The car used to run good but started an intermittent error code 16 and 36. The car would randomly shut off and turn back on. My first instinct was to not replace the Opti but i did and that was where all of my real problems started. ECT was New All wires from the PCM to the sensors tested out. Basically since i replaced the opti it would run until it warmed up then run realy rough and die. I put the old Opti back on and nothing changed. Last week when i tried to start the car it would basically start and pop off then die so i replaced the pigtails to the igniter/Coil and no spark since. Replaced the ICM and no spark at all. Checked all constant power, key power, 5 volt reference and grounds and did not see an issue. Whatever the probem is has completeley gone dead. Tried another PCM Tried to Flash Tried To read and log but will not log. Any advise will help.

 

Did you check the voltage on the white wire from the PCM to the ICM pin “B”?

4th Gen LT1 F-body Tech Articles

If you don't have the indicated AC voltage on that wire, it's possible the PCM is not receiving the low resolution signal from the Opti (DTC 16).

And you are unable to pull codes from the PCM?

What brand was the replacement Opti?

 

The Opti on the car said made in Taiwan, i put it back on because the cheap ebay Opti i put on was not timed properly. Changing the opti back did not make the surginging and dying issue go away. I do have another optical sensor also. The white wire has continuity to the Pcm so i am assuming that the pcm sees pulses from the opti at the low resolution circuit and inverts that to AC current. How many volts AC am i supposed to see at the ICM? I honestly do not know if either Opti was Degreed properly but it ran really good with the one that is on the car now. Somebody put a lot of money into the engine and never finished it. The Opti on the car was new when the engine was built, looked perfect inside but did get a little oil on it. Just trying to get a plan in mind before I try to work on this thing again, it has been a major waste of time.

 

Did you scroll down in the Shoebox link I posted. All the info on testing the ICM is in there. Also has checks to insure the PCM is supplying the Opti with 12 volts to power the optical module, ground, and 5 volt reference for the high and low resolution pulses.

 

Yes, i looked through all of that. The Diagram should be all i need as far as the functions and thier locations for testing. 2 things that i am not 100% sure about though I see people using an oscilloscope and probe the white wire, could i get an acurate reading off 20VDC on a meter and would a 1 man switch to the starter do the same or does the computer actually have to see a signal that key is being turned. Also looking at the plug configuration for the ICM the order of the CADB is obviously not sequential and may catch a few people offguard. I am sure that was done when the diagram was drawn up on CAD But the plug is marked ABCD. It's supposed to be hot out for a couple of days so i am going to focus on the projects in the building in the mean time.

 

The discrepancy between the diagram pinouts and the actual sequence on the connector is clearly called out in the article. The wiring diagrams are taken from GM documentation. You'll see the same “CADB” on the diagrams in the factory service manual. These procedures have been on the Shoebox site for more than 20 years and have proven useful to hundreds, or more likely thousands of people.

The signal from the PCM to the ICM is not a pass through of the low resolution signal from the Opti. The low res signal is coded to allow the PCM to determine which cylinder is approaching top dead center on the compression stroke. The PCM uses this info to generate a new pulse (pull-down from 5V reference) telling the ICM to fire the ignition coil at the correct number of degrees before TDC. It is a pulse, not an inverted AC current. It just happens that if you use an AC voltage setting on the meter you should see a 1-4 VAC reading on the meter. All this comes out of the factory service manual, including the diagrams included in the Shoebox procedure.

The ignition key must be providing power to the PCM and the ignition system. The engine must be rotating. Get a friend to turn the key to start, or if the leads are long enough put the meter on the windshield while you turn the key to start, or use your push button.

 

I worked on it a while earlier. The first thing I did was check the white wire to the ICM . White wire to possitive 20 VDC range and negative lead direct to battery. Had a square wave of 4.9VDC and 0VDC . Still does not get spark when i plug into the ICM Tried 3 different ICM's . I am running an MSD coil. Now i have to test all 3 ICM and all 3 Coils. Everything else seems good. My anti theft did kick in on me and it would not crank so i pulled the key out for 10 minutes. Cranked again and still no start. injector fuses are out because it still pulses the injectors with no spark. Smells like gas if i crank with the injector fuses 7.5 AMP in the fuse block. Has good grounds to the Heads, checked it 5 ways. Idk about these Lt1's maybe once it clicks i will understand what i do not know.

 

The ground for the ICM pin “C” is a black wire with an eyelet on the stud, driver side head, that hold the ICM/coil mounting bracket. Verify that ground. The stud should also have a braided ground strap from the chassis, and an eyelet with 2 tan/white wires that provide one of the two grounds for the PCM.

http://shbox.com/1/ICM_coil_studs.jpg

Historically, the MSD coil seems to be less reliable than the stock coil.

http://shbox.com/1/coil_testing.jpg

 

It has been a while since I messed with the car. When i checked the 5v pulse to the ICM it would get 5 volts but it would fade to almost nothing. Today I yanked the Opti and installed a new optical sensor with the cap and rotor from a new Chinese unit that looked like it was about 7 degrees out of time. I tried cranking it and got no spark, plugged a stock coil in and it fired right up. That MSD coil i am assuming is no good. No error 13 or 36 but it was Err43 ESC Failure and Error 48 Mass air flow system failure. I have to look into that and i also have a ticking sound maybe lifter, maybe bent push rod. This thing has no miles on it so i am not 100 percent sure. My Idea is to pop the rocker covers off and use my 1 man switch to spin it over to locate the noise.

 

DTC 43 is the knock sensor. That won’t prevent it from starting. When DTC 48 sets, the PCM ignores the MAF sensor, and defaults to the speed-density method of calculating mass air flow, engine should still start. DTC 13 is for an O2 sensor, not something related to the engine not starting.

 

I had the knock sensor unplugged , thinking the ticking was affecting the spark but it was not. The sound it is making almost sounds like a broken lifter to cam sound. It started out intermittently now it is constant. I have not gotten to work on it yet. Those push rods were factory scored, I do not think that they can hold up to the springs in the heads. I did not put it together. It ran really good for about a year. It did break a push rod once. What grade push rods do you recommend? I think Speedmaster is sufficient for a 400HP build.

 

Why are you running two threads on this? Basically, I answered your other thread regarding the codes. Really confuses things. Pick one thread and I'll close the other.

https://www.camaroz28.com/forums/lt1...-knock-889862/

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Delete the Other Thread.

 

Before I get to the tuning I am going to address the ticking sound. I pulled the rockers Scorpion 1.60 #10008526, push rods look stock average length 7.192". The rocker on intake valve for Cyl. #3 has a deep gouge in the aluminum all the way into the cross pin for the roller so i am going to have to replace that one. That rocker was on of the ones that came loose, i never checked them before I had it running assuming they were set. 3 of the valves have a divet across the valve tip where the roller wear patch is, might have to just put a new set of valves in it. Wear pattern is not perfectly on center but looks like it hits center at full lift. I will also have to use some heat treated push rods. As far as tuning goes, I need to verify that I am using the file that i have calibrated for the 4.10 Gears. I tuned it with TunerProRT and Flashed/Log with EEHack/FlashHack. Seems like it is running rich at idle. There is a narrowband guage on the car, it reads 11.2:1 at Idle but it does have a bung so i can run my AEM X-Series. I just pulled it out of the way to clean up around the building and it seemed pretty smooth driving around the block. Torn apart now.