Many thanks to team-zr1, Fox, BOBSZ06, and all who advised me concerning this concern. It seems that my problem is related to high ambient temperature because it has disappeared now that the summer heat has moderated. I did check the DIC for PCM codes--none were found. I will continue to drive and enjoy this fantastic car thru the cooler months and maybe find a solution to the problem next summer if it recurs. I really appreciate everyone's input. :chevy

 

Anyone know why there is knock when the engine is cold and at idle? I think mine does this only when the engine is cold. I have autotap -- all seems ok except for KR under WOT but no such thing during idle...

 

Your long term fuel trim could be off and when going to WOT your too lean.
Best would be if you can e-mail me a trace via a PCM scanner and then we would know exactly what needs to be tweaked.
Just because LTFT is rich lets say does not mean at WOT you have the same ATF.

You may find at WOT, O2s reporting less then .890 mVolts.
Also look at what timing is at when in WOT.

John



[Modified by team-zr1, 5:16 PM 9/9/2001]

 

John,

Thanks for the info. Here is a snap shot of what happened during WOT with KR:

Ignition timing was around low 20's. KR as high as 5. O2 B1S1 is around 0.91. Both fuel trims are at 0 and cell is at 22.


Let me know if you want to see the entire file.

Thanks

 

Your WOT timing is way too low, it should look somewhat close to mine ( around 27 degrees during WOT and I have 11.3:1 compression)
What are your mods ?

http://teamzr1.com/greatwot.html

This is multi WOTs filtered from the same recording.
E-mail me your trace and let me analyze it and let you know what I see.
Lets see the difference in knock if its more prone in cell 22 then in non wot (cells 1-19) for then it's easier to know which way to tune via a MAFT.

John

 

John,

I would die to have your spec's -- man, zero KR and near 30 degrees of timing!

Here's a link to some autotap runs
http://briefcase.yahoo.com/bc/sbkim/...c=bc%26.view=l

If you don't mind, I will also send you my latest run file via email. Love to hear back your comments. Bascially, it seems like my KR issues arose after I installed my Powerloader. My only other mods are Vortex and Corsa Indy's.


BTW, what sort of scanner tool are you using?


Thanks


[Modified by sbkim, 4:52 PM 9/10/2001]

 

I looked at the traces, You LTFT shows a bit rich,
rich reduces timing and that is clearly seen in the trace.

When at WOT your a bit too lean and that causes knock and that reduces WOT timing by 4 degrees plus. Try to get O2s reporting around .910 and see what knock is at WOT. The maybe tune leaner to .900 mVolts, check knock again and maybe spit the difference in last tune.

Your PCM is not tuned correctly for good WOT performance.

You need to use like a MAFT and lean out using BASE switch but richen up a bit for WOT. Tune until WOT timing gets to around 27 degrees but zero knock at WOT. This may mean adding a bit of knock at non WOT but who cares about city driving being a top performer.
Really though, you need to play a fine line in going lean to increase timing but not enough to kick in big retarded timing. due to pings.
Get used to adding unleaded race fuel with crap street gas.

Get rid of that crappy autotap, Ease enhanced powertrain scanner is a much better diag tool. I can get you a discounted price if you choose that route.

Keep in mind the weather will soon be getting cooler and the knock issue will be reduced until hot weather comes back so if you MAFT now then test and tune when it gets colder and go back to summer MAFT settings when you need to.

Tis a bitch you spend the bucks for custom PCM coding and still have to hand tune via a MAFT, IMHO, if a C5 is a MN6 type, then keep stock PCM code and just go with a MAFT. At least with a MAFT you control the ATF ratio.


John


[Modified by team-zr1, 7:27 PM 9/10/2001]

 

John,

I would be interested in one of these scanners. Also, is there good information that comes with it on how to use and set up? Or are there other posts somewhere else, here on the forum?

Thanks. :cheers:

 

You can start here http://easediagnostics.com/scantool.htm

All the info is there and they also have a demo online.

You can contact me and I will teach you how to use this scanner, record the PCM for traces, how to analyze the test traces and how to use it to tune your C5. Ease charges $350 plus shipping but if you contact me I'll get you at least 10% discount.

John

 

John, do you think that one still should tune their LTFT's close to zero (with stock injectors) even if they're getting O KR @ WOT and 30 degrees of timing (my case). My LTFT's are a little lean but I'm not getting any KR. There are two theories of tuning LTFT's: 1. You can tune the LTFT's to zero, then adjust WOT. 2. Lean out the LTFT's as far as you can before getting KR then tune WOT to be stoichiometric. Thanks man.

 

Hi Levi, it looks like you also have come a ways since we both had lots of issues back in the spring. Sounds like you got your's pretty clean as to knock while still having good WOT timing.

To me its a fine balancing act, to get the best timing which means running on the lean side but not lean enough to kill off timing due to knock due to that leanness.
I have done both methods yo have metioned and found I had better luck in gettig LTFT real stable running at dang near close to zero and then useWOT switch to fine tune. I keep in mind the base switch is the course setting if you will and WOT switch is the fine tuner but alwasy keep in mind both switches are additives to each other and go back to my baseline as to the 8% lean LTFT and then wht the offset is when i added the SVO 30s and what the over all difference is to fuel %.
My case is worse in tuning then those using stock injectors and stock engine compression for I have to fool PCM to shorten the pulse width ( leaner) but keep the timing at WOT correct for what a engine at 11.3:1 compression can handle.
Method #2 seems so much harder to obtain best tuning setting since going so lean with base and then trying to just use fine tune (WOT switch) changes moe when the temps or gas grade changes.

So are you happier then wht you were seeing in PCM scans last spring ?

John

 

Yes, John. I'm pretty content with what I have tuned to now. I have avg LTFT's of around 5 and WOT of .89 (I know they're crappy at high voltage) and zero KR with 30 degrees of timing. Every few times on a WOT run I'll get .3 or .4 KR but it's so minute that it doesn't affect anything. It pulls much better now that I have gotten it all squared away. How's yours running at the track now? Later, when I get H/C, I'm going to get the SVO 30#'s and tune to zero like you have and go from there. It's fun stuff

 

Well you got one heck of a better leg up then I did when going with the SVO 30 to solve the ill issues I had due to PCM coding. At that time veryone told me i was nuts going with larger injectors but in the end I learned a hell of a lot, got them tuned in and in the end am telling engine there is less of a load by setting MAFT -15 lean. Much better then telling PCM to go richer ( more load) and reducing that timing that also kils off torque.

Dang only 1/2 degree knock, you got a sweetheart now, heck you might be able to dial even more leannnes and gain more timing esp with the cooler weather coming.

My 4th dyno since January shows tuning has had good gains with RWHP but the torque really woke up well and both showed up in better E.Ts and topend at the drags. Will test again at drags in a few weeks and then a real good test doing the Route 66 open road race in Nov.

Don't know if it's been fun but the learning curve in lying to the PCM has been very interesting and good long term experience to have.
The larger injectors did ed up to be a good path to take, plus has spare juice when I need injector pulse width on longer.
Also I notice engine needs less work to obtain the same speeds then a C5 with stock injectors for PCM thinks there is much less load.


John

 

Thanks John. I'll be in touch! :yesnod: