OneCrazyCorvette

My 84 crossfire is having a little issue with timing advance. When reving up the car the timing begins to increase with rpm but then eventually will drop off if you push it all the way the timing will go to 0 degree's and die. I've tried the usual by unplugging the knock sensor which is new anyway. As I scrolled though my haynes manual I found a section on the electronic spark contol module and the ELECTRONIC SPARK TIMING MODULE. I have replaced the ESC module but found a test for the EST. It went as folllowed.
The test says to run the car at 2000 rpm and take note of advance.
with a base timing of 6 degrees when the car ran at 2000 rpm the timing went to 22 degree's. Does any one know what the total advance is standard I know the base is 6 but what should the finish be at WOT. Then the manual states if you short A and B as if reading codes on the diagnostic alcl connector check the timing again. It says the timing should change. If the timing does not change it states that the EST is bad. My timing did not change at all. So my problem is this If it is bad. I cant find it in the car. please help.
thanks everyone. :banghead:

jfb

The ESC module only retards the spark timing when the knock sensor detects knocking. Spark timing is controlled by the ECM. If you have spark timing problems, the ECM is the source of timing.

OneCrazyCorvette

Why does the EST fail the test. Does the test sound valid. Also is there a way to test the ECM. It appears all other functions of the ECM do work. It will indicate proper codes if you unplug sensors such as the MAP. The car sat atleast a year but was running OK when parked. I also do agree it could be the ECM I'm just trying to rule out all the options.
I was wondering if the EST is also called the egnition module that is located in the distributer.
Thanks

jfb

The ECM sends a signal to the spark module in the distributor (a pulse) telling it to generate a spark. I will ask my Corvette mechanic tomorrow and see what he has to say about your timing test failure.

jfb

I talked to my mechanic who works only on Corvettes for a GM dealer. He said to be sure to disconnect the EST wire when you set the initial timing and that when the engine has no load, the timing will not advance fully when you increase the rpm. Do you have driveability problems?

OneCrazyCorvette

Yes what is happening is the car will accelerate as long as you hold very little throttle if you go pas about 25% the car starts to retard timing. I have replaced all kinds of sensors.
knock,map,cts,esc,tps- and set correct,fuel pump, fuel filter, injectors,
my fuel pattern looks good and actually now after fixing the injectors the car is very rich. Ibelieve this in part to be because of the car not advancing. If you watch the car with a timing light and hit the gas the timng goes up and then will retard.

OneCrazyCorvette

I forgot to mention we did disconnect the wire for timing the car it's tan with a black strip. So if i understand this correct the EST is the flat half moon shaped module that is located in the distriuter?

Dominic Sorresso

The EST module is IN the distributor. Need to remove cap and rotor. You'll see it o n the base of the distributor with the harness attached to it. My recommendation is to replace it with an Accel unit. Don't use the Dyno-max crap. Had two of them die on me prematurely. Also, make certain you use white grease when installing it back on the distributor mounting pad. Don't use dielectric. You want the heat away from the module otherwise it will beakdown prematurely.
If timing doesn't advanc when you hook up the black/brown EST wire, then you're in limp home mode. That's why car starts but runs like garbage.


[Modified by Dominic Sorresso, 11:12 AM 8/7/2003]

jfb

I think that is called the electronic spark module and it generates a spark and provides a tach signal and a reference signal from the pickup coil. The ECM takes info from throttle position, O2, etc and determines how much advance is required and sends a pulse at the right time to the spark module to generate a spark. At low rpm with no engine load, spark timing is advanced due to the fuel burning slow (fuel burns proportional to the cylinder pressure, low pressure with low engine load), then as you increase rpm (no load), engine losses increase (engine load increases) and timing will have to be retarded. Maybe this is what you are seeing.

HWoods

how many miles are on the car? Still the original timing set on the engine? I think the stock 84 engines had a neopreme gear on the timing sets, so it may need replacement.

OneCrazyCorvette

The car does have high milage about 140 k I did replace the module in the distributer with one from the local advanced auto but as we all know it could be just as bad as the origanal. Maybe i'll try another one just in case. I do have a friend with a scan tool I'm going to give it a try tonight I'll let you know. Thanks for all the help I think I'm getting closer.