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#1571 - 10/13/01 07:08 PM Mods causing less performance  
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EvilZ06,
I have analyzed the test runs that we did at my garage this weekend and promised I would give you some results to use to help show the problem and to help resolve it.

Two test runs were done with outside temperature of 85 degrees.
Each run consisted of 12 miles of 15 miles of distance, using all RPM, gears, and throttle ranges. This included stop/go city and highway driving while I monitored and collected PCM functions status while you drove the car in the manner you do.

Both test runs used the exact same roads and distance to limit any changes and 2nd run was done within 10 minutes of completing first test run.

The following is what I determined via PCM data collected via a Ease enhanced powertain scanner connected to the PCM.

] Mark's Z06 Test Results

NOTE: the trace consisted of over 3,600 PCM read cycles, but to make this viewable using less screen space, the above was sorted to show knock and lean AFR issues. Also content important has yellow background.

Your surging issue is due to your long term fuel trim being 22 percent too lean. The removal of the MAF screen itself did not drive the leanness to that high of a level, but the other mods combined took your Z06 from being a performer, to high heat generating engine.
Even with the MAF screen installed, the existing mods drove the AFR out of a performance window.

You can see within this results sheet :

LTFT far to lean
Lean condition drove engine knock high, for both WOT and normal driving conditions). Cell 22 is WOT when TPS ( throttle) is greater then 99.5% on. Cells 1-19 are when you are pushing on the gas pedal, but not to the floor.
As seen knock is ocurrung in all cells and TPS position.
causing lessor performance at WOT due to timing on;y being an averge of 25 degrees ( about 3 degree loss, that also lowers maximum torque).
As seen by the injector pulse width, the PCM was attempting to go richer but could not achieve better then the 22 % lean average.
Intake Air Temp (IAT) was 5 degrees hotter then outside temps, thus air intake needs to be improved for IAT should equal outside temps when moving fster then 20 MPH.
The engine water temps spiking 220 degrees further hinders a lean condition, and the lean AFR itself helps drive the engine temps up due to hotter internal temps due to too lean buring AFR forcing pistions, sparkplugs, etc to run much hotter.
You'll notice engine knock was present no matter if the RPMs or speed were low or high.

The surging issue was clearly due to the leanness and to test this and to also reduce the knock issue. I hardwired in a MAF translator and simply set the AFR to reduce from a 22% lean down 5% to 16%.

Apon doing that and then repeating test run, knock went from being triggered 43 times to only 14 and all surging was gone ( but not totally when A/C is on).
By further adjusting AFR with the MAFT, both ill conditions can overcome the mods causing the conditions but I do not agree in total to this type pf fix.

The reason is to fight off a lean condition this far off of being perfect ( a LTFT of zero) you have to drive the PCM to go richer which them means it also drives WOT timing down that will also reduce performance.

You can either resolve the mods causing this over lean condition by vendor correcting or removing such mods.

Use the MAFT to drive LTFT as close to zero, but lean enough to maintain about 28 degrees of WOT timing, but not at the expense of increasing knock, which wold retard that timing

Or as I and others have done go with a larger injector such as SVO 30s, and tune out richness, that means going leaner, drives WOT timing up.

I suggest for next testcase, you adjust base of MAFT another 5% richer and re-scan PCM to determine if that is a short term correction.
Feel free to contact me for more idepth information of test results.


Quote
Originally posted by EvilZ06
Hi,

Over the weekend I removed the screen from the MAF on my 2001 Z06. I also drilled a hole in the throttle plate as per Halltech's instructions and completed the idle relearn process.

I certainly don't have any problems with surging at idle, BUT i do have significant surging when in motion. Example: I was crusing along the freeway yesterday at 65-70mph, around 1500-2000 rpm in 6th, and the car was surging quite badly. Under acceleration the car performed well, the problem seems to be when you back throttle.

If I pressed the gas pedal to bring my speed up a little, and then let off, the car would buck and surge and felt generally very rough.

I called Jim this morning and he told me that this is to be expected with a 2001 with no screen and that the problem is caused by a lean fuel condition. My car is NOT throwing any codes though. I am going to try the NEW Halltech Z1000 filter to see if this improves things any.

Is anyone running a Halltech TRIC with a 2001 and no MAF screen that has fixed the surging?

Anyone else have any suggestions???

If I can't fix it then the screen will have to go back in because I can't live with the car the way it drives now! frown :-?

TIA! :cheers:
[


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#1572 - 10/15/01 05:46 PM Re: Mods causing less performance  
Joined: Dec 2000
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teamzr1 Offline
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teamzr1  Offline
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Joined: Dec 2000
Posts: 4,864
America
EvilZ06,
here is my finding as to the PCM scans I analyzed with the Ease powertrain scanner.
For ease below I show the findings of the two test runs we did that were the same distances of the tests we did last week.

SVO 30 Injector tests

When we first did PCM scan testing, as you can see (top result report) the long term fuel trim was 21% too lean
WOT timing about 23 degrees.
Overall timing about 27 degrees.
4.2 mS injector pulse width,
non WOT, 16.2 mS WOT pulse width.
43 engine knocks, costing an average of over 4 degrees timing retard.

Due to the mods installed causing a hugh lean condition, engine knock, lower WOT timing and Ca crapgas, I knew this Z06 would respond best with the SVO 30 injectors and a MAF translator, rather then the general hype of "if it does not work, S-can it and go back to stock".

As I had mentioned in the past, going with the larger injectors gave a better outcome of not only tuning in the PCM via a MAFT, but also obtain better overall performance, rid surging, and reduce injector duty cycle.

You notice then in bottom test results how well the PCM and engine accepted the larger injectors and MAFT settings.
(NOTE: Weather was 85 degrees)

Overall timng went up to 32 degrees.
WOT timing gained 4 degrees which is also a gain for torque.
Injector plusewidth showed reduced duty cycle for both WOT and non WOT condition.
LTFT was reduced by 50% ( we can and will dial even more of that put and not effect inducing engine knock)
Knock - NONE, not even a .01, and that is with the crapgas and we allowed water and air temps to be higher then the "before" test

This once again showed that many of these high dollar mods can have an ill effect to overall performance but rather then just threw them in the junk can, by doing the proper PCM tuning and understanding the functions used bv the PCM.

As we began our first test run after installing the injectors and tuning the MAFT, I watched EvilZ06's face and he was caught off gaurd as pulling away from a stoplight, that now having good engine timing also woke up the torque and he hit the rev limiter far quicker then he could have before. smile


[QUOTE]Originally posted by EvilZ06
After talking to John I decided to upgrade from stock to the SVO 30# injectors. This meant that instead of setting the MAFT to 10% rich, we were able to go 10% lean.

Once the injectors were installed we performed an idle relearn (with AC on and off) and then took another test drive with the Ease powertrain scanner.

The results- absolutely ZERO KR at any speed or rpm and we also gained around 2 degrees of timing at WOT! laugh The car feels very strong and pulls hard.

I will be dynoing the car on December 1st at the next bay area dyno day. It will be interesting to see if the SOTP holds up!

Hopefully John will provide a more detailed explanation, and possibly put up the scans.

Thanks! :cheers:
[/QUOTE


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