Does a sooty tailpipe imply poor tuning ?

shaqjeep · Post by **shaqjeep** » Tue Jun 20, 2006 6:19 pm

I have my 258 jeep running good with MS1 V3 board with MSnS code and basically a 1989 GM 4.3 TBI approach. I tuned it while driving with a portable Hirobo exhaust gas analyzer (aiming for 14-15:1 range in cruise). For high load tuning I replaced the rear axle with a water brake. The engine runs much better, other than a slight hesitation off idle. Fuel consumption is better than the carb...perhaps 10% or so (bit early to tell). My after start enrichment may not be optimum...and may be a contributor (?). It was sooty with the old carburetor.

What bothers me is that the tailpipe is very sooty in mainly city driving. My 1989 Jimmy 4.3l stock is not nearly so sooty... Does anybody have the scoop on what a sooty tailpipe implies ? Perhaps somebody has a feel for the AFR at which soot becomes noticeable ? It does not burn any oil whatsoever.

mops · Post by **mops** » Tue Jun 20, 2006 6:34 pm

my tailpipe if sooty aswell...

I run 15-17 afr's on cruise and 13-12.5 afr's at 100kpa. but mainly i drive slowly, keeping afr's lean, I was expecting pipe be whiteish colour, while is dense black.

I cant really lean it out any more because it will start missing on cruiose. I could possibly enlean a littel bit high load (not sure whether it is a good idea). However what I did noticed, that durning fast throttle movements (i.e. chanigng gears) - elpecially throttle releases, afr's run very rich 10-11:1 for a brief time... I dont think that might be causing sooty looking pipe ? aswell my plugs look kinda sooty.... not excessive, but slightly rich... as I said, I cant really lean it anywhere significantly...

fscott · Post by **fscott** » Tue Jun 20, 2006 7:26 pm

The prettiest tailpipe I've seen was on a Beechcraft Baron. After a five hour flight with the engines running lean of peak for all but takeoff and descent, the pipes were a lovely tan color that would, on a sparkplug, mean a perfect mixture.

I really wanted to pull a plug and look at a piston crown. I bet there was hardly and carbon buildup in there.

A little soot isn't a bad thing, but a lot does mean you're running rich.

Fred

shaqjeep · Post by **shaqjeep** » Wed Jun 21, 2006 1:34 pm

Thanks for the interest. I really need a long highway drive for which I may up the accel enrichment threshold to eliminate this as a cause. With the exhaust gas analyzer hooked up as I drove, I could see how long the mixture stayed rich after a throttle change/accel enrichment event and it was surprisingly long.

I hate starting an engine when there has been fresh white snowfall and seeing a big soot stain shortly afterwards (of course warm up enrichment has a role in this too).

Chrisfol82 · Post by **Chrisfol82** » Thu Jul 06, 2006 6:33 pm

Hey Shaqjeep, Can you post your msq file? I also have a jeep 258 that i just got running on MSII V3 and it would help out alot to have a base point to start out on. I got it idling nicely but it hesitates sputters and backfires if you try and accelerate above about 2k RPM.

Anyways i just thought if you had a good running jeep engine it might be a good place to start.

PSIG · Post by **PSIG** » Thu Jul 06, 2006 9:16 pm

Any engine that has seen rich times during tuning will have a sooty tailpipe for a very long time as the tailpipe does not generally get hot enough to burn the soot off. You can clean the soot off or burn it off with a torch or in the oven on max or clean setting, although it will destroy chrome or discolor platings if you burn it off. If this is not important and you just want to tune the richness out you can use the datalogs.

If you're not sure if the soot is from accel or warmup enrichments, you can clip clothespins to the tailpipe. The wooden type works best. Put one on and start the car. If it's clean after warmup, then goose it - checking occasionally to see the color of the clothespin. It should only take a few minutes to determine if you still have a sooting issue and when you're getting it. Old tuner's trick...

Hope that helps,
David