Hello all
I have a 2005 Nissan Frontier with a 4.0 motor in it and I recently had a fuel line cleaning done in the hopes to eliminate a tapping sound in the motor. The Nissan Mechanic told me that it could have been carbon build up and was causing the engine to tap, so I went to another garage (the Nissan dealer was just a bit too pricy) and had this service done.
Before the service I was getting 15-17 mpg in the city and 18-21 on the hwy. After the service I am getting 10-12 in the city and no more than 16 on the hwy. I am at a loss.
This service was to help my mpg and it has killed it. I am just frustrated, one mechanic told me he thought my plugs were fouled out, but the dealer tells me that my chk eng light would come on if they were, I also pulled two of the plugs, and they appear to be just fine.
Any suggestions on why this is happening would be greatly appreciated.
Cheers
Well first off those Fuel Line cleaning scams are NOT worth it. If the injectors were really clogged you would have noticed it. If the truck was running fine then there was no need for it.
As for the plugs…the dealer is full of it…the check engine light will NOT come on if the plugs are bad…Well maybe in EXTREME cases.
When was the last time you had a tune-up?? When was the fuel-filter and air-filter changed??
How long have you driven it since the fuel line cleaning?? It could just be a simple calculation error.
I agree with Mike a “fuel line cleaning” is usually a scam, and especially on an '05 model Nissan.
If you ever have a problem with an injector, even a very mild problem, it will be noticeable at an idle. The idle will be slightly rough or the engine may stumble a little now and then. If the engine idles smoothly then the injectors are fine.
Eyeballing spark plugs to determine their condition is a pretty iffy proposition unless you have a lot of expertise in this area and if you’re going to go to the trouble of removing them then why not simply replace them.
A plug may appear fine but misfire when under compression and heat.
I think I’d try to figure out the tapping sound, that sounds a bit more serious than losing a couple of miles per gallon. I assume that the fuel system cleaner didn’t fix anything there?
HI all and thanks for the responses. I did the fuel like because the truck has 55k on it, it was high mileage when I got it. I did not pay the dealer price, but it was still pretty good.
MikeinNH
I did not know if the check engine light would come on or not, I just figured that the truck was so smart it would do that LOL. I have not changed the fuel filter ever, but the air filter is new, less than 5 k on it. I have put about 3 k on it since the cleaning in early november.
OK4450
I just went by my service managers advice, the plugs were brown, not black and looked to be ok but like you said, who knows. I cannot change them because two of them are under the air intake manifold and there is NO HUMANLY POSSIBLE way to get to them, I tried trust me, hours of trying and bloody knuckles…
mrjosh
your assumption is correct, it actually has gotten worse since the cleaning. The mechanic, who usually is spot on, thought it was carbon on the valves, hence the induction service. I am still under warranty, but without a real issue the garage wont tear the thing apart without costing me a few hundred bucks…
I am at a loss
You might want to get another diagnostic opinion at a different shop.
Check on the engine for wires or hoses they may have left disconnected. The vacuum hose to the fuel regulator may have been left disconnected. When the air filter was installed, a sensor may have been left disconnected. Ask around for a mechanic who knows engine management systems.
I recently had a fuel line cleaning done in the hopes to eliminate a tapping sound in the motor.
Huh?
Before the service I was getting 15-17 mpg in the city and 18-21 on the hwy. After the service I am getting 10-12 in the city and no more than 16 on the hwy.
Anything else change besides the “service” being done? Much colder weather? Seasonal change in gasoline formulation? Tire pressure low due to cold? Long idle time to warm up the cab? Has the truck been through these weather/driving conditions before, and what happened to the mileage? A 30% drop in mileage is a bit steep, though, so as others have suggested, look for things left unplugged on the engine.
“Carbon on the valves” is not going to cause a fuel mileage or tapping problem.
If this is a tapping sound that occurs constantly, even at idle, then that sounds like a valve lash problem; sticky lifter basically.
If this tapping is actually a rattle that only occurs on acceleration, and especially when the engine is warm and under a load, then that could point to an EGR system fault.
Plug symptoms can be a bit like injectors also. If you have a plug or two misfiring a little bit it can often be noticed while at an idle. You may feel a slight roughness or stumble now and then.
You might consider having AutoZone, Advance Auto, etc. pull the codes for you. They will do this for you free.
If your fuel economy is really tanking bad enough to be a problem then the CEL will illuminate and/or there should be a code or two present in there.
Other than that, I agree about checking things over to see if something is not plugged in correctly, or at all.
(A few months ago I saw a car that had a CEL on, mileage was down, etc. and the problem was that someone had only pushed the MAF connector about halfway in when they changed the air filter. It looked fine during the initial visual insp. but a little nudge snapped it on in and out the CEL goes.)
"If this tapping is actually a rattle that only occurs on acceleration, and especially when the engine is warm and under a load, then that could point to an EGR system fault. " This is exactly the problem I was having. the mechanic, in a now obvious ploy to get more of my money, suggested the fuel line cleaning. I do not know what the egr system is, or how to check, but I had Auto Zone check out the car with their tester and there were no faults.
It has gotten colder, but not that much, and we had cold weather before, so I elminated that. They changed the fuel over here in October or maybe even September, so I scratched that one off. I do notice that when it idles the mpg tool on the truck drops to a severe low, like it is dripping gas. I do not know what I would need to check to see if everything is on tight, and I hate to go to the garage for that because they will charge me 85 an hour, just to check the hoses (Greedy Bastards)…
The vaccum line to the fuel regulator sounds promising, if I knew where that was at LOL…I went on and got a service manual ordered, I miss the chilton books of old, so maybe that will assist me in finding some of this stuff.
Thanks for your help so far everyone!!!
I just went by my service managers advice, the plugs were brown, not black and looked to be ok but like you said, who knows. I cannot change them because two of them are under the air intake manifold and there is NO HUMANLY POSSIBLE way to get to them, I tried trust me, hours of trying and bloody knuckles…
I’ve replaced the plugs on this engine…Yes there are a couple plugs that are little bit of a pain…but took me less then an hour to replace all 6.
Well, now, I don’t think your mechanic was trying to rip you off with the fuel system flush. It’s also called a “top end flush” and it’s prescribed for cars which have a lot of carbon buildup.
While I agree with ok4450 that carbon buildup on the valves isn’t going to cause pre-detonation (“pinging”), carbon on the pistons can cause pre-detonation, and I suspect that was what your mechanic was using the motorvac for.
That said, checking the fuel pressure regulator is a good idea. Finding it might be a little tricky on this car, but if you can see the fuel injectors and fuel injector rail (that the injectors attach to), just follow the rail around and you will eventually see a cylindrical hunk of metal attached that has a vacuum fitting. Hopefully, you will see the vacuum line just laying off to the side.
How did you get the two under the manifold? I am very curoius to know, I don’t have the right tools obviously, and I do not want to take the manifold off.
There was enough room to put the socket on it…then I put a wrench on the socket.
f I cant find it then when I get my service manual I will be able to indetify it…It would be great if that was the issue.
No hoses were off. I had the Garage check it today when I had the oil changed. The Tapping sound he said is the Knock Sensor kicking in when there is pre detonation, the knock sensor takes over and slows the fuel so the combustion can catch up with the fuel. I did notice, I put an additive in the oil from Valvoline with this oil change and it is gone.
I am wondering if the tapping sound is from not the right oil weight. I know they use 5w 30 but I have always used 10w30. I was due for an oil change and the tapping was really noticable, but now the oil is new and the oil additive is in there, it purrrrrrs like a kitten.
Now none of this has helped me with the crappy gas mileage, and I am still at a loss on this. They checked the plugs, no foul no errors no lines lose ARGHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
I sincerely hope there was something lost in the translation here.
Are you seriously saying this garage stated the tapping is a “knock sensor kicking in”?
The part about the knock sensor “slows the fuel” is also way off base. The knock sensor makes no sounds nor does it have an affect on the fuel itself; it only provides an electronic signal to the ECM.
The purpose of the knock sensor is to retard the ignition timing. This is done electronically by the ECM (computer) and without going into a thesis on the entire operation I will say that the timing varies by the cylinder and by the nano-second.
Maybe I’m taking their comments too literally?
If the problem disappeared after an oil change and an additive the problem was more than likely a sticky lifter or valve lash adjuster. Normally this problem would be heard even at an idle and the oil weight should not have an affect on this.
No clue on the fuel mileage. With no CEL illuminated, no codes, and plugs burning brown in color all point to normalcy. The only thing I can think of would be that possibly the gasoline blends have changed in your area over the winter.
Your mileage is not that far under the EPA estimates of 14 and 19.
Thank you for the Response
let me rephrase they said that the noise was from somepredetonation and the knock sensor would take it out, not make the noise. I am sure I messed up what he said how it works, I apologize. The thing is, the noise DID NOT go away. It did on the trip from the garage to work (I think they have a zone over the whole area that it does not act the same when I take it there as it made no noise when I had the mechanic in the car). On the way home it was as loud as ever, and it is constant on the accelaration. So his theory (the Mechanic) that the Knock Sensor would make it stop tapping once it kicked in, is not accurate or that is my problem. I would guess that if this was not working then I would be getting kicked out by some code or something would be flashing blinking or what not.
I have one more thing to check in the air filter. The garage also told me that the blend of fuel was the issue, but this did not start till late november, and we turned in october to our wonderful winter mix. This also coincided with the fuel induction service, so I don’t know. I cannot help but to think that this is something very simple, it is just baffling enough to be something obvious.
Thanks for al of the responses!!!
This “knocking” sound may be pre-ignition (also, called “Ping”, or “knock”). You can check “ping” at www.wikipedia.com. To me, “ping” sounds like valves rattling heavily in a tin can. When it’s operating correctly, the Knock Sensor will detect when knock begins and inform the engine computer. The engine computer retards timing to stop pinging. The fuel mileage is reduced on an engine which has retarded timing.
To prevent “knock” from occurring, use a HIGHER octane fuel. Because of various reasons, an engine may need a higher octane fuel than originally recommended.
This is not knock I dont think from that. Here is how it drives as I was trying to get it down so I can show the mechanic next time. it goes like this when I am at a red light with a flat or slight grade in front of me…grrrrrrrr ratatatatatatata shift (20 mph) grrrrrrrrrr ratatatatatatat shift (30) grrrrrrrrrrrr ratatatatatatatata (constant at 45-50).
as for the mileage, I checked the air filter, and a 3rd of it was soot black, I could not knock it off, it was stuck to the filter. I could see throught the middle of the fitler but not the outside of it. Could this be the mileage problem?