RonD.

88 951 stock 26/6 Russell Berry Max HP chipset,3 bar PR,K&N cone type filter,Bursch test pipe w/ 3" cat-back w/ Magnaflow muffler. Lindsey boost enhancer as boost controller set at 18 psi(4th at WOT). Car runs great pulls strong but on cold start-up I'm getting a fair amount of wet black soot from the tailpipe on my garage floor. Just started doing this recently. Any thoughts?

V2Rocket

If there's a lot of humidity that seems normal...
Do you have a wideband gauge?

RonD.

No wideband/afm Also, car tends to pop from the exhaust on deceleration, especially after some red line pulls in 3rd and 4th.

fejjj

You really should consider adding a Wideband. Anytime you modify your engine and add boost, it is very important to monitor AFR.

Chris Prack

Ground problem would do it.

ramius665

Without a cat, this sounds normal. Agree with Chris, a ground problem could also cause a rich running condition. You're running too rich when you start shooting fireballs on throttle lift at WOT.

951pcarguy

Which component is causing the Ground problem, and what needs to be grounded? I'm having the same problem with my 87 951 w/ Lindsey Quad MAF and 3" Exh w/o Cat, so I was wondering if I might be having a similar issue. I already replaced by O2 Sensor and it helped a little, but it still pops and deposits soot over the bumper and rear end, especially after long high-speed runs (like Baltimore to Watkins Glen in Rt 15 passing all the Corvettes on our way home from the United Sportscar race!).

fejjj

There are multiple grounds in the engine compartment of your car.

Do a search and there are location charts on the internet.

You need to unattach them, clean them really good, add some dialectic grease and reconnect.

raleighBahn

You mention on cold startup - but is it fine once warm? You could then rule in or out sensors based on open loop and cold loop topology.

Soot on bumper is par for the course in my experience, being alpine white doesn't help me. It's all relative though - how much soot are you getting?

RonD.

Fine when warm. Soot only on exhaust tip after driving. No soot on underside of bumper.

raleighBahn

Ok - so cold start is open loop. Once the car is warm, it goes into closed loop.


//Some edits
During open loop and WOT, the O2 sensor inputs are not read. So if you are getting this problem on cold start, it is probably not the o2 sensor.

I believe the DME crank sensors, temperature sensors, fuel pressure, and ignition system.

I would at least measure resistance on any water/air temp sensors that would be relied on at cold start that have influence on the air/fuel decisions and compare them to spec in the workshop manual test plan.