My Po300 thread

[Crazyjoker77]

Okay i think ive read pretty much every post on the internet about Po300 but still have not come to any conclusions on what is causing mine. My mods are in my profile.

The Symtoms

-when i start the car up first thing in the morning it fires up right away but will stall out completely after a lil while (30sec to 2min)(as well it idles high and pull about 18"hg which seems normal.)

-when im driving it it will backfire and stall out. the wierd thing is that it is completely random when it happens although tends to happen more at steady state cruising.(if the car is still in gear it will start up right away and act like nothing happened if the clutch is in when it happens the car stalls out completely and i either have to pop the clutch or crank the starter. and she fires right back up.)

-at idle it usually idles right at 850rpm but sometimes will drop to 750-790 and my gauge will read 15"hg as well the motor sounds very lopey as if i had cams. If the car is idleing at 850 and i step on the brakes hard my vacuum will suck down to 15" and the idle will drop down and stay there till i rev it alittle bit then it will resume its proper idle.(although it could possible be the other way around my rpms fall causing low vacuum instead of my vacuum causing low idle?)

-as well the cars performance is very inconsistent sometimes it will pull very hard at the slighest throttle other times it feels as if timing is being retarded. also the rpm at which my turbo spools also seems pretty inconsistent.

What I've done

-new plugs ngk br7es gapped at .28
-wires are new oem with less than 10k on them
-coil packs all test within spec (primary and secondary)
-pulled ecu to check for leaky caps
-checked coils on ISC

Other notes
-mabey every 40 or so backfires the code Po300 will pop up i clear it immediatly with my logger.

-I also sometimes will get the code for my FP solenoid if i turn my car off for 5min or so then start it back up but the thing is i have the solenoid bypasses and just have in sitting on the firewall with the connector still on(although ive only gotten this code once since ive bypassed it)

-and yesturday while i was letting my car warm up idleing i came back and had a code for misfire cylinder 3. (first time ever seeing that code and hasnt come back since)


i did do a boost leak test from my lower IC pipe. During which i found some intersting things.

-First off my GM mas was leaking slightly from between the metal housing and the plastic case on the upstream side.(not audible but when sprayed with soapy water it bubbled)

-i had another leak from the top of my blitz BOV from the adjustment screw(which i assume is a vacuum leak as well since its on top of the diaphram) I replaced mine with a friends brand new blitz and his leaks just as bad as mine does...

-the third leak is from my FPR right from where the top half meets the bottom half(again not audible but forms bubbles)

even with these leaks my test performed good i would pressurize it to 25psi
it would bleed down to 18 in about 12sec
bleed down to 10 in another 12-15seconds
then it would hold 9-10psi indefinatly...
which i believe are fairly good results especially considering i still have some small leaks.


-I've ordered a few things that im waiting on arriving which include a wideband o2, a aeromotive FPR with gauge and a egr blockoff so i can remove most of the vacuum lines in my engine bay.

Questions

1)Im going to check the timing is all i have to do is pull the upper cover off and turn the motor till the timing marks line up or do i also have to remove the lower cover and check to make sure the crank is lined up as well?

 

[Artago]

well a little update been driving the car and it actually seemed to be getting better to the point where it would never backfire or stall out anymore(except if i tried to drive the motor cold)

BUT yesterday I was cruising and got on it pretty hard in first gear to get ahead of a truck from a set of lights so i could turn left at the next set of lights a half block down. got to the set of lights and as i went to take off the motor just shut down. I attempted to start it for probably 3mins just cranking sometimes it would kinda fire up but die out almost immediately. just as the light turned yellow the car fired up and i pulled out of the intersection parked immediately and left the car running and poped the hood.

As soon as i got out of my car i smelled a rather strong odour that smelled very much like burnt clutch (although it could of very well been the diesle fumes from the truck that stomped on it since i pulled in front of him then sat in the intersection for 3min trying to start my car) the smell dissipated rather quickly. while quickly inspecting it on the side of the road nothing looked out of the ordinary nor did it make any funny sounds.

Although at the time it seemed as if my harmonic balancer/crank pulley had some play in it. I babied the car home and had no issues on the drive there which was about 5km. got it back to my house and looked at the crank pulley from underneath and couldnt notice any play.

Decided to do a oil change on it today and pull off the splash shields so i could get a good look at the harmonic balancer and see if the rubber part has started to seperate. It looked very healthy to me and seemed to have no play in it. The oil came out normal and didnt have anything in it to concern me.

Now im getting very confused as to what the hell is happening with my car...

only things i still have to check are
-Crank position sensor
-Fuel filter
-Tune(somewhat o2 trims are accurate and wideband is reading pretty close to what it should)
-front o2 sensor(while i am getting a reading from it i am doubting the accuracy of it and if this is off my fuel trims will be off and therefore causing my tune to be way off)


only other thing i would like to bring to everyones attention is that i had a issue very similair about 6-7k miles ago where i gunned it down a valley coasted for a little bit in neutral as soon as i put it back in gear and loaded up the engine the engine shut down exactly like it did the other day at the intersection. Except that when it happened going back up the hill i could not get it to start back up and had to have it towed to a shop. The shop found that my crank Sprocket had worn the little notch (keyway) almost 2.5x the size it should of been. I seen the sprocket for myself and it was in horrible condition. this sproket being loose gave it enough play for the backing plate to chew up the crank position sensor. Im just a little concerned that this may be the case again but am a little concerned at what would be causing this sprocket to wear?(hopefully not crankwalk as its a 7bolt motor from overbore.com that ive put less that 20k miles on yet.


Also Artago did you find out anything more about the leaky FPR i noticed you put that post in most of the Po300 threads.

Sorry for the long post but i just want to get this damn car reliable again.

Hey, I haven't done anything with the leaky FPR yet but my car is off the road while I send me V-Trim back to Bullseye Power. It has a bunch of shaft play and it's still under warranty. I was thinking of checking my timing cause the shop did it and I don't trust them. My car will be off the road for the next 2-3 weeks so I'll post back when I get it up and running again.

Tom

 

[Crazyjoker77]

well just a little update my i drove my car to work this morning and on the wayit threw one po300 just as i was almost at work it would surge sometimes and i got a po301 that would come back every couple of minutes. when the CEL would come on the car would buck/surge then go back to normal. I'm still awaiting my NGK wires but would still like some other recomendations

 

[Artago]

well just a little update my i drove my car to work this morning and on the wayit threw one po300 just as i was almost at work it would surge sometimes and i got a po301 that would come back every couple of minutes. when the CEL would come on the car would buck/surge then go back to normal. I'm still awaiting my NGK wires but would still like some other recomendations

Hmm.. see that's strange. Mine doesn't really buck. I can feel it misfire under decel only, but it doesn't buck. I just feel the misfire through the steering wheel.

Anyways, my turbo is still out... while it's out I'm going to be rebuilding the TB to fix a TB shaft leak. Once I get it all back together I'll know more. Catch up with you in a few weeks.

Tom

 

[Crazyjoker77]

just another little update got 2 po300 on the way home within a period of less than a min. po301 never showed up again...

Im starting to think i've got seperate problems as really each code has different symptoms.

when the po300 pops up which is when im usually just cruising around 3000rpm (+/- 500rpm) the CEL comes on my exhaust note changes (kinda sounds muffled) and the car loses all power and if i put the clutch in and let the rpms drop down to idle as soon as i let the clutch out all is good and i clear the code and continue on my marry way.

when i was getting the po301 this morning (first time ive seen this code) it was happening when the car would do its little backfire and the car would kind of cut out more than buck. I mean the rpms would drop a couple hundred or so for a split second then everything will go back to normal. I can usually tell when it is going to backfire as the car builds boost a bit slower and just kinda feels sluggish then it will backfire and it will go back to being fast. Also this usually happens as soon as i ease on the accelerator after having my foot off it for a little bit or while im cruising it never happens while im idling/decelerating.

 

[Artago]

The question is why? What's causing all this? All the pieces are there, just gotta put it all together.