396V8

Hi all

i witnessed the dyno runs of a friends L98 1988 Corvette with ARAR.bin, car is totally stock.

at Wot, AFR goes down to 0.85, but suddenly, at 3050 rpm it shoots up to 1.1 and settles to 1.05 (Dyno1 pic)

i assumed, this comes from the ARAR.bin, where the PE change vs rpm leans out at exactly 3200 rpm..

so far so good, i changed this table PE % change to AFR vs rpm, to 0 all the way up
using the calculation, this should come out as a 12:1 AFR from 3050 rpms all the way up

on the 2nd run, same thing, just at about 4200 rpm..(dyno2 pic)

so, what happens here?
i found nothing in the .bin to happen at 4200 rpm

MAF dying? Fuel Pump dying? coil dying?

i searched the forum, but didnt come up with a solution

so, please take a look at the graphs, maybe you can point me in a direction

thank you

RBob

iTrader: (1)

Check the TPS voltage when at WOT, then check that against the TPS malfunction code parameters. With the voltage too high the ECM will start a code 21 in process.

That drops the ECM out of PE mode...

RBob.

396V8

Hi RBob

thanks for chiming in!

unfortunately, we didnt log, because datamaster trial expired, therefore i advised him to buy the software, so that we can continue

the dyno guy assured me, he was WOT all the time, so, if a 21 was set, it should have come earlier - just a guess

i would say, a tuneup is on order, plugs, cap, coil, rotor, fuel pump/pressure, aso

what i can say, during the dynoruns, no check engine was set, i assume, i high TPS would set a code, therefore set the light

thank you

RBob

iTrader: (1)

I takes time for a malfunction to light the SES and then set a code. There are delays between these occurrences.

It is easy to have a malfunction with no SES, and then a SES with no stored code.

RBob.

396V8

hi RBob

thanks again for your input

i noticed also very high spark retard under Wot, seems theres more to done on this chip
car is getting a new exhaust an some goodies, then will be dynoed again

i will post results as soon as i have them

greetings

Orr89RocZ

iTrader: (20)

If it went lean under load it makes sense to see high spark retard because it likely was detonating/knocking.

Does sound like it dropped out of pe mode. If not an error code causing issue, check for mechanical issues like fuel pressure loss

396V8

Hi Orr

the spark retards start instantly as the throttle goes WOT, also in the region, where the mixture is ok (12.5 :1)...every other condition than Wot, no spark retard..so this seems to be real knock!

the car will be "tuned up" anyway, so the usual suspects will be checked & changed

thanks