Hi guys, I finally got a chance to borrow my friend's scanner. The purpose of this scan was to figure out why my car idles rough, and possibly why there is detonation.

The motor is an 89 LO3 5.0 TBI V8. It has 70k on it, 30k granny throughout 12 years, 40k teenager throughout 3 years. Its timing is at 4 degrees advanced. It also has true dual exhaust which causes a Code 32 on the highway since the EGR valve isnt opening. I need to get a neg backpressure valve to solve this.

I started the car, and it does the usual high-idle thing until its "warm." It then stops at around 550-675 rpm for a while until the t-stat opens at 160 degrees and it rises to 750 rpm. Right after the high idle, the rpms are not steady and the car runs a little rough. After it hits 750 rpm, the idle is still sort of rough but the rpms are steady.

I did a readout of the Scanner Results and here they are:

PROM C -------- 381
Air Switch Solenoid -------- OFF
Loop Status -------- Closed (was mostly closed even though car was warmed up past 180 degrees)
Rich Lean Flag ------- Mostly Lean
Async Mode -------- OFF
Learn Control Enabled
Manifold Air Temp ------ 104 degrees
Block Learn
Knock Sensor -------- 73
Battery Volts -------- 14 volts
Oxygen Sensor -------- 500's (While idle was rough, jumped from 400's to 800's.)
Integrater ------- 182
Throttle Sensor -------- 0.66 volts
Engine RPM ------- 750 rpm (Was in 600's before tstat openend)
MAP Sensor ----- 1.09 volts
Coolant Temp ---------- 177 degrees
Idle Hi Motor Pos ------- 39 steps
Air Divert Solenoid ------ ON

Is there anyone here that can help me out decipher if these readings are normal? I have performed regular maintenance and its all in good order. I really need to get this figured out since I'm out of ideas. Thank you for your time.
Adam

 

An integrator of 182 indicates that the computer really wants to richen the mixture (no BLM but even with one cell it doesnt give much indication of the overall fueling as teh ecm sees it). Other then that it looks normal. Get winaldl or some other scanning software so you can actually datalog.

 

Well, your TPS voltage is a little high and are you sure that you have your timing set at 4 degrees advanced? That seems to be off a bit!!!! And you are getting a lot of knock counts there, should be between 0 & 1.

 

The xmitted knock is actually just the msb of the knock counter so that number is total counts detected/256. It really doesnt tell much unless you can see what the knock counter is doing while the car is running. It could have just picked up the 18,688 knock counts while the motor was cranking, or you could have a detonation problem.

This is why you need to get a datalogging system going. You really cant see much just from one frame.

 

I have a 14 second stream of the data and the knock stayed at 73 after the crank and didnt move.

And yes, I made sure that the timing was at 4 degrees advanced. It WAS retarded a bunch and the detonation was still there.

Also, isn't the loop status supposed to be open after the car is warm?

 

No, open loop is when you first start the car and it doesn't read the sensors yet.

Closed loop is when it reads data from the O2 sensor and MAF etc...
Think of it as a circuit, open means the sensor (O2, MAF etc.) data doesn't pass through while in closed loop the data reaches the ECM.

 

Ok, well the reason why I'm confused is that it starts in closed loop. What do you guys think is wrong?

 

Nobody has any ideas? This has got me stumped.

 

It should start in open loop and then after around six minutes go into closed loop. Pretty much in open loop the computer will ignore the O2 readings and just command whatever afr is set at the time.

 

I understand that but do you guys have any idea why the ECM would start in closed loop instead? Because thats whats happening.

 

possible bad ECM or chip.

 

Possibly a bad CTS sending a false signal to the computer telling it the car has warmed up enough to go into closed loop?

Anyway, just a thought.

 

The CTS is brand new :P

 

Well was just a thought.

Something you can check that caused me no end of problems and lots of money is the ground wires on the back of the left cylinder head. Had corrision on the crimped on ring terminal. I replaced the connector, soldered it, end of problems for me.

I realize my set of problems were different from yours, but still worth checking to make sure the computer has a good ground connection.

Good luck.

 

Sounds good, I'll check em. I also have an extra computer that I will install. Whats very interesting is that there is a label on my computer that says it was refurbished from GM. I bought the car with 30k original so its weird. I do have an extra computer that I will install and see what it does. Thanks

 

Is your scantool putting the ecm into ALDL or any other mode? Looking at my calibration, I seem to remember that in ALDL mode, closed loop will be forced.

 

I think it depends on the scan tool. I have an Auto X-Ray unit and it shows open and closed loop on the readout.

 

Well its an Auto X Ray also and it did switch into open for a split second when the car was warm a few times.