This question is about how the ecm work with the knock sensor. I have a bad issue with a 90 Iroc-Z, a bad engine fail, runs, but like in only 6 or 7 cylinders, and have a 42 code, yes, this code is form the electronic spark timing, but I put all the ignition system from another running car (my daily driver 91 Trans Am), distributor, coil, inclusive cut the distributor wires near the ecm and made other harness to the distributor to be sure there aren't any short or cut in the wires, but nothing. Ignition system is OK, but code 42 persist.

Today with my scanner I had compared knock sensor reads in both cars, and aren't the same. In Trans Am scanner read 0, but the Iroc reads variable numbers each time I crank the engine, from 1 to 101!!!!

About this, could a bad knock sensor promote the ecm going crazy, and will can't drive the right advance, and flash the 42 code from the EST??

 

Code 43 would be KS failure if you are running $8D mask.
Code 42 is for distributor pulses and module problems.
Confirm the pickup coil wires are not reversed in the distributor. That can cause issues.
Cranking knock is difficult to say if it is real or not because of the starter noise could give false indications.
Also did you clear the codes (remove fuse or battery) after you changed the distributor ,etc.
Check the Memcal in the ECM is not looses and all the connectors going to the ECM are in good too.
HTH,

 

Thanks for the reply. I know that all the ignition system is Ok, becouse I test the Iroc with a running Trans-Am distributor, and the fail continue, I cut the distributor wires near the ECM, and made another wiring arness only for the distributor (to discard possible cut or ground anywhere with the ignition) and nothing change.
Test the Iroc ECM in the Trans-Am and the car run very well with the Iroc ECM (the TA is also a 305 TPI). I suspect of the KS becouse I seen an unstable readings with the scanner when the car is "bad-running" as well as the advance is also very unstable (scanner reading) till the code 42 flash, but even with the code 42 present, and the ecm in limp mode the engine fail.
Today I checked the KS resistance and wiring, and all appear to be normal, but today I had seen a fail in the O2 sensor and code 44 also was displayed, I am crazy with this car.
Now I suspect about any bad ecm ground, but not enough bad to see it with the polymeter. I am studing all the wiring diagrams, but can not understand where is the ground that could affect mainly to the ignition system, and ramdomly to the other sensors, like the KS and the O2 sensor, with the MAP, TPS, and temp sensors I don't detect any problems for now.

 

Could be a problem with the ECM if it runs good with the other unit.
You could substitute a 3.9K resistor for the KS to make it not respond to anything and see if things are the same. (That is the 350 KS value, 5.7 L motor)
If you have 305 substitute the correct value, I don't remember at the moment what it was.

This could all be tied to the ground wire at A12 on the ECM.
There appears to be internal connections from B9, B6, and B5 as well that all go to ground through the A12 pin.
B9 = VSS ground
B6 = MAP & MAT ground
B5 = TPS & Temp ground

Check that "D1" is also grounded and connecting at the ECM too while you are there.
Not sure how they would relate to the ESC error except that all of the signals you are having problems with are the "analog" signals routed through devices "U5" (main analog to digital chip) and "U6" analog to digital chip (multiplexed through "U5" device) on the board. I can't tell where those devices are grounded from the schematics.
If there is an issue with the U5 on the ECM you would need to replace the ECM.
I hope not but if swapping the ECM fixed it that could be the result.
John

 

I think you missunderstand me, (or not??) Car with the fail is the Iroc, but the fail is the same with his ECM, and with the Trans-am ECM, and the TA with the Iroc ECM runs very good.

Is not the same, but today I start the car with KS disconected, and the result was te same fail in idle, but this time display 42 and 43 codes.......


Today I checked all grounds at the ECM conector, even put a wire from this grounds (one by one) direct to batery negative, but anything change, checked this in A12, D1, D6, D7, and E15, but anything change,

Then I press the small contacts in the ECM conectors, to assure good contact, but continue the fail.

Not allways the engine fail the code 42 is pressent, and I am very curious about one thing: when the engine fail, if I disconect any of the passenger side injectors (one at time) nothing change, but if I do the same in the drivers side the fail is more notorious. I check with a test ligth in the injector conectors while this ocurr, and all inyectors make the same flashes.

More than I test, less I understand......

 

This may give some other ideas to try.
https://www.thirdgen.org/forums/diy-...549-could.html
His problem was a miss on #2 cylinder that lasted a long time.

Check those passenger side injectors with ohm meter. You may have an issue there.

 

Passenger injectors was checked and was about 15ohm (or 16, don't remember, but just the same as the other side).
Those rear heads grounds was checked days ago, dismounted, cleaned and mounted, but nothing ocurr.

I don't made a wire between the heads and battery like they say in the post you link, I am tired of this car. This is a favor for a friend, mine car is the 91 Trans Am. I ask to the Iroc owner about the car hystory, he bought it with broken engine, restore it, (engine and all around) and is unknow who put his hand in it before actual owner. Months ago, with this problem yet, but without finish the rest of car, I found two conectors out of his place (interchage?...... my english..... sorry), was the KS and the fan switch of the passenger side head, and like this and now, that I know that someone made a **** with it who know what time ago...... I see that I can't solve this problem.
Tomorrow my friend will go to the local dealer and will see if they can do anything, perhaps here in Spain I know this car better than the dealer (here is Opel dealer.........) but I am not a proffesional electrician and don't have sufficient tools to go than advanced than their.
If they find this issue I will post it here, I am desperate with this car, is the first car I could not repair,,

 

still have this problem? try this out. " possible air solenoid stuck in upstream position blowing air in ahead of 02. With engine running & fully warm, pinch off hose from air pump to exhaust manifold. Scan 02 volts & integrators for change." MY friend had similar problem like u and was sending out a code 44. he disconnected the hose and the problem went away

 

Sorry, I forgot to tell you what was the problem. It was partialy solved. Main culprit of this issue finally was a bad lifter adjust. I don't understand why yet, but when hot If I rev the engine over 2000 rpm. exhaust valve of cylinder #4 don't totaly close and when I think in check for compression in those cylinder only have about 5.2:1 cr. Then, I adjust all lifter the next day (with cold engine) and this fail was out.

Now the code 42 (dist. ref) remain occasionaly, and don't know why. Engine sound and run great, but the code is present. I swap complete distributor, and ecm of other running car and the code is there. I think in any issue with the wiring, but can not find it, and my friend (the owner of this iroc) says that he can live with it.

In resume, I was thinking that the fail on the engine, and the codes were the same problem, but not, one was the code, and other the fail (run in 7 cylinders), the fail was solved, the code is present..........