# Hey guys, new member, 94 sentra fuel/pinging issues.



## Pittsdriver (Aug 5, 2008)

Hey everyone,

I have a 1994 Sentra SE with the 1.6. Ever since Ive owned it, its pinged on 87 octane. I had the car serviced at Nissan where they did a full tune up and all that. I checked the timing myself a while back and it looked right on. I want to check it again tonight to make sure. The car also seems to be getting not so good gas milage. What is the tank capacity on the 94 sentra SE? I dont think I should need to put in 91 normally something is causing the pinging. If its excessive carbon deposits, anything to clean that? Something like seafoam I assume? Any help, quick checks and pointers would be really appreciated.


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## greenbean699 (Jan 18, 2004)

I could be wrong but i believe the take holds 13.3 gallons. help your engine out by getting the 91 or better octane rating.


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## Pittsdriver (Aug 5, 2008)

is it normal to run 91 in these cars??? Right now I'm getting about 275 a tank. Plugs looked ok but I couldn't check the timing my light is a pile of crap.


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## Centurion (Sep 5, 2002)

Mine had been pinging for years even when running premium. I just started using Mobil1 0W-30 oil and it hasn't done it since; and yes, I know the connection between the two dosen't make any sense.


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## roadrunner (Jul 13, 2008)

Interesting you are having pinging problems. My 94 1.6 won't ping no matter what I try. I am running 87 octane and currently have the timing set at 22*BTDC. I've advanced it as far as the distributor will allow trying to get it to ping but it won't. I am afraid to leave it advanced to the limit but it seems to run okay and perform decent at 22*. Mileage is 23-26 all stop and go (mail route) 106 miles with 110 stops daily plus 11 miles to and from work.


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## greenbean699 (Jan 18, 2004)

roadrunner said:


> Interesting you are having pinging problems. My 94 1.6 won't ping no matter what I try. I am running 87 octane and currently have the timing set at 22*BTDC. I've advanced it as far as the distributor will allow trying to get it to ping but it won't. I am afraid to leave it advanced to the limit but it seems to run okay and perform decent at 22*. Mileage is 23-26 all stop and go (mail route) 106 miles with 110 stops daily plus 11 miles to and from work.


i'm guessing you didnt time it in "timing mode"


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## TheBrownRobert (Aug 28, 2007)

To your mileage question: I have a 1.6/auto (no A/C) and I get about 270 miles to a tank with 100% city driving (average 26.5 MPG). I use regular gas in my car. This pinging problem seems to be common in Sentras.


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## roadrunner (Jul 13, 2008)

Sorry greenbean699 I have the OEM service manual and timed it according to the instructions therein. I might add I am a 40+ year veteran mechanic with dealership experience so am no novice under many different hoods. Also as to your "timing mode" that would be rather moot since advancing the distributor to it's physical limits rather exceeds any differences unhooking any sensors or relays might cause. No ping was able to be induced under any circumstances.


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## sonicgundam (Aug 15, 2007)

just because it isn't pinging doesn't mean it's not detonating.

pinging related to fuel = pre-ignition, which leads eventually to detonation. you can't hear detonation, because it occurs at the same interval as the spark. detonation is silent, and it's deadly. pre-ignition is often mistaken for detonation. essentially they're the same, but occur at different times. pre-ignition is on the power stroke, where as detonation is at TDC on the power stroke.


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## roadrunner (Jul 13, 2008)

Rather than argue semantics:
Knocking (also called knock, detonation or spark knock, pinking in UK English or pinging in US English) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise time in the piston's stroke cycle. The peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. It should not be confused with pre-ignition (or preignition), as they are two separate events.

Abnormal combustion (Detonation)

When unburned fuel/air mixture beyond the boundary of the flame front is subjected to a combination of heat, pressure for a certain duration (beyond the delay period of the fuel used), detonation may occur. Detonation is characterized by an instantaneous, explosive ignition of at least one pocket of fuel/air mixture outside of the flame front. A local shockwave is created around each pocket and the cylinder pressure may rise sharply beyond its design limits. If detonation is allowed to persist under extreme conditions or over many engine cycles, engine parts can be damaged or destroyed. The simplest deleterious effects are typically particle wear caused by moderate knocking, which may further ensue through the engine's oil system and cause wear on other parts before being trapped by the oil filter. Severe knocking can lead to catastrophic failure in the form of physical holes punched through the piston or head, either of which depressurizes the affected cylinder and introduces large metal fragments, fuel, and combustion products into the oil system.

Detonation can be prevented by the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate; enriching the fuel/air ratio, which adds extra fuel to the mixture and increases the cooling effect when the fuel vaporizes in the cylinder; reducing peak cylinder pressure by increasing the engine revolutions (e.g., shifting to a lower gear); decreasing the manifold pressure by reducing the throttle opening; or reducing the load on the engine. Because pressure and temperature are strongly linked, knock can also be attenuated by controlling peak combustion chamber temperatures at the engineering level by compression ratio reduction, exhaust gas recirculation, appropriate calibration of the engine's ignition timing schedule, and careful design of the engine's combustion chambers and cooling system. As an aftermarket solution, a water injection system can be employed to reduce combustion chamber peak temperatures and thus suppress detonation.

Knocking is unavoidable to a greater or lesser extent in diesel engines, where fuel is injected into highly compressed air towards the end of the compression stroke. There is a short lag between the fuel being injected and combustion starting. By this time there is already a quantity of fuel in the combustion chamber which will ignite first in areas of greater oxygen density prior to the combustion of the complete charge. This sudden increase in pressure and temperature causes the distinctive diesel 'knock' or 'clatter', some of which must be allowed for in the engine design. Careful design of the injector pump, fuel injector, combustion chamber, piston crown and cylinder head can reduce knocking greatly, and modern engines using electronic common rail injection have very low levels of knock. Engines using indirect injection generally have lower levels of knock than direct injection engine, due to the greater dispersal of oxygen in the combustion chamber and lower injection pressures providing a more complete mixing of fuel and air.

An unconventional engine that makes use of detonation to improve efficiency and decrease pollutants is the Bourke engine.

Pre-ignition

Pre-ignition (or preignition) in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events.

The phenomenon is also referred to as after-run, or run-on when it causes the engine to carry on running after the ignition is shut off, or sometimes dieseling, in reference to the fact that a heated diesel engine may, by design, run without an external ignition trigger so long as a suitable fuel/air mixture is supplied to the cylinders. This effect is more readily achieved on carbureted gasoline engines, as the fuel supply to the carburetor is typically regulated by a mechanical float valve and fuel delivery can feasibly continue until fuel line pressure has been relieved, provided the fuel can be somehow drawn past the throttle plate. The occurrence is rare in modern engines with throttle-body or electronic fuel injection, as the injectors will not be permitted to continue delivering fuel after the engine is shut off, and any occurrence may indicate the presence of a leaking (failed) injector.

Preignition and engine knock both sharply increase combustion chamber temperatures. Consequently, either effect increases the likelihood of the other effect occurring, and both can produce similar effects from the operator's perspective, such as rough engine operation or loss of performance due to operational intervention by a powertrain-management computer. For reasons like these, a person not familiarized with the distinction might describe one by the name of the other. Given proper combustion chamber design, preignition can generally be eliminated by proper spark plug selection, proper fuel/air mixture adjustment, and periodic cleaning of the combustion chambers.

I know this makes for a long post. Sorry, but it should clear up any misconceptions. Personally I can hear the difference between ping and detonation as can any trained ear of experience. My 94 is doing neither. Best I can explain the difference is pre-ignition or pinging sounds tinny and higher pitched much like a very loud lifter noise while detonation sounds much deeper and lower toned more like a loose main bearing knock noise. The extreme danger range is when you hear the higher pitched noise undertoned by the lower knocking noise. Imminent engine failure is under way at that point.


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## greenbean699 (Jan 18, 2004)

have fun fixing your engine with your "supposed" 22*BTDC timing. :loser:


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## IanH (Feb 11, 2003)

maybe the knock sensor is retarding the timing ?


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## roadrunner (Jul 13, 2008)

IanH said:


> maybe the knock sensor is retarding the timing ?


I'd considered that possibility and disabled the knock sensor to check it out. No difference. 
BTW, glad to see your comments are more mature than those of greenbean. I'd thought that people could deduce from my posts in this thread I am no novice working on cars. Apparently beyond some people's understanding however.


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## sonicgundam (Aug 15, 2007)

roadrunner said:


> BTW, glad to see your comments are more mature than those of greenbean. I'd thought that people could deduce from my posts in this thread I am no novice working on cars. Apparently beyond some people's understanding however.


i think it was the fact that you claim to have advanced your timing to 22 degrees BTDC on a stock GA with regular octane fuel that had us tossing up the BS flag in our minds. and that you have detonation and pre-ignition backwards. lest you care to argue with my professors, who are not only 40 year experienced mechanics BUT also have been trained to teach the next generation.


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## greenbean699 (Jan 18, 2004)

sonicgundam said:


> it was the fact that you claim to have advanced your timing to 22 degrees BTDC on a stock GA with regular octane fuel that had us tossing up the BS flag in our minds.


i couldn't have said it better. 22 degrees 

i dont care how many years you have been working on shit, it only took me 5 mins to read the FSM and find that that the ga16de has to be timed in timing mode to change the base timing. just turning the distributor and setting it to 22 degrees doesn't mean its the real time.


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## sonicgundam (Aug 15, 2007)

greenbean699 said:


> i couldn't have said it better. 22 degrees
> 
> i dont care how many years you have been working on shit, it only took me 5 mins to read the FSM and find that that the ga16de has to be timed in timing mode to change the base timing. just turning the distributor and setting it to 22 degrees doesn't mean its the real time.


plus, if you were a proper tech, you would have read the FSM and done it properly. the reason for the abruptness more than anything, is that you're handing out false information, and that's not a good thing.


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## roadrunner (Jul 13, 2008)

Just an FYI for both greenbean and sonicgundam: First of all the information I posted regarding ping, pre-ignition, and detonation is not from my own head this information is a copy/quote from wikipedia. If it's wrong quarrel with them. I quoted them as it was much easier than getting out a manual and scanning it and attaching it after editing it down to applicable passages. Arguments always seem to erupt when discussing these problems no matter how experienced the techs are. I only posted them to benefit those who might not be aware of the similarities of the three problems.
As to the FSM or OEM or whatever you choose to call the factory service manual, Yes I have it and have read and re-read the section on timing as well as some others I had interest or questions about. Apparently, correct me if you feel I'm wrong, but in your readings of the FSM you've overlooked there are two ways to time the 91-94 Sentra 1.6. The first method requires a consult tool which I do not have and it refers to setting the timing in "timing mode". The second way tells how to do the timing and idle speed setting manually when you do not have a consult or access to one. This is the method I used. The disturbing part to me was the fact that I was unable to make the car ping even when advancing the distributor to it's physical limits which I assure you is a lot more than 20*. I didn't mark the pulley or use an advance capable light to determine the timing at that point as I was not comfortable setting it that high anyway.
Essentially my manual says for non-consult method: warm up engine, run ECM in diagnostic mode to check for codes (I found none) and O2 function, shut off engine, unhook TPS connector, start engine, rev engine 2-3 times 2000-3000 rpm, let it idle (725rpm+-25), check and correct timing with light to 10*+-2* idling in neutral. At this point it then goes back into rechecking and resetting idle speed if needed. I did this several times moving the timing up to where it is now (22*).
If there's a better/easier way to do this I'm all ears and no I can't afford a consult tool. I've priced them and unless I were going to run a shop and use it a lot it isn't practical for a home-repair type situation which is where I am now since I quit working on vehicles for the public not long ago.


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## IanH (Feb 11, 2003)

Thanks you for the detailed write up. This is basically what is in the sticky in the forum, so no problem there.
http://www.nissanforums.com/ga16de-1-6l-engine/118530-definitive-guide-how-adjust-timing.html
quite a few people have posted their experiences here, and many have had problems getting the ECU into timing mode. 
this means obviously they cant time the engine properly. 
Since I have not done this yet i cant tell you "how to tell" if you aren't.
What you are saying goes against what some of the others have found and represents a problem, so either something is broken or you are not in fact in timing mode.
So can someone post how to tell if you are in timing mode and how to tell if you aren't?
And I think that if it isn't pinging then maybe the knock sensor or something else is putting the ECU into limp mode ?


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## roadrunner (Jul 13, 2008)

*Timing issue*

Thanks for your response IanH. I don't think the car is in "limp" mode. The manual refers to this as "fail safe system". The condition of operation chart indicates that if it were in fail safe fuel injection would be simultaneous instead of sequential (can't tell on that score), ignition timing is fixed at preset value ( as checked with light it advances normally with increases in rpms), fuel pump relay is on when running off when stalled (don't know didn't check), IACV-AAC valve full open (idles and adjusts normally), and cooling fan relay on meaning fans on all the time (fans cycle normally with rising/falling engine temps. Additionally the check engine light would be on steady (it isn't). From my reading it appears that the only time this mode would be activated is in the event of a failure within the PCM itself. It appears to me any other failures might negatively affect performance etc but would simply set a code in the PCM and possibly turning on the check engine light which could be read through the diagnostic procedures. I've found no codes other than 55 indicating no codes present.
As for the knock sensor what I read says it won't put the car in fail safe mode (limp) but it can, if signal is sensed as abnormal by the ECM, retard timing throughout the operating range. I'll admit I don't know on that one. I'm still reading to see if there's a way to operationally check it other than simple resistance checks etc. I haven't found it yet if there is.
One other thing bothering me is your continued references to "timing mode". I have found no reference to this in all the reading in the FSM. Are you sure you are referring to the 91-94 B13 1.6 engine? Perhaps this something required on other/ newer models? Not saying it isn't right. Just saying I can't find any references to it in my manual. Either the FSM or a Haynes manual I bought before I discovered how woefully inadequate it was as concerns specifics on the Sentra timing and emissions systems information. Not a bad book. Just short on specifics if you want to dig deeper into the technical aspects of electrical systems etc.

Don't know if it makes any difference but my Sentra is the Jap built model with 1.6 DOHC VVT engine.


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## IanH (Feb 11, 2003)

the link i added is for the 91-94 GA16DE, and the 95 - 99 is basically the same procedure, the layout of the idle screw etc is in different places.
Yes that is the same 1.6 VVT made in Japan.
The "timing mode" is the ECU mode that allows the base timing to be adjusted.
All the reading I have done here and on NPM when it was publishing Nissan article say you must have engine in timing mode to set the base timing, and 10 degrees is recommended, (12 max for regular fuel i think), and 15 degree max with premium.
the three throttle blips with the engine up to temp puts the ecu into timing mode. the timing marks should not then move unless you turn the distributor.
you must also set the idle speed to spec first. 
i don't know what gets it out of timing mode, maybe a shut down and re-start, or just opening the throttle.
As i said earlier some people reported problems getting it into timing mode.
If it is not in timing mode that would explain your advanced timing and no knocking.
i think at this point you know its not in limp mode or fail safe.
i might have a go at my 200sx SE-R over the weekend and let you know how it goes and if i learn anything. ( the instructions for the SR20 are the same !!!) but timing spec is a bit different.


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## roadrunner (Jul 13, 2008)

IanH, I think you are correct on the in/out of timing mode and I have followed those directions exactly which is what seems confusing to me regarding our disagreement. When I've been using the light the marks do not fluctuate at all either. I think what would take it back out of timing mode would be the shutdown combined with the TPS reconnect and restart as this would seem very similar to the switching from one diagnostic mode to the other of the PCM as associated with shut down and restart when running code and O2 sensor diagnostics.
As a side note I took the car on an 850 mile trip this past weekend with speeds ranging from 65-80 on a combination of two lane and interstate. Got 33.2mpg with no problems/other issues all on 87 octane regular. I don't know if this good or bad for this car but seems pretty fair to me considering it's an automatic trans.
Car was due for an oil change and I went from 10w30 to 5w30 now the weather is cooler. I'll let you know if this seems to make any differences as I noticed another member posted it seemed to for him. If so perhaps difference in VVT reaction due to lower oil pressure throughout operating range??? Just speculation so don't jump on me for it. Ran out of time and daylight today to do anything else to it so perhaps tomorrow I will try once again to time it and re-verify.


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