Mongo

Thanks for the reminder on the flappy. I think I need to do mine and check mine. BTW, I saw someone mention a new MAF could be out of specs (or uncalibrated). How is that possible? Is there a way to recalibrate an MAF? I thought the computer does the calibrations based on the needs of the engine and the program the ECU is running.

Hey Bigs, you might have driven the car too long and got used to the power....maybe you should let someone new to GTS cars try it out

mark kibort

proportionately, the curves look good. Just shifted down a bit. get the actual HP numbers so we can see if it was corrected "correctly". (not SAE!)

also, as far as knock sensors, it sure seems like the entire curve is shifted as I said and flappy is working. also, notice that the hp curve doesnt like the 12:1 rich range , where it drops off power. (pink line) even the other blue line when it gets in the 12:1 range for a quick duration, drops the hp torque curve down a bit right at 4500 for a couple of hundred rpms. because the other stronger line is at 13:1 for most of the run, i would think that is the optimal mixture range. I think if it had a knock, it would be more of an abrupt drop in torque/hp.

get the actual numbers and lets see if its a adjustment error.

putting that curve on heathly curves, it doesnt look as it is falling off any faster than any other 300hp S4 engine. (dont have a GTS curve to look at, but i suspect that it would have the same shape, but more HP)

MK

worf928

If the EZK/LH has determined that it cannot find the knock sensors then timing is retarded. I don't recall at the moment if the timing is backed-off until the fault is cleared, or the battery is disconnected, etc.

The above and my previous did not refer to 'sensing of knock' but the EZK/LH finding a fault in the system.

John Speake

Andy,
Any new or rebuilt properly MAF will be within 0.25% of calibration standard. With an O2 loop car, the A/F ratio will be set to stoich, which will take account of moderate ageing, air leaks etc at idle and cruise only.

At WOT and hitting the throttle, the LH goes off loop to enable the enrichment necessary. Then you ARE very reliant on good MAF calibration.

BTW the fuelling at WOT is not just mapped on RPM. COrrect WOT power requires a good MAF.

Regards

Tom. M

oh yeah..forgot that the O2 is out of loop..
either way though....getting oil in the intake during acceleration will show up as richness on the A/F meter....and being that it is not gas being burned..but rather oil...the power output will decrease..

that is what I was thinking..whether or not it came across that way haha

later,
Tom
midlman@rennlist.net 89GT

P.S. The 92-early 94 gts were known for consuming oil...whether or not it can be seen as burnt oil out the exhaust...

bigs

Hey! There's an idea! And probably someone down closer to sea level so we can correct for altitude, right?

I actually considered that I may have become accustomed to the power of the car. But then the dyno numbers seemed low to Dave and me. However, it may very well be just normal drivetrain loss and altitude.

I think this thread has given us a few ideas to test however.

Mongo

I've become accustomed to my 944 feeling a little sluggish....ok maybe that attributes to 928 ownership

But hey I'll be the test pilot then! Mongo go weeee!!!

mark kibort

get the "actual" numbers and we at least can rule out the conversions of the correction factor.

if its only corrected 8-10%, we know that may be the issue.

you can always do a 60-100mph run. ive done hundreds of these. if you can get in the 7-8 second range at altitude, you are probably just fine.
320 rear wheel HP is about 6.5 seconds at sealevel and close to stock weight. (light side)

MK

Ketchmi

Hey Mark, all our dyno runs are corrected the same amount. I have an 87' S4 5-speed on the same dyno today doing 287 rwhp with the same SAE correction. (our X-over, without cats) Without correction, the graph shape doesn't change and is still low in comparison to other cars we have dyno'd. The same day we dyno'd Big's car, we dyno'd our 86.5' and the 87' without any changes to the dyno. It self compensates for temp and humidity. The altitude doesn't change much between runs.

Neither Bigs, nor his car, or even me for that matter are on the light side.....

As far as getting used to the power, I have to drive the supercharged 89' frequently and it seems like a bit of a slug to me now because I'm used to it. 420/430 rwhp doesn't even get my heart beating faster anymore. (that's why it's in for an upgrade to 500rwhp!)

mark kibort

Just double checking. by the way, what was that correction factor?

I wonder what is causing the lower numbers

probably is some spark thing. (or was the ebrake left on slightly?)

this was an auto too, so that could be part of it, right? 270 /.8 =338 flywheel hp, and thats only down 10-15hp from rated. (and 350-370ftlbs of torque depending on the efficiency factor for max torque .8 vs .85)

Mk

Ketchmi

We know it's not missing much horsepower, maybe 20ish.

C'mon Mark, e brake?

bigs

OK. I can ask stupid questions because:

1. I'm not a wrench

2. I have no pride...

I'm running straight 30W Mobil 1 in the GTS. (Because my daughter gave it to me as a Christmas present, that's why!) Could this grade of oil have anything to do with slightly sluggish performance?

SharkSkin

Having seen the chart, I can see that it's the incosistency from 4000-5500 RPM that is of primary concern. Lots of good suggestions above -- while on a dyno(of any kind - even a smog dyno) you could watch for erratic timing numbers as you pass through that RPM range. You could also pop the cover on the flappy pivot shaft and put a piece of tape on the shaft to see if it behaves erratically. Dyno tuning/diagnosing can get expensive; if you can borrow a smog dyno you can make the observations above without actually needing to have HP/Tq info. Something else you might try if you're willing to round up the necessary hoses/tees/etc is to bypass the breather hoses; IOW connect them together into one large hose that leads to a coffee can full of pot scrubbers, then plumb another hose back up to the intake fittings. This would at least eliminate oil ingestion as a possible cause. Might be a lot of work for nothing, as oil ingestion would be very unlikely to affect just the first and third runs in such a bizzare way. OTOH, oil ingestion could lead to detonation, retarded spark, and all that that implies but again I would expect it to do so more consistently.

If I were betting, I would put my money on an intermittent flappy or knock sensor system being the problem in the 4-5.5K region. Most likely electrical, but possibly vacuum on the former.

As to the generally low numbers.... no bet. Another suggestion though would be to check for worn bearings that might increase the driveline loss. Any transaxle/CV/bearing noise? Also, unusually heavy rear tires/wheels could account for a difference in measured RWHP on a roller dyno.

worf928

The LH diagnostic matrix offers only one other item not already mentioned or ruled out - tank vent solenoid valve - as a "poor engine power" culprit.

Schocki

Didn't read all of the replies...
Are there any fault codes in the ECU?