kindaslo

I've searched through the forums for all I'm worth, so now I bring my question to you all.

97 vette 408 stroker, custom ported lq4 heads, comp 230-234 591-598 113 cam, comp shaft rockers, comp beehive extreme duty springs, comp pushrods, mototron 60# injectors.

I've been working on part throttle ve tuning for a few days and have the car driving nicely no stumbles now. I decided to start on high rpm/wot tuning last night and found that the car hits 5200-5400 rpm and just falls on it's face. Exhaust note completely changes, car loses all power; however if you stay in throttle it will continue to increase in rpm.

My first thought was bad/fouled plug. Replaced with new tr55 still have problem.

I've made significant changes in the ve tables, cylinder volume, and idle airflow tables.

I've made some minor chanes (+.005 in pe), and more spark at idle.

I currently have maf fail at zero, but have tried setting it back to stock thinking maf may remedy, but it still breaks up at high rpm. I've been through every table looking for some major jump in numbers at 5200 or 5600 rpm and can't find anything.

So the question is how do I test coil packs? Look for misfire codes in hp tuner? Has anyone had this problem?

Any help is appreciated in advance.

kindaslo

nobody has any ideas?

DrkPhx

iTrader: (15)

What MAF are you running? I would first check the fuel pressure and make sure you are getting the corect fuel psi at WOT. Have you data logged a run with this problem and what DTC codes are you seeing?

jimmyblue

iTrader: (11)

First check that cat overtemp protection is disabled
(presuming you are running w/ no cats). COT jumping
up should be dead obvious in the front O2 readings.

kindaslo

Stock MAF, but maf Fail is set to zero so it should have no bearing on this.

Thiss problem is not at wot, it is an rpm problem regardless of tps.

No DTC codes. The only thing funky with the datalog is that bank one seems to get slightly lean 750 mv readings.

kindaslo

COT is disabled. Have no cats with rear 02 sims.

kindaslo

I can post up the datalogs if anone wants to ssee, but they don't really have anything way funky to them.

kindaslo

Just looked at datalog from last week, and car did rev to 6300 no problems. I'm going back to that tune, nd if it still won't rev I'll star tpulling coil packs and checking voltages. Any idea what I should look for?

94SS

To the dyno shop so you can see what is going on.

kindaslo

What would a dyno tell me? I'm looking for constructive advice here please. I could obviously just apy someone to fix the problem, but there are no local shops who work on cars like this.

94SS

Fuel Pressure, Air-to-Fuel, Horsepower, Torque and RPM. The Dyno is great it can show you if you are rich or lean, ignition problems, transmission issues, you may be able to hear noise that you may not hear on the street, it makes it easy to see what is coming out the exhaust and you can see if you have a smooth power curve.

Then you need to make sure you log some parameters like this and between the datalog and the dyno pull you should be able to figure it out pretty quick.

INLET AIR TEMP
COOLANT TEMP
LONG TERM 1
LONG TERM 2
SHORT TERM 1
SHORT TERM 2
MAF FREQUENCY
LOAD
MAP(KPA)
IDLE AIR DUTY CYCLE
ENGINE SPEED
THROTTLE POSITION ABSOLUTE
BATTERY VOLTAGE
SPARK
KNOCK RETARD
O2 VOLTAGE BANK 1 FRONT SENSOR
O2 VOLTAGE BANK 2 FRONT SENSOR

If you can post a data log with all these parameters someone should be able to point you in the right direction. And maybe even post your file.

DrkPhx

iTrader: (15)

I would save the coils for last if it worked before. But I would definitely check the plug wires for ohm resistance and also check to see if you are getting individual misfires for any specific cylinder. I would also freeze frame the data (if possible) exactly in the rpm range where this is happening and just check the basics like injector pulse rates, fuel trims, O2 readings, etc. But first put the old tune (which is known to be good) back in first.

joecar

What about: did you increase the predicted air flow table...?

If computed airflow exceeds predicted airflow, PCM throws a DTC and goes goes into reduced power mode.

kindaslo

No reduced power I maxed out that whole table at 5.

kindaslo

went back to old (working tune) still misses at 5500. dtcs are maf (fail set to zero) traction control circuit and knock sensor low voltage. no misfire codes. only thing that looks suspicious is bank one o2 milivolts go slightly lean when it happens (drop from 850 to 700) this makes me think I'm losing spark. I've also developed a bucking at part throttle problem in the last few days. I have a second set of coil packs I am going to try tonight. any other ideas?

DrkPhx

iTrader: (15)

Can you please list all of the DTC's? The fact you're getting multiple, unrelated DTC's indicate you might have one circuit that is bad.

kindaslo

p0103- MAF sensor circuit high frequency /this should be from having maf freq fail at zero/
p0327 - knock sensor circuit low voltage (ses) (history) (immature)
p1571 - traction control torque request circcuit (pending) (istory)(immature)

kindaslo

OK here is the current tune and a datalog of it driving today.

Tune
Datalog

If you look at the log, I hit about 5200 rpm and the bank one o2 mv drops to almost zero indicaing raw fuel typically; however go a bit further down and i hit 5600 rpm with no o2 fluctuations. The problem occured both times.

94SS

Fuel trims are definitely way off should be atleast -2 to -8 at all times. Do you have a home made ported MAFor ported throttle body?

kindaslo

NO they are both stock pieces. In a later tune I have them dialed in no problems, with the same issue. This was just the (working tune) that I had re-installed yesterday.