I still have a lot of learning to do with cars, so some of what I'm about to ask may seem pretty newbish...

Overview of the situation:
My car started stumbling/losing power a few days ago and the service engine light would come on at that same point in time. It got so bad, the car died and left me stranded on the side of highway. After that point, it would not fire up again (only turning over). While waiting for a tow truck, I was able to get it to start up again (had cooled down maybe for 30 minutes). After running for a while it stumbles again and dies. So, I thought that it seems like as it heats up, the issue arises. However I tried letting it run in my driveway once home, and it ran for a good 25-30 minutes without dying at all. I did see the service engine light come on briefly, but did not die again... Anyways, the issue is just very intermittent, can't figure it out...

Codes:
When doing some searching, I discovered the two codes my car is pulling are related to the following:
-Code #43: Electronic Spark Control.
-Code #46: Vehicle Anti Theft Fault. (Really I don't care about the code 46 as much though. My primary goal is to get the car running properly again, which I imagine the code #43 to be the culprit)

I've done some further searching in the forums and found people with Code #43 often will have a bad knocking sensor or ESC module. I replaced the knocking sensor maybe 4-5 months ago, however have no idea where the ESC module is located at on my 91 vette. Where is that at?

I also found the following document that provides some assistance with troubleshooting the code #43 (http://members.shaw.ca/corvette86/Code%2043.pdf), however I don't quite understand the whole process really, specifically where the 24pin connector it refers to is even located at. What does that mean when it says: "Back probe ECM A-B Connector Terminal B7 With a voltmeter" in laymen terms.

Parts
Here's some more information on firing components that have been replaced/tested recently in case you all find that helpful:
-Distributor/coil/rotor (3,000 miles ago)
-Spark plugs/wires (5,000 miles ago)
-Ignition Control Module (tested good at autozone yesterday, initially thought that was the problem)


Thanks in advance for any insight on the issue.

 

DavesC4,

I will try and answer some of your questions. Please keep in mind I have an 87 and I believe the ESC system is the same. The troubleshooting procedures you are using from Agent86 should apply to your car also.

1. The ESC module is located next to the blower motor assembly. Open your hood and look on the passenger side near the firewall. Just aft of the wiper fluid tank behind the right wheel you will see the ESC module connected to the big round blower motor assembly. Mine has 4 wires going into it.

2. The 24 pin connector is one of the two connectors that go into your ECM. One is 24 pin, the other is 32 pin. B7 is the pin which controls ESC signal. The way the ESC system works is the knock sensor has a small crystal inside that produces a small voltage when it vibrates or "knocks" and sends this signal (voltage increase) to the ECM which then retards timing. The sensor is fail safe (if it fails, it assumes knock and retards timing).

3. Backprobing refers to "sticking" the multimeter/voltmeter probes into the back of the connector instead of the side which normally plugs into the other connector.(male/female). If you know someone who knows how to use a multimeter, maybe they can help you troubleshoot this problem.

I hope this helps.
John

 

Thanks a lot for the clarification John. That definitely helps me out with a better understanding of everything!

I'll have to try out the troubleshooting procedures and see what I come up with this weekend.

 

esc module is internal on the ecm on a 90-91 .... 43 can be the result of a bad magnetic pickup coil. some symptoms cylinders not hitting, strong fuel odor, timing discrepancies, I have had one fail but was on a 83 Z-28 CFI. it had all these symptoms also used the large cap hei/est distributor like yours.

 

Thanks for the info Jeff! I haven't had time to troubleshoot the issue in depth yet, however will do so tomorrow. Here's my current plans;
-Replace the ECM (have a spare one sitting in my garage)
-Replace the Knock Sensor, even though may not necessarily be needed (ordered one at Autozone, should be here tomorrow)
-Follow the wire from the Knock Sensor to ECM as closely as possible to ensure no visible breaks or damage. If I do find something, I'll try to replace that wire, which may be easier said then done...

So far my symptoms do not seem to be similar as yours. Cylinders appear to be hitting, no fuel odor or timing discrepancies, just an intermittent issue with complete loss of power/stalls. However, if I complete the above steps and am still having the intermittent issue, I will more then likely try replacing the magnetic pickup coil that you mentioned as well. Thanks again.

Dave

 

you know now I think of another possibility. there is a 4 terminal plug buried behind the distributor. On my 90 at any rate the locking clip for it broke and it became unplugged and triggered a code but I never checked the code. there is also a single tan wire with I think black stripe by the brake booster if its unplugged you'll get a code for esc.

 

Dave, I'm not sure if much changed from my '90 to your '91, but according to my FSM, the Knock Sensor connects to connector A (Yellow or Dark Gray) 11 of the ECM, with a dark blue wire. Naturally, "A" is the connector closest to the fender and there is no room to back probe, so you must unmount the ECM to have room.

Unfortunately, I only have the White copy of the main FSM and it is inaccurate in helping with troubleshooting, as it shows an external ESC module, where the Red Electrical supplement shows a direct connection to the ECM from the knock sensor.
I don't want to mislead you, but you could check for continuity on the wiring harness from the sensor to the ECM. other than that, I'm not sure what you should read at the ECM connector.

 

Connections are definitely something to check for in any scenario with troubleshooting. I have scanned around the engine bay for anything that would be lose, could not find anything... Also I know the exact tan wire you are speaking of as I've had the same issue before a couple years back, lol. Not sure what that little guy goes to though.

Thanks for the info gw962. I believe the Knock Sensor on the 91 does go directly to the ECM, or at least that is what it appeared to look when I 'attempted' to trace the wire, however was kind of difficult to do so, I was unable to tell for certain which port the wire went to on the ECM.

Fortunately, I do have some good news with my current situation . After replacing the ECM with my spare and the Knock Sensor, my car appears to be running solid. I hate to jinx myself by coming to this conclusion to early, however I cannot reproduce the #43 service engine code after letting the car idle for 20 minutes, then driving it for an additional 15 miles. I could be wrong, but I wouldn't think a bad Knock Sensor would totally prevent my car from firing (would it?). The issue was initially intermittent, so I'll have to give the car another few days or so to see if it acts up again. I'm sincerely hoping it was just a faulty ECM and the car behaves herself for a nice while.

 

Hmmmm. If the Knock Sensor is telling the ECM there is a knock, the ECM will start to retard timing in 4 degree increments. I forget how much the total can be however it can cause problems with driveability should the component (KS) send false signals to the ECM.

Drive and monitor.

Let us know.

 

it not only does that but at start up the ecm maxes out timing to create detonation just to test the knock sensor. Or it does something to that effect.

 

So far I'm looking good as far as the Code #43 goes.... However having issues with my VATS, looks like I should have paid more attention to that code #46 after all, lol. Had an issue earlier when trying to start the car it wouldn't even bother turning over. Pretty sure it's VATS associated... Time to do some more research on VATS. I remember hearing of a module that can trick that VATS into thinking the proper signal is getting to it at all times (which essentially eliminates your VATS system), I may need to pick that up, would come in handy at least if I experience the issue again. Appears to be intermittent.

 

just change the tumbler set and that will end your trouble for a few years.

 

Use a DVM to check the resistance across the pellet in your key.
Drop your drivers side knee bolster and find the 2 wire connection coming down the column from the lock tumbler. Unhook the connector and check the resistance with the key in the switch. The numbers should match. This will let you know whether or not you have a bad key switch.
If the resistance doesn't match, try cleaning the contacts in your switch and the pellet in your key with electrical contact cleaner and a q-tip. Check the numbers again.
If the resistance checks out OK, jumper your ALDL, A to G to read the CCM data. I'm not sure which module you need to check (at work, no FSM available. I'll post more info tonight, unless someone beats me to it.) but there will be a read out for the VATS A/D count. Post the count and I'll check it against the FSM for the proper number. This will tell you if the CCM is accepting the key resistance or if there is another issue. Mine turned out to be a dirty connection into the CCM, giving me the dreaded "intermittent", and a reading outside the acceptable limits for my key.
As for the bypass, you can make one up using resistors from Radio Shack that match your key resistance, or pick one up from a vendor.

 

OK, adding to your CCM readout on the speedo display...
Once any codes are displayed and the display switches to manual mode, the trip monitor will show 1.0. Use your Trip/Odo button to scroll to 1.2. When 1.2 is on the trip monitor display, push the ENG/MET button to scroll to 06 and a 3 digit number should show to the right of 06. This is a value that the CCM "sees" as the key code (it should be b etween 033 and 212)
Once you've determined your key code, you need to verify that your readings fall into the CCM's acceptable range. If not, there are various reasons we can troubleshoot. When I had my issues last year, the reading would fluctuate between 215 and 222 which was way out of range.
Sorry for being so wordy, but I know how aggravating this issue is.

 

Thanks for the detailed info gw962! I will have to 'attempt' to try your suggestions to see if it's reading in range. I only said "attempt," because I'm not the most technical person when it comes to cars, but I am always up for learning new things, so we'll see how it goes ...

Thanks for the suggestion as well jeffp1167 in regards to the tumbler set. I've actually replaced the whole steering column last year. I 'think' the intermittent VATS issue was present before and after the steering column swap, so in theory, I would figure it's probably not any of the components or wiring in the steering column but I suppose it's possible. Also another thought, when I've had this intermittent VATS issue, my spare ignition key would not work either. It seems like everytime the issue re-occurs, if I wait for 10 min or so, I'm able to start her up without any issues. Just really weird....

 

Also, I remember when getting key copies last year, the dealership said my key is a "Code #9" for resistance. What should be the proper range for the CCM with that?

 

Key# Value (Ohms)
1 392
2 523
3 681
4 887
5 1130
6 1470
7 1870
8 2370
9 3010
10 3740
11 4750
12 6040
13 7500
14 9530
15 11800


CODE RESISTOR VALUE IN OHMS
1996 GM Vats

( 1 ) 402
( 2 ) 523
( 3 ) 681
( 4 ) 887
( 5 ) 1130
( 6 ) 1470
( 7 ) 1870
( 8 ) 2370
(9 ) 3010
(10 ) 3740
( 11 ) 4750
( 12 ) 6040
( 13 ) 7500
( 14 ) 9530
( 15 ) 11800

 

so if you have a #9 key then find a 3k ohm resistor and disconnect the orange and white wire connector at bottom of you steering column then isert the resistor ends into each wire and see if it starts.

 

Thanks Jeff!

 

Dave, I'll check the FSM tonight (yes, at work again, this is my weekend..) and post the CCM range for a # 9 key around 8:30. The CCM shows a value that is different than the ohm readout. As noted above, it ranges from 033 to 215.

Checking the CCM data isn't difficult or technical. Send me a PM and I'll give you my cell number and I'll walk you through it, if you want.
A paperclip in the ALDL, slots A (top right) and G (bottom left), key ON, not running, and the data displays in the speedo/ trip odometer.