Very Rough Idle and P0300
 

So, to preface, I have looked through every thread I can find that have the same issues and I am at a complete loss. I have been chasing an intermittent misfire and a extremely rough idle (hot and cold) for about 3 months now. I have a 1998 Blazer LS 4x4 2 door with (from what I have been told) a 2001 engine. I have replaced the following items in this order:
Fuel Filter
EGR and EGR tube
Upstream O2 sensors
Distributor Cap & Rotor
Crank shaft position sensor (successfully performed relearn with my iLink400)
Plug wires
Plugs (correct AC Delcos)
Updated to MFI fuel injector

I have been able to confirm:
-Correct/Good fuel pressure
-MAF Sensor working properly

Full story:
It all started with the rough idle and power loss. Power loss was complete and total power loss (engine cut off) while accelerating to high way speed (full throttle), issue seemed to be fuel related so I replaced the fuel filter and haven't had the issue since. To add: it had sat before I bought it so it also could have been old fuel. Next, I was able to determine I had improperly functioning O2 sensor (B1S1 from a code). So I replaced both upstream sensors. The rough idle persisted. At the time the only codes I was getting was for the EGR. Checked it and it seemed fine. Turned out the EGR tube was cut out and crimped closed, so replaced hose and code left. Now is when I start to get the misfire code. It started as just a P0300. After some investigating I noticed a screw was missing from the distributor cap so replaced cap and rotor; no change. Next I did the Crank shaft position sensor but did not know it needed to be relearned until recently (so it was driven without being done so for maybe 50 or so miles more on that later). Now after doing so I started to get a P0306, great I thought, isolating the issue! I decided that this was a good time to do plugs and wires. Did them, greased them, and torqued to spec. Before this, there was an actual noticiable miss that could be heard as the engine idled but now I was back to the P0300, still rough idle, but no misfire. Other than the rough idle the engine seemed to be running fine with no misses (still seems to be as of writing). I read this article and decided to update to the new version of the spider injector. ISSUE PERSISTS. This is when I learned on here that the crankshaft position sensor needed to be learned. Ordered a iLink400 as it was recommended on here, is generally inexpensive, and could perform the task. Completed the relearn and STILL get the P0300 code and crazy rough idle.

If you have read this far... thank you. I have spent hours reading into this issue and way too much money on this piece of junk. I did buy the vehicle knowing it had issues because I wanted to learn more about engines/how cars work. If anyone could point me in a direction of where to go next I would greatly appreciate it. I really want to defeat this thing...

Should be able to trigger the PCM to do a cylinder balance test with the I-link 400. Report results. Also check cam sensor retard and report results.

If we don't find something here quickly, probably should go back to basics and do both a cranking and a running compression test. If done correctly it should definitively eliminate any mechanical problems with the engine.

https://support.alldata.com/article/...pression-tests

LES! Thank you so much for your reply! :D
I'm struggling with the iLink400 in performing those tasks... I am not all too sure it is capable...

I'll pull my Ilink400 out tomorrow sometime and see what you need to do to get there. Until then,....

CMP Retard can be found in "Engine Data 1" of the GM PIDs (assume you downloaded the GM PIDs from the I-link website and installed them).

Cylinder Power Balance is found in the "Fuel" section of the GM PIDs. Doesn't seem to be a complete canned program like I am remembering to check/compare all automatically (like in my HP Tuners software), but you can disable each injector (cylinder) one by one to evaluate if it makes a difference in how the vehicle runs. Least difference with injector disabled = cylinder missing the most (contributing the least). To get scanner into the mode you have to press emergency brake just enough to turn the IC brake light on, and then hold the brake pedal down while starting the vehicle and hold it there. Turn the key on but don't start the vehicle until the second time it tells you to do so. I found I could feel the shorted cylinders much better from about 2000 rpm, but that will defeat the purpose of the test at idle - better to test at both RPMs. I do believe the IAC motor remains locked during the test. You can see the IAC counts in the display if you scroll to them. If you want to check rpm drop from a steady 2000 rpm or higher, you can adjust the depth of a small flat screwdriver blade with the wedge of the tip in between the throttle stop and throttle arm - and that should hold RPMs steady.

I'm looking for hard data - cylinder/rpm with each injector disabled compared to no injector disabled - at idle and at 2000. Also CMP Retard in degrees (positive or negative).

Good luck


https://cimg4.ibsrv.net/gimg/blazerf...45de483f16.jpg
https://cimg5.ibsrv.net/gimg/blazerf...26471dae0b.jpg

Looks like I lost him. Hasn't been back since his last post. Oh well, have better things to do with my weekend.

Les, my apologies. Your input is extremely valued. I am an active duty military member, father, and full time student. Unfortunately my ability to work on the vehicle and access the forum is late nights and weekends time permitting. I hope to dive into your very thorough advice this weekend. Hopefully I can become more familiar with the ilink. Again, my apologies and thanks.

OK. Thanks for your service. We can go at whatever speed you want. But are you sure you really have time to work on it? These diagnostic procedures can get pretty lenghty.

Perfect. Thank you for you support. I can definitely make the time. I bought the blazer to learn more about engines, so its not a chore for me. I plan to spend a good part of a day over the long weekend diagnosing from what you've suggested.

To prepare; I was looking over your instructions and it seems that your ilink interface looks different than what I have experienced when using mine (it is possible that I am not accessing the correct functions). Here is everything currently installed to my tool:
https://cimg5.ibsrv.net/gimg/blazerf...cbc221bf15.png
Does this seem to be everything I need or am I missing the PIDs? If so could you help me find the link on the vident site? Having trouble finding any downloads on their site in regards to PIDs/any software really. If needed I can get pictures of my ilink specifically tomorrow.

Again, thanks so much for your help.

AFAIK that looks right. Its been a while since I did this update on mine. FYI on the Ilink400 screen i started by selecting the GM icon (not OBD2 icon). If we can't otherwise resolve things i will post a video of how to get there on the scanner but I prefer not to have to do that.