2002 Chevy s10 Blazer P0300 - Stumped.
 

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!:icon_wheel:

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

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.

OK so here's the deal with watching the STFT on both banks as well as the 02 sensors.

P0300 set; Closed loop.

Under idle:
STFT1 is -30%
STFT2 is -8%

O2:

B1S1 .060 - .800
B2S1 .060 - .800


2500 RPM in Park

STFT1 is -7% - +7%
STFT2 is -7% - +7%

Can you do the fuel trim test with the MAF unplugged. At idle, 1500 rpm and then 2500 rpm?

Just to make sure I am reading that right.

Bank 1 is -30% fuel trim reading not +30%

If your getting -30% then the possibilities are leaking injectors, O2 sensor problem bank 1, exhaust leak before 02 that side, low compression or a FPR that is leaking to that side.

What was the LTFT bank 1?

I was thinking MAF but that would affect both banks.

I will do this this afternoon and report back. I did swap a brand new MAF Yesterday, but no change. I need to go fire a new cat in the 95 I Just fixed with this same issue. Cap/rotor/plugs/wires and spider assembly. Sold.

Yeah you are reading that right it's Negative 25-30. I suspect an O2 as well, as it seemed to be moving slowly. If I am not mistaken, bank 1 is the side where cylinder number 1 is, right?

Okay, I did the test with the maf unplugged as you asked;

Results:

@IDLE:

STFT1: -30.5%
LTFT1: -10.9%

STFT2: -25%
LTFT2: -10.9%


@1500 RPM

STFT1: -9.4 to -18.0%
LTFT1: -14.8%

STFT2: -1.6 to -10.2%
LTFT2: -1.6%


@2500 RPM

STFT1: -6.3 to -21.9%
LTFT1: -7.8%

STFT2: +0.8 to -5.5%
LTFT2: 0.0%


I did notice that maf plugged in or unplugged the O2B1S1 V moves really slow, while O2B2S1 moves very fast with the voltage variances. O2B1S2 (after Cat) moves slow, within limits.

I think the slow moving B1S1 is bad. But would this cause my P0300 code? I don't know for sure. I could say (from my memory) that a slow upstream O2 being sluggish perhaps tells the PCM that that bank is running lean, so the PCM adds more fuel? THis would make sense of my screwed up Negative STFT values on B1, right?

Yeah replace the 02 sensor. They are supposed to cycle fast .1 to .8 constantly at idle. Heat is your best tool for removing the sensor.

The PCM is thinking its running rich, thus taking away fuel, making bank 1 (drivers side, cyl #1 side) run lean. Negative fuel trim. A positive fuel trim means the PCM is adding fuel.
Its easier to see what the 02 sensor is doing if you graph it.

Do you think that O2 has anything to do with the P0300?

you could have a bad cam sensor. just had to do mine. your better off replacing the whole dizzy instead of just the sensor the bushing can go bad inside the dizzy throwing off the cam sensor

I meant to update this post. Thanks to Burned for helping me via PM.

Hooked up a live data scanner, saw my STFT1 was -25%! Watched the 02's and sure enough the upstream on bank 1 was moving very slow and pinned out around .800mv. I changed that 02, and now while its moving faster, it's not moving as fast as 02B2S1.

Upon further investigation, I did a spark check all around. All was well.

I knew my problem has to be on the Bank 1 side, since STFT1 was so damn high. IT only went positive when I induced a large vacuum leak at the PCV port. "She's not breathing right" I thought.

Hooked up a vacuum gauge and it was reading between 5 and 15 with erratic jumping at idle. Snap throttle to 2500 RPM and rapid decel shows it goes to 0 at snap, on decel goes to like 30, then back to 5-15 with the rapid erratic jumping.

Did a compression test and;

Cylinder 5: 150 PSI
Cylinder 3: 0 PSI
Cylinder 1: 150 PSI

Cylinder 2: 150 PSI
Cylinder 4: 152 PSI
Cylinder 6: 155 PSI


On cylinder 3 I pumped some motor oil in there to do a wet compression test. It didn't rise at all, still 0 PSI. I suspect valve train issues. I am going to pull the valve cover tomorrow, then probably the head. A brand new Surefire head is only $200 my cost through commercial at auto zone. I'm thinking the new head is the route to go, so long as the cylinder on #3 isn't also damaged.

So I have taken off the Bank 1 head. That wasn't enjoyable!

Isolated the no compression on #3;

https://i.imgur.com/36FiA4N.jpg



https://i.imgur.com/lBx5p1Q.jpg

Installation Guide:
Installing The Cylinder Heads

Nice guide! Thank You!

Might want to recheck fuel pressure and leakdown after you get it back together. Both of your results are low. KOEO, fuel pump running needs to be 60psi to 66psi and it must remain above 55psi for at least 10 minutes after the pump shuts off. Don't worry about engine running pressure, GM does not publish any engine running pressures for this system.

Thanks Hook. Will do when she's running tomorrow. Head is on, full 150 PSI on compression check now on 1,3, and 5.

Gotta finish hooking up the flange for the Y pipe tomorrow, put the belt on, re-install steering shaft, cap/wires, and she should be going strong.

They really don't make that drivers side head easy to do the torque degree with eh? Had a hell of a time getting that thing done.

I am not sure why I didnt do a compression check after the fuel pressure check. Thinking the 300 is usually secondary ignition really threw me for a loop. I was a GM tech for a number of years. I suppose i'm getting old :-)

She's running like a top today. Only thing that came up was P1345. Going to redo the distributor tomorrow. I know I am at least one tooth off. I marked it, but I have taken that thing out twice in the last week, and I forgot what marks where what :-(.

Should be easy enough. TDC #1 on Compression. Check Balancer for line to be at the V mark. Make sure the dist. is lined up right, slide in, and should be at the #6 imprinted on the dist plate.


Quick question, well 2 really;

1. These screw holes for the caps are junk on these distributors. Anyone know a fix for this? Should I drill them out a small bit and use a bigger screw, or what?

2. Oil pressure hot at idle? Gauge seems a little low (had this before I fixed with it) doesn't knock or anything, but it's below 40. But it rises while driving, etc. Also a little over 40 when the engine is cold.

No "V" mark, both lines need to be positioned like this:

Attachment 31565

As for the distributor cap screw holes, an aluminum distributor will cure the problem once and for all. Skip White has them online at an excellent price, both on their website and Ebay.

Nevermind, I found the two marks.

First should be at the V and the second should be at what looks like 5 o'clock?

Yup, and if you rotate the crank by hand to line it up, make sure you only turn it clockwise, (never counter clockwise) then make sure the rotor is pointing at or near the "6" on the distributor, (they usually don't line up perfectly). Then pull the distributor and reset. Might have to turn the oil pump drive a bit to get the distributor to fall all the way in. Keep in mind that when aligning the marks, they will line up with #1 piston at TDC compression and TDC exhaust, that's why it's important to make sure the rotor is at least close to the "6" before you pull it, (not off 180 degrees).

Thanks for the help Hook. Did exactly this and she worked great. Purs like a kitten, and no more p1345!

She's finally ready for sale.

This forum is an invaluable resource!

Shinned her up today, and she's out on the road for sale!

Thanks again for all of your help guys. Slowly but surely my automotive diagnostics skills are starting to make a return.

:icon_beerchug:

Glad you got her going, thanks for posting back, and good luck selling her.