Howdy,

I've been experiencing some trouble in the form of highway engine stumbling recently. I have an 04 Vin X 4wd Blazer, in which I just replaced the engine last summer due to a portion of the cylinder head breaking off and destroying all of cylinder 6 and flooding the engine with coolant (Ikr? Crazy). Needless to say, I'm over that, and I was able to find a replacement engine with 107K miles and clean fluids. Installed, and everything has been great...except one thing. Whenever I am on the highway doing greater than 50mph, and either trying to give it roughly 3/4 throttle or climb a hill, the engine seems to miss a lot, with significant drawback on power. If i keep my foot lightly on the gas, no missing, but slowing speeds obviously. If the A/C is on, it usually contributes or makes it worse. Flooring it usually restores power. Seems to like to miss a lot right around the 1700-2000 rpm cruise range when load is introduced. Driving in town, even through large hills and valleys, engine runs great. Rarely if ever do I get a SES light, but when I do it is usually solid for P0300. Hooking up my TorquePro app to my OBDII, it appears that Cylinders 2 and 4 take the most misses, followed by 3 and 5 if it's a severe event (pretty rare now). I think the SES stays off most of the time because the episodes aren't long enough to trigger it. Not sure. Regardless, here's what I have for you:

Regarding the engine I've replaced these within the last year:
-Engine w/ used clean Engine assembly of 107K miles
-MAF (2 times, found out the hard way buying cheap chinese crap, got a Duralast now and working fine)
-A/C Compressor
-Distributor cap and rotor, both with AC Delco
-Spark Wires, Duralast
-Spark Plugs, NGK pre-gapped
-Exhaust Y-Pipe, including new Catalytic Converter since the old engine blew the OEM.
-All HO2 sensors along the Y-Pipe, AC Delco

Took a look down the throttle body and see no signs of carbon buildup anywhere within. Very clean. Compression is 165 +- 5 psi on all cylinders. A recent fuel pressure test showed Key On Engine Off at 58psi leaking down to 51psi after 10 minutes. With engine running, Idle is around 50 psi, while revving it up from the engine bay pops it up to 56 psi and falls back to 50psi shortly thereafter. Oil pressure is usually 40psi at idle, 60psi cruise. Keep in mind, this issue never happened with my old engine, so I feel like it could be safe to say that the problem is somewhere within this engine. Any input would be greatly appreciated.

Thanks,

Jon

 

Check cam sensor retard. Torque Pro isn't going to do it. Need Car Diagnostic Pro from Google Play Store (use same Bluetooth OBD2 adapter) and enable GM PIDs in the app. Should be zero plus/minus 2 degrees.

Because the ignition is triggered from the crankshaft, If the distributor gear gets worn then the rotor ends up lagging behind in position and spark can jump to wrong place. The goofy circuit-crossed distributor cap doesn't help. Because the PCM adjusts timing to different amounts at different loads and RPMs, having cam sensor retard off can cause misfires at different loads and RPMs. Cam sensor retard is a measure of the relationship between crank sensor and the cam sensor located in the distributor. If cam sensor retard has been causing misfires, then replace the cap/rotor again (for long term) when you have corrected the cam sensor retard and verified the misfire has gone away. Typically distributor gears are the thing that is worn but worn timing chain may prevent it from ever being perfect. If you replace a distributor gear, remember that with a locked position distributor, 13 teeth on the gear will give you different rotor position (14 degrees) depending on the orientation of the gear on the shaft. So note the position of the roll pin (between gears or on top of a gear, on the side of the shaft facing something on the rotor). If you are off 14 degrees or so after repairs, you know what to do. Otherwise some people put different clamps on their distributor to unlock it and just turn the distributor body. Either way, always look for play by wiggling the rotor back and forth before attempting to adjust. Should be no play.

Also be aware that Torque Pro makes a mistake on the V6 for misfire for a couple cylinders (gets them switched). Use the alternate PIDs (*) in Car Gauge Pro to correct for the V6.

Good luck and best wishes for a successful repair. Keep us posted.

 

Storm Blazer Jon - I see you are online - know that I added more to the post above.

 

Thanks for your willingness to help! I just got home from driving it 500 miles today, so I'll work on your suggestions in the morning and post back some results.

I do want to ask about the conditions for a CASE relearn though, as I've been reading up on it tonight. After I swapped my engine, no relearn was done because I did it at home. Additionally, I used my old distributor from my old engine and threw a new rotor and cap on. Perhaps the issue lies somewhere in there? How much does it typically cost for a mechanic to do a relearn and what would it accomplish, if anything? Regardless, I'll check the distributor drive gear for wear and go from there.

 

Not doing CASE (crank sensor) relearn can cause a false misfire to appear as a P0300, but will not cause an actual felt misfire. Usually a crank sensor relearn will cost $50-$100 or so.

This is teaching the PCM the normal crank sensor waveform for your vehicle, so it has something to compare to when it tests for misfire.

 

Have some new information now. First off, I could not make either of the other apps besides TorquePro work with my OBDII Bluetooth device, so I opted for another method I found online about adding a custom PID. It worked, and now I see Cam Retard data in TorquePro. I hooked it up and went for a drive (see attached graph) and found the retard was around -5.5 to -7.5 while driving, and around -6.5 idling. I do have an occasional stumble idling. I've also attached an image of the distributor gear, which looks very good to me. If I recall correctly, it is fairly new, and looks new. The rotor wiggles back and forth a little bit, I'm not sure how much is too much. Anyways, I'm assuming that a cam retard of -7 could be responsible for my problems. How do I go about adjusting it towards zero?

 

Distributor gear looks good. Don't worry about wear there.

I really don't fully trust any of the user-added PIDs to Torque Pro, but I do applaud you to get it to work at all - I never could when I tried it some years ago. If you read the Torque Pro forum, they have been estimating factors for quite some time.

Could you please post here the exact formula that you entered. Could be useful to some people and I could do a comparison to the other apps. I do actually like Torque Pro for certain things like graphing! Seems strange it was the only one that would work with your OBD2 device, but Torque Pro does do a good job of checking all communication protocols. I personally recommend the BASF OBD2 adapter as found on Amazon. Cheap and works great! Faster polling of PCM for PIDs also. I got 30+ polls/sec on my 2001 Blazer which happens to be checked by Torque Pro! This can be important if you are monitoring multiple PIDs at the same time. Each PID takes time to give back data.

Again I do know that a V8 has a different PID vs s V6 for cam sensor retard, but they both hit zero at the same point. The further you go from zero, the more the cam sensor retard is skewed between the two. Car Diagnostic Pro has an alternate PID for the V6. If the gear is good, then slop/wear must be in the timing chain/gears - but not worth replacing it when you can turn the distributor just a tad and get it to zero (which it seems that you can read zero accurately). For -7.5 I think you can elongate the bolt hole in the clamp with a dremel to get enough movement to go to zero. If not you can replace the factory clamp with one from a SBC and rotate to your heart's content.

Turn the distributor counter-clockwise to increase cam sensor retard. -7.5 to zero should not take much rotation. Raise Rpm above 2000 or so and then let idle to take a new reading.

Zero spec is not critical - anywhere -2.0 to +2.0 should be fine. Mine sits at -2.0.

Good luck and best wishes for a successful repair.

 

I used "((signed(A)*256+b)*0.063)" as the equation for the CMP Retard. I ended up starting with a retard of -7.5 degrees. After I put the distributor back in yesterday, I turned the distributor as far CCW as I could with the factory "fork" hold-down, then tightened the hold-down bolt there. So, currently, the distributor sits as far CCW as it can go without further modification.

As I did some extra research this morning, I noted that there are indeed two different formulas (one of V6, one for V8) as you had mentioned, but nobody ever concludes which one is which. One uses the multiplier I used, 0.063, while the other uses a multiplier of 0.024. So, I went ahead and fired her up today and got readings using both multipliers:

*0.063: -4.8 degrees
*0.024: -1.8 degrees

After going on a test drive, it appears that I have restored power on the highway and no more "felt" misfires either. Still a bit of a rough idle, nothing crazy though. I'll hold off on full judgement for a couple more days. When I used the smaller multiplier, I only got a range of about -1.5 to -2.2 degrees throughout normal driving, versus my results yesterday with the higher multiplier which yielded a much larger range of -5.5 to -7.5. In short, I believe the 0.024 multiplier is to be used with the V6? If this is correct, I should be within spec now after yesterday's adjustment, and the returned power would appear to corroborate. If I could have gotten the other apps to work with my BAFX Bluetooth OBDII I probably could have avoided all of this, but for some reason Torque only works for me.

Here's how I added the CMP Offset PID in TorquePro that I found on another forum:
-Settings
-Manage Extra PIDs/Sensors
-Hamburger Button at Top
-Add Custom PID
-OBD2 Mode: "221301"
-Long Name: "Cam Retard Offset"
-Short Name: "CMP Offset"
-Minimum Value: "-100"
-Maximum Value: "100"
-Scale Factor: x1
-Unit Type: "Degrees"
-Equation: " ((signed(A)*256+b)*0.024) "
-OBD Header: "6C10F1"
-Does not override any PID

Finally, I threw my misfire counter up while driving, and usually only noticed the misfire counters popping some numbers right as I take my foot off of the gas. I'm not sure if this is normal or not, but the "felt" misfires did not occur on today's drive as they usually did, which is a good thing. If the felt misses are gone for good, should I still be replacing the cap and rotor again, even if they are ~1500 miles used?

 

Thanks for the info. Sometime this holiday weekend I'll enter and see which custom PID (if any) matches up with Car Diagnostic Pro and Dash Command. I know these two do match each other.

If the felt misfires are gone, then don't need to try to replace anything - just enjoy. If they come back after a while and cam sensor retard is still OK - then you can replace them

I was thinking you never did a Crank Sensor Relearn after engine replacement. I wouldn't sweat a few non-felt misfires on misfire counters unless they cause a pending misfire or turn the SES light on. If that happens, you may need a Crank Sensor Relearn - but remember that will not change any real misfires - only correct their detection. The relearn procedure stores a waveform in the PCM that engine operation is constantly compared to. Too much difference and it flags a misfire.

 

Here is my Blazer (CMP Retard idling - one read after another):

Torque Pro 0.063 = -2.6
Torque Pro 0.024 = -1.0
Car Diagnostic Pro STD PID = -0.9
Car Diagnostic Pro alternate PID = -2.7
Dash Command = -0.9
Vident i-Link 400 Hand Held = -1 (no tenths shown)

I trust the Dash Command and Vident single CMP value the most because they presumably filter their PIDs and make you pay extra for the GM ones. I think I may have been mistakenly telling people to use the alternate when in Car Diagnostic Pro (when in fact it was the two alternate PIDs for the misfire counters that should be used). In any case if you can get (probably with difficulty) the alternate CMP retard in Car Diagnostic Pro down below 2.0 you are really close to zero.

Looks like the Torque Pro formula works fairly well. Thanks for that! Why don't you put the 0.024 formula in a post again and title it "Torque Pro Custom CMP Retard (Cam Sensor Retard) Formula for Blazer V6". I'll make it a sticky in this forum and once it hits Google you will be forever famous!

Was you the guy that I worked with a while back who couldn't get other apps to work?

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Car Diagnostic Pro


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Dash Command:


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Torque Pro with Formulas: