There are only a couple of things the ECM can't monitor which could cause behavior like that, the MAF and the fuel supply. Stream the TPS and APP sensors on your scanner when it misbehaves. If the TPS follows the APP normally, then the throttle plate is opening and your problem is most likely fuel starvation. If the APP jumps with the pedal but the TPS doesn't follow, then the ECM is overriding the throttle input and keeping the plate closed, that would indicate an induction issue.
Slow acceleration
08 Altima 2.5s, recently installed used engine and trans...TCM from original car but TCM reprogrammed and car ran fine. ECM from original car. New valve cover, new cat and 02 sensors.
Driven a few hundred miles now and no codes yet BUT after it gets to operating temp, acceleration from dead stop is super slow, almost non existent and then all of a sudden it gets up and goes. If I put it in park and try to Rev engine, it does so suuuper slowly. If I turn off the car and turn right back on acceleration is fine for a while and then repeats. Brake lights not on when it happens so I don't think it's the brake sensor that other have experienced.
Throttle body? Intake system? Other Ideas?
Anything is much appreciated!
Driven a few hundred miles now and no codes yet BUT after it gets to operating temp, acceleration from dead stop is super slow, almost non existent and then all of a sudden it gets up and goes. If I put it in park and try to Rev engine, it does so suuuper slowly. If I turn off the car and turn right back on acceleration is fine for a while and then repeats. Brake lights not on when it happens so I don't think it's the brake sensor that other have experienced.
Throttle body? Intake system? Other Ideas?
Anything is much appreciated!
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Thanks so much for the reply! So if it's fuel starvation, any idea what the fix might be? Same for the induction issue, any ideas on the fix? Trying to narrow it down to something I can try replacing to see if it fixes.There are only a couple of things the ECM can't monitor which could cause behavior like that, the MAF and the fuel supply. Stream the TPS and APP sensors on your scanner when it misbehaves. If the TPS follows the APP normally, then the throttle plate is opening and your problem is most likely fuel starvation. If the APP jumps with the pedal but the TPS doesn't follow, then the ECM is overriding the throttle input and keeping the plate closed, that would indicate an induction issue.
If it's starvation it's probably a dying pump. There isn't much to the fuel system in gen3~5 Alties. The regulator, filter, and check valve are all built into the pump assembly, so anything that goes wrong is usually inside. If it's induction then a goofy MAF would be the likely culprit, you could confirm that with a scanner by streaming the MAF readings. QR25 Alties are like most other Nissans, they have no MAP sensor to give the ECM a cross-check for the MAF. The ECM simply has to trust it, so if it starts lying to the ECM without "flatlining" and dying completely, you get bad behavior with no codes.
Thanks so much! And then upon restart i guess it takes a minute for the "bad behavior" to start up again because it kind of resets temporarily?If it's starvation it's probably a dying pump. There isn't much to the fuel system in gen3~5 Alties. The regulator, filter, and check valve are all built into the pump assembly, so anything that goes wrong is usually inside. If it's induction then a goofy MAF would be the likely culprit, you could confirm that with a scanner by streaming the MAF readings. QR25 Alties are like most other Nissans, they have no MAP sensor to give the ECM a cross-check for the MAF. The ECM simply has to trust it, so if it starts lying to the ECM without "flatlining" and dying completely, you get bad behavior with no codes.
Any idea if the connection in the circled area was loose and not connected very well would have caused damage to the MAF? I temporarily taped it up because the foam that was there was gone.
Yah, the ECM resets run parameters when you cycle the key and uses preset parameters for the first few seconds after startup, so you can certainly see repetitive responses to repetitive error conditions. That duct joint you circled is no real concern, it will only cause the engine to suck slightly warmer air than it would without the leak. It isn't a real problem like air coming in someplace past the MAF, that would be a vacuum leak and would affect the way the engine runs. Stuff upstream from the airbox doesn't matter much, I see plenty of customers with clunkers that are missing that whole duct and still run fine.
Gotcha...Yah, the ECM resets run parameters when you cycle the key and uses preset parameters for the first few seconds after startup, so you can certainly see repetitive responses to repetitive error conditions. That duct joint you circled is no real concern, it will only cause the engine to suck slightly warmer air than it would without the leak. It isn't a real problem like air coming in someplace past the MAF, that would be a vacuum leak and would affect the way the engine runs. Stuff upstream from the airbox doesn't matter much, I see plenty of customers with clunkers that are missing that whole duct and still run fine.
Now that you mention it, I do notice my fuel gauge on the dash isn't working like it's supposed to, goes back and forth between F and E...I suppose that's another sign the fuel pump may be on its way out and reason to think my acceleration issue might be that as well
There's usually a common ground on the fuel pump connector and they're prone to burn up when a dying fuel pump draws too much current. Make sure to check it while you're in there. If any of the pins are blackened, replace the connector with a new pigtail. It's a common issue, so you can find pigtails all over eBay and Amazon if the parts store doesn't have one.
Thanks for that tip. And you're referring to the main plug on the top of the pump...one of the pins inside of that connector?There's usually a common ground on the fuel pump connector and they're prone to burn up when a dying fuel pump draws too much current. Make sure to check it while you're in there. If any of the pins are blackened, replace the connector with a new pigtail. It's a common issue, so you can find pigtails all over eBay and Amazon if the parts store doesn't have one.
Yep. The middle pin on most models.
Thanks so much for the information! Been in the dark with this and this certainly gives me a starting point. I appreciate it.Yep. The middle pin on most models.
Had a follow up if you dont mind, I'm going to disconnect battery and install fuel pump soon...figured while I'm at it I'll clean throttle body...anything special as far as "relearn" I have to do after connecting back and starting up? Or can I just connect, start and drive?
Usually you can just drive unless the car has had an IAVL (Idle Air Volume Learn) or CTPL (Closed Throttle Position Learn) with the dirty body, such that cleaning the TB will change something. But a periodic IAVL and CTPL are a good idea anyway if it has never had them, electronic components like the MAF can experience electrical "drift" as the silicon components age. I fixed one Versa some years back which hadn't had an IAVL in 8 or 10 years, the MAF readings shifted by almost 30% after I calibrated it. Considering your engine inhales roughly 9K gallons of air for every gallon of fuel burned, 30% is a very big deal. That's why for customers I do the procedures with every tuneup or induction service.
I've looked up some videos on the relearn process which includes turning off and on and the pedal cycles and all that...will doing that process take care of both the IAVL and CTPL all at once? I didn't see separate videos for each.Usually you can just drive unless the car has had an IAVL (Idle Air Volume Learn) or CTPL (Closed Throttle Position Learn) with the dirty body, such that cleaning the TB will change something. But a periodic IAVL and CTPL are a good idea anyway if it has never had them, electronic components like the MAF can experience electrical "drift" as the silicon components age. I fixed one Versa some years back which hadn't had an IAVL in 8 or 10 years, the MAF readings shifted by almost 30% after I calibrated it. Considering your engine inhales roughly 9K gallons of air for every gallon of fuel burned, 30% is a very big deal. That's why for customers I do the procedures with every tuneup or induction service.
No, they're separate. CTPL is the easy one, you just cycle the key 2-on-10-off three times. IAVL is the more-involved one. One can affect the other, you should do CTPL first.
Thank you much appreciated, going to see how it goes.No, they're separate. CTPL is the easy one, you just cycle the key 2-on-10-off three times. IAVL is the more-involved one. One can affect the other, you should do CTPL first.
Hey there, fuel pump install went well, cleaned up throttle body, wasn't too dirty, did the relearn (hopefully correct)...only thing I haven't got yet was the MAF...not sure if you can see this vid but this is what it's doing. In park, I'm flooring it and it takes its sweet time finally revving up... Does the same from take off...flooring it and hesitates to rev
Have you checked for a plugged exhaust? That's one other thing the ECM can't monitor very well. There are two good ways to check it. One is a vacuum gauge. The intake manifold should read near 20" idle, if it gradually tapers way off when you raise the RPM, the exhaust is plugged. The other way, since it's relatively easy on a QR engine, is just to remove the A/F Sensor (front O2). If it revs freely with the A/F removed from the exhaust manifold, it's plugged.
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