturdy little car. Has vert wheels, msd, adjustable shocks (KYB?), e-fan, s5 taillights, cone filter, an apexi muffler, and a few other things. Hugs the road better than my '85 S with shocks, springs, a bigger sway bar, poly bushings, etc (but stock wheels & tire size).

It's been "lightened" pretty good: it's missing the A/C and the blower settings don't seem to work; the power steering is removed; the hatch interior & spare tire are gone as well as the carpet; the airpump is gone and it has a "straight through" cat which I never got a clarification on. I don't think it's hollowed though it is louder than my racing beat "streetport" exhaust on my 12a, but I blame this on the Apexi muffler with its coffee-can tip. Has a real sloppy shifter, not sure if it's bushings or the spring.

I've driven it about 200 miles. Doesn't seem to drink any coolant, pulls pretty strong, shifts good except for second-to-third at real high rpms (may be the sloppy shifter; I've only tried it twice.). Uses very little oil and the MOP seems to be working.

Smoked a little when I started it this morning, as the PO says it does sometimes.

Here's my question: It backfires when shifting or letting off the gas over 4k rpm. I'd blame this one on the missing air pump or potentially hollowed cat. Sitting in place, revving up to 6.5k gets a good backfire and a puff of blue smoke. The backfire I'd anticipate, but is the smoke normal?

could just be your oils seals starting to wear down and when you left off the throttle you get blow by? due to the negative pressure?

Frank

I couldn't say (in fact I don't know if that scenario is common, plausable, or what). I got a pretty good deal on this car, so I'm not expecting much. I wouldn't mind rebuilding the engine as a project. It seems to have fine compression, so I guess I'd just do a soft seal kit.

PO said the oil was changed the day before yesterday so it only has about 225 miles on it, but it's perfectly clean and doesn't smell like gas or anything.

Set your TPS to 1 volt with warm engine. Do a search if you need more info, but that cured backfiring in my last 2 sevens.

I'm going to have to read about the TPS mod, but I don't think that I'll get to wrench on the car for a little while. School just started here and I've been real busy.

Hmm, it doesn't have a cat at all. It's got a pre-silencer, though I can't see much more from under it.