If the PCM is replaced with a different one, the new one needs to be flashed to the VIN at a GM dealer. The crankshaft position sensor relearn must be performed after the flash. It requires a scan tool capable of initiating the relearn. Each crank sensor is unique and the PCM needs to learn it. Once the relearn is initiated by the scan tool, the PCM does the rest.

If the crankshaft position sensor is moved, removed, replaced, or disturbed in any way, the relearn must be performed. If the timing cover is moved or removed, the cover must be replaced, and the crankshaft position sensor relearn must be performed.

Camshaft retard needs to be checked, (and adjusted if necessary), each time the distributor is loosened or installed.** Once it's set correctly, and the hold down bolt is tightened, it's fine, as long as you don't loosen the hold down bolt. The data can only be viewed on a capable scan tool, (or software program). To adjust camshaft retard, the distributor is rotated slightly. As far as I'm concerned, the adjustment should be called "camshaft position sensor alignment". That is exactly what the adjustment does. I'm not familiar with the ones that Burned posted above, so I can't tell you if they can view camshaft retard or perform the crankshaft position sensor relearn. Typically it requires a "high end" scan tool, the el cheapo $500 jobbies at the auto parts store can't do either one. Hope this helps.

**Replacing the cap and or rotor does not affect camshaft retard.

 

The software I posted (Scan XL + GM Enhanced addon) does read camshaft retard. It will not do a crank relearn, it is not a bi-directional software at this time

 

Thank you. To do the relearn, sounds like I need to have the vehicle towed to a dealership?

 

You will need to get it running first, The Crankshaft position sensor relearn only makes a final accuracy adjustment inside the PCM and can only be done when it is running. Needing a relearn will not keep it from running.

Camshaft Retard setting also is done while running, so you must get it running first.

If it runs with one PCM and not the other then the problem is most likely with the PCM or the Security system. A Security relearn can be done by attempting to start (crank engine) and release key but then leave the ignition in the run position (turn off accessories, heater, radio ect.)and wait until the Security light goes out (~10 min), shut off, then do this twice more and it should start the next time.

If it does not crank you have a different problem.

 

Burned, the crankshaft position sensor relearn does not require bi-directional capabilities. All the scan tool does is initiate the relearn, the "meat & potatoes" is done by the PCM.

Bromanjr, spot on perfect, on all counts!

 

I am replacing the distributor with a very nice billet one from Accel. Among other reasons, I had stripped the threads on the one side where the rotor mounts to. I didn't really torque it, but it stripped right out. Because I don't have a scanner that can read the camshaft offset and because I was frustrated continuing to waste so much time, I took it to the dealer for $115/hr and asked them to install the distributor and then if any problem remains, investigate the misfire issue.

They quoted me $115 for the distributor install, but I really had to press them to install it because the Master Chevy tech at the Cadillac/Saab dealer didn't know how to set the base of the Accel distributor because it is rounded like the hold-down clap. In contrast, the stock unit has a square clamp that grips a square area of the distributor shaft. He told me that without a timing light "like the instructions say [for the Accel distributor]," he doesn't know how to get it within spec. (Apparently they don't think they have a timing light at the shop because "everything is computerized now"!) He claims you don't need to make any cam offset adjustment on a stock dist installation because the clamp only lets it go in one way and you just need to make sure the rotor gear is realigned into the same gear. It was a little disconcerting given what I have heard here and the fact that even with the square clamp the stock dist can likely turn at least 5 degrees in either direction.

Especially with my MSD 8.5mm wires, Accel coil, Accel billet dist with new cap/rotor, and MSD 6-AL ignition, I want everything to be perfectly calibrated. I mean, hell, I could just slapped in a dist, but I wanted it calibrated. I am hoping that with the rounded base of the new dist he will be compelled to check the cam offset, although I have no faith that he will adjust it to zero if it is still within the +/- 2 degrees spec. I think I will just find a way to verify the cam offset and either adjust it myself or take it back if it is not set to zero.

I am in a wheelchair and don't have an extra set of hands, and so turning the crank to TDC and all that would be a lot of hassle and time consuming, I'm thinking, so paying the $115 and having the dist installed and calibrated would be worth it for me. I would normally just do it myself, but I have spent so much time trying to diagnose the misfire that I just needed a break. Once it is set, I will still need to calibrate it again when I install the marine intake (which I have but can't find injectors/fuel rail anywhere for it -- any help?), so I think I may invest in the software that Burned posted. I did buy the bluetooth OBDII connector that he posted, and it arrived today. Is there any comparable software, do you know? ScanXL (what he recommended) looks good and affordable (~$250), but I just want to make sure I won't wish I bought some other software after the fact.

The mechanic also told me that there is no need to do any crank relearn, that it is all done automatically. I am not familiar with the issue enough to know either way. What you guys told me seems logical, although my truck did start right up when I put the original ECU back in. I would have experimented with getting the new ECU working except from having the truck sit so long and cranking it so much trying to start with the new ECU, the battery was dead. Instead of continuing to mess with it by following the Pass-lock security disable procedure mentioned in an earlier post, I decided to just save time by getting it running and driving it to the dealer instead of towing it in. So although it was cranked many times with a different ECU, it still started right up with the old ECU back in. So I guess a crank relearn is not necessary?

As for the misfire issue, the problem may be solved. I had put stainless steel mesh breathers on the valve covers and threw out the tubes running to the intake, including the PCV valve. The mechanic attributed the misfire to a lean condition at idle due to the massive vacuum leak that the engine could not overcome. Sounds logical, although I did this same thing on my '95 OBDI Sonoma without issue. I assumed it wouldn't be causing an issue on this vehicle since the same thing on my '95 had no effect. I don't understand how the same vacuum leak on a '95 caused no issue. Since the passenger side routes to the intake duct, that can have no effect on idle; so I am guessing the driver's side that pipes into the manifold is to blame. It looks like it passes through a sensor mounted on the manifold, and I am guessing the PCV airflow continues into the idle air bypass.

With the breather on the manifold covered, the mechanic claimed the vehicle seemed to idle fine. I believe on my '95 I had a cap on the manifold where it would normally feed from the PCV. Because I saw what looked like a sensor on the current engine, I installed a breather instead of a cap so as to not stop airflow and throw a code. So there is a breather on both valve covers and a breather on a piece of tubing coming from the manifold -- three total. Why would I do that, you wonder? I didn't want hot, dirty air being recycled through the engine, whether or not any negligible gain in horsepower would result. I had since been convinced it would be better to keep the solvent blow-by out of the oil and instead into the intake. I also wanted to clean up the engine bay. I wish there were a good compromise. I could do catch cans, but I don't know how well they work, they likely take up a decent amount of room, and the air would still be hot (not a big deal, I know).

For the record, I was planning on reinstalling the PCV system, but I was waiting till I could figure out the enigmatic misfire seemingly caused by the secondary ignition system that was comprised of an array of new performance parts. I guess I would have been waiting a while. I hope all will be good now. I guess it's true that the most seemingly complex problems are often caused by the most simplest of things. I knew it had to be something simple, I just couldn't figure out what. Stupid me.

I'll keep you posted when I get the truck back Monday and can investigate things myself. I'll also update on the mystery of what the dealership will end up trying to charge me. They told me what codes it had, so maybe they will try charging me $90 for the "diagnostics" that was limited to what I told them when I dropped the vehicle off. I told them I will fix the PCV system myself (via junkyard), rather than spending hundreds of dollars (who knows, it's a dealer) on a couple plastic tubes and a China PCV valve.

Oh, and the dealer was trying to tell me how the new ECU I was trying to use would not work because it needs to be flashed with the correct VIN. This doesn't make sense to me because if the ECU is the brain, who (what) is it reporting to???

 

A timing light is obsolete on this engine, Accel should know this, and the "Master Chevy tech at the Cadillac/Saab dealer" should know this as well. He should also know that camshaft retard needs be checked, (and adjusted if necessary) when installing a distributor on 96 or newer 4.3L. Your billet distributor base is round, just like the hold down bracket that came with it. The distributor installs just like the OEM, and the teeth must mesh properly with the camshaft gear teeth. If the teeth are not meshed correctly, P1345 will set in memory and the SES light will come on. After your distributor is installed, camshaft retard will be fully adjustable. The only exception would be if the camshaft position sensor hits the intake manifold, and if that hapens, the distributor is off at least one tooth!

The crankshaft position sensor relearn is NOT "done automatically". It must be initiated with a capable scan tool, which the dealer should have, (Vetronix TechII) along with a capable technician, which the dealer should also have The relearn MUST be performed after any of the following: The crankshaft position sensor and/or timing cover are moved, removed, replaced, or disturbed in any way, or the PCM is replaced. When the PCM is flashed to the VIN, the crankshaft position sensor relearn data is set to a default value. The engine will start and run with the default data, but not properly. Each crankshaft position sensor creates a magnetic field that is unique. The sensor directs the field in the general area that it needs to be. When the tone ring on the crankshaft interrupts the field, the sensor sends a pulse to the PCM. The relearn "shows" the PCM where the field is focused in relation to the crankshaft position. The data is stored in the PCM until the next relearn overwrites it.

PCV is a calibrated vacuum leak below the throttle plate. Plugging it off will cause negative fuel trim data. Not to menton increased sludge build up in the engine, and the risk of explosion due to insufficient crankcase ventilation.... not a good idea. If plugging off the PCV hose makes it idle better, the engine is running lean and fuel trims will indicate positive.

Your last question about flashing the PCM to the VIN.... The flash supplies the PCM with data pertaining to your vehicles specific rear axle ratio, tire size, transmission type, transmission final drive ratio, ignition timing, injector timing, EGR, EVAP, data for each cell that the engines operates in, etc, etc, etc. The flash burns in all parameters that the PCM monitors & controls.

Every sensor, (input) has an effect on calculations and adjustmnts, (outputs) that the PCM makes: If the crankshaft position sensor data is inaccuate, all calculations and adjustments will be inaccurate. If camshaft retard is out of spec, crossfire will occur in the distributor cap and the PCM will not be able to detect or accurately identify which cylinder is misfiring. Hope this helps.

 

The bill was $120 for one hour of labor, which included the installation of the new distributor, reading the codes, and capping the vacuum leak. I'm very pleased they didn't try to rape me. It was a pleasant dealer experience -- for the most part.

The dealer called Monday morning and told me they couldn't install the distributor because it won't go in all the way and that this was confirmed by measurements taken. Instead of calling them back, I scavanged the internet looking for any complaints of fitment. All I read was praise, including from Blazer/Jimmy owners. I figured it had to just be that the oil pump was not rotated to allow the dist gear to drop in. I assumed a master tech would certainly understand this, but now I'm thinking he was just disdainfully ASSUMING it was a fitment problem simply because it was an aftermarket part.

About an hour or so later, they called back and told me the tech used his own "special race tool" and was able to get it installed and that it is now ready to be picked up. Huge relief. I was worried the employment of the "special race tool" would be grounds for inflating my bill. Thankfully, not the case.

Although he told me it is not necessary to be done, the tech stated on the bill that he initiated a crank relearn. That is good to know. Apparently he calibrated the camshaft retard or it would have the light on. I will check the offset tonight with the new software I purchased.

The vacuum leak did solve the misfire problem, thank God. I also now have a shiny new distributor, and I learned that the stock distributor was not only stripped out in one of the rotor's mount threads, but also the plastic was cracked through in both thread sets for the cap. I can definitely recommend the Accel unit. Although very pricey, it is very well built and has several very nice features including a wire screen in the underneath of the base and a large oil port on the billet shaft. I had a billet unit from Summit Racing, which closely resembles the stock plastic unit, but the Accel blows it away. Maybe it won't add performance, but it is certainly a more durable and robust unit that will outlast the others (and it looks awesome).

Thanks to Burned, I purchased the Palmer Engineering software, ScanXL Professional with the GM Enhanced Diagnostic Add-on. I'll try it out later tonight, but it looks pretty cool. I had read at least one other poster mention that he can interface the software with his vehicle through the hardware included with his Jet DST tuning package, which I also have. I hope that the bluetooth adapter I received a few days ago will work, as claimed by Burned, because it would certainly make things easier.

Thank you so much everyone for your help!!!


PROJECTS (inter alia):

Reinstall PCV system.

I can finally return to some of my other projects, including the swap of my JL 1000/1v2 to my JL 1200/1v3 that I use to power my JL 13w7.

I also need to replace my cruise control module with one I have from a junk yard, but I am going to sand blast it first (same with the original ECM). I tested the multifunction switch at the connector at the under-hood module, replaced the brake switch, and since I lost cruise soon after washing the engine and later learned there was no rubber seal on the connector for some reason (maybe it was added in later years due to an earlier oversight?), it MUST be the module. I need cruise back!

I finally still need to remove the fan clutch nut, having failed for several hours so far with different techniques, including a couple with an air hammer.

 

I was actually inquiring as to what monitors the ECU. While the ECU monitors all the sensors in the car, and contains all the constants, including the VIN, what other system monitors the ECU in order to disable the vehicle if a new ECU is installed? Is there just a security system box somewhere that monitors the VIN of the ECU??? If so, does it monitor anything else other than keyless entry?

 

"special race tool"???? there's a new one. I wonder if it's similar to a muffler bearing alignment tool. In other words, the oil pump drive wasn't lined up.... woops. He didn't want to look like an idiot, so he fed you a line of crap instead.

The crankshaft position sensor relearn that he did: The data will remain in that PCM until the next relearn overwrites it. You can remove and install that PCM as many times as you like, and as long as you use that PCM in the vehicle, the relearn data will be correct for your crankshaft position sensor. If you replace it with a different PCM, you need another relearn.

"what monitors the ECU?" The PCM monitors itself using OBDII. There are several modules in the vehicle that are networked together. Each one monitors itself and data is viewed on a scan tool capable of accessing each module. Each module monitors a specific system: PCM, powertrain control module, BCM, body control module, EBCM, electronic brake control module (ABS), TCCM, transfer case control module. They all share data via classII communications. For example: The Passlock system is monitored by the BCM, if it detects a theft situation, it sends data to the PCM and the PCM disables the injectors.

Does this help?