Running with a Slight Sputter?

[Gebo]

Just finished tuning up my 94 Nissan Sentra 4 cyl. Plugs, OEM wires, OEM distributor and rotor, OEM air filter, cleaned MAF Sensor with MAF Cleaning spray, cleaned throttle body and IACV with throttle body cleaning spray, set idle and set timing at 12 BTDC following service manual. Have run 1 can of RedLine "fuel system cleaner" through first tank of gas and am currently running Amsoil's Fluid additive in this tank. Got 35 mpg on first tank.

What I want to know is what could be causing a slight sputtering under load at lower RPMS like when going up a hill when you are almost where you need to downshift. Not lugging the motor. Just a heavier load. It does it all the time and most people may not even notice it. They would think it is just losing power. It's a slight miss under a load.

What have I missed?

 

[Gabe]

Fuel filter??

 

[oggb]

Fuel filter/fuel pump perhaps.

 

[Gebo]

Oops, I forgot to tell you I just installed a OEM fuel filter.

So a "failing" fuel pump would do this?

 

[Chris142]

nissans eat coils

 

[Gebo]

please explain

 

[Oil Changer]

Air in the fuel system from changing filter?

 

[Gebo]

It did it before I changed the fuel filter.

 

[ARCOgraphite]

If eveything is OK then carbon on pistons, valves and gummy rings cause poor cyl balance. Sound like you may have a weak ignition or poorfuel atomisation or both. Check all engine to body and bat - to transaxle grounds as well as the 12V+ to coil. Problems can occur through the ignition SW (keyON) circuit too.

Hope you dont overdo it with silicone grease on the boots - this stuff is a good insulator. Wire terminals just need a tiny wipe in the boot hole with a mono layer of goo on your pinky.

 

[Astro14]

I think air in the system would be gone quickly...

Most likely is either: weak spark (so, with new plugs and wires, it's more likely a coil...) or an injector that has a poor pattern...the injector may not have been addressed by cleaner, sometimes, you just have to replace one...

 

[mechtech2]

A plugged filter would show up at high RPM and load.
There is less flow at low/mid speeds, and if it only misses then, I'd look elsewhere.
Sounds like ignition malfunction. Could be the coil.
But there are so many parts! Could be the TPS, or EGR system. Even the MAF.

 

[Gebo]

How do you check a coil?

 

[ARCOgraphite]

If it "sort of" runs, Replace it. If you want to play Dr. Frankenstein, You could stress-test it with a plug with the ground terminal snipped off, hold it close to any good bare metal car GND then slowly increase the gap until the spark goes elsewhere - but if it can make a HOT 1/2" spark, its most likely GOOD.
Plug gap is OK? Most likely 1.1mm gap? Be aware that most plugs have insulator varnish on the terminals and the wire boot female terminal has to gouge through the varnish. If your new wire boots have springs - you can have trouble.

 

[Gebo]

I notice the plugs are "hotter" than the stock plugs. NGK4's vs NGK5's. Would this make a difference ? I know that is not the entire plug number, I'm just trying to show you they are one grade in heat range different....

 

[OVERKILL]

Originally Posted By: Gebo
I notice the plugs are "hotter" than the stock plugs. NGK4's vs NGK5's. Would this make a difference ?


So you put in hotter plugs? Why?

And it does sound a lot like a failing coil.

If you have a scanner, you should be able to see the misfire counts for each cylinder. If one of them is way higher than the others, you know where to start looking.

 

[Gebo]

I put new NGK 5... plugs in 2000 miles ago when the original owner had it. I changed the wires, distributer, rotor, etc. I was just doing the lady a favor. I didn't know that she had taken it in to a local shop between the time I replaced the plugs and they time I bought it from her and they replaced her plugs. I know...sad but true...

 

[Gebo]

I don't think I can use a scanner with this car. If you know something else, please help me.

 

[OVERKILL]

Right, missed the fact that it is a 1994. I see you say distributor, so it only has the one coil then too.

I'd change the plugs back to what they are supposed to be for starters, and make sure they are gapped properly.

 

[Trav]

Being a 94 you need to find someone with a scope, it will show any sort of ignition failure quickly.
Look for air leaks in any rubber boots going from the throttle body to the air cleaner or vacuum leaks in hoses or connections also.

Did any plug seem a lighter color than the others?

Edit: Do you have access to a cheap vacuum gauge?

 

[Gebo]

Originally Posted By: Trav
Being a 94 you need to find someone with a scope, it will show any sort of ignition failure quickly.

I don't know anyone with a scope. I'll google and see what it is.


Look for air leaks in any rubber boots going from the throttle body to the air cleaner or vacuum leaks in hoses or connections also.

Will do.

Did any plug seem a lighter color than the others?

I'll let you know tomorrow.

Edit: Do you have access to a cheap vacuum gauge?


What would I do with it?

Thanks for the suggestions.