Hello Techs,

This vehicle is fixed. The primary purpose of this post is to discuss cause and effect of scan data and ultimately show how powerful the PS3423a is.

Vehicle is a 1995 Chevrolet Camaro with a 5.7 liter VIN code P engine. This LT1 engine is sequentially fuel injected and utilizes an Optispark (ABITS) type II distributor which is the vented style.

Several modifications have been done and I’m not aware of all of them. It has been supercharged and the PCM has been chipped. There is a boost pressure and air/fuel gauge mounted under the IP. The LH pre-cat O2 sensor wire has a blue scotch lock on it which feeds the A/F gauge. There is a 5 speed trans in place of the original automatic. And to top off this mess, there are headers!

Complaint is lack of power when slightly accelerating. First thing I do is check for any DTCs. There are two codes for the skip shift solenoid. Imagine that! The PCM was programmed for a Borg Warner T56 6-speed trans. I just ignored it.

As I’m approaching highway speeds in fifth gear I noticed sort of a “fish- bite” or “chuggle” sensation. I then start recording this on the Tech 2. I gave it a little more throttle and it became more pronounced. I get the car back to the shop and upload my snapshot. Have a look.



What would be your next move?   

         Hello there.
  The O2 sensor is a voltage generator.The only way to measure the voltage on a single wire 02 sensor is to ground it( through the Scope or DMM).The a/f ratio gauge likewise will not work if it is not grounded and becomes a drawer of amperage-as it  grounds, somewhere in it's circuitry, some of the entire current produced by the O2 sensor.
       That will cause a lowered voltage signal by the sensor to the ECM.
        The ECM is interpreting that lowered voltage as lean, and attempts to enrichen to correct.
 I agree with Jarvis-Samuel and I think the  Air/Fuel gauge is the cause of the  problem.

Hello Gentleman, hope you do not mind my playing along?

Afraid I am not overly familiar with Chevrolet fuel trim stategy but is it not odd that the primary long term fuel trim increased without a consistant increase in the primary short term when the throttle was snapped?

Paul Summers

Thank you Mr. Grotti

Shaking my head I missed it on my first look but bank 2 has a perfect stoichiometric block learn value of 128 while bank 1 has a block learn value of 158 which indicates that the PCM is enrichening the A/F mixture to compensate for a lean condition based on oxygen sensor feedback. 

If I am on the right track I will have to do a bit of homework as I am unfamilair with the engine control system.

Paul Summers

Hi Edwin,

It had a lumpy idle. Fuel trims at idle were 128, 121, 128, and 118. At 2000 rpm, they are like what you see on the graph. I didn't go to WOT, but at 81 % throttle angle, the left O2 was 905mV and the RH was 870mV. I did current ramp the injectors and they were ok. Also I attached the First Look Sensor to the fp regulator and the waveform looked perfect.

There is no intake vacuum leak. Idle fuel trims would have shown this more so than off idle conditions when the intake air pressure is higher.

Do we have excess O2, or lack of HCs, or a combination of having too much of both?

Nothing wrong with being curious. Try this out.


Ignition problem? You tell me. 

Autonerdz Productions presents this flash movie of ignition on this '95 Camaro. This is at idle when the engine is running a bit lumpy. 

http://www.autonerdz.com/flash/95camaro.html


 

Correct, The OE ignition system does not provide multiple sparks. However, which I should have mentioned in the beginning, this has a Crane Fireball ignition controller. I believe it is a HI-6S Digital Multi-Spark Ignition (an inductive design).

No need to see the coil current ramp. The problem is isolated to one cylinder as seen in the movie. From left to right, the firing events are 5718436572. This is using #7 as a sync because it was easiest to get to. A faulty coil would have shown up in other cylinders as well.

You want to see ignition control? You did. I think what you meant was ICM inputs, correct?

Let me explain a little on how this system works. There is no CKP sensor. There are two CMP sensors which are of the optical variety. One disc has two sets of slots in it it. There are 360 slots for high resolution which are equally spaced apart. This is used for timing control. The other eight slots which are of different widths tells the PCM which plug is being fired. Both signals are sent to the PCM. The PCM then sends an ignition control signal to the Ignition Control Module (ICM). Naturally the ICM will control the coil.

Is there a triggering problem? Not at all. We are isolated to a single cylinder.

Now its time to determine from the secondary ignition capture of where the fault is based on the irratic spark line disturburbances.