Smokey exhaust - now what?

[js43lotus]

Finally sorted the title issues associated with importing my 93 Chim to the States. Got the license plates and new 71r's installed Saturday and took her for the maiden drive. I stopped in a car park after about 5 minutes and notices a significant amount of smoke coming from the exhaust pipes. At first I thought it was water vapor, as it was a cool damp day, but after another 10 minutes driving the exhaust smoke was still there at each stop light. Took it on a motorway run for another 10 minutes and when I stopped the exhaust smoke at idle was still there. Never noticed this issue during the multiple times I ran the engine while I was restoring the car over the past year.
Here is what I know:
- 83K actual miles on the 3.9L Cat engine, idles smooth and accelerates strong (with no smoke)
- 45+ psi oil pressure & new oil is crystal clear
- New coolant is clear & no loss in level after it cooled - So I don't suspect a head gasket coolant breach
- Water temp remains low (cool day) even on motorway
- My mate drove the car periodically in 2017 with no smoke issue (while I was waiting for it to reach import age)
- Car has been garaged all of 2018, but started periodically with no smoke while I rebuilt brakes/suspension/etc
- Black soot visible at exhaust tips. Wiped clean with solvent, but soot returned after next run.

So, where to start? I suspect possibilities are perished valve stem seals, worn valve guides, worn piston rings.
- Since smoke is only prevalent while at idle, not while driving or accelerating, could the crankcase vent be allowing oil through under idle vacuum?

Thoughts from the group???

Thanks, Jerry

[jojackson4]

What colour is the smoke?

[blaze_away]

Could be either
1. Over fueling
2. Burning oil

1. Over fueling get it to a garage/tuner for emmissions testing. Usual suspects are ecu temp sensor maf tps lambda probes ignotion components

2. Burning oil get a compression test and leak down test. Usual suspects rings valves valve stems and seals.

Once you know what the smoke is you can then fix the problem

[Loubaruch]

Have you by any chance put too much oil in the sump?

[Boosted LS1]

Go for the pcv system first. Disconnect it from the intake suction side and blank it off. See what happens next.

[js43lotus]

All good suggestions and worth checking out. Let me try to respond:
- Smoke color light gray and dissipates quickly, which is why I first thought coolant breach. But it has no classic sweet or oil or raw fuel smell.
- When I changed the oil I filled it slowly to the amount denoted in the bible. When dead cold, it is exactly at the full mark on the dipstick.
- Blazeaway, if I can learn how to load the Rovergage program onto my laptop, should I be able to check for all of the "overfuel" ECU conditions you mentioned?
- PCV blank-off trial: I will try this to see if that changes the exhaust.

Thanks to all for your thoughts!

[blaze_away]

Rovergauge will show the values but emmissions test will show if youve got corrrect AFR and if theres unburnt hydrocarbons. Rovergauge is a good starting point though.
Forgot to add a 3rd point
Could be steam as result of head gasket failure compression test and leak down would detect that.

The other siggestions also made are wuite valid too.

[ruhall]

What's your valley gasket like? I had similar symptoms ( few years ago now) and it seemed to stump most people, ie no obvious smoke on acceleration after a long downhill descent on closed throttle etc. Valley gasket was damp with what appeared to be a slight coolant weep from thermostat housing and pas fluid from one of the connections under the reservoir.

Eventually replaced valley gasket and rocker gaskets which seemed to cure it. I'd initially thought it might have been a piston ring as it was first noticed after a lay-up. Thought was that a small amount of oil was being sucked in through deteriorating valley gasket after idling for a short period. Symptoms were not noticeable at any time other than after idling for a while.

[QBee]

If you think it might be oil or fuel smoke, rather than water vapour.......

What spark plugs are you running?
The standard factory recommended B7ECS are, in my opinion, too cold and too shrouded, and tend to soot up and mess up ignition.
I run BPR6EIX in my car and have no such issues, though you could run BPR6ES instead.
My TVR expert, after seeing how clean my plugs are at every service, has started fitting 6s in all Chimaeras and Griffiths now.