Trying to resolve my sons running issues on an '04 Sentra 1.8L MT. The car hunts pretty bad, and went into limp mode. We got codes for a bad pedal sensor which we replaced. I also replaced the air filter, cleaned the MAF and TB and checked the intake hose for cracks. I found weathering in the folds, but no vacuum leaks.

After replacing the pedal sensor and clearing the codes I now get full range of RPM's, but it still hunts all over. I tried the TB relearn steps, but cant get the SES light to start blinking like its supposed to, so I cant complete the cycle. Now when we try and drive the car it dies as soon as you let the clutch out. No engine codes. When I scan while running I get a FUELSYS1 OL-FAULT message, and the I/M system doesn't reach readiness.

I've hunted the interwebs and have found this issue reported by others, but never any resolution. Can anyone shed any light on where to go next?

Nissan ECM's won't take an IAVL if the idle speed is above 1K RPM or so. The transmission also needs to be warm before it will execute, which the book doesn't mention. To get the idle down, we pull injector connections if they're reachable or coil connections if they aren't. The IAVL is much easier done with a scanner that has work support. I have a 'Droid phone and use Torque Pro with an ELM327 diag adaptor when I'm away from the shop and can't use Consult3+. Total cost under $20.

Tks for the response. My idle speed is staying below 1K no prob, it idles around 650-750 as it should. I got the engine up to operating temp before attempting IAVL, but I dont know how to get tranny warm - or if it even matters on a M/T? I thought temp sensors were only on the A/T?

Do you believe the issue is the relearn? I'll keep after that if so, but I don't want to burn a bunch of time and $ trying to relearn if that's a symptom of another problem that needs to be resolved. Would the IAVL fix the FUELSYS1 OL-Fault code?

No, there's no tranny temp consideration for an M/T. "Hunting" can mean a lot of things. A better description of what and when it misbehaves, along with a DTC code instead of a description, would help a lot. Nissan ECM's are totally dependent on the MAF with no MAP for a cross-check, so the stalling problem still could be from a MAF that's way out of calibration.

All of my other vehicles are pre-OBDII, so this is new to me. When you say DTC, I assume you're not talking about a check engine code which I am not getting any? What data should I be looking at?

I'll attempt to describe as best I can:
Engine fires right up, RPM's are steady'ish around 675-750 or so. No SES light
If I step on the gas, it revs up to several thousand RPM's smoothly and settles back down
When I put it in gear and try to move the car it dies, I cant keep the RPM's high enough, when I let the clutch out they dip and the engine dies
After attempting to move I get a hard start, and then the RPM's range from ~400 to ~1600, hunting up and down, car runs rough and when I try to idle, it dies

The issue came on over the course of a few weeks until the car would no longer run and died on the side of the road.

DTC stands for "Diagnostic Trouble Code" in OBD-speak. So let me get this straight, if you aren't getting codes, where is your "FUELSYS1 OL-FAULT" message coming from? If it's your scanner and there are no fault codes along with it, it might imply that your ECM is kicking offline. "Informational messages" like that vary from scanner to scanner, you'd have to check the scanner manual. I have seen ECM Relays cause issues like what you're describing, and low voltage at the ECM can cause it to drop out and become incommunicado. That's especially true on an early OBD-II like your Sentra that only uses the K-Line on the OBD port and not the CANbus.

Here's what I have for scanner results. No SES codes, and no DTC's, just a handful of I/M systems not reaching readiness and the car dies under load:

VStar650CL wrote: ↑

Wed Mar 30, 2022 4:59 pm

DTC stands for "Diagnostic Trouble Code" in OBD-speak. So let me get this straight, if you aren't getting codes, where is your "FUELSYS1 OL-FAULT" message coming from? If it's your scanner and there are no fault codes along with it, it might imply that your ECM is kicking offline. "Informational messages" like that vary from scanner to scanner, you'd have to check the scanner manual. I have seen ECM Relays cause issues like what you're describing, and low voltage at the ECM can cause it to drop out and become incommunicado. That's especially true on an early OBD-II like your Sentra that only uses the K-Line on the OBD port and not the CANbus.

I get the message when I have the scanner turned on while the engine is running, it provides a 'current state' message for a bunch of different items, that one jumped out because it seems to indicate an issue. However, I don't get any actual error codes showing. The rest of the stats are rolling numbers that unfortunately don't mean much to me.

I'll check out the FSM for what kind of voltage I should be getting at the ECM.

I'm not familiar with that scanner, but what it appears to be showing in that pic are SRT results (Self Readiness Tests). I don't even know why scanners show the Evap, that's always "unready" as soon as the last EONV test completes. I digress, sorry. If it isn't the ECM Relay, there are really only three things the ECM has to trust and can't monitor in some fashion. One is the MAF, since Nissans generally have no MAP to cross check it. So a lying MAF (as opposed to a dead one) can cause all sorts of invisible grief. The second is cam and crank sensors, which the ECM will often detect only if they "flatline" but not if they're missing teeth and lying about rotational position. The last is fuel delivery, whether that's pump pressure or clogged injectors. One thing you can try that's easy is some combustibles (Brakleen, Gumout, etc) down the barrel past the air filter. If it fires, then you know it's fuel starved.

I went back to basics on this and checked it for vacuum. Below vid is the result:

[youtube]https://youtube.com/shorts/6yA00dWfMlA?feature=share[/youtube]

Thats directly off the manifold. While the clip is only 10 secs long, you can see the flutter and how low the vacuum is. Interestingly immediately upon start up I had ~28" (I live ~1000' elevation) and it slowly went down as the engine warmed up. This video was about the mid point. After a few minutes the car died.

I ran a smoke test and came back with no leaks. Im pretty mechanically inclined, this makes me think valves or timing, but this issue didn't show up until after I dealt with the other problems (I replaced the fuel pump, cleaned the MAF and throttle body and replaced the throttle pedal assembly.) Could a damaged MAF lead to this? doesn't seem like it would change the vacuum, unless there is some sort of computer controlled advance that's getting off?

Im at a loss, and could use a hand.

Disappearing vacuum generally means only one thing, an exhaust blockage. Check your cat.

VStar650CL wrote: ↑

Sun Apr 03, 2022 8:41 pm

Disappearing vacuum generally means only one thing, an exhaust blockage. Check your cat.

I really appreciate your chiming in on that one. I don't think i would have ever gotten to a blocked cat causing receding vacuum. I'll check it out.

rock_rat wrote: ↑

Mon Apr 04, 2022 8:25 am

I really appreciate your chiming in on that one. I don't think i would have ever gotten to a blocked cat causing receding vacuum. I'll check it out.

You're most welcome. The simplest way to verify it (although not necessarily easy on a rusty '04) is to remove the A/F (front O2) sensor so the engine can breathe a little through the hole. If all of a sudden the vacuum increases, one or both of the cats is clogged.

Well, vstar for the win on this one. I temp-tested both cats last night and got 75-100* warmer pre-cat than after. On both. So I pulled the exhaust pipe from right after the front cat and got noticeably better vacuum (a steady'ish 15") and smoother idling. My guess is that one of the cat's died a while ago, and the increased load killed the other one. two new cats en route (CARB compliant, that hurt....) and fingers crossed that this is the last issue for at least a little while.