Hey everyone, Im new here, Ive been fixing up a 2000 Chevy Blazer 4x4 to drive and Ive got it pretty much fixed up, I just cant seem to figure out why at highway speeds in overdrive at 2000 rpms the Blazer seems to hesitate and buck, but if you accelerate above 2000 rpms or let off the gas and fall below 2000 it stops. The check engine light only comes on sometimes, then sometimes when I drive it, it doesn't come on at all. When the light is on, the code comes up as a cylinder 1 misfire, but Ive already replaced the distributor cap and rotor, spark plugs, and wires. The only other car I have owned was a 1988 Thunderbird to which this truck is a different beast for me, so I figured I would find a forum to join since you can usually get good information from them. I also have freeze frame data I could post if that might help narrow down my problem.

Thanks in advance,

Ethan

 

Sure post your freeze frame and we will see if anything sticks out. Do you have a scan tool that will display live data?

 

I have an Actron cp9175, it's kinda old. I dont think it does live data. Anyways here is the freeze frame data, I have absolutely no idea how to interpret it, though I plan on trying to learn lol

DTC that caused freeze frame: P0300

Throttle Position: 0.0%

Engine RPM: 616

Load Value: 3.1%

Air Flow Rate: 5.40 GR/SEC

MAP Sensor: 40 KPA

Coolant Temp: 197 degrees F

Short Term Fuel Trim1: 1.5%

Long Term Fuel Trim1: -3.4%

Short Term Fuel Trim2: 2.3%

Long Term Fuel Trim2: 0.7%

Short Term Fuel Trim3: 95.3%

Long Term Fuel Trim3: 34.3%

Short Term Fuel Trim4: 85.9%

Long Term Fuel Trim4: -29.5%

Vehicle Speed: 0 MPH

Fuel System 1: CLSD

Fuel System 2: CLSD

 

So doesn't appear to be a fuel problem or vacuum leak at exact time code was set, since O2 sensors are controlling and fuel trims are normal. Also O2 sensors, MAP sensor, MAF sensor, and coolant temp sensor are reading normal and do not appear to be a cause of the problem - so I would advise forgetting any idea of replacing them/cleaning them *****-nilly in an attempt to fix.

That pretty much leaves ignition system as the likely possibility, and it is true that the Blazers have a lot of problems there.

One common thing is that the distributor gear gets worn and that points the rotor to not quite where it should when the spark plug is fired and the spark can jump where it should not. This also puts a lot of stress on the cap and rotor to contain the spark (why we recommend only Delco). The position of the rotor can be easily checked by monitoring the cam retard using a capable scanner. Cam retard should be 0° ± 2.0°. If it is very far off, the distributor should be pulled and the gear checked before adjusting to 0°. The Vortec distributor is locked in place by the factory hold down and and adjustment will require elongation of the hold down bolt hole to gain any adjustment.

Most inexpensive scanners will not monitor cam retard on Blazers, however most do at least some basic OBD2 live data. However I know of two Android apps that will. Car Gauge Pro ($8.95) for 1998+ Blazers and Dash Command ($10 + $10 for specific extended GM PIDs for your Blazer) for 1996+ Blazers. Dash Command user interface is much more developed, but either will work fine. Both apps use a Bluetooth OBD2 device to connect. I recommend the BAFX OBD2 device sold on Amazojn ($23).

If you want to continue, I will expect you to check cam retard next. Let me know if/when you have the capability.

Les

 

Okay thanks, I will look into checking the cam retard and get back to you! Again, thanks so much for the help.

 

My Blazer shows misfires on #1 when at idle but is fine otherwise....opposite of yours. I suspect it is the fuel injector spider just needs to be replaced. If you could update this when you check the cam retard and perhaps solve the problem, it may help me with mine.

While waiting for the reading cam retard capability, check the distributor shaft play. The OEM distributor has a plastic shaft housing which just does not last. If this Blazer has over 100k miles on it, plan on replacing the distributor. Good thing is that Skip White has a nice all aluminum distributor for like $50; just be sure to replace the cap/rotor that comes with it and use Delco parts.

 

I will definitely post an update when I get the chance, Ive had other things come up in the past couple of days but now that its the weekend I should be able to get out there and take a look at it.