FE just keeps droping no matter how much I hypermile

[JanGeo]

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.

[R.I.D.E.]

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

[theholycow]

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.

[txe5502]

Originally Posted by JanGeo

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.

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.

[txe5502]

Originally Posted by R.I.D.E.

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

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).

[txe5502]

Originally Posted by theholycow

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.

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?

[dkjones96]

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.

[JanGeo]

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.

[theholycow]

Originally Posted by JanGeo

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.

It is killing his power...

Originally Posted by txe5502

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.

Great point about the brakes, though.

[txe5502]

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!