Sentra 97 AFM or fuel pump? (or maybe something else)

Found spec in FSM (GA16DE):

1.0 - 1.7v at idle (in "N", no load) 1.8 - 2.4v @ 2,500rpm (in "N" no load) Rechecked, unless it's an intermittent "dry solder" problem with AFM the AFM is within spec.

I wired a test lite at the fuel pump and laid it on the rear window shelf. When the car was running the lite would be on - when it stalled the lite stayed on, meaning I was getting power to the pump. I would jump out and squeeze the fuel return hose while cranking the engine from under the hood. No fuel pressure pulse detected. Fuel pump faulty. Replaced pump - problem solved.

On my kids car the same sort of symtoms. I wired a test lite as before. Except no power to pump when it stalled. Located the fuel pump relay and when it went into a stall, I jumped out, felt the relay and it was way hot. Replaced the relay, problem solved.

Both situations were intermitant without any set times of failure. And if I let the car cool down for 5-15 minutes it would clear up until next time, Maybe 5 min or an hour.

I would also chech the Crank and Cam sensors. These should show up as a "no crank signal detected" or "No crank reference". You might want to get an OBDII reader and see if your storing any codes (The idiot lite on the dash doesn't always come on for all trouble codes).

P

--- news://freenews.netfront.net/ - complaints: snipped-for-privacy@netfront.net ---

Me wrote the following:

Don't dismiss a clogged cat converter.

I wasn't suggesting that the cat was the problem, just suggesting another thing to check. I had a similar problem with my 86 Pulsar. It didn't happen all at once but just got worse over time. It turned out to be a clogged cat. Replaced it and all was well.

Robbie, I saw your other thread, and assumed, as I was with mine, that AFM was the most likely culprit as it's a common fault, but it checks out okay, the signal voltages are even, within spec, - and the typical MAF failure symptoms of uneven idle / hesitation aren't there. Bill, I've got a spare cat/exhaust manifold assembly here, but I doubt that's it, as when it's not missing/cutting out, it's running very well under load/high revs. (OTOH if it's coil/ignition related and I don't get this sorted properly, I guess I could kill/overheat the cat) Plugs are fairly new, leads etc seem good, and anyway when it cuts out under load it's a very hard abrupt cutout on all 4 cylinders, not a typical symptom of one or two bad leads or plugs. I now think the fuel pump etc is okay, I removed back seat and cover, and can feel the fuel hose pressurise and pulse when engine is revved. I don't have a gauge to put inline to check pressure, but it's probably okay. If I pull the fuel pump fuse under load, cutout from fuel starvation isn't as sudden/abrupt as what's happening, it slows, sputters and dies, rather than just completely cutting out "hard". It is also only happening when engine reaches normal operating temp - when it's cold/warming up, it's running perfectly. Danmed nuisance, as it takes a couple of "laps" up and down around local hills for a test run. This car (japanese domestic market model) doesn't have an OBDII connector, it's not throwing a CEL and I can't check for (pending) codes. It's making more sense to me now that it could be the coil, breakthrough/arcing only when engine is warm/under load, as the ECU changes ignition signal based on load and engine temp. The distributor was leaking oil from internal seal, fixed some 20,000km ago and clean as a whistle now, but it has had engine oil sitting in it, so that might have eventually "got to" the coil (coil is inside distributor).

No OBDII connector?? Seems to me that all cars {Asian at least} were OBDII compliant starting in 1996. Prior to that they were propriatary OBD using various methods for pulling codes.

P

--- news://freenews.netfront.net/ - complaints: snipped-for-privacy@netfront.net ---

That may have been for models sold in the US market. For JDM (and other markets) I think OBDII became standard by about 2003 for most Japanese manufacturers. This has a proprietary OBD connector (mounted in the fusebox). There are some alternatives to OBDII readers such as:

some reason I'm getting a malware warning from Google Chrome for parts of that site - I think it's an error, but be careful)

Bingo!

Bought a used distributor from a wrecker's yard this morning (pulled it out myself from a low km wreck, and took the cover off to check it was clean inside), swapped them over, set timing, and problem fixed. (Mine wasn't hesitating on acceleration, or idling rough, which is typical symptom of MAF going bad, but it was a fuel-starvation like miss under load, only when warm, with no CEL).

Cheers / Me

Bugger it - I should never have posted the above - premature smugness on my part. Sure enough, later today on a slightly longer run, it started showing exactly the same symptoms - so bad I was lucky to get home, as it completely died a few times. I have since cut the cover-plate from the MAF, removed the PCB, resoldered all components / connections on the PCB, cleaned (carefully with small artist brush and CRC carb cleaner) the hot wire and temperature sensor resistor, reassembled, glued cover-plate back down with RTV, and have taken the car on several truly long runs - problem seems to finally be solved. So dammit, it seems that it was the MAF / AFM after all. I can return the used distributor, but it was quite cheap, from quite low mileage car, and when I set timing with inductive light, at idle speed the new distributor seemed to be much steadier/less "jumpy" than the old one was, so although probably not the cause of the problems, the old distributor was probably not very good / marginal anyway.

Thanks - I see that the "consult" cables and software is also available here, USB version, about US$80 or so. There's a design issue with these MAFs, on GA15DE and some other Nissan motors, the MAF is combined in the throttle body, so it gets hot. I think on some GA16DE, the MAF is on the intake close to but separate from the throttle body, and probably gets less vibration and less heat, but they can still be a problem. It's running perfectly now.