Hello All,

I've got a 2002 Chevy Blazer 4.3 W motor. First let me start off by saying a few things; I Have read all of the P0300 posts/forums, some of the stuff I already tried already, and the other diag steps I did try. Also, I was a GM tech for a number of years in this time period, so I am fairly familiar with these nightmares. However, I had access to the Tech II back then, don't now. All I Have now is a basic code puller, and limited access to a live data scanner.

Symptoms: Very rough idle, flashing check engine light, serious shake and hesitation off the line. P0300, nothing else. Smooths out under higher rpm's, and while driving. Coming to a stop, she feels like she is going to die. Engine Oil Pressure drops to 20 under this rough idle condition while hot. Cold oil pressure at 40+

That being said, This thing is throwing the dreaded P0300 nightmare. I Have run through the following;

Plugs, wires, cap rotor. Inspected old plugs, nothing worth mentioning. NO arcing on the cap/rotor, and cleared the vent tube.

Checked for vacuum leaks with carb cleaner, visual inspections, and nothing found.

Did a fuel pressure check 58-60 KOEO. Leak down test fails and drops to around 30 after 10 minutes. Running it was around 60. Tested at the rail, suspected FPR, changed, new plenum gasket, TB gasket, etc. FP gauge I rented is broken now, so waiting on another one to re-test.

Changed fuel filter, it was dirty and clogged.

Had limited access to a friends el-cheapo live data scanner. Looked at the LTFT and STFT - results;

Everything else was +/- 9% except Bank 2 I believe on STFT which was about -25-29% in closed loop.

ECT read: 196F when it was warmed up.

02 Sensors:

Up stream: MV small steady fluctuation indicating it was working
Down Stream: Fast Fluctuation. Indicating the cat was doing it's job and the sensor is ok.

TPS: Here's where it gets weird. While it was missing bad at idle in park, the TPS read 0%. Snap throttle to about 80%. While the engine was running, I unplugged it, plugged it back in, and it read it was at 15%. Shut the truck off, dc scanner, start it back up, and even at KOEO said it was at 15.3% - Snap throttle, on return stays at 15.3%. Reset ECM goes back to 0% --. Unplugging when car running, no change in misfire condition. No change in engine speed, or sound. However sometimes if you plug it back in when the engine is running and snap the throttle, the engine rpm stays at 3,000. Gotta shut the truck off. Odd I think.

IAC seemed to be within normal limits, removed, inspected and cleaned anyway. - No change.

MAF (can't recall the readings, but I seem to remember it was at 25 G). Unplug test, nothing changes, no change in RPM, engine idle, nothing. I cleaned it anyway, but much like the TPS, no changes seems odd to me.

The exhaust feels like its got some back pressure issues, like a clogged cat but the 02 readings seemed to be fine, so I am still not sure about this. I might pop out the upstream 02 tomorrow to see if this makes any change.

Also worth mentioning, while after I changed the FPR, I had my fiance crank the engine (coil DC) and pulled each of the spider injectors. This truck already has the MPI upgrade, so no poppets. Each injector pulsed and spit out a little fuel. IT wasn't a fine mist, it was like a shot, and this happened on multiple revolutions. I don't know if this is normal, or if it should be like a normal injector and spray a mist?

I don't see signs of a head gasket issue, no oil in water, or water in oil. When I pulled the plenum, it didn't appear that anything was leaking fuel wise. I Haven't run a compression check on it, because I think if it were a valve/cylinder issue, it would also throw a code up for that misfire on that cylinder. Which it isn't, just 300. I wish I had access to find the Misfire counts on each cylinder, then maybe I would have a better idea of where to start narrowing things down.

I also checked the distributor for play, nothing out of the ordinary normal play for a helical gear, such as this. SWaped out coil and Ignition Module. No change.

Any help would be appreciated. I am working on buying a scan tool, because this is like peeing in the wind at this point. If I am missing something, please feel free to point it out.

Thanks!

 

MAF reading should be 4-5g/s at idle.
Get another fuel pressure and leakdown reading.
Bank 2 is running rich. Any exhaust leaks on that side? Was the bank 2 02 sensor fluctuating from 0.1 to 0.8 volts at idle?

 

What make of plugs did you use?
The only ones that really work are A/C Delco as others just seem to break down and cause a misfire.

 

I thought the MAF was high, but lacking any scopes, I couldn't be 100% sure, But that would really cause a P0300?

I am hoping to just buy another FP tester tomorrow. 2 now from autozone are busted. Thanks to the last renters for not cleaning it and allowing the rubber to swell. I will do that and post back.

I didn't see, hear or feel any exhaust leaks.

AS for the 02 on B2, I will have to get that scan tool and check again. I think it was, but can't recall for sure. I remember that it didn't look abnormal.

 

Delco Double Plats. There were iridium ones in there when I picked it up.

 

Have you put an in-line spark plug tester between the plug and lead to make sure that you have got the correct spark and that your not just relaying on the fact that they were new.

 

I Haven't, but I will do that today. I did short the coil lead out to be sure there was strong spark from the coil to the Dist. The old screw driver trick. Spark was blue, was strong.

I'm going to to go pick up a spark tester today. Apparently someone liked the one in my box better than me, and I couldn't find it the other day.

 

Update:

FP leak down test: KOEO 53-54 psi.

10 Minutes key off: 48.5 psi

Running bounces (jittery) between 56-59

 

Visual Inspection Injector Assembly

 

Burned, thanks for the responses thus far.

I have been messing with this thing most of the day. When I suspected the fuel system leak down was an issue with the FPR or assembly, I pulled the plenum like in the link you provided, and visually inspected the intake for leaks. I Had my fiance turn the key on/off a few times as I looked for any gas leaks, etc. I didn't see any. I still replaced the regulator while I was in there.

The Fuel Pressure test today looks within the 5PSI leak down limits on the 10 minute mark. Unless I am mistaken on limits.

IN further looking at that website you linked, I haven't tried a cylinder balance test on the cap. But if memory serves me correctly, wouldn't that throw a P0301 (for cylinder 1) misfire if indeed it was just 1 cylinder misfiring, and not the 300 code I have now?

Also, I have access to that live data scanner again today. I was mistaken in my original post about the MAF readings. They are 5-6 G. Did a wiggle test on the harness too.

Short of doing the power balance test, and subsequent compression tests, I am at a loss.

02 sensors are still reading good. Pulled one before the cat on the pass side bank, just to make sure the cat wasn't stuffed up.

The -25% STFT was actually bank 1, not bank 2 when I first posted.

I have this scanner for a few days if there is any specific values you would like for me to record and post. Please let me know.