stalling problem

[shorkeyc3]

Ok well I also have a topic on this problem on a Corvette forum but here it goes...

My Vette will stall at idle when I stop at a light and am therefore in drive with my foot on the brake. If I pop up the headlights, she stalls almost immediately,with headlights off she ends up struggling and stalling but it takes much longer.....Also, the problem is truly there when the Vette is warmed up pretty well. At cold, she doesnt seem to stall. Ive all ready replaced the intake gasket. I disconected the vacuum at from the hose coming out of the base of the carb and intake. I actually dropped my gauge! It still works but doesnt go under 10! So my readings might actually be reality+10. Now, by putting my gauge where I put it, there was no vacuum going to the headlight or braking system so I can rule out an leaky hose, check valve or anything in those systems! The gauge read 23 and seemed decently steady. The needle was moving but the rpm is also varying slightly so the vacuum gauge varies slightly but stays pretty much around 23. Giving her gas doesnt make the reading go up with is a good sign if Im not mistaking...Now here is the weird part, if I pull the headlights up with vacuum disconnected, they of course dont pop up but the Vette stalls almost immediately! The lights are of course drawing current when turned on. So Im now wondering if this is an electrical issue? Could the alternator be producing insufficent current and turning on the headlights is too much for it to handle?
Another thing to note is I have a current draw for sure as the battery dies if I dont start her up for 1-2 days. I changed the battery and if I disconnect the battery, she fires right up after a couple days so there is defenetly a current draw. Could the draw be strong enough to cause a stall when in idle and the headlights on with my foot on the brake?

If any of you are thinking timing, I set the timing at 36. My mechanic cut off the vacuum advance and said to set it without vacuum advance. I reconnected the vacuum davance tonight and it didnt solve the problem...

So I would really appreciate some advice and opinions here. Sorry for all the details but I think they are important...

Chris

viewtopic.php?f=55&t=1241&p=3037&hilit=+sensor#p3037

 

[grumpyvette]

if you were local Id say stop over and we will diagnose and correct the problem, each problem comes down to isolating the case and correcting the fault once its tested to be the true cause, usually thru adjustments or replacing defective components
The first thing ID do is VERIFY the CAUSE, OF THE PROBLEM FOR THAT, THRU ISOLATING AND TESTING, COMPONENTS AND SYSTEMS
A SHOP MANUAL IS ALMOST MANDATORY,
THESE LINKS should help

viewtopic.php?f=80&t=728

TPS (Throttle Position Sensor). .54 Volts Idle, ~ 5 Volts Full Throttle.

IAC and TPS Adjustment
http://www.thirdgen.org/tpimod2

viewtopic.php?f=55&t=1241&p=3037&hilit=+sensor#p3037

If your not 100% sure somethings working as designed how can you find the problem,to start you need to hook up a timing light, fuel pressure gauge, V.O.M. meter and vacuum gauge at various times.
first get thru the basics
yes IM well aware your sure this is a waste of time!
yes IM fully aware that you might have checked before, DO it as if the first time you ever saw the car was NOW!
verify the ignition timing is advancing when the engine rpms increase and that total ignition advance reaches about 36 degrees at about 3100rpm
verify that you've got NEW plugs that are gaped at .045"
use the V.O.M. meter to verify the ignition wires all read under 500 ohms per foot MAXIMUM
replace the rotor and cap
check VERY CAREFULLY that the FIRING ORDERS CORRECT
verify you've got about 13 volts at the battery and it stays steady at 13 volts when running
verify the ignition coil polarity, wiring and connections
use the V.o.M. to verify that the voltage doesn,t change when the headlights are switched on
disconnect temporarily and pull the head light fuse and see if it isolates the problem
plug all vacuum lines from the intake except the vacuum advance,and see if that temp cures the problem
remember its a process of ISOLATE, TEST, then repair
let us know what you find
loose connectors or corrosion on connectors, is also possibly a cause

you can get info off the internet, but testing will require knowledge of each component function and how to test along with,the ability to isolate each potential cause, and verifying its correct or defective function

START BY PULLING TROUBLE CODES

ALDL 201 (OBD I)

1981 Corvette (L81) models have a very simple computerised ignition timing system. There is very little diagnostic information available with these cars. The GM shop manual is recommended for this vehicle. The ALDL connector is under the centre console ash tray.

1982 Corvette (L83 Crossfire) models had a more detailed ECM, much like later vehicles. The location of the ALDL connector is under the centre console ash tray. The diagnosis is more simplified, but similar to later vehicles.

From 1984 until the end of the 1993 model year a 12 pin ALDL was used. After that, a 16 pin ALDL connector was used. The 1994 and 1995 model year still used the OBD-I system even though they have 16 pin connectors. The 16 pin connector in the 1996 C4 is used for the much more complex OBD-II system and a scan tool is required to discover the OBD-II system's secrets.

For the '84- end of '93, 12 pins:

Pin "B" is the diagnostic enable pin and pin "A" is ground. Grounding pin "B" to enable the diagnostic readout of the ECM/PCM.

To recover the codes, short pins "A" and "B" together using a small section of electrical wire or paper clip.

With the ignition turned OFF, short pins "A" and "B" on the ALDL.

Turn IGN ON (but not to RUN).

The "Check Engine" light (early C4s) or "SYS" light (later C4s) will flash a Code 12 (a single flash followed by two flashes) and will repeat three times (Flash (pause) Flash Flash (long pause), Flash (pause) Flash Flash (long pause), Flash (pause) Flash Flash (long pause).

Code 12 is a delimiter or marker code to show where the error code string begins and ends.

After the three Code 12 flashes, you will either get an error code (or codes) or you will get another string of Code 12 flashes if there are no trouble codes stored.

All codes are repeated three times with a long pause between each code group (36 or Flash Flash Flash pause followed by six flashes, repeated three times, folowed by a long pause with any additional codes stored then flashed).

The "Check Engine/System" light on with engine running means the condition(s) are currently present. If the light is not on during RUN operation, the limits were exceeded at some point in time and the event was recorded in memory, but the reading has since returned to the normal operating range.

Remember to remove the shorting device from the connector after you have read the codes.

Clearing the Codes

To clear the codes from memory, remove the negative battery cable for a minimum of 10 seconds.

Disconnecting the battery will clear all stored codes and and any stored memory (radio button presets, clock, trip odometer, average gas mileage memory, power seats). Your ECM/PCM computer will also have to relearn timing/mixture/exhaust emissions.

Make absolutely certain the ignition key is turned OFF. If you connect the battery with the ignition switch ON, you can destroy the ECM/PCM module.

For 1994 and later models, you will need to recover the codes using a special procedure involving the speedometer and the odometer as explained in the service manual or use a special diagnostic device known as a scan tool.

For the '94 - '95, 16 pins (but still OBD I):

Beginning in 1994, you short pin "12" to pin "4" and once again turn the ignition switch to "On" without starting the engine.

The speedometer will display any codes using the same protocol as the 1990-1993 model but there are some changes in the designation for the modules plus additional modules are added:

Module "1" is still the CCM module.

Module "4" is now called the PCM module (Powertrain Control Module) because automatic transmission computer control was added to Engine Control Module in 1994.

Module 7 (on the 1996 model only) is the RTD module. (This is the Real Time Dampening module which replaced the Selective Ride Control module in 1996).

Module 9 is the ABS/ASR module number from 1994 through 1996.

Finally, Module "A", the DERM (Dynamic Energy Control Module --- the air bag control module) will be requested to show any codes.

Just like the 1990-1993 display, you read the codes on the speedometer and read the module number on the trip odometer.

Again, you can cause the codes to repeat by turning the ignition off for five seconds and then back on.

Turn the ignition off and remove the short to restore normal operation.

1996 to 2004 Corvette (OBD II):

Turn IGN ON, ENG OFF.
ON DIC, Press RESET button to clear any warning messages.
Press and hold OPTIONS.
While holding OPTIONS, press FUEL four times within 10 sec.

Go into an AUTOMATIC mode to shows all parameters: PCM-TCS-RTD-BCM-IPC-RADIO-HVAC-LDCM-RDCM-SCM-RFA. If there are no problems, you will see "NO MORE CODES" on the ICP display.

The computer displays two kinds of codes, CURRENT and HISTORY, designated "C" or "H". A CURRENT code indicates a malfunction is present in the system whose module is displaying data. A HISTORY code indicates a past problem.

When the screen displays MANUAL DIAGNOSTICS, select the desired module by pressing the OPTIONS button to go forward or the TRIP button to go back. Press GAUGES to go forward or FUEL to go back.

To exit the diagnostic mode at any time, press E/M. If you want to erase or CLEAR codes, press RESET.

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