I had the same problem with my 02 Ls it turned out to be the Distributor Ignition Pickup

At first I thought there was dirt or metal flakes in the Distributor so I changed the cap and rotor cleaned out the Distributor with contact cleaner (it was kinda worn)
It still did it but not for like 3 days I then changed the pickup and it hasn't come on since some times if l 2 years now but mine is all stock w/68,000 miles

 

Distributor pickup? You talking about a pickup coil? I have a cam sensor, crank sensor, and ICM. I have a new distributor also

 

sry I have been working a tun of hours
No I said Distributor pickup That is what I wanted to say lol here is a link
What I Think was going on was it was getting hot and throwing codes
It never ran bad was just bugging me

http://info.rockauto.com/getimage/ge...6T_PRIMARY.jpg


http://www.rockauto.com/catalog/livecatalog.php

 

The "Distributor pickup" in the link is actually the camshaft position sensor. The PCM uses the data from it for determining camshaft retard and, along with the crankshaft position sensor, to detect misfires and identify which cylinder is misfiring. The sensor itself will not affect engine performance, even if you unplug it.

 

Hello,

Brought this old thread back up with an update. I have been chasing this misfire under load problem for a while now. Tried everything under the sun to get rid of it. Decided one day to run a test with my scanner hooked up while recording the misfire data from the cylinders. Went to a local mountain hill that always gave me a problem when accelerating up it. Got the truck up to 60 mph when all of a sudden I lost power and the check engine light started flashing. Looked down at the laptop and saw cylinder #5 go from no misfires to several hundred. Right then I knew I was dealing with a mechanical problem rather than electrical.

After scouring the internet I came across this TSB from GM

Here is the TSB:

Subject: SES Light and P0300 When Towing , Cruising Uphill or on Hard Acceleration - 4.3 5.0 5.7 accelerate cruise cylinder head RPO L30 L31 L35 LF6 LU3. DTC P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 PIP3081 - (07/23/2004)

Models: (96-02 Chevrolet Astro) and (96-02 GMC Safari) and (96-00 Old Body Style Chevrolet Suburban) and (96-00 Old Body Style Chevrolet Tahoe) and (96-02 Chevrolet Express) and (96-00 GMC Yukon) and (96-00 Chevrolet Old Body Style C/K Truck) and (96-00 GMC Old Body Style C/K Truck) and (96-02 GMC Savana) and (96-99 P32 Cab and Chassis) and (96-02 Chevrolet S-10) and (99-02 Chevrolet Silverado with 4.3L V-6 Engines (96-02 GMC Sonoma) and (96-02 GMC Sierra with 4.3L V-6 Engines).

The following diagnosis might be helpful if the vehicle exhibits the symptom described.

Condition/Concern:
The vehicle may exhibit a SES Light due to a P0300 and misfire. If the misfire is related to the information below, it will typically happen while cruising uphill, pulling a trailer or on hard acceleration and then stop misfiring shortly after returning to an idle. Typically, cylinders 3,4,5 or 6 will be the ones to experience this.

Recommendation/Instructions:
If the P0300 diagnostics did not isolate a concern, the following may help:
Remove the valve cover, valve springs and valve seals on the effected cylinder or cylinders. A small wire tie or rubber bands can be placed in the valve stem keeper groove to prevent the valve from falling into the cylinder. Rotate the valve while moving it up and down in the guide to see if it binds. If a binding valve is found, remove both cylinder heads and use either of the following methods to increase the stem to guide clearance:

• Send the head out to a machine shop and advise them to increase the valve stem to guide clearance to 0.002 inch per guide.
• Hone the guide with a 9 mm hone, such as Snap On BCG249, until a clearance of 0.002 inch is obtained. This will usually take about 4 strokes of the hone.

Reassemble the cylinder heads using new valve seals.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

I pulled the heads and this is what I found. Cylinder #5 circled in red:


Runs great now!

 

Excellent post and information.

 

 

Did you ever find a solution for this? I know its been a while, but I am having the same exact problem. At 75 MPH flashing engine light and have misfires on both 3 & 6 just like yours. I have a 2003 extreme .

BTW this is for Tazz9690

 

There are many possibilities for misfire problems, not just one answer. Sometimes you get lucky and stumble across the solution quickly but usually you have to systematically work your way through the problem.

Do you have a scanner, can it look at live data?

What have you tried so far?

How does the truck run when the light is flashing?


George

 

Wow I haven't been on here in 10 years but I just got an email notification.

Unfortunately, I was never able to resolve the issue. Shortly after these posts, I started my automotive training at UTI and needed reliable transportation after I graduated and moved across the country. I ended up trading the Blazer for a Jetta to get to and from school, then when I moved across the country, I traded that for a Kia. The Blazer Extreme was definitely a cooler car than those two and I wish I would have been able to get it squared away, but my technical/diagnostic abilities as a high schooler were very limited. Being a 10 year automotive tech at this point, I'm confident that if I had the same issue now, I'd be able to get it correctly repaired without throwing the parts cannon like I did back then.

Hopefully others with the same problem had better luck than I did. This was a blast from the past, reading through this thread reminded me of how helpful and kind everyone on this forum was way back when. Hope everyone is doing well, whether you still own a Blazer or not!