barza21
15+ Year Contributor
- 148
- 46
- Oct 11, 2006
-
Fairbanks,
Alaska
Hello All,
I am here once again seeking help with my issue I can't figure out. This is a follow up to last year's post regarding the same issue. I had time to take a look at this car again this year and nothing has really changed. The issue at hand is a misfire that happens pretty frequently at idle and when reved up while in neutral. There are no codes for misfires, but I can hear and feel them when I hold the throttle open and rev it to 1500-2000rpm. A WOT pull doesn't reveal any misfires that I can feel or hear.
While I'm driving and under load, the car drives fine. I don't feel any buckling or misfire. Once again, no codes for anything. I did notice this year that if I am going downhill and engine braking, that if I give it a little bit of gas and get it to about 19in/hg on the gauge, it buckles and doesn't like it. That same 19in/hg is at what I idle at and what it sits at when I rev and hold. So, I suspect this is related to my main problem.
Other than that, everything is the same. I am on ECMlink running speed density. I've checked for leaks and recently rebuild the throttle body thinking that maybe there was something in there I couldn't see and causing a problem. It didn't change anything. Additionally, I also rechecked compression this year. I am sitting at about 160 across the board. A leak down test reveals 98% seal across all cylinders. I've checked the base ignition and mechanical timing as well. I've checked the mechanical timing in all the ways possible listed on this site. It looks fine every time. Plugs have been replaced, ignition cables swapped around, PTUs swapped, I've experimented with different fuel pressures and adjusted in ECMlink. Nothing has helped. I bought a vacuum gauge to see more accurately what the engine is going, but nothing. The vacuum gauge moves around a bit because of the misfire, but sits around 19in/hg. I've discovered that even when making it run in open look, it'll still hiccup, but not as bad as it does when in closed loop.
To me it seems like a cylinder is running lean. I can't figure out which one. I've pulled cables and turned off injectors (in different combinations), but the moment that I do that, it stops misfiring. It just runs rough because it is running on 3 cylinders. The injectors installed have been cleaned and flow tested.
I've looked at signals with an Oscope and they seem normal, but I am not 100% sure what normal is in certain instances. The cylinders look similar to each other. The signals from the different sensors seem to be getting to the ECU and verify against what I see on the scope.
At this point I wouldn't be surprised that I have overlooked something incredibly simple and have totally dismissed it.
I am seeking assistance because I am at the limit with it. I really am. I am getting to the point where I am not enjoying this car since I can't tune it because of the issue it has. It is incredibly frustrating. I like working on the thing, but not when it is am issue that has repeatedly been kicking my behind.
I am seeking some much needed assistance from anybody. Almost any suggestion will be tried,
.
Thank you!
P.S. Here is the link to last year's post.
www.dsmtuners.com
I am here once again seeking help with my issue I can't figure out. This is a follow up to last year's post regarding the same issue. I had time to take a look at this car again this year and nothing has really changed. The issue at hand is a misfire that happens pretty frequently at idle and when reved up while in neutral. There are no codes for misfires, but I can hear and feel them when I hold the throttle open and rev it to 1500-2000rpm. A WOT pull doesn't reveal any misfires that I can feel or hear.
While I'm driving and under load, the car drives fine. I don't feel any buckling or misfire. Once again, no codes for anything. I did notice this year that if I am going downhill and engine braking, that if I give it a little bit of gas and get it to about 19in/hg on the gauge, it buckles and doesn't like it. That same 19in/hg is at what I idle at and what it sits at when I rev and hold. So, I suspect this is related to my main problem.
Other than that, everything is the same. I am on ECMlink running speed density. I've checked for leaks and recently rebuild the throttle body thinking that maybe there was something in there I couldn't see and causing a problem. It didn't change anything. Additionally, I also rechecked compression this year. I am sitting at about 160 across the board. A leak down test reveals 98% seal across all cylinders. I've checked the base ignition and mechanical timing as well. I've checked the mechanical timing in all the ways possible listed on this site. It looks fine every time. Plugs have been replaced, ignition cables swapped around, PTUs swapped, I've experimented with different fuel pressures and adjusted in ECMlink. Nothing has helped. I bought a vacuum gauge to see more accurately what the engine is going, but nothing. The vacuum gauge moves around a bit because of the misfire, but sits around 19in/hg. I've discovered that even when making it run in open look, it'll still hiccup, but not as bad as it does when in closed loop.
To me it seems like a cylinder is running lean. I can't figure out which one. I've pulled cables and turned off injectors (in different combinations), but the moment that I do that, it stops misfiring. It just runs rough because it is running on 3 cylinders. The injectors installed have been cleaned and flow tested.
I've looked at signals with an Oscope and they seem normal, but I am not 100% sure what normal is in certain instances. The cylinders look similar to each other. The signals from the different sensors seem to be getting to the ECU and verify against what I see on the scope.
At this point I wouldn't be surprised that I have overlooked something incredibly simple and have totally dismissed it.
I am seeking assistance because I am at the limit with it. I really am. I am getting to the point where I am not enjoying this car since I can't tune it because of the issue it has. It is incredibly frustrating. I like working on the thing, but not when it is am issue that has repeatedly been kicking my behind.
I am seeking some much needed assistance from anybody. Almost any suggestion will be tried,
.Thank you!
P.S. Here is the link to last year's post.
1G - Cylinder Pressure Waveform interpretation
Hello All,I need some help interpreting some of the waveforms that I was able to capture using my labscope. The vehicle is a 1991 TSi AWD. The waveforms pertain to in cylinder pressure test while running (at idle only. I have snap throttle events if requested). Based on what I see on the...
www.dsmtuners.com
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