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The car is a 1995 A32 Maxima, though this is an Australian delivered model with 166,000km on the engine. It gets fed PULP and has regular servicing every 3 months. Its recently developed a problem which is a pain in the rear end to identify apparently. The problem: - Starts up fine, usually runs without a problem during the initial warm up stage - though on occasion it runs rich - After warm up, it will randomly start running rich and stall - If it doesnt stall, I experience a fairly massive loss in power - When its experiencing this problem, the idle is rougher - not noticeable in any other way than vibration through the steering wheel - When accelerating in this state, there is a massive drop in power between 900-1200 RPM - My fuel economy sucks. I've gone from 650km/tank to 400-450km/tank Anecdotally, cold or hot weather increases the chance of the problems occurring. Between 20-25c, the problems don't seem to occur often, but occur either side of that temp range. The only thing I do know for certain is that during warm up (open loop), it tends to run fine without any problems. The second it switches to closed loop, the problems will start to appear. I've had 2 mechanics look at the car, neither of them have had any idea. The work done so far: - EFI specialist (called by mechanic 1) found issues with the fuel pump, so this was replaced. It fixed some of the stalling issue, since now the car will almost diesel along at around 200rpm as opposed to cutting out entirely - AFM was cleaned several times (mechanic 2) - EGR Valve, BPT EGR Control Valve and EGT Sensor were all replaced (mechanic 1) - At the time of the EGR valve replacement, the intake was taken apart and cleaned due to some "weird gunk" being present Using a OBD1 / CONSULT adapter and Nissan DataScan I. These are the things I've noticed: - LH O2 and RH O2 seem to randomly show different results, varying by anything up to 80 (scale is 0-100). Generally speaking, they stay constant during the issue period (Nissan DataScan FAQ says that they "oscillate(s) between 10 to 90 when engine is running in closed loop"). For reference, I had the car running at 2000 RPM in neutral and LH went from 90 -> 10 -> 80, where the RH stayed at 80-90 (2 second window). Later on the RH did the same thing, but this didn't occur as frequently - When the car returned to normal operation, both O2 sensors oscillated as stated in the FAQ - A/F Base (which "is a percentage of a fuel map setting currently used to run engine in closed loop") would sit at 87% during the problem time but then switch to 100% when normal(ish) operations resumed. NDS reported the car running rich, black smoke (clearly rich) visible soon after the A/F base change - Timing would drop from 42 to 26 during the same window Other things: - Airflow is consistent, doesnt really vary - Injectors seemed to be flowing fine, no real variation (I'm ruling out leaky injectors, as the car is easy to start after stall) - Battery was fine, though its been replaced in the last 3 months as were the terminals I'm already about $1k into this with parts replaced + labour (though, I did get some other stuff done at the same time) and don't really wanna keep sinking money into a car that has a supposed market value of $3.5k. Mechanic 1 had suggested that it might be the CAS early on, but nothing since. So, my theory is that either one or both of the O2 sensors are bad - the difference in readings between the 2 sensors (at the same point in time) seems to indicate some sort of issue. Am I on the right track here? Anyone got anything else I should look at?
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Jun 14, 2015 05:04
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| # ? Apr 25, 2024 09:52 |
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It sounds to me like the engine is losing communication with a sensor and going into an engine protection mode or limp mode. running rich to avoid going lean and melting the important bits. Maybe check if there is a difference between the expected voltage of important sensors and the actual reading. crank position, cam position, MAP/MAF, IAT. Being tied to external temperature makes me think intake air temp sensor or something with a similar function.
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Jun 14, 2015 05:12
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Hows the condition of the harness? (grounds, loom integrity, routing, etc)
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Jun 14, 2015 06:44
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I did forget to add, when the EGR etc all got replaced, the car didnt have any real problem bar from the ever so slightly rougher idle. That gradually got worse into what I'm seeing now.Powershift posted:It sounds to me like the engine is losing communication with a sensor and going into an engine protection mode or limp mode. running rich to avoid going lean and melting the important bits. The external temp thing has me lost as well,. admittedly I cant say for certain that its within that range since I'm not measuring ambient temps in the engine bay nor externally - its just what is stated for the current temps on my phone. Measuring the voltages will be interesting though for reasons below. I'm not the most mechanically astute person but given that its basic troubleshooting (identify, analyse, eliminate, rinse and repeat) I thought I'd have an ok shot at it, but the intermittent nature of this makes it really loving hard. I cant pick a pattern, which makes it hard to narrow down which sensor it might be. All I can say is what it isnt. cursedshitbox posted:Hows the condition of the harness? All the wiring etc is fine, as I had it checked out when I took the car from the folks (they had it sitting around for 6 months doing nothing, as they replaced it with a Lancer station wagon). Its all pretty good for a 20+ year old car, honestly (Melbourne winters arent exactly bad by comparison to some of the US winters. No salt on our roads here) Going through the service notes on all the receipts, the other things I can add: 1) Crank Angle Sensor doesnt look like its an issue, they tested it and only got 1 erroneous result in the 10 days they had the car. 2) 2 years ago, the previous shop manager said to potentially look at the state of the exhaust as it was rusting - though I've asked, the current mechanic doesn't believe it needs replacing yet There is a spanner in the works for me - there's a tenant in my apartment block who's a real loving bitch. She complained to the body corporate about me working on my car several times. I have no real ability to do any significant work on the car as a result. So I have to restrict myself to stuff that doesn't look like I'm working on the car, else there's a big shitfight. One question, if the exhaust is ridiculously rich, what happens if the EGR injects it back into the combustion chamber? How does the O2 sensor react to this? Next time, I'll try to log the data and post some stats here so that it can be a little more useful than my observations.
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Jun 14, 2015 08:04
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Did you ever replace your coolant temp sensor? That's the first place I'd look, since it sounds like it's running rich when you're in open loop, too.
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Jun 14, 2015 18:07
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Steak Flavored Gum posted:Did you ever replace your coolant temp sensor? That's the first place I'd look, since it sounds like it's running rich when you're in open loop, too. Was just about to post this. The coolant temp sensor is often a different sensor than the one outputting to your gauges and if it's hosed it can tell the ECU the engine is cold when it isn't which leads to bad things.
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Jun 17, 2015 06:15
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Also, there is pretty much nothing in the world that will make your engine run more rich than the ECU thinking it's 40 below. That's 300+% fuel enrichment territory. edit: They're < 20 bucks and super easy to replace on your model year, apparently. http://www.amazon.com/Standard-Motor-Products-TX78T-Temperature/dp/B004BTL0GY/ref=sr_1_1?ie=UTF8&qid=1434519289&sr=8-1&keywords=tx78t Steak Flavored Gum fucked around with this message at 06:35 on Jun 17, 2015 |
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Jun 17, 2015 06:30
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8ender posted:Was just about to post this. The coolant temp sensor is often a different sensor than the one outputting to your gauges Particularly true on Nissans of that vintage. The dash gets its reading from a sensor near where the upper radiator hose connects to the engine (possibly screwed into the neck itself), while the ECU usually gets it from one either screwed into a head or into the block near the water pump. KingPave, you said you or your mechanic had access to a Nissan CONSULT tool? That tool should be able to pull the engine temp value from the ECU, which would tell them if that sensor is hosed. Should also be able to pull a temp reading from the ambient air sensor.
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Jun 17, 2015 07:31
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Will answer all the coolant temp sensor questions with this post.some texas redneck posted:Particularly true on Nissans of that vintage. The dash gets its reading from a sensor near where the upper radiator hose connects to the engine (possibly screwed into the neck itself), while the ECU usually gets it from one either screwed into a head or into the block near the water pump. Based on Steak Flavored Gum's post, I went off and ran the car with the CONSULT adapter plugged in with Nissan DataScan I running. Annoyingly I forgot to log the data, but the temperature showed normal when the fault occurred. Temp slowly went up to 88c according to the software. Interestingly, I saw the a variation of the anomaly with the o2 sensors again. The left hand bank o2 sensor reported 90/100, where the right hand bank sensor was dropping to 35/100 then up to 80/100 then down to 15/100 for 1-2s at a time. During this time (whole issue lasted for about 90s or so, and did not re-occur after that), the ECU was reporting A/F ratio as rich. I might step back and have a friend have a look, I think I'm too fixated on the o2 sensors. Given that the coolant temp sensor is an easy fix, I'll just go and buy/replace it regardless - no harm in doing so. KingPave fucked around with this message at 10:41 on Jun 17, 2015 |
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Jun 17, 2015 10:38
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88C is right where it should be running, so I think your temp sensor is fine. At idle, you should see the primary O2 sensors fluctuate roughly every 0.5 to 1 second (I don't think you'll have secondary sensors, as catalyst monitoring wasn't a thing on most vehicles until OBD2 came along). When an O2 sensor fails, they generally fail full rich, so I think you may be on the right track. They're not used during open loop operation - so not when the engine is cold, and not under heavy acceleration. If you can get someone to ride with you and watch the outputs, try just driving at a steady speed, and maybe vary the speed slightly. Both sensors should go full rich if you accelerate hard, as they're not used in that scenario, so keep that in mind. You should see them rapidly fluctuating at roughly the same time while driving. I don't know about on your side of the pond, but replacement O2 sensors are relatively cheap here ($50 or so for a 4 wire from a parts counter).
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Jun 18, 2015 11:25
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Yeah, looking back over your initial post it seems like the CTS is probably okay. Still not a bad idea to replace it, though, given the easy access (at least it's not a Miata!) and low cost. They *do* go bad with some regularity. Narrowband O2 sensors are poorly named. They essentially do not have a band.  If the heaters in your O2 sensors are going bad, or if they're totally fouled (which they probably are at this point, given the rich running and the seeming impossibilty of doing a full-power WOT run) then that would really skew their output and could be the source of your problems. Have you checked whether or not the throttle position sensor is reading correctly? Most ECUs drop out of closed-loop running at wide throttle openings because there is essentially zero chance that they'll do any good. If your TPS isn't working right, then you might get problems from that, too.
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Jun 18, 2015 17:49
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So, bringing this thread up again just to post results. O2 sensors were cactus. They were caked solid with carbon deposits. I had the mechanic install two new O2 sensors ($30/each from the US, to buy the same parts here in AU is $95/each) and there's an instant improvement. The car doesn't feel like its towing a trailer and an extra 500kg in weight anymore, and it definitely isnt stalling as much. Additional bonus is the lack of a black cloud following me, though I imagine the cat is well and truly cooked. As another bonus, a 60km round trip isn't drinking 1/8th of a tank of fuel anymore. But the weird RPM issue (fluctuations, lag and it stalling) at, and near, idle is still there. The car is good at 1500 RPM or higher. I'll need to break out a multimeter and test out the TPS, though given the intermittent nature of it I'm not sure if I'll see it. Half tempted to buy a replacement TPS and install it, assuming I don't strip the screws.
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Jul 26, 2015 02:51
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The low rpm issues sound like a vacuum leak to me, maybe try spraying carb cleaner (or whatever they use these days) around the intake tract to see if it smooths out at all.
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Jul 26, 2015 05:47
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Find a friend with a smoke machine. gently caress tracking down vac leaks without one.
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Jul 26, 2015 17:46
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+1 for vacuum leaks. Testing for vac leaks without a smoke machine is not that bad. If I am not mistaken once it's warmed up your Max will start and run perfectly happily as long as the fuel pressure regulator vac line is hooked up, it doesn't need any of the other lines to run. To drive you only need the brake booster line and one for the auto tranny if that's what you've got. So basically just grab yourself a little pack of vacuum caps and unplug everything except the FPR (and maybe replace that vac line anyway, just so you know you are starting from good ). Then just put stuff back in a process of elimination and see when the problem starts. Make sure to test the one-way check valve from the brake booster by blowing in it from the "engine" side (you shouldn't be able to blow through it.) Honestly on a 20-year-old car in Australia I think you may as well just replace all the vac lines as you go anyway. I am assuming here that the mechanics who cleaned the AFM and took apart the intake put everything back together properly so you don't have a vac leak in the intake itself; if you did you'd likely have problems all the time, not just at low RPM.
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Jul 27, 2015 00:30
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| # ? Apr 25, 2024 09:52 |
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1st Edition ADandD posted:I am assuming here that the mechanics who cleaned the AFM and took apart the intake put everything back together properly so you don't have a vac leak in the intake itself; if you did you'd likely have problems all the time, not just at low RPM. Yep, though it was the EGR valve, EGT sensor and BPT valve He also did a check for a vacuum leak too without much luck. Also put in a couple of cans of upper intake cleaner too. BTW, the idle issue is intermittent. I drove today around 40km and didnt have the issue occur once. Still scratching my head about this one.
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Jul 27, 2015 11:47
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