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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Hi guys, I was hoping you guys can help me. I've read a lot online and I'm still struggling with diagnosing my problem. I'm rebuilding my 92 Z28 TPI, I've getting code 43, the car goes into limp mode and runs poor. I've replaced the knock sensor, the wire the goes to it (there is continuity), all vacuum hoses, repaired header leak, new plugs, wires, injectors, etc. Timing is at 8 degrees btdc. What I haven't done is replace the timing chain, motor has 110k miles, and also I haven't replaced the ECM or PROM. I was wondering if there is a better way to diagnose the problem, I've already spent a good amount of cash.
If the EST is inadvertently left in bypass after setting the base timing, that could contribute to the 43 error code being set.
Also, if the cooling system is altered so that coolant does not achieve 195°F (unless the ECM was programmed differently) that can contribute to the 43 error code being set.
If the EST is inadvertently left in bypass after setting the base timing, that could contribute to the 43 error code being set.
Also, if the cooling system is altered so that coolant does not achieve 195°F (unless the ECM was programmed differently) that can contribute to the 43 error code being set.
Thanks. Please remind me what is EST? I don't think I did this.
I did put a 180 degree thermostat and also replaced the temperature sensor so that the fans can turn on sooner. Fans didn't work so I just wired them directly so they can be on all the time. So maybe it's the ECM.
Last edited by severe97; Jul 25, 2021 at 09:03 PM.
Electronic Spark Timing needs to be bypassed (essentially deactivated) in order to set the base ignition timing. After setting the timing, the EST is reattatched, allowing the ECM to control timing using the ESC functions.
Since the thermostat has been changed, and if the programmed temperature parameters have not been changed to match that, if the coolant does not reach 195°F the ECM cannot complete its detonation system checks when the throttle position is above 4.0 V.
Also remember that the 1990-up TPIs used the ESC module integrated into/onto the PROM, and did not use a separate external ESC module. If the PROM has been changed to used a remote/switcher PROM, the ESC needs to be integrated into the remote adapter to provide ESC operation.
For reference, error code 43 -
"The ECM did not detect a knock signal during near wide-open throttle operation with coolant temperature above 194°F, or;
The knock signal was present for 5 seconds or more during normal engine operation."
Electronic Spark Timing needs to be bypassed (essentially deactivated) in order to set the base ignition timing. After setting the timing, the EST is reattatched, allowing the ECM to control timing using the ESC functions.
Since the thermostat has been changed, and if the programmed temperature parameters have not been changed to match that, if the coolant does not reach 195°F the ECM cannot complete its detonation system checks when the throttle position is above 4.0 V.
Also remember that the 1990-up TPIs used the ESC module integrated into/onto the PROM, and did not use a separate external ESC module. If the PROM has been changed to used a remote/switcher PROM, the ESC needs to be integrated into the remote adapter to provide ESC operation.
For reference, error code 43 -
"The ECM did not detect a knock signal during near wide-open throttle operation with coolant temperature above 194°F, or;
The knock signal was present for 5 seconds or more during normal engine operation."
Thank you, this is very helpful. I did unplug the EST wire before setting the timing then plugged it back in after.. One thing to note is, I get code 43 soon after turning on the car. Even when the engine is cold the SES light is on. Does that say anything?
Based on your feedback, I think I'll need to program the PROM, I want to get rid of the VATS anyway so might as well. I had found a tuner on this forum who does PROMs, heard good things about him. I would just ship my PROM to him, unless I can buy one somewhere?
Thanks again for the info, very helpful.
Last edited by severe97; Jul 26, 2021 at 12:04 AM.
I’d try diagnoses before replacing or programming out the ks. I have memcals as well if needed and can disable your vats. If it does turn out to be the ecm summit racing has a 77-7730 for a good deal.
is this a l98 or Lb9 your working on ?
From my notes (old ones) the ECM will advance timing in steps when at full operating temperature (195° and up) and above 4.0V TPS input to attempt to create a detonation input. I believe there is a 2S timer for the routine as well. The theory is much like the initial ESC/KS test, so once a detonation input is received the ESC wiull back off the timeing in single steps to eliminate knock and determine the peak advance limit. This occurs on every run cycle, so long as the conditions are set (temperature, TPS, and run timer).
I would have to go back and analyze the BIN hack fully to get those conditions since I neglected to make more detailed notes a couple decades ago.
Excellent point on testing the filter circuit. With 30+ year old components, stuff happens.
Interesting , I had just assumed that once up to operating temp and driving forced knock occurred without a high tps voltage. Thanks for that information
Knock sensor testing strategy changed over the years. The most significant difference is that the $42 & $61 ('165/747 & '8746) ECMs apply timing advance for the test all at once, or in only two large steps, while the $8D test slowly applies spark advance in until knock input is detected.
Some early years’ ECMs test the ESC system by forcing knock to occur when in the first Power Enrichment mode of a run cycle, with the ECM expecting knock sensor input as a result. The ECM adds spark advance in up to two large steps. The first test initially adds about 10-12̊ of timing advance to whatever the current timing happens to be (base timing plus any programmed advance at the time). If the first test does not create knock sensor input, the second test step is performed. The ECM adds about 20-22̊ advance as a second test step. If an input is detected during either step, the test timing advance is removed and an internal flag is set to indicate a successful test. After two failed attempts to force knock counts, the ECM will set Code 43.
Tat is a lot of timing to just add on top of whatever timing is already present. This is why it can be audible and can also be a bit alarming. Basically stock engines are typically not damaged by this test, but a modified engine could suffer damage as a result of this “normal” test routine.
Furthermore, using fuel with too high an octane rating can cause this test to fail. Also, too low a coolant temperature can cause this test to fail. In a stock L03 F-Body, run some 91+ octane fuel and the Code 43 can be set even though there is actually nothing wrong with the system or hardware. Change to a 160° thermostat as so many people seem to think is appropriate without further programming, and a Code 43 can be set.
Perhaps those reading this will now have a more thorough understanding of why I have consistently advocated not going below a 180° thermostat unless reprogramming is done. This phenomenon is but ONE effect of incorrect coolant temperature.
Another side effect is that until the ECM successfully completes this test, Power Enrichment Spark Advance and Highway Spark Advance are also disabled. Thus, the practice of using unnecessarily high octane and changing to a colder thermostat in order to “make more power” can cost you all the power enrichment timing advance, making you substantially slower by constantly operating at only base timing.
Disabling code 43 will prevent the test from running. However, without also applying a “work-around patch” to the ECM binary, code, PE and HW spark advance adders will be disabled.
In other (later) years he scheme was changed. These later ECMs used a knock sensor with a 3.9KΩ resistance, and use a 4KΩ pull-up voltage divider in the ECM input line to bring the internal 5VDC reference signal to around 2.5V (very similar to the O² sensor input signal conditioning). The signal from the sensor goes to both the internal knock filter circuitry and an ADC channel.
The ECM in these systems will slowly advance the timing and monitor the DC voltage on the knock sensor input wire until a knock sensor input is created. If an input is detected the test timing advance is removed and an internal flag is set to indicate a successful test. At a parametric threshold of added timing advance and test duration, the ECM will set a Code 43 is there are no detected knock inputs.
The ADC device is used to read the incoming voltage. It must remain at 2.5 volts (± about 0.2 V). If this value is not maintained, the ECM will presume the sensor or wire is either open or shorted to ground. Although the $8D code which uses this method and has a forced knock test in the code, it was not always enabled in the specific vehicle calibrations.
I’d try diagnoses before replacing or programming out the ks. I have memcals as well if needed and can disable your vats. If it does turn out to be the ecm summit racing has a 77-7730 for a good deal.
is this a l98 or Lb9 your working on ?
Got it, thanks. It's an L98, I'll take you up on disabling the VATS once I fix this issue.
ok here is an update. Knock sensor checks out fine at 3.86 ohms. I then measured the knock sensor wire with the ignition on (engine not running) and it read 11.21 volts. According to the flow chart, it's either the wire is too close to the spark plugs which is not the case or a faulty ECM.
FYI I never turned the engine on so engine temp was cold. Does that matter?
so I guess it's all pointing to be a bad ECM.
I read on another post that sometimes the knock sensor wire and the temperature switch wires are switched in error since they have the same connectors. I tried that and guess what, error code 43 is gone. WOW...
I would like to thank you guys who responded. I learned more about this car thanks to you guys. Thirdgen.org rocks!!
Just so you guys know, I did a full built on this car, from pulling the engine, adding headers and full exhaust, rebuilt the tranny, replaced suspension, rims/tires and every sensor there is...it took me more than a year but all worth it at the end. Now it's time to get it registered and insured.
Good that you found the issue. It's a lot of analysis to perform to locate such a "simple" error but having a deeper understanding of the systems involved is at least a small reward for your efforts.
