2007 Nissan Versa DOHC automatic 125Kmiles
I have an OBD2 tool, and would like to get tips for using it to “sleuth” the following problem. No check-engine codes have appeared. Intake vacuum is good, a steady 17.
Problem:
intermittent weak idle only when car is in “D”, “1”, or “2” with brake on, sometimes resulting in engine stall.
idle is always fine and steady (and a tad higher) in “R” with brake on, likewise in “N” or “P” with or without brake. Engine seems to also run fine in D with no brake (and no gas) applied.
engine seems strong/smooth when driving in any forward gear.
idle will sometimes “fade” when stopped at a stoplight in “D”, to below the normal (approx 650rpm). Sometimes engine will even sputter and die, but it restarts with no problem. Other times–even just a minute later at the next stoplight–the idle is no problem at all.
Has happened when engine is cold or warm.
I did the throttle position reset procedure (using key and foot pedal) for the car, but it did not help.
In past, I had noticed occasional dips in idle speed while in “D” at stoplight, but idle always recovered. It never resulted in a “sputter-and-die” until recently.
Recently I replaced spark plugs due to cyl 3 misfire (had CEL and high vibration). The engine runs smoothly now, except when it sputters like this, and has been driven about 50 miles with no new CEL.
Anything to look for in OBD2 data to diagnose this?
Yes, cleaned thoroughly about 10Kmiles ago, also recleaned a bit when replacing sparks just a couple weeks ago. (On this model, throttle body must be removed to replace sparks.)
You may still have the misfire problem; i.e. the first misfire wasn’t the spark plugs, but new spark plugs might help mask another problem, coil, injector, compression. Is your code reader able to check for pending codes? When computer suspects a misfire, it put a pending code in memory first, then if misfire continues it turns on check engine light and puts active misfire code in memory.
17 is on the borderline for intake manifold vacuum at warm idle, suggesting there’s some other problem remaining.
Just checked OBD2 device. I don’t see any capability of reading “pending codes” on it, although it has a variety of “data stream” measurements. I’m wondering if any of those might be useful in diagnosing this.
Regarding intake vacuum, I think 17 is in the “normal good” range for this model, from my reading notes. My other Versa (nearly identical) has run about 16 for years with no problems.
I see your logic, but no, my AC has not been on. I can’t think of any other abnormal power draw either.
Idea for anyone: Could this possibly be due to a bad MAF sensor that doesn’t trigger a CEL? If so, I could switch MAFs with my other (same model) car and see if that fixes it.
Bingo! Thanks for suggestion. Just took the readings. Crappy lean (high) fuel trim on this car, both short-term and long-term, even when running smoothly. I checked, tested, & cleaned injectors just a month ago, and they appeared to operate fine without clogs. Intake vacuum also doesn’t appear a prob. Switched MAF sensor out (with my other Versa) and that doesn’t solve the issue, so MAF is OK. I’m guessing low fuel pressure, possible fuel pump/pressure regulator problem. However, I thought low fuel pressure would result in hard starts, and this car never has a prob starting.
Fuel trim is usually spec’d as %. The % difference in the amount of gasoline the computer thinks it should be injecting based (primarily) on the intake airflow vs the amount it is actually injecting to satisfy the O2 sensor. Suggest to post your long and short term fuel trim in % units.
A couple of point to remember about fuel trim data
the computer is not able to directly measure the amount of gasoline it’s injecting. It only knows the injector pulse-duration time it has programmed. To infer the amount of gasoline injected it presumes the fuel rail pressure is correct, and that all the injectors are working to spec. If your engine uses a separate fuel pressure regulator gadget at the end of the fuel rail, remove its vacuum line input. there should be no gasoline in that line. If there is, the fuel pressure regulator is kaput & will have to be replaced.
the computer’s measure of the intake air flow presumes all the air into the engine is going through the MAF sensor. If there are any air leaks into the engine bypassing the MAF, it will confuse the computer & result in a lean fuel trim. Common air leaks are split/disconnected vacuum hoses, pvc system problems, and power brake booster problems. Air leaks often result in a lower intake manifold vacuum reading as well.
Just to add nothing, I’ll just say that the short term fuel trim is just what the computer sees instantly, and the long term is the average of the shirt term readings. I dunno how accurate the pulse width is on computing fuel used, but when I went four or five years without a working fuel gauge, I never knew how much was left, but the computer was able to calculate how much was used. Didn’t matter since I filled up every day anyway, but it was interesting.
When I had a lean or rich condition though beyond what the computer was able to compensate for, it was either a faulty maf or o2, but of course there can be other causes.
Would just like to “resolve” this post. After some tinkering and “thinkering” I eventually replaced the fuel pump/regulator assembly, and now the car works fine again. I didn’t want to think it was the fuel pump, because I had just replaced it maybe 10K miles earlier. Perhaps the bad one was yet another bogus Amazon part? I’m learning my lessons on those.
