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Got a little bit of a rough idle when at temperature and some rough acceleraton. Found a vaccum leak from a crack in PCV hose and changed that out but no real change. Had a new fuel pump and changed that out today and seems a little better but still have kind of a lopey idle and seems rough when accelerating. Checked fuel trims not sure what to interpret when looking at the fuel trim details below. Less that 10,000 on new engine, all sensors, injectors new as well. Have any thoughts or see anything that stands out in the data below? No DTC's or check engine light. 97 Z28 5.7 350. Thank you in advance.
Last edited by timmkatt6; Jun 27, 2020 at 09:15 PM.
You need to provide basic info about the car - model, year, trans, any engine modifications. From the data it's an OBD-2, probably “stockish”, but why guess. Was the data taken before or after the vacuum leak repair and fuel pump replacement? Did you check the fuel pressure before replacing the pump? What was the fuel pressure at idle with and without the vacuum compensation line attached, and out on the road under heavy engine load?
Min-mean-max is not sufficient data to do a meaningful analysis. It does show that there are cells where the LTFT's are subtracting a large amount of fuel on Bank 2, and adding a lot of fuel on Bank 1. Enough info to tell us there's definitely a problem w/ A/F ratio control, but without knowing which cells the LTFT's belong to, and the simultaneous engine operating conditions that produced the data, there's not much beyond that to be derived from this.
97 Chevy Camaro, Z28 4L60E engine is basically stock. I did not check the pressures before changing the Fuel Pump. I bought it when the engine went in and it was sitting around with the box collecting dust so figured I would change it and the fuel filter. Is there a logging software that would provide better stats or guidance how to grab better data? I have OBDwiz now.
I am not familiar with "OBDwiz". 90% of the data logs I get are from GaryDoug's software. To me, Gary's free programs are the best available. And he's a member here if you get into issues with installing the software, generating reports, etc.
Not enough info in your log. The scan rate is very slow, about one frame (line) of data per second. The PCM is updating almost 10 times per second. Useful logs generally have at least 5 frames/second. Otherwise, a lot of data is hidden.
Missing data (some of these may not be critical for the problems you are having):
- throttle position (column is there, but it's all 0's)
- LTFT Cell # (there are 19 different LTFT cells, arranged in a grid of MAP vs. RPM or used for idle, open loop accel, and closed throttle decel. Each cell has it's own LTFT Bank 1 and Bank 2)
- MAP (kPa or "Hg)
- Barometric pressure (kPa or "Hg)
- Closed loop indicator flag
- PE (power enrichment) mode indicator flag
- Fuel trim enabled indicator flag
- Engine run time
- IAC position
- Target idle RPM
- EGR duty cycle
- EVAP duty cycle
- Spark advance
- Knock retard
- Knock count
- Injector pulse widths
Redundant data:
-STFT's for pre-cat sensors are in there twice.
Unnecessary data:
- After-cat O2 sensor readings (generally only used for cat converter problems)
- STFT's (not used on LT1)
- fuel rail pressure (no input to PCM on an LT1)
I downloaded it, straightened out the decimals, hid the redundant of unnecessary data, etc., but all it really shows is that the LTFT's are all over the place, with the extremes:
- Bank 1 is adding up to 5.5% extra fuel in some cells and subtracting up to 11.7% fuel in others.
- Bank 2 is adding up to 15.5% extra fuel in some cells and subtracting up to 6.3% in others.
Anything beyond +/-5% generally indicates a problem. And in this case, appears the problems are specific to each bank of the engine. But without having the LTFT cell # for each of those readings, it's impossible to analyze any further.
Fred
I downloaded the GD Scan tool tool and using your recommended scans I found in other posts... Cold start warm for 4 minutes, drive for 10 varying throttle, 1 WOT to 5000 RPM and idle for 30 seconds at the end. Let me know if you can find anything that stands out. The scan tool did not record Barometric Pressure but it is at 29.71 while the scan is run. Thank you in advance!
Tim
Last edited by timmkatt6; Jun 28, 2020 at 09:35 PM.
From: Born on the Florida West Coast, now where can I retire?
Re: Rough idle / acceleration
OBDwiz and my OBD2 app only show the basic mandated parameters that are required by the government. To get more, you wold need an app like ScanXL from PPE. Even then the level of coverage varies greatly by vehicle make and year. The package would be about $180 including the added GM coverage. You can use your existing OBD-2 ELM327 cable for it.
However the best bang for the buck is an Android app called Torque for $5 (with the Torquescan free add-on). The downside to that is you use it on a phone and would need a good ELM327 Bluetooth adapter:
Where did you get the 29.71 "Hg from? 29.71 "Hg = 100.6 kPa.
At WOT (100% TPP) your MAP is only 87-88 kPa. That would mean you are losing 12-13 kPa through the air filter/inlet ducting. That is unreasonably high (unless filter is dirty). Also, at idle at the end of the log MAP is 27-28 kPa, where I would normally expect to see readings in the low 30's.
What is the elevation, relative to sea level where you live?
The problem is that the typical barometer reading at 2,400 feet above sea level is ~27.4 "Hg, nowhere near as high as 29.17" Hg.. When I asked where you got your number from, I assumed you got that barometer reading from an airport. Airports have to provide the pilot with the barometric reading at sea level (even if the airport is well above sea level). Then the pilot enters that sea level barometric pressure value in the Kollsman window in his altimeter, and the altimeter uses that as a reference to determine altitude of the plane above sea level, as the actual barometric pressure decreases with altitude.
Using 27.4 "Hg as the actual barometric pressure in your location helps your MAP readings make more sense, eliminating the MAP sensor as a possible issue.
Still looking at your data. There is something wrong with the A/F ratio control. The difference between Bank 1 (left side) and Bank 2 (right side) is 10 to 12% at idle. At the beginning of your data log, the PCM is using the "learned" LTFT's from previous operation of the engine. Bank 1 is adding 12% extra fuel, and Bank 2 is even, at 0%, neither adding or subtracting (delta = 12%). When idling at the end of the log, the PCM has "learned" new values from your driving for the LTFT's and is adding 5% extra fuel on Bank 1, and subtracting 5% fuel on Bank 2 (delta = 10%).
Something is causing Bank 1 to run lean (before LTFT correction) and Bank 2 to run rich at times.
Similar differences show up in driving, but I need to do more investigation to try and tie the magnitude of the corrections to the engine load. The after-cat O2 sensors are really strange. The after-cat sensors monitor the condition and efficiency of the catalytic converters. The converter essentially takes oxygen away from NOx, to eliminate that pollutant, and uses that oxygen to combine with (burn) unburned HC, turning it into water and CO2, and CO, turning it into CO2. The voltage reading of the after-cat O2 sensors are supposed to mimic the pre-cat sensors, but in a dampened form. The voltage swings on the after-cat sensors should have maybe 1/2 the voltage range of the pre-cat sensors. On your Bank 1, the after-cat sensors hang almost continuously for an extended period of time at ~700mV, (rich) while the Bank 2 after-cat sensor is seemingly stuck at less than 100 mV. (lean). Not something I can explain yet, because I seldom receive OBD-2 logs with their after-cat sensor readings.
Your idle RPM looks high. Stock programming for the 4L60E, fully warmed up coolant, is 550 RPM in gear and 650 RPM oin neutral. You are idling at 800+ RPM at the end of the log. Looked better at the beginning of the log, where the idle seemed closer to stock programming, just before and after the PCM went into closed loop. High idle sometimes points to a vaccuum leak, or air bypassing the MAF sensor in some way.
Fred
I found the issue! First, thank you for your time looking at this. My transmission bolts had worked their way out and were loose. I have headers so I did not notice it at first until I put the car on jack stands and with the engine running while checking for exhaust leaks under the car I heard a knocking noise. A stethoscope detected no noise from the oil pan or engine block but it was very detectable at the front of the bell housing/very back of the engine. I pulled the inspection plate and it became very noticable. At first I thought it was the transmission but PerfomaBuilt suggested checking the flex plate for cracks and if nothing there then possibly the torque converter. When inspecting and almost to the point of deciding to drop the transmission I grabbed where the bottom bell housing bolt is to pull my self to a different position and felt the bolt move. All three on the driver side had worked themselves out and the top one on the passenger side was gone. Only the two bottom on the passenger side were tight. When I put a light at the top it looked like a very small gap had developed especially on the driver side I got new bolts this morning and some blue locktite. Locktite on all the bolts and re-torqued them. Purrs like a kitten again and the knock is completely gone. All I can think of is that possibly the Knock sensor was picking up the noise and the ECM was trying to compensate but whatever was going on the issue is no longer there. I'm going to drop it down and run another scan on a test drive. Thanks again.
Thank you again.
