Pre-ignition in only one cylinder?

[Yuk]

One plug in my Sentra (E16i engine) shows text book signs of pre-ignition, the other three plugs look good to excellent. Why would only one cylinder be suffering pre-ignition? I adjusted the valve lash about a month ago, could I have done something to the valves to cause the pre-ignition?

 

[deepsquat]

carbon build up in that cylinder ..

 

[mechtech]

Do you hear spark knocking?
Maybe that cyl is simply leaner than the rest.

 

[Gary Allan]

Assuming it's multipoint injection (I haven't a clue what an E16i is) then that injector can be clogged or lame in some way.

I guess this would just be an extension of what mechtech just said

..except that you can maybe look for a slight vacuum leak that is isolated to that runner.

If you can't lock down a cause ..run a colder plug in that cylinder.

 

[2003TRD]

yeah most likely a hot spot from carbon or a bad injector. I would run some seafoam through the vacuum line, put some in the tank and put a new plug in. Check it frequently to see if you see the same thing. Or if you have the cash replace the inj.

 

[Drew99GT]

Did you notice this BEFORE you adjusted the valves? Perhaps you got the valves a hair too tight in that cylinder.

 

[Yuk]

quote:

---

carbon build up in that cylinder ..

---

None that I can see... If there is, what does that mean?

quote:

---

Do you hear spark knocking?

---

No.

quote:

---

Maybe that cyl is simply leaner than the rest.

---

How do I check if it is leaner? Why would it be leaner than others?

quote:

---

Assuming it's multipoint injection (I haven't a clue what an E16i is) then that injector can be clogged or lame in some way.

---

This car has throttle body fuel injection.

quote:

---

Did you notice this BEFORE you adjusted the valves? Perhaps you got the valves a hair too tight in that cylinder.

---

No sign of pre-ignition before the adjustment.

So, adjusting the valves too tight can cause pre-ignition?

quote:

---

I would run some seafoam through the vacuum line, put some in the tank and put a new plug in.

---

I've been using FP on every fill for the last 6 months and I put in a new plug last night.

quote:

---

Check it frequently to see if you see the same thing. Or if you have the cash replace the inj.

---

After driving 750 km today the plug is clean (except for a very slight green discolouration on the electrodes...

). I don't think changing the injector is in order, since this car has T.B.I. Am I right?

 

[punisher]

You can have carbon buildup on a piston or a chamber, sometimes all it takes is a small piece of carbon on a chamber or valve that gets hot enough to cause detonation. Frankly the only foolproof way to check for carbon is to borescope the chamber.

A vac leak in an intake runner can cause a cylinder to go lean, possible intake gasket. Sometimes engines have vac ports/lines that are installed into only one runner, if there is a problem/leak with the vac line or the component it connects to, you have a lean concern.

It might be possible to get preignition from adjusting exhaust valve to tight, less time on seat= hotter valve = preignition. Rare but possible.

 

[Smoky14]

I'm confused by the terms. Preignition; and it sounds like you mean detonation.
I'd be sure to OHM check the plug wire to that cyl.

 

[Drew99GT]

Adjusting valves too tight can overheat the cylinder which may cause detonation/pinging I'd imagine. Although if they were that tight, you'd probably notice a rougher idle and decreased performance.

 

[Yuk]

quote:

---

Smoky14
------------------------------------------------------------------------
I'm confused by the terms. Preignition; and it sounds like you mean detonation.

---

Often in repair manuals, like Haynes and Chilton's, there are reference photos showing various spark plug conditions and causes for the conditions. The damaged plug from my car matches the Haynes photo that describes the cause as pre-ignition.

quote:

---

I'd be sure to OHM check the plug wire to that cyl.

---

This is really interesting to me... After replacing the single damaged plug I drove for about 50 km and checked the replacement plug for signs of new damage. The plug lead end broke off and stayed clipped to the top of the plug. I don't know if it broke right then and there, or if had been cracked for awhile and just happened to finish breaking then. If the lead had been cracked for awhile that could have caused an OHM problem, couldn't it? The next 700 km were driven with a replacement lead.

 

[bulwnkl]

quote:

---

Originally posted by Yuk:
This is really interesting to me... After replacing the single damaged plug I drove for about 50 km and checked the replacement plug for signs of new damage. The plug lead end broke off and stayed clipped to the top of the plug.[/QB]

---

Could have been broken already, or could have broken when you took it apart that time. It's reasonably common for people to pull wires apart when removing them from a hot engine, especially if the wires were not super-quality in the first place. Not sure if it's by design or not, but the boots tend to stick to hot plugs.

 

[T-Keith]

Sometimes an engine design favors one cylinder in port design or heat dissipation, this can lead to a leaner, or hotter running cylinder. For instance the center cylinders of a bank often will get hotter, especially in a Siamese block. Also the closest the TB may get more air then the others. You may be close to pre-ignition on all of the cylinders, but this one is just over the edge. I would also look at PCV placement, this may cause problems with one cylinder. It could be a plug defect as well.

-T