The Blazer has 157,000 miles. The issue started all of a sudden. I drove home from work, 45 miles one way with no issues. The outside temp was about 20 degrees. No issued noted during the drive. Arrived at home but need to leave shortly after so I parked in the driveway and shut off the engine for about 10 minutes. Upon starting the truck there was a noticeable "miss". Upon trying to drive there was basically no power off the line and the truck was sputtering, almost back firing. What’s odd is that you can rev up the engine to anything over 1800 rpm and the engine runs smooth.

Here is list of checks that I have done. I replaced all the plugs, they actually looked very good but I replaced them anyway with new AC plugs.

I checked the compression and found all 6 cylinders to be about 175 - 180.

I needed to get gas as I was down to about a 1/4 of tank so I didn't think it was gas but I drained a sample to check for water from the test port. No water or contaminates.

I next checked the fuel pressure. I'm running 58psi key on and 56 psi running at idle. According to my manual this is within limits.

I have replaced the fuel pump within the last year. The pressure held for at least 5 minutes before removing the gauge.

I checked the coil and have readings of .5ohms on Primary and 5700ohms on secondary. This also appears to be within the limits.

I pulled the distributor cap and there was no moisture but the contacts were slightly white so I cleaned them.

I pulled the distributor and checked the gear. It appears to be "ok" as there is only slight wear.

I installed a code scanner and found P0300. I will attempt to attach the excel spreadsheet with the values.

I have checked all hoses for vacuum leaks.

I removed and cleaned the EGR value. I checked to ensure that it closed and was not sticking open to allow exhaust gas to pass by.

Upon doing research on this issue I'm initially suspecting injectors from looking at the black carbon buildup inside the intake plenum so I currently in the process of pulling the intake to replace the lower intake gaskets and to clean up everything. I figure if anything this should rule out an intake leak.

This issue just seamed very odd to all of a sudden happen with no warning especially after a 45mile drive home.

Is all of the carbon build up in the intake from the injectors leaking?

For the scanner data I cleared the PCM of all codes then set up the scanner and restarted the truck until the MIL was set and the data saved. I also uploaded the O2 sensor data that was saved, not sure why it only listed Bank 1 Sensor 1.

I will attempt to post a few pics I have to see what anyone thinks. Any advice on the scanner data or the pictures would be appreciated. Thanks in advance!!

 

do a full tune up, cap rotor and wires since you already did the plugs
i would use ac delco parts personally

 

I would also recommend that you have the coil and ICM load tested.

You might also want to have a read through a rather lengthy P0300 discussion (search for "P0300" and it will turn up).

BTW, the sensor information you provided really isn't any help... The real information is in the STFT and LTFT (short/long term fuel trim) numbers for each bank as these can indicate a lean/rich condition that the PCM is adjusting for.

 

Thanks Pack, I planned on replacing them upon re-assembly of the intake.

Swartlkk, I have read so much about P0300 that I think my head is starting to spin. So much of could be this could be that. This helped a little but didn't fix it.
The confusing part is why all of a sudden, I would have expected for something to jump out and say "I'm broke, fix me". Based upon my reading I find this almost never happens for P0300.
You indicated that the real information is in the STFT and LTFT (short/long term fuel trim) numbers for each bank as these can indicate a lean/rich condition that the PCM is adjusting for. What is this telling you? Those grabbed my attention also that is why I was strongly leaning towards the replacement of the injectors. What are you thinking? Do these numbers indicate a specific problem or symptom? It appears the benefits alone are worth upgrading the injectors even if there is not a problem with them.
Can someone clarify the correct part number to order? I found on this web site p/n 12568332.
Thanks!!

 

ACDELCO Part # 2173028 More Info {Includes Instructions for Conversion from Poppet-Style Invectors #89060439}

INJECTOR KIT,CENTRAL SEQ M/PORT FUEL

This is where I was going to buy my future injectors from. Its at rockauto.com and is the one stop for all my parts. I found that their prices are reasonable and their shipping is perfect for me, for most of the parts come from Cali and I live in Nevada.

You might benefit from tank cleaning your intake manifold. Mine was pretty nasty when I pulled it last March.

 

Having multiple injectors fail all at once is a very rare occurrence and I doubt that the injectors are your problem. More testing can confirm/deny that thought though.

Looking at the LTFT & STFT can tell you how the PCM has made adjustments for the conditions it is seeing. If you were to get a cracked exhaust manifold or a blown exhaust gasket/donut before the upstream O2 sensor, it could cause a false lean condition that causes the PCM to richen the fuel mixture in response. There are many other things that could also be contributing to a P0300 code, much of which is discussed in the MULTI page thread on the topic.

 

Just a quick update on where I'm at. I've pulled the lower intake to replace the gaskets with new Fel-Pro ones. I think this was more piece of mind than the real issue and at $29.99 for the complete intake gasket set a cheap fix and a little insurance. I knew the distributor needed changed as the cap hold down tabs were almost broke off from a previous owner tightening them a little too much so I was able to order a new GM distributor complete with cap, rotor and sensor for $69.99. I now see that these tabs being broken allowed the cap to slightly twist or even rock a little when installed. I have ordered a new ACDelco injection kit, got lucky and picked one up for only $225 with Bracket. I purchased new plug wires and a MAP sensor only because the old one broke as I was removing it from the upper intake plenum. The only thing left is to install everything once the parts arrive and we will see where I'm at.
Kyle, you indicated previously to have the coil load tested. I have checked with my local O'Reilly's and Advance auto and they can not perform this test. Who or how can this be completed?

 

The local Autozone, Napa, and Advance Auto can all do the coil and ICM load tests. It is dependent on the store though.

 

Here’s a Quick update. The last of the parts arrived on Saturday due to the holiday. I installed the lower intake a few days ago after having to make a run back to the parts store to upgrade the lower intake gaskets after reading about the improved Fel=Pro gasket on a different thread here. I installed the new ACDelco Fuel injection, the new GM Distributor, a new MAP sensor and new plug wires. She seems to run like a champ now and I can definitely tell the difference with the new Fuel Injectors. Well worth the $225 I paid for them. Total bill wasn’t too bad, $537 in new parts and I added a few new tools to the cabinet at $280 dollars and the truck runs great. Thanks for your help.

I have attached a photo of the cleaned lower intake. I’m only doing this to maybe help someone else out. Not wanting to use flammable spray cleaners it the garage with the furnace running I came up with a different solution for cleaning all the carbon. The wife a while back had bought me “Dawn Power Dissolver” for cleaning the baked on grease build-up on the deep fat fryer. This made cleaning the intake very easy. I ended up bringing the intake in the house and cleaning it in the sink. You spray on the Dissolver and let in sit for 1 – 2 hours, and then I used a tooth brush for some light scrubbing and rinse with Hot water using the sink sprayer. This proved to work very well for the runners as all you had to do was get the chemical in there and it did the rest. As long as you had patience and let it do its thing this was very easy. I ended up using an entire bottle as the really thick hard crusted areas took a couple of treatments but at $2.62 a bottle from Walmart this was a very cheap and easy clean up.

 

How did you get the lower portion so clean?I can see the top but how did you do it for the bottom?Im about ready to do that myself.I hope it works.