Hello folks.

I have a 97 GSR with about 160k miles on it by now. Sometime around 2-3 years ago, it started developing a black soot on the rear bumper. I don't remember if it came on suddenly or gradually. Now that I think about it, the car had always had a very light and occasional pinging problem, but now not anymore. Anyway, here are all the things that were changed or checked:

Cat
O2
PCV
timing belt
valve adjustment
timing
fuel injectors
fuel filter
air fliter
TPS checked
ECT checked (resistance seems about right)
IAT checked (resistance is either right or a tiny bit high. Reads 2.2kOhm at around 75 degrees)
MAP sensor checked (reads 2.9V car off and .9V idle around 1000 rpm when the car is not fully warmed up yet)
spark plug wires checked (they are the original wires, but the resistance is within spec)
spark plugs changed out and gapped
distributor cap looks ok
distributor rotor looks a little burnt - will change that out
no exhaust leaks found via soot spots or by plugging the muffler and listening

Some other observations:
the car burns about 1 qt oil every 1500-1000 miles, BUT it always used to do that, plus the soot is dry and powdery, not oily

before and after the new cat, the smog numbers both showed air/fuel numbers that were about right

gas mileage is about the same as always, e.g. 300 miles per 11 gallons

car drives just fine

I don't see any smoke out the exhaust

two of the spark plugs are black and two are nice and white / tan. I am not sure if this is from fuel or oil

Anyway, the only thing I still haven't checked is whether the fuel pressure is on spec.

 

Check for "sticky" injectors on the two cylinders with the "black" spark plugs.

Swap then with the other two and see if the "black" plugs fallow. 94

 

I would be very concerned about using a qt. of oil every 1000-1500 miles. Honestly though, I would start saving up for a good quality rebuild inlcuding rings, valve seals, and maybe +.5mm bore.

If its been pinging, then its may have gotten serious enough(or for long a long enough time) to damage the ringlands.

Also, as fcm stated, it would also be a good idea to have the injectors sonic cleaned and see if that helps out any.

 

I already replaced all the injectors.

 

Header and intake?
If so you need a tune. Ever honda I see that adds header and intake have a black bumper.
Everyone I own as one after installing tho parts.
It gets darker over time and depends how often you wash your car.

Now if its 100% stock, then I'd say the oil burning is stoping the fuel from fulling burning

 

Seems like oil is getting in. As far as I can figure there's no reason for only two cylinders to be running rich if the injectors are new.

 

anyone else fail to realize its a GSr and the little diaphragm at the end of the fuel rail may be acting up? seen about 2-3 times, so it is rare but those things can cause a "rich" condition

 

With new injectors, and the 1 quart of oil every 1000-1500 miles I will have to agree with GagnarTheUnruly it's beginning to sound like oil is burning, but I also agree that does not account for the rich burn.

At this point I would want to try a known working ECU/ECM.94

 

Burning oil will look VERY similar to a rich fuel mixture when it comes to reading plugs... Can you post up pics of all 4 plugs?

 

This is a picture I took a while back when the spark plugs were only 2 weeks old.

 

2 to the right look WAY lean, left 2 look oil "ish"

 

That is DEFINITELY oil on the 2 plugs. Like I said before... its time for a rebuild.