Trying to reduce engine noises and knock retard at high load I first "cleaned" the engine top and then flushed the crankcase with two products of this company: www.forte-nwe.com

Forté gas treatment (combustion chamber and lambda sensors cleaner) similar to GM top engine cleaner.
This product needs to be sucked in the intake using a vacuum tube during about 15 min for 400 ml.

Forté Motor Flush (400 ml) needs to be mixed to the old oil, let the engine idle during 45 min and the change oil + filter.
After this cleaning I filled the engine with the cheapest oil I found and replaced tha filter. After idleing 30 min I filled the engine with 5W30 mobil 1 and put another new filter.

The engine is a supercharged (5 PSI) internally stock 98 LS1 with 86'000 miles. AFR at WOT 11.5:1, total timing 17*, ECT set at an average of 195F.

Results...
- much less knock retard
- Fuel trims same as before (+/- 2%)
- The wideband during OL is 14.7 - 14.9 same as before
- no misfire (same as before)
- Engine noise same as before (I was hoping a lifter was gunked and wanted to free it with the flush)
- same power feeling as before (maybe a little less)
- higher fuel consumption

The consumption went from 18 mpg (short trips, no highway) to 15 mpg.

Have I removed that nice carbon build up that used to seal my high milage engine?
Do I have less KR because of less compression?
Can I brake something with this kind of procedure?

I still have the old spark plugs, are they maybe dirt now because of the treatement? (those are Champion RS 12 PYP (#7401) gapped at 1.05 mm = 0.041")
Those spark plugs are 34'000 miles old.

To be honest I wouldn't repeat the treatement...
Any idea about the increased consumption?

Thanks

Stefano

If decarb is seldom or never done with as old as that 98 is I would assume the buildup on top of cylinders was pretty thick which would have increased the compression and the tune was slanted because of that and now tweak of tune is needed.

Not sure if the sparkplugs used are same heat range as stock but in any case I would change them but go at least one step colder then stock like a NGK-TR6

Sorry but if decrab is not done and due to LS1s eating some oil it would not take long for carbon to built up again and another reason to use water/meth injection to keep cylinders and piston tops clean

Also if orginal knock sensors I would consider replacing them with the newer design then what 98s had.

As to MPG, again I would do good testrun with OBD scanner recording, analyze that data and tweak tune but I would do that after those sparkplugs are changed

This is te 1st decarb proedure ever.
Those are platinum spark plugs, 1 step colder than stock.
I'll probably replace spark plugs next week and perform a compression test, I'll then post pictures and results.

Stefano

EDIT: I'm not sure about the heat range: stock are AC 41-xxx and those are R 42-xxx maybe hotter than stock? (!!!)
I took a look at the Vortech instructions andthey say not to use platinum spark plugs (!!!)

I do not know the ranges on AC sparkplugs and reason I mentioned the NGK-TR6 as they are 1 step colder and use a shorter spark gap.
With boost that could blow out the spark is reason to use the 0.35 to 0.40 gap rather then stock is designed for like 0.55 and they cannot be bent down to short gap as that changes the shape of spark.

What happens with no boost and a shorter spark gap?
This is a daily drive and 95% of the time the engine doesn't see overpressure.

I use the TR6 with my stroked NA engine with no issues.

If no problems at idle ( after tweak of tune) then the plug will be fine for youe engine

And here the results of the compression test:
#1 172 PSI
#2 175 PSI
#3 177 PSI
#4 180 PSI
#5 180 PSI
#6 172 PSI
#7 180 PSI
#8 175 PSI

All the spark plugs look fine, look the same and have the same gap as I set them 34'000 miles ago (see the picture).
Nothing really explains the increased fuel consumption or the lazy engine feeling.
I replaced the spark plugs, just to be on the safe side.

After this job (very time consuming in case of a F-Body) I resetted the PCM and did an Idle Relearn.

Results:
Fuel consumption - no idea
Power - feels a lot better!
Fuel trims: are a little more on the negative side than before replacing the spark plugs (?)
Maybe it's the new spark plugs, maybe it's the PCM reset. However: it is different.
I'll post about the fuel consumption later on.

Stefano

If going through all that work you should also have done a leakdown test
The plugs in the image do seem to have lots of oil on the threads

If how engine runs changes after the PCM relearn would suggest the tune itself id off and a tweak is needed

oil on the threads... actually it's copper grease.
on the picture it shines as it was liquid, but it's grease.

I personnally don't have the equipment for a leak down test, as I asked in a garage to rent it they was like "leak what?"
Why are you suggesting to do a leak down test if the compression is at the level as I posted?

Not sure what that grease does but hopefully does not reduce the ground path the plugs need.

Compression test only reports max PSI and not if there are any leaks in intake or exhaust.

Leak down test your using an air compressor to inject high pressure into cylinder and then tool has 2 gauges to see what the incoming pressure was and you leave in for awhile and the other gauge then shows over that time if the pressure in the cylnder side is leaking down due to ring or head problems

Leakdown tool is cheap and then needing the air compressor