Topic: Stock Opel GT dyno-AFR looks dangerous

[Arabas]

this is a guy's GT dyno. he bought it used, full stock, no mods.
his engine went south and the dealer replaced his motor.

he felt the car running a bit strange, sohe took it to the dyno. his afr doesn't look promising.
he changed both fuel pumps, lambda sensor and one map sensor

i suggested to check both map sensors and also his maf sensor and check for air leaks.

he believes his problem could be the ecm (07 GT).

any guesses or any similar cases you have encountered? [ Guests cannot view attachments ] [ Guests cannot view attachments ]


ps replaced the images with more forum friendly sized ones

[Critterman]

Everything I have heard says the direct injection engines run leaner, because of the way fuel is delivered.  The LNF is a DI engine. 

[Arabas]

below i have a quote from a well respected tuner. this refers to a tuned LNF, but i assume it applies for stock LNF's too.

"The circumstance under which we really care about air to fuel ratio is at full boost.  We don’t want it going leaner than about 12.5 at high boost levels.  It is OK for it to go leaner than 12.5 during cruise, which should be 14.2 – 16.5.  "

so Critter, you say the dyno looks good?

[elff]

I've heard the same thing Critter has said related numerous times. 
Only problem is, I don't what it's supposed to be.

I'm going to open my HPT logs and take a look at my high speed high RPM times and give us a comparison

[Uranium-238]

I've got my stock Sky dyno sitting right here, and it touches 15:1 at 5500 rpm.

[elff]

Here is what I found on the HPT forum

the pid should just be "wb lamba bank 1" only since it reads in lambda and you are adjusting in lambda you make it the same..... calcuate it outside of hpt to see what you got is better plus .86-.88 is the lnf sweet spot so you dont really need to calculate much at all. everyone is different i though

.86 *14.7 = 12.642 afr .88 *14.7= 12.936 afr

I just went through a bunch of my logs and using the formulae
The lowest AFR out of all of the logging I have done on my car never drops below a mid 12s

So my logs and the above HPT quote seem to collaborate what your local guy is saying.  He is running really lean once he hits that 6000RPM mark

[Bottoz]

Here is my Stock Boost & AFR vs Tuned Boost & AFR.

As you can see, in stock form it starts in the 14s and tapers down to 13. Tuned it stays around 12.4 at WOT.

Arabas - Looks like our Stock AFRs are very, very similar... as they should be.




Uranium - 15:1 @ 5500 RPM @ WOT seems very dangerous.

[Carbon Sky]

Running as lean as possible gives you as much efficiency and power as possible, but puts the engine at greater risk.

Due to DI's ability to inject fuel at any time, and not only when the intake valves are open.  A DI engine can spray fuel during the compression stroke, if knock/lean issue would arise based on how much fuel was already sprayed.  So running closer to lean alone is not that much of a problem, especially while cruising.

However, under high boost conditions, especially at lower rpms, this lean condition can definitely be dangerous.  Thus I run stoich under light load conditions, and slightly rich under heavy load conditions.  The richest condition I run at is low rpm, high load, say when trying to build up boost.  It protects the engine a little more, and I swear, it even helps with lag reduction.  I'm no 100% sure as to why, but I think it has to do with unburnt fuel leaving the combustion chamber, and the expansion of gas leaving the combustion chamber, has more energy left in it (since it's still burning), which spools the turbo faster.

[Kelu]

Arabas: quick question ... he was at WOT when doing that dyno?

[Arabas]

Arabas: quick question ... he was at WOT when doing that dyno?

don;t know the guy in person, he just called me a couple of times. didn't ask him if the dyno wa at WOT, but hell, ALL dynos must be at WOT

[spoolin]

That's definitely the stock AFR. Here's the PE Lambda table from a stock tune.
http://i1052.photobucket.com/albums/s458/spoolinlnf/Car/pelambda.jpg

[Kelu]

If dyno wasn't done at WOT, it wouldn't get into the PE Lambda .... but I doubt, should be at WOT

[tazz]

I agree that looks like the stock PE setup and when it drops quickly at the end it's running off the COT table and why it's running richer.  Does he still have a CAT is is it a catless DP?  If he's catless he should just be setting that table to all 1's to disable the COT table.

[miller11386]

I know my car runs pretty consistant at:
14.7 during idle/cruise (under 5PSI)
13.5 under moderate accel / partial boost (6psi-15psi)
12.5 under WOT when at full boost (15psi-25psi)

[elff]

Going through my logs
They match that

[Uranium-238]

That was a stock tune, on a bone stock Sky RL. Keep in mind I did end up blowing up a turbo the following spring.

Now that I'm home I can post the graphs.

EDIT: It seems I read the paper copies back at my desk wrong...