I have a 1996 4.3L blazer where I just replaced the intake manifold gasket. I'm 99% sure I hit my marks exactly when re-installing the distributor. I noticed on some of the posts here that the cam retard needs to be reset to zero after loosening the distributor. My blazer runs good at idle and seems to run fine up to about 45 MPH. After 45MPH the tach starts jumping a little and the engine seems to have less power. No code gets set. This seems like I'm getting cross-fire under the cap at higher speeds-->Is this the cam retard being off a little? What should it cost to reset? Locally I have found 2 mechanic shops that say they can do it one costs $70 to reset and the other estimated $150.00 because they wanted to pull the distributor for some reason.

 

I'm not sure if it has to do with your symptoms, but along with the cam retard you'll need to do a Crankshaft Position Sensor relearn. I don't know the costs. But it takes a high end scan tool (like a Tech II the dealerships use). If the shops you took it to did not mention this, you may want to ask if the relearn is included in the price. If not, you may want to consider a different shop since they did not bring up the need to have it done in the first place.

 

Cross-fire can definitely be caused by not having the cam retard set to zero. It can also be caused by a poor quality cap/rotor.

The hole in the lower intake manifold is quite a bit larger than the distributor body where it meets the LIM. This allows for ~15 degrees of timing adjustment to accurately align the distributor to the rest of the engine's rotating element (cam & crank).

Most shops will charge 1hr labor even though it will only take a competent mechanic less than 15 minutes to perform.

The shop that is estimating $150 because they want to pull the distributor may be thinking that the distributor bushings are worn which is a possibility and shows that they are at least thinking about your symptoms and not just the work. You can pull the distributor and check for play in the bushings (both top & bottom) yourself before going in if you'd like.

One thing worth mentioning about your symptoms; 45mph is also the speed where the torque converter will lock up given low throttle input (cruising around). TCC (torque converter clutch) shudder could be causing the RPM fluctuation you noted. It would not have anything to do with a lack of engine power though. One way to see if this is what is causing your RPM fluctuation at 45mph would be to lightly tap the brakes while holding steady throttle. If the RPM rises and remains steady at the higher RPM, then you have verified that the TCC is not fully engaging when called for.

Cam Retard is what is modified while doing a Crankshaft Variation Learn procedure or CASE Relearn. The process is detailed in the tech article EDI Engine Timing.

 

Case relearn is for the crank sensor. Cam retard is for the cam sensor.

Why does a case relearn need to be done if your not touching the crank sensor or PCM?

 

I was incorrect in stating that Cam Retard is set during a CASE Relearn and should have said it needs to be set prior to and is typically done as part of a CASE Relearn on these vehicles. My mistake for not being more clear. The CASE Relearn is there to ensure accurate ignition timing as well as misfire detection. On newer vehicles with COP (coil on plug), a mechanical link as provided by a distributor is not present and the only way to ensure accurate spark timing is through a CASE Relearn which sets the specific correlation factor for the components inside the engine linking the cylinder position to the spark event. Cam Retard is a big factor in the life of the distributor drive gear, cap, & rotor on these vehicles. Having a fresh crankshaft variation correlation will help performance, but not necessarily extend the life of the previously mentioned components.
A CASE Relearn must be performed when any of the following components are replaced:

• Cam
• Crank
• Timing Set
• Distributor
• Distributor Drive Gear
• CMP Sensor
• CKP Sensor
• Timing Cover
• PCM

All of these components affect the correlation factor between the CKP sensor and the CMP sensor. If things are only removed and reinstalled, then setting the Cam Retard should be all that is required. The timing cover puts a monkey wrench into that statement though as reinstalling it into the exact same position is like being hit by lightening.

 

So, concerning the shops that the OP went to (if they know what they're doing), when the OP walked in and stated he needed his Cam Retard adjusted...they should have provided a quote for a CASE Relearn, not just a Cam Retard adjustment? Is that an accurate statement? In his shoes, I would go back to the shops and ask exactly what was included in the quote...and if CASE relearn is not mentioned, it'd probably be best to find another shop. Yes?

Is there reason to do a cam retard adjustment as stand-alone without doing the CASE relearn? If I understand correctly, from the article and comments, the CKP and the CMP must be adjusted/learned at the same time. Correct?

 

They typically go hand in hand. I am more used to the COP engines where there isn't such a thing as Cam Retard, but you do need to set the Cam Retard prior to running a CASE Relearn. However, doing a CASE Relearn would not be absolutely necessary if all you did was remove and reinstall the distributor. Setting the Cam Retard back to zero should keep things happy.

 

I took my blazer in to get the cam retard set to zero and have them do a CASE relearn procedure. After about 20 minutes the mechanic tells me that he isn't getting any reading from the distributor and that loosening the hold down and moving it around didn't help. He suggested a new distributor and assumes that would fix the sensor data feed for his scanner to plug in to.

Per my original post, this vehicle idles great and runs really good up to about 45 MPH. I assume the distributor needs a little adjustment. Would it hurt anything to move it around a little and see where it runs best?

 

If the CMP sensor were not putting out a signal, a DTC would be set. If there isn't any DTCs set, then the mechanic is blowing smoke. Most likely he does not have the proper software on his scan tool to perform the requested work.

 

Exactly. The PCM is receiving CMP data, or it would definitely set a DTC, no question about it. Don't waste your money on the incorrect diagnosis, he probably doesn't know where to find the CMP retard data stream on his scan tool, or like Kyle mentioned, maybe his scan tool can't access it. Find a tech that's familiar with your vehicle, and his scan tool.