tici

iTrader: (1)

As in the title...
What can go wrong during an engine flush and a decarb procedure?
- Oil pressure is ok (higher than before)
- no misfire
- no knock (less than before)
- fuel trims same as before
- WOT AFR same as before
- no codes
- good O2's reaction before and after the cats
- ...???

I haven't replaced the spark plugs after the decarb procedure: is that something I should do?

The fuel consumption went from 18 mpg (short trips, no highway) to 15 mpg and the car feels a little asleep.

Have I removed that nice carbon build up that used to seal my engine?

Have I ruined some valves that are now leaking?

Have I filled up the cats with crap coming from the heads + valves?

OK, this is not really an "advanced engineering discussion" but I felt it was the best section for this issue

Thanks

Stefano

1 FMF

iTrader: (1)

i would say the way the way you are measuring mileage: short trips no highway.
that can be a huge variable considering warm up time when the car is running open loop mode, and the biggest impact is you're not accounting for running time that you're not moving such as traffic lights, stop signs, how much you stop and go, and possibly the different routes you may be driving. If you're in lighter traffic then you're mileage will be higher because you're not wasting energy by always braking to stop then using fuel to re-accelerate, and if you drive one route that is flat vs hilly that'll have an impact also.

the best most practical way is to get the car fully warmed up, at least 5 miles worth of driving, then pull into a gas station and top off the tank, and top it off consistently either stop filling as soon as the pump shuts off or fill all the way till you see fuel in the filler neck. Then immediately get on the highway, with as little stop & go traffic as possible, and do your trip, preferably > 50 miles. As soon as you get off the highway, refill divide mileage driven by gallons refilled, that's your mileage with some degree of accuracy. Ideally if you can do I highway round trip and refill at the same station, that'll help rule out inconsistencies between pumps. After that, the next best thing is to do repeat trips and then if the numbers are consistent you can be pretty certain of the accuracy of your measurements. Right now, the difference of 3 mpg you're seeing is within the noise margin of the way you're measuring your mileage which i'd bet is a +/- 5 mpg swing. The shorter the trips and more stop & go traffic the less accurate and less consistent you're mileage will be.

tici

iTrader: (1)

Agree.
But I drive the same road since 6 years. Every day. Always the same way. Summer and winter. And the variations are so small... It's not good to check mileage as I do, but how is it now it's way too much. I never had that much and things changed just after the "treatement".
Tomorrow I'll replace the spark plugs and check the compression, whish me good luck!

By the way: I have 86'000 miles on this engine, this was the 1st decarb ever.

tici

iTrader: (1)

Spark plugs look good, compression is 175 - 180 PSI for each cylinder.
Any other idea about the cause of an eccessive consumption?

1 FMF

iTrader: (1)

if you're confident it's not a measurement error on your part,
my first guess would be the O2's, check AFR at part throttle cruise it should be 14-17. The O2's might be reacting ok but after doing a decarb and blowing a bunch of crap past them maybe they're partially fouled resulting in a signal to the PCM that keeps the mixture richer than leaner? just a guess.

what else changed? put new tires on the car? tire pressure still the same?
still get gas from the same place, and are you sure the formula of the gas didn't change? It would be a heck of a coincidence, but it's possible.
Is it an auto or a manual?

Manic Mechanic

iTrader: (3)

Describe what you mean by "Engine Flush and Decarb Procedure". Pouring Sea Foam into the brake booster line can easily wash out a cylinder.

Vernon

tici

iTrader: (1)

The O2's are fluctuating as usual between 50 and 950 mV and the PCM seems to like how they are doing (no codes).
The Wideband shows 14.7 - 14.9 while cruising (it's installed before the passanger cat).
Fuel trims have not more than 0.5% difference from bank to bank.
Nothing mechanical changed.
Gas is from the same place, the car is a M6.

Engine flush and decarb
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: http://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.

Manic Mechanic

iTrader: (3)

Somehow I missed your post where you checked compression and it was good. I've seen rings ruined from excessive solvent use so that's why I asked. Based on what you've seen and done at this point I would suspect carbon blockage in the covertors. It would cause your problem and could have happened during your cleaning.

Vernon

tici

iTrader: (1)

Converters are almost glowing during high load...
Do you think carbon deposits would survive this?
OK, everything is possible...
How can I check that without removing the exhaust?
I hate those messy jobs!

Manic Mechanic

iTrader: (3)

If they are glow then they are restricted. Carbon survives heat pretty well, I would pull it down and back flush them. With a water hose if I had to. Compressed air will work but you have to have someone working the air and another rapping the bottom of the cat pipe with a mallet to work the stuff all out.

Vernon

tici

iTrader: (1)

can a clogged cat increase the fuel consumption?
Why?

Sholdn't I feel a certain power loss?

Manic Mechanic

iTrader: (3)

Mileage goes down because the engine has to work harder to push out it's exhaust gasses, same way a low restriction exhaust can improve fuel efficiency.

You said it feels a little asleep, I assumed you meant power was off.

Vernon

tici

iTrader: (1)

Yes, less power.
I still can check:
-Clogged cats
-Dirt O2's (however: they respond fine and the PCM isn't complaining)
-Dirt injectors (maybe the "juice" washed the dirt from the manifold and the
injectors are now dirt, the spray pattern is maybe different than before and
fuel isn't burning completely)
- dirt MAP sensor

Next step: force the PCM to work in SD mode and see what happens (VE tune is done and should give the same fuel trims as with the MAF, las time I tried it was like that, if now it's different chances are that the MAP has a problem).

What els can I check?

Fuel here is $6.90 per gallon... that's why I care about consumption!

Manic Mechanic

iTrader: (3)

Here's my thoughts considering I'm a certified technition with plenty of high performance and standard prodjects under my belt. The only time I've seen cats glowing is when they are restricted. A slow O2 will cause one side to read way off and usually sets a code, two at the same time is another story. On this fuel injection system the MAF and O2's are over the MAP in importance.

Vernon

tici

iTrader: (1)

Yep, I understand what you mean.
So far the cats aren't glowing: I just assume that tey are so hot inside to eliminate the residuals that have (maybe) been dislodged from the engine during the cleaning.
Bot banks show the same fuel trims, both O2's are switching lean to rich as usual and the PCM seems to be happy with that.
Also the additional WB I have shows nice values... so I have 3 O2's sensors that are showing the same thing. I can't imagine that all 3 have exactly the same problem!
Is it possible that the tip of the injectors is dirt because of teh cleaning?
Is it possible that dirt injectors produce a wrong fuel pattern that can't burn efficiently?

If MAP, O2's, injectors, compression, spark plugs, AFR and timing are ok, what else can cause an increased fuel consumption?

I can imagine only cloggged cats... but I really hate to take this messy exhaut apart just to look inside

ae13291

iTrader: (8)

clogged cats can also be a problem too! is your engine running eratic? check the O ring seal under the egr pipe that goes into the intake! it may be melted!

tici

iTrader: (1)

Well, after 2 months the fuel consumption went back to where it was before, I would say even lesser!
No idea why, but maybe clogged cats + dirt O2's....
I replaced the spark plugs
checked the injectors (OK)
checked the compression (OK)
Checked all sensors (OK)
Nothing changed the fuel consumption, I just had to drive around for a while... ???