I have a 1996 Nissan Maxima and it gets worse on gas everyday it seems. When I first got it back in 2005 as my first car, I ran it very hard of course. I got about 28 MPG running it moderately hard sometimes. Then I began learning how to hypermile, I started by just accelerating carefully and making sure I am always in the highest possible gear, and throwing it in N while coasting, keeping the RPM down. After I began doing EOC, P&G, etc, I was able to stay around about 32 MPG! But now I have a problem and I dont know whats wrong! Now no matter how much EOCing, P&Ging I do and no matter how carefully I acccel and no matter how high of a gear I am in I can only get 22 MPG at MOST!


Info about my car:

V6 3 liters DOHC

2 BRAND NEW O2 sensors, 1 on each bank

BRAND NEW EGR valve hose

Changed transmission fluid just a few months ago.

Tires at 40 PSI


So does anyone know what the problem could be?

could be: injectors, fuel filter, cat converter, spark plugs, coil packs...to name a few.

if you can get to the fuel filter, it's a cheap fix to start with.

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Heaven is...http://www.youtube.com/watch?v=Z9JTwJ_1lzE

auto repair info...http://www.magicmechanic.net/napa-auto-center/

http://www.fueleconomy.gov/feg/calculatorSelectYear.jsp

http://www.obd-codes.com/

Is all that EOC ok for your transmission? Could it be damaged? Most automatics aren't EOC-compatible.

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Fuel filter is the original that was on the car from 1996 as far as I know but wouldn't that cause a lean burn? My car has that "rotten egg" smell as if it is too rich!

Spark plugs/coilpacks
At night if I open the hood I can see some blue arcing under the intake manifold coming from somewhere so there MUST be an ignition leak somewhere, but there is no skipping, it runs fine as far as I can tell, still this may be something I should check into.

Catalytic Converter
I checked the intake manifold vacuum and it stays about 20" even when I rev the engine, wouldn't a collapsed cat cause the vacuum to go down on higher RPM and not up?


This is very strange the symptoms I have here. I am losing gas mileage AND power! I remember that when I first got this car in 2005 it would really burn rubber from a stop! But now when once in a blue moon that I decide to "vent" a little, I have noticed that the tires won't even break traction now! So I have less power AND less FE. But it runs JUST FINE! My dad has been working on cars since the 1960's and was considered the "Town Mechanic" back then, still works on his own car, but he tells me there is NOTHING wrong with my car (but ONLY because it runs smooth)

This dropping gas mileage has been going on for quite a while now, about a year and a half, but I think my injectors AND fuel filter might be clogged now because some idiot who borrowed my car decided to put diesel in the tank like a fool! My god it spark knocked like crazy I had to just let it sit and idle that out so it didnt destroy the engine, but I get the feeling that even though I have a fresh tank of gasoline now, maybe the diesel has clogged the injectors and fuel filter even worse.

As far as the poor FE goes, that was a problem EVEN BEFORE the problem with the wrong fuel. So that isnt the only problem.



Well, Nissan tells me that my car can be flat-towed without removing the drive-axles so I think its alright just to EOC for at most a mile sometimes. Nissan seems to be pretty good with this on their FWD models (luckily for me).


Any ideas based on this new info?

Woops I forgot to mention one thing that may suggest maybe the ECU is bad!

About 2 years ago I had a 50 amp battery charger hooked up to my car. I had a voltage meter plugged into my cigarette lighter plug. While I was messing in my car the battery charger failed, but during failure, I noticed for about 10 to 15 seconds, the voltage meter got up to about 20 or 22 volts!!!! I quickly unplugged the charger! after that, my charger never worked again, and also, it fried my voltage meter, AND it fried my power inverter that I had. Could that have done some kind of electrical damage somewhere that would not throw any OBDII codes and would not disable the car or make it run bad, but just ruin FE?

Personally, I'd stick a bottle of isopropyl alcohol in the tank as a cleaner then take it out and beat the snot out of it, see where it went from there.

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I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice

And when you say beat the snot out of it I assume that you mean run it as hard as possible. Maybe thats a good Idea. Could acetone also work? What about this thing my dad found in an autoparts store from CRC called "Guaranteed to pass" that is a strong fuel system cleaner which the company guarantees that after using it you should pass inspection. Does anyone know if any of those might also do the trick for that?

I thought that was just alcohol with fuel system detergents added and some great marketing. Someone please correct me if I'm wrong.

-Jay

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Ok but what about acetone and what about alcohol? I have just poured some gasoline into a clear container with some of mom's nail polish remover (primarily acetone) and with some isoprophyl alcohol and it all seperated into 3 layers every time no matter how much I shook the heck out of it! This tells me neither of these will mix with the gasoline in my tank. So are you sure alcohol will work? And are the things I have heard about acetone doing the trick just rumors? It seems to me so far based on my tests that neither iso alcohol nor acetone will mix with gasoline.

Alcohol does mix with gasoline... In my area you can only purchase blended fuels... 90% gasoline, 10% alcohol. E85 is 85% alcohol and 15% gasoline. Fuel line antifreeze is alcohol as well. Drug store variety isoprophyl alcohol is watered down, so that may not mix with gasoline well. I'm not sure about the nail polish remover. There are other additives in it. These could be interfering with allowing it to mix with the gasoline.

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Hey guys you all miss the key infomation here - diesel fuel has sulfer in it and that is BAD for the CAT - you probably have a blocked cat - check for back pressure in the exhaust manifold and maybe the lack of free flowing pulses in the tailpipe at idle - open up the exhaust header maybe.
Also old leaking arcing spark plug wires can produce a weak spark but still run smooth until you load it up at low rpm.

Possibly a bad fuel pressure regulator, but the overcharge could certainly have damaged the ECU.

Poor performance could also be mass airflow sensor.

Any check engine light?

regards
gary

Yikes! That poor car...diesel, AND overvolted.

You really need to replace the fuel filter. You also need to clean the whole fuel system, maybe some bottled cleaner (commercial fuel cleaner product, alcohol, or pure acetone) could do it, but you may still need to get your injectors cleaned.

Fix the ignition problem too. That arcing can't be good. It's bound to cause some loss for you, in power, efficiency, and/or breaking additional stuff.

The cat may be blocked or just messed up, and is probably the source of your stench, in my opinion.

That's pretty cool about it being ok for EOC, though.

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Catalytic Converter
I have already checked for back pressure the only way I know how to and that is by using a hose on the intake manifold to measure vacuum and it is around 20 inches at idle and does not decrease with higher RPM, but instead increases.

Tailpipe free flowing pulses at idle
AH HA! You may have stumbled onto something here! I have thought about that before, but I always ignored it and thought it was maybe normal. At idle exhaust from tailpipe has "variable" pulses. However, this was also happening BEFORE the diesel.

Ignition Components
Well I really don't have spark plug wires I have direct ignition, coilpacks. BUT you are right, for some reason at constant throttle position, with low RPM it varies by about 200 RPM sometimes. Maybe thats why.

Yes I am very concerned about the ECU

On this car if the MAF does not give a signal, it is "rev-limited" to around 2500 RPM and that isnt the case.

Yes check engine light but only because of a bad Neutral Position switch and DOWNSTREAM POST CAT oxygen sensor (which I have been told by others, this has nothing to do with fuel mixture and does not affect FE).

First of all, I have no job, am having alot of trouble getting hired, and have a very tiny savings. I cant afford anything expensive like a new CAT or new injectors or new coilpacks!

Fuel Filter
I plan to replace this very soon, it is the original factory part that has 140k miles on it!

Cleaning of fuel system
I have gone to the local grocery store and got 2 bottles of Isopropyl Alcohol which I have just put into my gas tank and have already ran the heck out of the engine. This might help.

Injectors
Well if that isnt too expensive then ok but I am on a very tight budget so I cant do it if it costs too much.

Ignition
Is there any way I can fix the ignition problem without replacing my coil packs? They are very expensive! BTW I have direct ignition.

Catalytic Converter
Ok I certainly cannot afford a new one of these at the time. But I can tell you the thing with the variable pulses from the tailpipe at idle and the stench was already a problem before the thing with the diesel, its been that way for about a year or 2 now. IF the cat is causing a problem, then is it at all possible for a cheap fix such as cleaning or something like that?

Replace your wires and plugs.

Your car may not be misfiring but the arcing you are seeing is making your spark at the plug very weak. You might not think so but spark intensity can play a pretty big role in fuel economy and power. There is more than just lighting the mixture.

Check your plugs while you are at it. Not many companies were using long life plugs back in 96 and for all you know the plugs in there are coppers from 96. My 99 had the factory copper plugs still and had 62k on them. Additionally, you can tell A LOT about how an engine is running by the plugs, rich, lean, burning oil, all of that. Now, with reduced firing power I wouldn't be surprised if you had a bit of carbon on the plug.

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The CAT makes the unburnt hydrocarbons react with some small amounts of oxygen in the exhaust gasses and if it doesn't have the correct fuel mixture it will make your mileage drop and because the CAT may be fouled up from the diesel sulfur it may have trouble getting the A/F ratio correct to clean up the exhaust. Check the O2 sensors for fouling as well since they come out easier than the CAT pipes. You could try starting it up without the exhaust but I am not sure what would happen without the O2 sensors operating properly.

Spark PLUG CHECK is the first thing - check them for fouling and proper gap - no cost work - the arcing only applies to conventional ignition wiring so with direct ignition you need to look at proper spark plug gap and fouled plugs.

Engine intake vacuum is not really a great indication of exhaust back pressure being caused by a blocked CAT however a visual examination of the cat guts if possible or practical may be in order to see if there is any yellow crusty buildup in there. Also soot in the exhaust is a great indicator of a rich A/F ratio causing fuel loss.

The fuel filter is probably a waste of time since that would only affect high performance output but not mileage - any blockage severe enough to affect low speed light throttle mileage would kill high output power levels completely.

Check for other things like how well does it roll - are the brakes dragging - jack up each wheel and check for ease of rotation.

Scangauge the engine at idle to see what fuel consumption is. Borrow one if you don't have a scangauge.

A few ounces of Gumout in the gas or acetone would probably help too.

It is killing his power...
Great point about the brakes, though.

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Ok everybody, heres the latest info I have for you:

Catalytic converter
I have actually filled my exhaust system with water via a hose before just for the idea of a clogged CAT. Not really sure if that was a good idea or not, but I figured just MAYBE it might help with any buildup in there.

Spark Plugs
I have replaced these. My engine was bad when I got the car, rebuilt before I had it and it was a very bad rebuild job, began knocking due to a crankshaft which had evidence of being turned with a pipe wrench by a mechanic before the car was mine! I bought an identical engine from a junkyard Infiniti I35 which has the same engine and is basically a rich person's Maxima, also made by NISSAN. Of course when I installed this new engine, I changed the plugs and put the best ones I could find for this engine!

Wires
I dont have these. I have direct ignition. One coil pack for each of 6 cylinders!


Another thing I have thought of
Muffler and pipe
I know this sounds crazy but a while back in a parking lot I noticed a stupid kid cramming sticks into my tailpipe and really cramming them up in there tight and as far as he could push them. I tried to get them out but couldnt reach them and I knew it would create backpressure and kill FE but I figured that either the pressure would eventually blow them out or the heat would burn them up. Possiblly this hasnt happened though! I dont really know as I have no way of seeing in there. I will go and look with a flashlight now! I cant believe the nerve of that stupid kid to do that!!! ugh!

My first thoughts were an 02 sensor, so I think you may have hit on the problem with the downstream 02 sensor being bad. Unless I am mistaken if the downstream sensor isn't sending the correct voltage back to the ECU it causes the upstream sensor to adjust the air fuel mixture. I only have one oxygen sensor on my my '88 Escort, but when it went bad a couple of times in the cars lifetime my FE would drop about 25%. I would definitely check it out and also try to find where the arching is coming from that would explain part of your loss of power and FE both. You can usually tell if a car is running extremely rich by removing the 02 sensors and if they are black with soot it is running too rich. They should have a light tan color ash on them if the air fuel mixture is close to right. Maybe you could find any ignition parts you need in a junk yard. My wife's car is distributor less ignition and I bought a complete coil pack for $50. at a junk yard.

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OK good news! I checked and there are no foreign objects up my tailpipe! So I must have been right about the back pressure eventually blowing the sticks out!

Nail polish remover is watered down a lot. Isopropyl alcohol needs to be about 68% pure or better, methanol needs to be about 95% pure or better, and ethanol 98%ish. Anything lower and they dump the water. Don't know if acetone can hold any. 70% IPA is easy to find, I wouldn't recommend it in winter as solubility drops with temperature, watch out for cheapy 50%, it's okay for cleaning electrics, or prepping for paint or glue, but don't put it in your tank. 99% IPA is available at walmart here in quarts.

Many "fuel system cleaners, emissions cleaners, octane boosters" etc are IPA, those that aren't are close to mineral spirits/varsol and some are pretty close to ATF. Some fancier ones are a blend and have additional cleaners and solvents like 1:1:1 Trichlorethane. But I figure if you can't get it right by trying straight IPA or varsol, then the spendy stuff ain't likely to do anything either. Depending on the promises on the bottle and how shiny the packaging is you can pay $15 for 125ml of isopropyl or mineral spirits. Even if you pay the "expensive" rate of $4 or so for a 500ml/pint bottle of 99% IPA you're still probably paying under half of what the cheaper stuff costs. If you wanna dig out MSDS sheets to see what's in your favourite snake oil, alternate names for IPA are isopropanol and 1:propanol and if it's 99% of that and 1% "Proprietary ingredient" I'd bet on that being water.

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I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice

It would affect fuel flow not pressure - you could get pressure as normal at low throttle use but when you really open it up at high RPM it would be starved for fuel and bog down. It is very rare for a fuel filter to cause problems - not impossible but very rare.

Checking the plugs again would show fouling right at the cylinder level and even if they are gapped properly if they are sooty then you KNOW the A/F mix is way off.

Water in the exhaust is NOT a great idea if the exhaust valve is open and you crank the engine it can draw the water into the cylinders and . . . need I say more? Normally when the engine is running the flow is for the most part always out of the cylinder by the exhaust but under low speed conditions it can backflow a little. . . . ASK ME HOW I KNOW!

ok I have purchased 2 quarts of 70% IPA this morning and put in my tank. I put it in my tank this morning but I didnt get much sleep so I am afraid to drive. So what I did to get around driving sleepy but running it hard was putting it in [P]ark and then using a combination of my "gas pedal depressor" air conditioner, headlights, all interior lights, rear defogger, 2400 watt power inverter with several electric heaters and hairdryers plugged in, and everything else I could think of to load the engine down, then I used my gas pedal depressor to hold it at 2500 RPM parked for a while and run that 70% IPA through the fuel system. I did it for a while until the engine temp began to rise then I cut back on throttle and load, and a few minutes later I turned it off and stopped, figured if ANYTHING runs the heck out of it and blows carbon/gump out then that did very well! But I dont know what the results of this will be yet because I first need to figure my mileage, which will take another week at least.

Yes I know I know.... Waterlock can occur because water dont compress. Dumb idea anyway

That "run" must have REALLY HEATED UP THE CAT!! YEAOOOOOWWWWW and that is not recommended because it can cause fires under your car - man you are really dangerous!!! ha ha ha.

Sounds like you don't have a scan gauge . . . I hope you are not calculating the fuel mileage wrong . . . seen that happen before too.

Well if anything you cooked the cat really well maybe burned off any contaminations that were inside it.

Just so you know I run acetone in my xB and when it is all warmed up and idling - if you take a whiff of the exhaust you can't smell anything but warm moist air coming out the tail pipe.

You are right, I dont have a scan gauge, I cant afford it, but I am pretty sure I am calculating my mileage properly. I fill up full, and when I get gasoline again, I fill up full again, and I see how much gasoline I used, and I divide the number of miles traveled by gallons of gasoline. That is how I get my mileage. Well I wasnt really so sure that it could catch on fire, but at least its clean now! A question I have for you is if it can catch on fire like that going that RPM with those light loads, then why can it not while driving (which is a MUCH heavier load)?

Also I wonder if anyone has any other ideas on anything else I can do? Anything else it could be?

I really appreciate everyone's help with this! I wasnt expecting THIS much help and support thanks!

SHEEEEEWWW I just smelled my exhaust after warming up at idle, and OMG its TERRIBLE! My nose is STILL burning! Maybe that could indicate something.

Edit:
I forgot to tell that now that I have put some 70% IPA in my tank my exhaust seems to have beads of water condensed inside!

Yup when sitting still there is not much air flowing past the CAT to cool it so it gets extra hot - not recommended to even idle the car in traffic for too long either or drive over grass. My BMW R100S pipes get glowing RED hot in a minute if there is no breeze cooling them and you just throw a few revs - more noticeable at night in the dark.

Yeah it sounds like the cat is fouled up and not reacting with the fuel properly but it could also be the engine. Another way to tell is to measure the voltage on the O2 sensor and see what it is. That will tell you what the engine and ECU is doing to the fuel mixture.

My exhaust stings a little when warming up but after driving and checking it - smells like clean fresh air.

One other thing people forget sometimes is how is your oil consumption - is it using a lot of oil and is the oil clean and full.