I have a 1987 vette with a new 383 (mini ram, 30lbs injectors, AFR 195 heads, 10:1 compression, .580" lift / 240* @ .050" duration). The chip was supposed to have been burned while the engine was on the dyno, but i am starting to suspect that further tuning might be needed.

It is running very rich (plugs are fouling quickly). Based on the scan data below, it looks like the ECM is seeing a lean condition and adding a ton of fuel to compensate.

Would the knock sensor readings cause the ECM to see a lean condition and add fuel? Wouldn't the O2 sensor (heated) pick up the rich condition and correct it? Or are these sensors fighting each other?

I have a ZF 6 speed with a single mass aluminum flywheel and definitely get the "rocks in a can" noise at idle and sometimes during acceleration. Would this be sending the knock sensor into a fit?

Any help / insight would be greatly appreicated as i am definitely new to this type of tuning.

Thanks!
Dan

The following is all with base timing at 17* btdc (set with EST disconnected) because it would stop running if I tried to retard it any more than a few degrees. Is it possible that this PROM / engine combo was set up for 17* base timing?

Vacuum reading at idle - 10Hg steady
Fuel Pressure set at 47psi (no vacuum hose connected, would drop to about 42 psi with vacuum)
Engine has no EGR, AIR, etc., and no catalytic converter
ECM does not throw any codes
AC Delco 41-629 plugs gapped at .040

PROM ID 102
Loop - closed
4th gear engaged?
Knock Retard 0* at idle, 5-10* when revved
Knock Sensor - first It read 0, then 242 at idle, jumps from 28-38-47 when revved
Idle air meter position 60 steps at idle, up to 100 steps when revved
coolant temp 180*
AC clutch disabled
Injector pulse 1.8-2.0 ms at idle, up to 7.0 when revved
desired idle 850 rpm
Engine load 45-50 at idle, up to 211 when revved
TPS .58 at idle, up to 4.48 when revved
1st gear engaged?
MAP 1.03 - 1.05 volts at idle, same when revved
MAT 66.2* F (yeah I have the useless relocator)
Engine RPM - 880 at idle, goes up when revved
CCP purge OFF
CCP Duty cycle 0.0%
Mass Air Flow 9 gr./sec at idle, goes up to 65 when revved
EGR duty cycle varies between 8-25%
Air diverter solenoid ON
Air switch solenoid OFF
Battery Voltage High - NO
battery voltage 14.1
O2 ready
O2 sensor - fluctuates between 68 - 796 mv
O2 cross count number continues to rise
TCC status not locked
Fuel pump sensor 13.9 volts
Learn control enabled
Blk Lrn Cell 1
Block Learn 160 at idle, goes to 128 when revved
Integrator - 132-142 at idle, 128 when revved
Rich / Lean flag - Lean at idle, Rich when revved
Spark Advance - 24-26* at idle, 39.9* when revved
Park / Neutral Detected

 

I think the base timing should be around 6-8. Are these numbers on a dyno and in gear? If not and just revving the engine in neutral, you should not see a load that high.

 

I tried to set the base timing at 6* - 8* btdc (with the EST disconnected), but the engine would die as soon as i got to about 12*. It really did seem to start up and run best (if you could call it that) at 17*.

The numbers I listed are the readings from my Auto X-Ray scan tool while the engine was idling in neutral, with the occasional rev to see what the readings would do.

 

Unless the chip was set up for your base timing to be that high, your whole timing table is off and you are running way advanced and that could be contributing to your knock.

With BLM's that high at idle that may be why it want's to die when you retard the timing. I would try giving it more fuel, preferably just at idle and backing your timing down and then see if it starts. If you cannot change this in the chip and you have an adjustable FP regulator you can up the FP, but remember it will add fuel across the board.

 

I THINK the chip was set up for the base timing to be that high, as it was the timing figure my engine builder said produced the best dyno run. I have tried to reach him regarding the chip burn, but of course have not heard back from him yet.

I thought the same thing too - that this timing was very advanced and could cause knock and/or a lean condition. But, i don't hear any knocking or pinging, and the plugs certainly indicate a very rich condition. That's why i was thinking that the knock sensor readings are being falsely picked up from my transmission.

If the ECM sees knock and thinks the engine is running lean, it would call for more fuel, correct? But wouldn't the O2 sensor detect a rich condition and straighten it out? Are the sensors fighting each other?

I don't have the capability or know how (yet) to change the chip tune myself, but i will increase fuel pressure significantly to see if this helps get me to get the timing back down.

 

I don't think the two sensors are fighting each other, they are just doing waht they are supposed to do, the O2 sensor is telling the ECM it is lean and the ECM is adding pulse width, that is not to say that it is making the car rich, it can only do so much, but with 30 lb injectors you have plenty of ability to correct for lean.

The ESC is doing it's job, but whether the knock sensor is picking up real engine knock or something loose banging against the block it cannot differentiate.

What surprises me is that both the BLM and INT numbers go to 128 when revved in neutal, that looks like power enrichment mode. I don't think that should happen unless you are in gear, but then again I don't know what the chip maker has done.

 

I converted from the old 4+3 to a ZF 6 speed. Maybe this has something to do with that?

Too many variables - ahhhhhhhhh!!!!

 

I have a ZF 6 speed with a single mass aluminum flywheel and definitely get the "rocks in a can" noise at idle and sometimes during acceleration. Would this be sending the knock sensor into a fit?

yes. my ZF needed a service and was making that noise, it threw everything off. it had no power, check engine light, and just sounded like crap. press in your clutch give it a try?

 

I was thinking the same thing shortly after my last post. I can see the knock counts in real time with the scanner, so if i see a significant decrease in counts when i push in the clutch, i'll at least know where ONE of my problems is coming from...

thanks for confirming!!

Dan