I'll keep it short, 1993 GXE auto 67,000 miles, not a misprint
Exhaust stinks to high hell since I got it, but got better mileage then
Poor fuel mileage ~15 mpg city 18 highway
Recently, surges on light acceleration, very sensitive throttle from a stop, just jumps off the light no matter what. When its cold it will sometimes accelerate smooth and then jump like I gave it more throttle which I didn't. Im going to do a few things to try to fix it but I wanted to know if anyone knew specifically what it was. Im planning on the following repairs/mods now:
New:
air filter
fuel filter
replace last 4 injectors so all are new
clean out TB and upper plenum
change all vacuum hoses
plugs
cap and rotor
warpspeed y-pipe
new cat and stock cat back exhaust is horribly rotted but not leaking afaik

I think I read about some sensors, could it be the knock sensor or possibly the coolant temp sensor? No CEL right now.

Update, O2 sensor verified good, ecu diagnostics show nothing.

 

CEL is for decoration. look in the general maintenance sticky (#19 i think?) to see how to check for ECU codes. I'll bet it's either your O2 sensor or your Coolant Temp Sensor (not to be confused with Cylinder Head Temp Sensor, which is about 4 inches away from it. CTS has 2 pins and a yellow plug. CHTS has just a clip and grounds through its casing into the thing that i forgot its name but it's where the top of the thermostat hose goes into, and where the upper radiator hose goes.

 

I will check it out, forgot to mention the o2 is new btw, thanks.

 

notalk before that list = basic maintenance is done. Youre lucky to have engine running...

And why wires are missing from the list? Why : http://www.cardomain.com/ride/748507/12

Also run tranny self diag = tst TPS
http://www.cardomain.com/ride/748507/21

 

i had a new o2 as well but later found that i had a broken wire on the harness. i spliced in another wire and grounded to the cat heatshield, and my MPG went up 40%.

 

No offense but I was probably a little too brief, if it wasn't right it got replaced. Im not lucky to have it running. The wires are new NGK from the last owner. I will run the diagnostics and see what happens. I dont believe its the tranny, it works very well and the car has never been abused, ever, no seriously! Ok lets see then....
Fuel filter changed by last owner, less than 20K on it
Air filter dirty but not awful
New wires
Plugs gapped correctly, but old
Cap and rotor look ok, I cleaned up some carbon buildup recently
O2 sensor new, no reason to suspect wire damage as the car has never been in an accident.
Throttle body a little dirty
Passes emissions no problem
2 dead injectors replaced, the rest.....?
Tranny oil changed twice but never a full flush
new timing belt and tensioners, etc..
fresh coolant and thermostat
I think that covers it all........

 

Ngk wires may then be ok, who knows...

Replace the cracked hoses. Also IACV cleanup.

Platinum plugs last 60k. Std plugs 6k. You dont 'see' how they are, after that mileage theyre semi dead.

Even new cap can leak, needs sunshine brightness, just looking wont reveal leaks...

Tranny test has TPS diagnostics - that is why...

Groundings, see p10.

Injectors may leak intermittently, car has been mostly standing, means lots gum residue. Running few miles 5k rpm or cleanup may help...

 

On the same vehicle that is heavy on fuel?

 

Yeah, go figure, my heavily modded 3000 GT VR4 wont pass for beans and this thing has numbers so low I almost asked to be retested lol. I guess a rich fuel mixture in this car doesn't have as much effect on emissions as you would think.

Wiking I dont think its the cap because rain or moisture has no effect on how it runs. Like I said, some things need attention but nothing that would kill mileage like this. It used to get about 21 in the city, so about 6 MPG or about 30%. Obviously its a rich condition, but the question is why? Is it retarding timing because of a faulty knock sensor or coolant sensor, or is it leaky injectors dumping fuel? A clogged cat? Or something else?

 

neither has mine. **** happens. stuff rots. stuff breaks. if you don't want to check it b/c you assume it's in good condition, then don't complain when you keep chasing the dragon and it still isn't fixed. not saying for sure it's the problem, but it's foolish not to at least verify that it's OK. takes 5 minutes with a multimeter, an FSM, a beer, and a barking dog distracting you.

http://s164.photobucket.com/albums/u...0sensor%20fix/

 

You list the main issues - still I'd first swap the plugs. If theyre Bosch, nothin else is needed.

KS can be easily bypassed (read p.9) and engine pwr boost is noticeable if its bad.

THE GROUNDINGS, especially distr gnd.

Fuel leak on engine - all evaporates w/o trace?

O2 not really working = always on open loop?

 

How about 3rabbits?

 

hey man, whatever floats your Wiking ship.

 

Wow you guys are harsh! Im not saying that its NOT the O2 but you know how you just know its not whats going on? It would be the most incredible thing to me to find a problem with the O2 wiring, when I swapped the sensor I investigated and nothing even resembled suspicious. I will def try bypassing the knock sensor, thats an easy one to do and I dont mind easy things first so I can narrow down where Im looking. Checking continuity for the O2 sensor at the engine ecu will be on my list just for laughs. The plugs need to be changed but that wont give me a 30% drop in economy, so I know its something more than that.

 

check the injector harness for corrosion. Your MAF might also be the problem. If it`s the MAF .. Let me know ... I got some for sale

 

New things, DOA [dead on arrival]. Would not be the first time. Life on this cursed planet just is harsh, fast always eat the last... O2 problem just fits the bill perfectly.

But the plugs, o why go savin on em? Got to have smtg at hand to throw the magpies... The only way to verify plugs is to view the heated plug spark under full pressure, needs tst bench.

 

First post states new plugs coming, all the replaceable tune up stuff will be changed as precaution for trouble making and routine maintenance. Maybe I posted this too soon, I just wanted to make a list of what to check after those items. So my list is growing, I will post the full tune-up list of items later and you can all add/edit what you think it might be. I will just go down the list and see what happens!

 

You know, sometimes you just have to throw out what you THINK you know. You may be suffering from a multitude of things adding up to 30%. One thing I haven't heard you say you checked is tire pressure. You can lose 1-3 mpg just from low tire pressure. Also make sure you don't have a caliper that's sticking or a wheel bearing that's failing.

The following is all going to be general stuff, but in general, the Maxima is JUST a car and adheres to the general rules of general car maintenance, generally. Any car needs three things to run. Air, Fuel and Ignition. And you need the air fuel mixture to be the right ratio to get any kind of burn. Air and Ignition are pretty easy to sort out. Start there.

If you're going to bypass the KS I would suggest building a bypass that can be toggled on and off. That way you can see if there is a difference while you're troubleshooting, thus troubleshooting your KS at the same time.

Install fresh plugs, cap and rotor. They are CHEAP and will eliminate them as culprits. Clean all the grounds you can find. Bad grounds cause weird, hard to trace problems. Ignition wires are next. With fresh ignition parts and clean grounds you have effectively ruled out the ignition as a problem.

That leaves fuel and air.

Spend the 5 bucks for a new air filter and another 5 on the PCV valve. Also, spray carb cleaner around all the vacuum lines while the car is idling. Any place your spraying that the idle changes is a leak in the vacuum system. Change all the hoses that are leaking. Or just go ahead and change all the vacuum lines anyways because it's a 17 yo car and it isn't expensive and it won't hurt.

If your O2 sensor isn't working properly your car will go into a "limp" mode and dump in extra fuel just to make sure you don't dentonate while it can't tell what's going on. I believe the Max has a four wire O2 set up, a heater circuit and the O2 sensor circuit. If you put a VOM on the O2 circuit you should see fluctuation between 0-5v. This means the O2 circuit is working and detecting lean and rich conditions. If it DOESN"T fluctuate, then the O2 IS BAD. Next is the Cat. If it's clogged then you will get crappy mileage. It will get clogged if your O2 sensor is/was bad and you run in "limp" mode for too long. It'll also get clogged just because it's old. The factory only designed them to last through the warranty period (80K ??). That's LONG over now.

Now you're down to fuel.

Replace your fuel filter. Another $5-10 part that rules a problem out and is just a good general idea. Also replace the incoming and outgoing fuel lines with Fuel Injection rated gas line. Don't forget new clamps.

You could make sure that all of your injectors are trying to fire by using a mechanics stethoscope ( or a long screwdriver) and listening for the click, click noise. All six should have the same volume/rhythm although you can't get to the back 3. You can ohm them out. But all that tells you is if they are in electrical spec or not. If they're anything but between 11-12 ohm they're out of spec.

If you've replaced all the ignition and filters I've suggested and the FIs all sound right and check at 11 ohm then the FIs may be firing but with a bad spray pattern (not atomizing completely) or just plain leaking.

Try running a can or two of Seafoam through your gas. This is the best fuel system cleaner I've found yet. You can also run it directly into your intake to clean the intake plenum out. As with ALL Fuel system cleaners I recommend that you change your oil once you've run that tank of gas out.

This is by no means an exhaustive or even authoritative article on diagnosing your problem.

 

o2 is 3-wire. see my pics. unless it's that one circuit grounds through the casing and another circuit has a wire for ground. but as far as physical wires it's just 3.

not necessarily trying to be harsh, just that I did most of the stuff you said, got the same MPGs you get, and that's what my problem was. the wires can theoretically break anywhere along the line. The FSM will have you test for +12v, gnd, and signal (signal will have you test relative to an ECU pin). How long ago was it when you swapped the o2 sensor, and what was your MPG like immediately before and after you changed it?

 

bad mileage may be attributable to driving technique and use.
my car went from sub 14 to 18mpg just by changing my commute. toss in a driving style change and I'm now up to about 19.5 mpg.

 

likewise with my normally-tame driving style and a little 5spd swap, I was able to get from 23mpg on the a/t to 29mpg on the m/t.

but i was thinking he had said that this was an ongoing problem..

 

As far as surging have you considered a jumped timing belt? I had one bounce around for a while and would surge like crazy and dog at other times.

 

I am lucky to be able to say we are not yet burdened with annual emission tests, but on a technical note I would have to say that if you passed emissions and the fuel economy is still bad, you have one of 2 situations:

1. The test performed or the tester performing it is useless. Extra unburnt fuel in the outlet will undoubtedly fail you if emissions were done right (from what I have seen reported here and elsewhere the vehicle is not only tested at idle where things may be wonderful)...................... or

2. As Brian said - your driving style is the real governing factor

 

I guess it will just stay in open loop, thus consuming more.

The problem with O2 is the poor technology in its infancy: the signal level is 0-1V. 'Nothin' is needed to degrade such a signal using ten foot cabling with corrosion etc...

Only way is to test AND measure the signal at ECU. Swapping may not help at all. Also, THE swap at that mileage is an harness error alarm indicator itself ---> Why swap as the sensor itself is robust and typically dies 'only' by the mile?

 

How do I tell if my O2 sensor is good/bad also the braided GND wire is severed and the weld holding the bracket on near the flex-pipe is seperated is this important to be grounded?

 

Self diagnostics etc... check http://www.cardomain.com/ride/748507/9

There is a reason for groundings, find a replacement and repair. May or may not interfere with the already very poor signal level...

Make sure the connection is real and all the way...
see http://www.cardomain.com/ride/748507/10

 

I really do appreciate the help I'm getting from most of you but can we please leave the newbie stuff in the newbie forum? No I dont leadfoot it around town, I drive with my wife and 1 year old in the back and I dont drive any different than when it got 30% better mileage. No, the tires are not flat and I didn't notice. No, the brakes aren't seized and smell like they are burning up all the time. The car drives as smooth as any I've been in and its dead quiet so wheel bearings are not about to fall out either. The O2 sensor is new and the harness is fine, checked it at pin 29 at the ecu. No the timing belt is not skipping teeth, I put it in myself and it runs like a top, all the time, once it warms up. If I said in my first post, I'm going to change it, I will, but thanks for the extra reminders. I really do appreciate the input but please understand that I am on a higher level of maintenance than most and the simple things have been checked already. I will keep you all posted of further diagnoses, I will be running the diagnostics today and report back. I hope no one is offended, thats not my intention

 

I haven't had a VG before, but on my VE, I had similar problems when my Idle Air Control Valve was all gummed up and at the same time, my coolant temp sensor was bad.

Car was surging and erratic. I didn't let this condition go long enough to check mpg.

CTS did not turn on my CEL (those things are worthless) but it did throw the proper code when I manually checked the ECU. That was about $20 and maybe 5 minutes.

On the VE, the IACV has kind of an "s" pattern, so you can't really clean it unless you take it off. Mine was terrible inside. Once I replaced the CTS and thoroughly cleaned the IACV and TB, then put on new gaskets, everything was great.

Like I said, I haven't owned a VG, so some of those guys might want to add something to my info.

Also, I don't know about your surging problem, but if you have broken exhaust manifold studs (very common on all Nissan V6s) it could be something that is hurting your mpg and won't show up on the emissions testing. Think about that one -- more emissions are leaking out near the engine and less through the tail pipe.

 

my braided thing is broken but my 02 works fine. But i will ground that too soon.

2 things to the OP:
you checked the pin 29 but did you check the power source and ground continuity too?
also did you ever say whether or not you checked your ECU codes? i only found that word once in the thread, on my first post in it.

 

noob stuff is sometimes forgotten even by the experienced and should never be ignored. a truly experienced man knows that a reminder of the basics is a good thing as they are oft forgotten.

having your wife and kid in the car does not preclude you from being a poor driver, and being a lead foot is not the only way to reduce MPG while driving.

I am not saying mechanical issues are totally out of the picture, but MPG has many things affecting it.

 

The surging problem, just to clarify will be like this: start the car and start down the block, it finds a steady RPM and you can feel it pulsing ever so slightly and then give it a little more gas and woah, didn't give it THAT much....hmmmm. Thats about it, once its warmed up it doesn't do that, only very touchy pulling away from a stop. If the exhaust studs are broken its the quietest exhaust leak there ever was. Its whisper quiet, no ticking or any indication of a leak. Again Im the second owner and the guy I got it from was in his 60's and neither of us ever drove it hard, this is my family car, I only get from A to B with it. Thanks for the other suggestions though. Oh and no I have not had a chance to run the diagnostics yet, but checking the O2 sensor wires for continuity confirms a good harness at least.


Ok, I really resent this comment, I know the point you are trying to make but the fact that my driving habits, style, environment, location, fuel type and overall car usage have not changed but the mileage HAS, is what I am saying. No need to insult my driving as it still has nothing to do with the problem.

 

This is a car forum, If one needs help, he comes here to ask b/c he doesnt know and THEN he has to take all answers in... I guess here's no iq limits? At least I can still go babbling under Greenys guidance...

Exhaust leak with no sound - stud broken but still in place ---> O2 signal freezes and works only when accel. Come an see feel how it goes...

If u havent got this, then u just dont know - you sit in total darkness. See now how my front RH stud broke 3days ago ---> the awful 0-1V flip flop SIGNAL semi-MISSING. No help in adding extra stud ...cant reproduce this video:

http://s305.photobucket.com/albums/n...arP4301988.flv

I am not saying that you have missing O2 signal, but dont brag you have it when you just cant prove it is there... And dont complain on Cape's or Automators advices as he really knows what he is talking about and better.

 

Do you seriously mean to tell me you think your wacky O2 voltage is from a broken exhaust manifold stud? Also, Im not knocking anyones advice as long as its relevant. FWIW I really know what Im talking about too, but every car is different. Do you know what a code 0402 is on a 2000 Toyota Corolla diagnostics? I do because I had to find out for my in-laws car. Point is, if you have a weird problem or the car is prone to certain problems, they are easy to point out to people who know cars but may not know the particular faults inherent to a certain design. Case in point, my first car was a 1987 Mitsu Starion, it developed a stumble on acceleration, turned out it was a pinhole in the diaphragm on the vacuum advance on the distributor. The mechanic I went to was a specialist on that car and knew the issue instantly, $70 part later, problem solved. I already said I checked the obvious and was going to replace many of the parts to change on everyones list of causes, I just wanted the less obvious ones, thats all.

Anyway, just to update, the ecu diagnostics show nothing, code 55. In fact, I had to break the plastic coating covering the ECU, I guess it never had been touched before.

 

That code was a real surprise. Anybody heard about this weird code before?

 

I think we are just trying to help out with possibilities. Maybe not the most likely things, but stuff that commonly goes wrong.

These cars rarely throw any kind of code except a 5-5. I have never had a CEL come on. I figure when that sucker lights up, my engine is toast. Electronic diagnostics are basically worthless. For most of us, these problems are trial and error, with help from others.

You mentioned a 2000 Corolla and that is OBD II, which is a giant leap forward from OBD I, which our Maximas are.

I was thinking about another thing -- Throttle Position Sensor? Just throwing more possibilities out there...

 

My bad it was P0420 in the corolla. Catalyst system efficiency below threshold. What it means is the second O2 sensor is reading that the cat is not doing its job. But it also is very common to that car that a dirty MAF sensor is incorrectly reporting the info to the ECU tripping the code. This is what I am talking about, the hard problem that is inherent to the design, like the fluctuating idle on my friends Honda Odyssey that was caused by a pressure switch on the power steering line. If i were on those forums these would be the things I would suggest. I would not ask the corolla guy if his commute is different or if he drove in a puddle, I would tell him to try cleaning the MAF. I would tell the Odyssey guy to test the pressure switch, not check if the floormat was stuck under the pedal or maybe he had heavier shoes on that day.

I think this is sarcasm about the code 55? Not sure, hard to understand what you mean sometimes. If you were serious, code 55 means there are no codes.

 

So basically the on-board diagnostics are practically worthless? This is the first I hear that, thank you for the heads up, I will try testing things individually then. Thats the most useful advice I've had so far!

Yes I'm aware OBD2 is light years ahead of what we have, but yet I'm glad I dont have it! lol

I could certainly check the TPS out, again, I was under the impression that the lack of a trouble code meant it was all working ok. Trouble is, I dont want to just go changing sensors to find out what it is, I hope the testing procedures can sniff out a truly bad part. It could get expensive to change all this stuff just to make sure.

 

if you do not have a 55 then you have a problem. but simply a 55 doesn't mean "close the hood and drive happy" tho, b/c the diagnostics miss a TON of things. There's only so much a computer can understand, as it's not a human brain. So error codes are a good starting point, but do not tell the whole story.

 

You would be surprised how often a timing belt can go slack and jump a tooth. Doesn't hurt to look, part of the reason I'm leaving the top timing cover off this time around.

 

I gotta say if you don't like someone posting a diagnostic tree for you, then FREAKIN IGNORE IT, noob or not. It's freakin simple. See what you want to read and just freaking ignore any thing you don't think appies to you. Just hit NEXT.