Random misfire at idle and can't figure out what's wrong
#11
08-05-2011, 04:06 PM
In the 3100 world the ONLY way you might see the EGR blockage is by removing the throttle body, most of the time there is a clump of crud sitting in that end of the passage way. But it's also possible the blockage is a tiny clump stuck somewhere in the passage that you won't see.
The way I've used to clear it was remove the EGR, using carb clean, spray that in the cast aluminum passage going to the upper intake. Use a large length of something easily flexible (I use about a 2ft section of old speedometer cable). Work that cable in and around, twisting and pushing until enough of it has gone tin that you KNOW it made it to the other side of the passage (I like to then spray more carb clean and run the cable back and forth).
It can be a real pain the first time you've done it (the cable I use sometimes won't go right through).
I just looked at a GM shop book for a 3400, if your crankshaft sensor was changed, they recommend a re-learn process. But not the case here (and requires a scan tool).
Looking at the rest of what's in the list on that manual that you have not done is:
Loose/Bad ground connection
Clean EGR Passage
MAF Sensor (I would start with the MAF sensor cleaner)
Crankshaft Position Sensor
PCM
The way I've used to clear it was remove the EGR, using carb clean, spray that in the cast aluminum passage going to the upper intake. Use a large length of something easily flexible (I use about a 2ft section of old speedometer cable). Work that cable in and around, twisting and pushing until enough of it has gone tin that you KNOW it made it to the other side of the passage (I like to then spray more carb clean and run the cable back and forth).
It can be a real pain the first time you've done it (the cable I use sometimes won't go right through).
I just looked at a GM shop book for a 3400, if your crankshaft sensor was changed, they recommend a re-learn process. But not the case here (and requires a scan tool).
Looking at the rest of what's in the list on that manual that you have not done is:
Loose/Bad ground connection
Clean EGR Passage
MAF Sensor (I would start with the MAF sensor cleaner)
Crankshaft Position Sensor
PCM
I was reading about the EGR operation and if my understanding is correct, the EGR valve should only be in operation above idle. That being said, I'm thinking that maybe the valve is opening up when it should and then not closing for whatever reason and that is causing the misfire. The only problem with this theory is that if the EGR valve is not in the proper commanded position, it should set a code for that which it isn't.
My roommate has a Buick Century or something like that with the 3.1L. I'm thinking I'll rob some parts off of that for trouble shooting purposes.
Thanks guys, keep the suggestions coming.
#12
08-05-2011, 04:49 PM
I just plugged my scanner in and here's what I got. The only thing that stands out to me is the highly negative fuel trims. What does that mean?
ABSLT TPS % 0.4
RPM 733
CALC LOAD % 2.7
MAF LB/M .61
MAP "HG 11.2
COOLANT 163F
IAT 95F
IGN ADV 22.O
ST FTRM1 % -7.8
LT FTRM1 % -21.9
VEH SPEED 0
FUEL SYS 1 CLSD
FUEL SYS 2 N/A
O2S11 (V) .610
ST FTRM11 % -7.8
O2S12 (V) .150
ABSLT TPS % 0.4
RPM 733
CALC LOAD % 2.7
MAF LB/M .61
MAP "HG 11.2
COOLANT 163F
IAT 95F
IGN ADV 22.O
ST FTRM1 % -7.8
LT FTRM1 % -21.9
VEH SPEED 0
FUEL SYS 1 CLSD
FUEL SYS 2 N/A
O2S11 (V) .610
ST FTRM11 % -7.8
O2S12 (V) .150
#13
08-05-2011, 06:24 PM
Join Date: Apr 2010
Location: Mentor, Ohio
Posts: 12,217
Unfortunately, the few times I collected data like what you got, I compared it to another similar car to see what is different. Right now, I don't have access to the snap-on scan tool OR my wife's Impala (3400 equipped).
As I said, I'm not an expert in these readings, but looking at the O2 sensor voltages, I believe O2S11 is in reference to the upstream O2. Does that number stay at that value? My gut is saying that is possibly the wrong value. If I can get the scan-tool and my wife's Impala together, I will gladly compare notes (that will probably be tomorrow).
Another thing that controls the fuel trims, as I understand, is data from the MAF. It is probably worth getting a can of the MAF cleaner and following their directions, see if it helps.
As I said, I'm not an expert in these readings, but looking at the O2 sensor voltages, I believe O2S11 is in reference to the upstream O2. Does that number stay at that value? My gut is saying that is possibly the wrong value. If I can get the scan-tool and my wife's Impala together, I will gladly compare notes (that will probably be tomorrow).
Another thing that controls the fuel trims, as I understand, is data from the MAF. It is probably worth getting a can of the MAF cleaner and following their directions, see if it helps.
#14
08-05-2011, 09:36 PM
Here follow these steps for the code. If there is something in the chart diag that you need then let me know I'll get it.
P0300 Diag
P0300 Diag
#15
08-06-2011, 09:57 AM
Thanks for the help guys. I actually compared these readings to my friend's '02 Buick Century with the 3.1 and those fuel trims were the only numbers that were significantly different. I was hoping maybe the MAF numbers would be different or something like that but they turned out to be almost identical. I think one of the laundry list of things I did was clean the MAF sensor but it was only a quick cleaning. I'll give it a more in depth cleaning today.
#16
08-06-2011, 10:11 AM
I may be way off base here but I don't think has anything to do with the MAF. I skimmed over the diag procedure and don't even think it's mentioned. Looks like mostly spark related.
Thanks for the help guys. I actually compared these readings to my friend's '02 Buick Century with the 3.1 and those fuel trims were the only numbers that were significantly different. I was hoping maybe the MAF numbers would be different or something like that but they turned out to be almost identical. I think one of the laundry list of things I did was clean the MAF sensor but it was only a quick cleaning. I'll give it a more in depth cleaning today.
Last edited by 03.SS.montecarlo; 08-06-2011 at 10:14 AM.
#17
08-06-2011, 01:03 PM
I don't think it's the MAF either but I remember seeing somewhere that it could be a cause but being the numbers were good it rules that out. Some gasoline and a match may be the next step. Ahhhhhh!!
#18
08-06-2011, 01:19 PM
Join Date: Apr 2010
Location: Mentor, Ohio
Posts: 12,217
Well, you ruled out me checking the Impala today. Sorry I did not get to it sooner.
As I understand the MAF detect how much air is entering the system to adjust the amount of fuel accordingly. It's common when using an oil-based air filter that if the filter has too much oil, it gunks the MAF just enough that it throws crap readings. Another "trick" you can try is while the car is off, unplug the MAF, see what happens. The computer will attempt to compensate for it not being there.
Also, don't forget to try that "roto-rotor" thing with the EGR passage, just to ensure it's clear of debris.
I know I'm not the only one curious to what is going on, but I'm hoping a resolution happens soon and I really want to know what it is.
As I understand the MAF detect how much air is entering the system to adjust the amount of fuel accordingly. It's common when using an oil-based air filter that if the filter has too much oil, it gunks the MAF just enough that it throws crap readings. Another "trick" you can try is while the car is off, unplug the MAF, see what happens. The computer will attempt to compensate for it not being there.
Also, don't forget to try that "roto-rotor" thing with the EGR passage, just to ensure it's clear of debris.
I know I'm not the only one curious to what is going on, but I'm hoping a resolution happens soon and I really want to know what it is.
#19
08-06-2011, 04:11 PM
I hate to say it but I think the next step is taking it to the stealership. I'm sick of throwing money and time at it. Thank you all very much for your help, I greatly appreciate it. I'll be sure to post whatever the findings may be.
