I purchased a 91 firebird formula with a rebuilt 305 TPI. At that time, i knew nothing about the engine. The check engine light was on, and after a lot of trial and error with the EGR system, I realized the problem with the engine was the ESC, or electronic spark control module. It was nonexistent in my car. The wiring harness for it wasn't even there. Does anyone know why it would have been removed during the rebuile, or any tips for fixing the problem.

 

91,

Welcome Aboard!

I'm operating strictly from memory, so don't take this as "Gospel". To my recollection, beginning with the 1990 model year, 'F' cars received a new design ECM with greater memory adressing capability. Instead of 16Kb or RAM as with the older ECMs, the system used can address 32Kb or RAM. This allows a lot more funtionality of the ECM, so many functions that were separate, discrete modules were integrated into the ECM. The VATS system and ESC are examples. This should explain the abscence of the separate module and wiring on your car. The function is still there, but it is part of the 1227730 ECM. The change accompanied the switch from a MAF control scheme to speed/density control.

 

Don't take this the wrong way, but it doesn't sound like you're doing too well with trying to diagnose that thing by yourself, sounds liek you're just confusing the hell out of yourself. Try taking a step back and bringing everybody up to speed with what your problem is, what codes you're getting, and anything else you can tell us about what is wrong.

BTW, vader is right, the ESC stuff is all located on the memcal in a 90-92 car, no seperate module as in the earlier cars.

 

Good point Ed. I'll start from the beginning, but it's going to be a lot of typing...

I purchased the car with the check engine light on. When I scanned the computer, it was code 32. I diagnosed the problem and determined it to be the EGR solenoid which I replaced. I cleared the error codes, started the car, and the check engine light was still on. I checked for the code, which turned out to be 43. I put the car up on the lift, and saw that the knock sensor was in rough shape, so I replaced that, cleared the error codes, started up and still had the code, which is when i started searching for the ESC at which point i became very confused, due to some component location facts overlooked by the Haynes manual. Besides the error codes, once I got the EGR valve hooked up correctly, when I would be driving, my idle would be sinusoidal and incredibly low and the engine would be sluggish. When I would put load on the engine, it would begin to miss so badly that the car would jerk violently back and forth. I hypothesised that now that I was getting the desired combustion temperatures and the computer thought the EGR valve was working correctly, it tried to advance the timing, when it ran into trouble because of some ESC component malfunctioning, which caussed all of the missing. To temporarily solve the problem i unhooked the brown wire to disable the ESC system, and i unhooked the EGR vaccume lines so that the car would run smoothly without trying to do anything with the timing. This solved the problem to the extent that I could now enjoy my car, but I still had the check engine light glaring at me and through my reading, i have heared that the ESC system is very good on that engine and I'd like to get it working again. Now knowing the full story, hopefully someone can offer me some starting point or confirm my thoughts about the problem, or even better, a solution.
Thanks for your help

 

When at a standing idle, is the idle speed and quality a little more "linear"?

Were you able to test the old sensor? By "rough shape", do you mean visually, mechanical damage, connector problems?

Your current error code is likely caused by the ESC bypas connector being unplugged. You may indeed have other ESC issues (among any others) but will constantly display a DTC for the ESC system if the ESC has been bypassed (connector opened) with the engine runniing.

You'll be the one dedevising the solution. We'll just be able to relay what we know about the systems. You'll be tesing and repairing based on your skill and knowledge - including anything you may have learned here.

If you have a timing light at your disposal, you should be able to determine if the ESC is working at all. After adjsuting the base timing, you can reconnect the EST bypass and note any change in advance. It should be a substantial timing increase at idle.

If the ESC is trying to advance timing at idle, try tapping on the side of the engine on the lower right side (near the detonation sensor) to see if the ESC will retard the timing accordingly. You may need to enlist an assistant for this unless you have really long arms. If the timing doesn't retard with these signals, then advance afterward, you may have an ESC issue, or a failed sensor/poor sensor connection.

Another thing you can do to test the ESC separate of the sensor is to install a 3.9K ohm resistor in place of the sensor temporarily. If the base and idle timing react correctly with the resistor in place but not tyhe sensor, your sensor is still suspect (it is possible to get a failed or incorrect part from your supplier).

Give those a try, and let us know.

 

Hey Fmla... this sounds a lot my my cars symptoms... see my post:

"Erratic idle, stumbles, and hard start when warm"

Mine is doing the same type of things. I've fooled around with my EGR and my mechanic told me my car was knocking bad. I haven't tried to disconect the EGR yet or bypass the knock sensor with the 3.9K ohm resistor, but I may this weekend.

I can't hear the car knocking and my mechanic told me the sensor appears to be working, but I don't know if he tested or bypassed it or just SWAGed it was fine.

FYI - bubbz89 says his car did similar things and he fixed it by replacing the O2 sensor. I may be testing all of these.

Let us know if you come across a fix.

 

I wasn't able to test the knock sensor, by looking at the sensor itself and condition of the connector, i decided to replace it. I still have the old one though, I like to save all my old parts. How would I go about testing it?

I know the ESC is doing something, just, the wrong thing. When I have it hooked up, it advances the timing to such an extent that the engine misses. I'll have to try the resistor idea, once the temperature permits outdoor work again, but would I connect the resistor inline with the wire from the knock sensor?

Also, while looking at some wiring diagrams from the haynes manual, which I learned I can't take 100% to heart, that there appeared to be two knock sensors on the engine. Is this true, or are they illustrating two of the possible locations of the knock sensor on different model years?

 

Yep. Mine looks pretty bad too. Almost like the connector got too hot or something. I think there is only one knock sensor on my car (91 RS 305 TBI)... passenger side block.

As far as the resitor... I think you want to disconnect the sensor and wire the resitor into the connector/wire in place of the sensor. By putting it in line (in combination with the sensor), you will still have varying resitance. The idea is to provide a stable and valid resistance that does not tell the ECM your engine is knocking... thus retarding timing.

As far as testing the sensor goes... I'd try the ESC test Vader descibed with a resistor in place and see if the ESC is working appropriatley (by connecting/disconnecting the EST bypass wire and observing the timing change at idle). Once you determine the ESC is working, you can test the sensor as Vader described (by tapping on the side of the block while monitoring timing at idle).

Otherwise, I don't know any way to test the sensor. I'm sure there is a valid voltage/resistance range, but I don't know what it is. I'll do some checking and see if I can find the range.

 

garone91 is correct. The resistor should be installed in place of the detonation sensor, not in series with it. Since the sensor is an electrodynamic device (it generates a slight current as a result of detonation), the signal level is very low, and can be tested in-circuit with a working EST system, on a dedicated sensor tester that will capture the signal, or with an oscilloscope.

 

So let me get this straight. I unplug the wire from the knock sensor, stick one end of the resistor in the sensor, and stick the other end in the connecting wire. With that done, the car should run the same with the EST on or disabled if the ESC module is working correctly because it no longer thinks the engine is knocking?
Thanks

 

Well, not exactly. Unplug the KS electrical connector, then place the leads of a resistor in each of the two connections on the connector. The resistor will REPLACE the sensor, not augment it. This will assure that the sensor itself does not send a detection signal to the ECM, but doesn't do anything to test the wiring harness. Still, we have to eliminate one item at a time. Without some resistance in the circuit, the ECM will detect the open and assume the sensor had failed. 3.9K ohms is about right (and a commonly available value) to simulate the load of a good sensor.

Basically, the system works in this way:

The distributor shaft reluctor induces a slight current in the pickup coil every time one of its rotating poles passes the fixed poles. This signal is sent to the HEI module, which conditions the signal and sends it out terminals 'A' and 'C' to the ECM.

The detonation sensor sends a ground signal to the ESC moddule (or ECM in later cars) whenever a knock is detected. The ESC module conditions the signal to a 5VDC pulse and signals the ECM.

The ECM interprets both signals and sends a pulse back to the HEI module on terminal 'D', which controls the timing of the HEI module switching transistor. All of this occurs within about 0.03mS, or 33,000 times per second.

If the ECM is given a detonation signal, the timing of the pulse is delayed briefly to retard timing. Lacking the pulse, the ECM will time the spark signal based on engine RPM and temperature.

So, if connecting a resistor in place of the KS solves the problem, we can presuime that the KS has failed. If it does not solve the problem, we need to check the wiring harness for grounding and reliable connections to and from the ECM. Any ground in the return line from the sensor would be an indication that the sensor was detecting constant deetonation. Any open in either of the lines would signal to the ECM that the sensor had failed, and force a backup spark mode.

On the rare chance that you have a second failed sensor, try inserting a resistor in place of the sensor. If that doesn't solve it, start looking at the connector, wiring harness, and ECM card edge/harness connections.

 

And another thing - The lack of distributor reference pulses to the ECM from the HEI module can also cause erratic operation or no ignition signal.

I mentioned the possibility of an open circuit, which can include the connections at the HEI switching module, especially the smaller ones on the 'D' and 'E' terminals, and the small four-wire conneector for the distributor itself. You might also check the filter capacitor in the distributor base while you're in there, and make sure the HEI module ground connection is good.

The ECM grounds are also important to the operation of this system.

 

Does this mean that I do have a second knock sensor? I took another look at my wiring diagrams, and it shows one plugging in directly to the powertrain control module, and another plugged into the ESC module. According the wire color, the one I replaced went into the ESC.

Also, I took a look at the wiring harness that goes into the knock sensor. There is only one wire that plugs into it. This is also illustrated in the wiring diagrams. But at the module, next to the lead to the terminal there is a ground wire. Does this mean I have to take the computer out and place the resistor there, or is there something i'm not seeing.

Is there a way to test the wire going from the knock sensor to see whether or not it's grounding out by hooking up an ohm meter or some other diagnostic device?

Thanks for the help:hail:

 

i believe he meant the new sensor u just purchased could be bad.
there is only one knock sensor on our cars.

 

So, is there a way to test the wire connection from the knock sensor harness to the ESC with a multimeter?

 

Connect the senosr end of the wire to ground and then check the resistance at the ECM end also to ground. You might see a fraction of an ohm if it's good. Maybe even a single digit. Anymore than that and it's probably bad.

Or instead of using ground you could just run a wire off the ohm meter to the sensor end. Ground is usally more handy though.

 

91,

I probably mislead you. There is only ONE sensor on our ThirdGen cars, and there is only ONE connector on th ewiring harness. One lead of the resistor should be placed into that conneector, and the other lead grounded. I forgot that the sensor ground was to the engine case instead of through the harness - my bad.

 

No problem Vader, thanks for the advice. I'll let you know how it turns out.