agent00kevin

Hai Yall

Ahhh where to start...

I guess at the beginning huh?

Ok, so one day, which was alll the way back on 9-11-2012, I decided to change my fuel filter, as preventative maintanence. The truck was fine, no CEL, no problems with it. I just figured since I had recently rolled over 100k miles, and had driven it 16k of those myself, I might go ahead and change it out. Couldnt hurt, right?

Wrong.

I couldnt get the nut off first, so I soaked it several times with PB Blaster, my favorite penetrating oil. Still no go, and I would up rounding it off pretty badly in my multiple attempts. I figured well, there no problem, so Ill just leave it on for now and change her out later.

Unfortunately, now there was a problem. I started the truck up and it idled horribly, sounding like it was missing out on a cylinder. I didnt have a scan tool, so I assumed that when I was down there cranking and beating around on the fuel filter, I had rattled some junk loose and/or plugged up the filter. So I went a bought a section of repair line, used a compression union, and replaced the pipe, filter still attached to it and all. Now I have my new filter on, yay!

But wait - dont party just yet agent00kevin.

I still have the miss! Nothing has changed! OMGWTF!

So I verfied the lines were on correctly, no leaks, and it was good. Hmmm so what now? I went to the injectors, thinking maybe something funky had gotten out of the filter, past the regulator and into an injector. I just bought 4 new BWG ones, not remans - new. Installed them and waited to hear her purr.

NOPE.

Ok ok, not the filter, not the injectors, but its got to be a fuel problem, right? I mean it didnt happen until I jacked around with the filter.

So I broke down and bought a cheap scantool, that just gives me the codes and turns me loose. I got a p0303 to start, so I cleaned the plugs, then swapped out my Accel Super Coil for a stock one I still had - known to be good last I used it. Still the problem, but no p0303 any more.

After installing tghe new injectors the problem was there but much less noticeable. Before, the SES light would come on and eventually start blinking at me in death mode. After installing new injectors, no SES light most of the time but codes are stored.

I had a p0172 now, with an occasional p0301. Pulled the plugs again; black sooty velvety coating. (just on plug #1, and #3 the first time around)

Running rich, I went and got a fuel pressure regulator and a TPS sensor. Still no dice - but now its the fun part.

Im getting a p0300 now consistently, though it doesnt illuminate the SES light. The p0172 has cropped up once but that is out of probably 20 tests by now.

It idles better with a new Accel Coil pack (returned the 2,3 coil pack because I thought that was it) BUT I can still hear a slight putter put in the exhaust note. It still wont illuminate the SES light, but it will give me a p0300 code when I scan it.

It runs fine at idle besides the light putt - but much much better than when I started.

After a few minutes it will start choking itself when I tap the throttle. If I do it manually from under the hood, I can kill the engine by ever so slightly opening the throttle. Not every time, but some times - the rest of the time it will stumble, choke and then rev up, sounding great when it finally revvs up. I run the scantool again, pulling a p0300 consistently. I clear the code, start her back up, and she revs fine again for a few minutes. I can shut her off when its revving normally (outside of that slight but perceptible putter put from the exhaust) and I wont get any codes.

It doesnt seem to be related to engine temp; because I can clear the codes and immediately restart the engine at full operating temp and its fine. It seems to be time that it needs to stumble, not temp. I initailly thought somehow I screwed something up when installing the new injectors, as easy as that is - but it doesnt always choke itself. Just after a few minutes of running. - Do the injectors have to face a certain direction? I installed them at the same angle as the retaining bracket's slots. I think they were facing forward (the harness/plugs that is) and now they are not. Maybe one or all of them are not properly aligned? The problem was present before, but worse than it is now. (Thats why I dont think its the injectors)

Im down to running a fuel pressure check and a compression check. Im also tempted to replace all the plugs because they are Autolites and I hear GM trucks do not like them. (that and the cost is minimal in comparasin to the $500+ Ive already spent) I had no problems with them before though.

The Breakdown:

New Parts:

Fuel Filter
Coil Packs (One New, One a couple months old, also tested with stock Coil packs - problem persists)
Plug Wires (about 2 months old - no arcing visible)
Plugs - also about 2 months old, cleaned, regapped, reinstalled
Injectors - BWG - NEW, not Remans - 2 days old
Fuel Pressure Regulator - New today
TPS Sensor - New Today

Lastly, I dont rule out bad gas. I had just filled up about 5 miles from home that day. How would I test for that?

agent00kevin

Forgot - 1997 S10, 2.2L

kevinkpk

You're throwing parts at it. You should also compress what you've done. I cannot spend the time trying to diagnose you're post as it is too long with non essential information.
Now, this problem started with just replacing the fuel filter?
If that is all, and you have a misfire with black electrodes on two plugs, it is misfire, and you should feel it.
My take is as you suggest gasolene, but it more than likley is in the injectors. Add a good injector cleaner to your gas tank. Thats for starters, good luck!

agent00kevin

It describes the entire process I went through, which I thought might be relevant. Especially the part where I got to the codes and when they occur, and what happens after I clear them. I think that stuff is very relevant since it details an entire diagnosis process.

I have brand new injectors, which seemed to help but not completely solve the problem. The bottom of the post breaks down in a list what I have replaced already for those who dont want to take the time to read the entire diagnosis/testing process. I find it highly unlikely that the brand new injectors are clogged or dirty. I would find it possible that they are facing the wrong direction. But dirty/clogged? Doubtful. I do think its bad gas because it seems to take time, and it immediately goes away after clearing the codes. I think the LTFT is going up and up and up to try and compensate for poor fuel, but it just cant because the fuel is bad. I could easily be wrong, but if anyone thinks that makes sense, please speak up

* I cannot feel the misfire until the sputtering starts, but I can hear it.
* Once the sputter starts, I can feel and hear it. It also sounds like the throttle body is sucking much more air than normal - this is when it can be killed by hand under the hood
* Most of the time it wont throw a p0300 before the sputter, which seems to take about 5 min to start. Once it sputters, it gives the p0300. Again, it takes 5-10 minutes for this to happen.
* The injectors, FPR, TPS Sensor, and fuel filter are all new
* The problem was immediate - not one sign of problems until I filled up the tank and then changed the fuel filter.

I would, however, say that going out and buying a can of injector cleaner after installing brand new injectors would be throwing 'parts' at it. Who buys a can of injector cleaner to run though brand new injectors? Aside from that, who wants to run their car while misfiring? That can cause CAT damage, ruin o2 sensors, or worse, cause internal engine damage.

While I appreciate your help, I think that skipping an entire diagnosis process and telling me to go buy injector cleaner (for brand new injectors) isn't the type of advice I am looking for. Im more looking for someone who can take the time to use all of the information I posted to help.

agent00kevin

And for those who dont like reading long posts:

Started after replacing fuel filter and filling up gas tank
No SES light, still p0300
Replaced injectors, TPS, FPR, Fuel Filter - which resolved several other codes w SES light
Runs fine for 5-10 minutes, then will choke when applying throttle
Can clear codes and runs fine even if warmed up for another 5-10 min, then will revert to what feels like 'flooding' the engine
Occasional p0172 code, 1/5 tests now IF that much - no longer a prevalent code
No other codes, no SES light
No apparent issues prior to gas fillup/new fuel filter, but did not have a scantool before then. Codes may have been stored previously without illuminating SES light.

My opinion: Most important factor is that the engine will run great after clearing the codes, even when fully warmed up to operating temp. Revs fine without bogging down/stuittering but can still hear a slight misfire in the exhaust note.

Edit: Also noticed as I was testing the exhaust was puffing a very light bit of steam until I revved it up. Every time I let it back down to idle, it puffed steam. I dont say smoke because it wasnt thick enough to really be called smoke - but it was definitely present. When revved above idle there was no steam.

Also, I unplugged the O2 sensor on the downpipe and she ran fine for the test period. This is why i suspect fuel - because the o2 sensor is no longer detecting a lean condition and telling the injectors to add more and more fuel to try and compensate. Tomorrow Ill pump some gas out into a clear glass jar and see what happens. I'll report back with my findings!

agent00kevin

Eliminated the possibility of bad gas. Drained 12 gallons and refilled with V-Power. Still starts to hesitate and sputter after it runs for a few minutes. Also put new plugs in. Clear the codes and restart it immediately and its fine.

I unplugged the O2 sensor again at the downpipe and will let it run for a while to see if thats the problem. Next Ill unbolt the muffler and see if its stopped up, then the CAT and see if its somehow plugged - though it has about 14k miles on it, and it should be fine.

I dont think the o2 sensor after the CAT has anything to do with the fuel trim so for now Ill leave it alone.


Still throwing a no check engine light p0300.

kevinkpk

try another fuel filter. If you had crappy gas, you could have contaminated the new one.

agent00kevin

I left the O2 sensor unplugged and the problem does not reoccur. I installed a new O2 sensor and the problem came back - until I unplugged it. After clearing the codes and leaving it unplugged, it was fine.

So logic would tell me that the O2 sensor is detecting a lean condition and the PCM is adding more fuel when there is no lean condition, resulting in the LTFT going up until it is too rich to run properly.

*sigh* I might have to take this one to a shop. Ive done about everything I can for it. If leaving the sensor unplugged doesnt hurt my economy or make the SES light come on Ill leave it unplugged and see how it drives for a day or two.

kevinkpk

The upstream cat O2 has an equation into fuel scedule. Can you have the cat checked for obstruction i.e. plugged?

agent00kevin

Yeah, Ill probably pull it myself. I just put a new one on about 14k miles ago; shortly after I bought the truck. It had 84k on it then; now it has 102k. Ill go spary it down with some PB Blaster and hope the nuts and bolts havent rusted into place yet.

I get no misfire codes at all if I leave it unplugged, so its got to be something to do with it causing the problem. Ive also got a leak somewhere in the exhaust manifold/downpie as I can hear it but I cannot feel it anywhere. Maybe its sucking air and the O2 sensor is reading it, thinking it is coming from the cylinders.

Off PB Blast the bolts and hope they come off fairly easy