Instead of taking my car to Nissan right away (and spending way too much money doing so), I figured I'd ask you guys for any hints on what might be causing the poor engine performance I'm suddenly experiencing. I'm willing to try some minor-to-moderate repairs/replacements on my own to see if I can fix the problem myself before having a pro diagnosis it.

Anyway, here's what's happening: just yesterday I started noticing vibration and severe inconsistency/hesitation during acceleration, at all speeds. Whenever I try to accelerate, the engine performs terribly now, hesitating but eventually speeding up. When coasting at constant speed, everything seems normal. With the manual transmission in neutral and the car in idle, the engine sounds fine, but the exhaust noise coming out of the muffler sounds different than usual -- it's like a "puff-puff-puff..." sound instead of the "white noise" that I think I used to hear when my engine was running smoothly. Also at idle, the RPM's are stable (tach is not bouncing around) and at the same level as usual. So it doesn't seem like an idle adjustment problem.

Any ideas? Exhaust system, perhaps? The air filter looks fairly clean (changed about two years ago), and I replaced the fuel filter about a year ago. I haven't had the fuel injectors cleaned. I replaced the platinum plugs at 60k -- now I'm at 116k and planned on replacing them in the spring. Could it be a worn or fouled plug? I've also done some searching and found these other ideas: (a) coolant temp sensor corrosion/cleaning (b) ignition coils (c) O2 sensor.

Also, I'm hoping this isn't related, but I grounded my VTC's about 6 weeks ago and the car has been running fine since. Gas mileage is good: 23-28 mpg.

This website (along with Craig Brace's site) has been a great source of money-saving information for a novice do-it-yourselfer like me.

Thanks for anyone willing to share some advice on this problem!

 

Sounds like one or more bad injectors to me...

 

Yep, sounds like fuel injector or something in that area.

Check the spark plug wire (resistance test), the spark plug (any fouling), the fuel injector (resistance test and/or ticking sound test).

 

a puff puff puff sound............hmmmmmmmm...
sounds like mine......hhahahaha!!! Yep, more than likely its the injectors. Does it sounds like a domestic??? Or you can say it sounds like a helicopter....am i correct??

 

I assume you are looking for things to check that are fairly easy and inexpensive to replace before shelling out the dough at the dealer. I don't think "sounds like injectors" really helps you much so here's my opinion.

Here are some things to check that are fairly easy to do.
1) Take out the plugs and see if any of them are discolored. ie... black and wet. They should be dry and clean. If you see one or more discolored(black), the injectors might be stuck. But you can try carefully undoing the injector plug and cleaning the inside of the connector(s). Maybe you should do this anyway to at least the front side.
2) Take out all the coil packs and see if the plastic housings are cracked. If any of them are, they are probably arcing. At the same time, inspect the connectors and clean them.
3) Carefully disconnect the maf connector and clean/inspect it. If it's dirty or if some of the contacts are not connecting good, it might make the car run odd.
4) Check ALL of your vacuum lines to make sure you don't have a leak.
5) Check to see that your EGR valve is working properly.
6) ditto with the PCV valve(pain to get at though)
7) Clean the throttle body. It probably needs it anyway.

 

Thanks for the checklist, Jeff. I'll go through it and see what happens. I'll also try testing the resistance of the injectors to see if one is obviously out of spec.

Could the problem possibly be from using 87 octane gas? I always put at least 89 octane in, but there have been a lot of gas station scams supposedly here on Long Island, where you pay for Plus or Premium but are only getting Regular. And I just filled up yesterday, which is when this started happening. Doubtful it's the problem, but I figured I'd mention it just in case.

And ShowMax: yes, the exhaust rhythm is kind of like a helicopter's "chop-chop-chop..." I guess...

I'll post results once I find some time to perform these tasks.

Thanks!

 

Just for clarification, VE's do not use spark plug wires.

 

My guess is the O2 sensor.

 

Yeah, I keep forgetting the VEs are distributorless.

 

Since starting this thread, I have determined the root of the problem: the outer electrode of cylinder #4's spark plug completely broke off.

When I replaced all the plugs with new ones, initially the car ran great, very smooth and with noticeably increased acceleration. But once the car got warmed up, the vibration and hesitation during acceleration returned.

What I believe happened is that the electrode that broke off was smashed by the #4 piston and is now embedded on top of the piston. Once the car heats up, this metal heats up much too quickly and causes detonation/preignition, which is the cause of the awful hesistation, vibration, and terrible acceleration.

(I performed simple resistance tests on the coils and (front) injectors, as well as a crude/manual power-balance test, and everything seems to meet specs.)

The plugs had been in there for 58k, and I was planning on replacing them in the spring (I guess I waited a bit too long ). They were actually the cheap Bosch #4202 plugs (which I didn't realize were the "cheapies" at the time when Autozone provided them to me), so maybe it's simply a case of the Bosch 4202's not being able to last 60k as I thought they were supposed to.

Also of note is the fact that the #4 plug was LOOSE when I removed it. I've read that a loose plug can lead to an overheated condition (too much oxygen) and electrode melting or other problems. But how did it come loose? It seems to me that either the plug suddenly or gradually came loose somehow after being tight for nearly 58k, or it was loose all along, or perhaps some other condition caused the electrode to break off and that led to the plug loosening.

Obviously, some degree of costly engine overhaul is needed to repair this problem. Is there any chance I could find a shop to repair just the #4 piston (and valves, perhaps) for a reasonable amount of $$$? Anyone think it's worth repairing this problem on a 1993 SE with 117k? Is there any chance that over time, if I keep running the car as is, that this piece of electrode that is embedded on the top of the #4 piston will eventually melt away/disintegrate and hence the problem might self-correct?

Since the #4 cylinder is pre-igniting and causing the terrible performance and vibration, I decided to try running the car with the #4 cylinder's coil and fuel injector disconnected. To be honest, even with the obvious loss of ~1/6 of my power, the car runs fairly well like this, with only a little bit of vibration, and it still gets reasonably good gas mileage. This might prove to be my economical "solution," unless someone convinces me that I'm potentially causing even more extensive damage to the car somehow by running it this way.

I'm running Bosch 4202's again (as I bought them before realizing they are most likely the problem), but I will certainly replace them at or before 30k.

Any insight you can provide is greatly appreciated!

 

Wow. I would see if you can get a mechanic to take the plug out on #4. Then use a small wire camera thing in the cylinder to verify that some of the plug is indeed imbedded in the piston. If it is, maybe they can use some special tools to pry it out. Hopefully you don't have a bent valve in there.

 

Good idea. That's the type of idea I was looking for, and I'll see if I can get a shop to do it.

Anyone have any thoughts on running (for the time being) with the #4 coil and injector connectors disconnected? It runs fairly well, actually. But with the injector disconnected, is NO fuel being injected, or could some small amount fuel perhaps be getting into the cylinder head anyway. If so, that doesn't sound like a good situation, especially since there is no spark to burn it (would the compression ratio be high enough to burn it?).

Any ideas on the root cause of this problem, so that I (and others) don't have the same thing happen again?

Thanks!

 

JUST REPLACE ALL THE SPARK PLUGS.

the electrode melted off because it probably was not torqued properly. If the spark plug is too loose, then heat will not dissapate to the cylinder head, and it will run incredibly hot, thats why it melted off. Its definitley NOT embeded in the cylinder head. If your lucky the remaining electrode in the cylinder melted and disintegrated getting farted out of the exhaust valve (hopefully not damaging the exhaust valve). But I would not worry about it.


There are a bunch of old threads from fourth gen guys who were blaming the bosch plugs for the electrodes burning off. But it was just because they didnt know what they were doing and they didnt tighten the plugs properly

 

I did replace all of the spark plugs, and as I said, the car runs great for about 1 minute before it has a chance to warm up. Once warm, it runs absolutely terribly, JUST AS BAD -- and similarly bad -- as with the broken-tipped spark plug. I've double and triple checked to make sure the plugs are tight, and they are. Consequently, to me, the preignition/detonation theory (which a Pep Boys tech posited over the phone to me) makes some sense based on what I'm saying here.

It would be great if the electrode simply "melted and disintegrated", but I'm not convinced that it did, which is why I think Jeff's suggested scope inspection makes some sense.

Moreover, the spark plug tip does not look like it "melted" off (though I don't discount the possibility that it may have), but rather it looks like a very clean break near the base of the outer electrode.

I may not have tightened this plug sufficiently 58k ago (I've since improved my technique by taking out the rubber part of the socket when tightening, and maybe I'll get a torque wrench for Christmas), but the plug lasted until now before causing this problem. If it wasn't tight initially, it seems to me that a problem would have developed sooner, no?

 

Also keep in mind over tightening is equally bad. If a its overtightened the ceramic insulator can crack, then there will be a path for the high voltage to leak and short to the cylinder block. Spark plugs are typically tightened to some where around 15 foot pounds. But what you can generally do is when install NEW (and only new does this apply), is to first tighten the plug by hand until it has fully seated, then tighten with the wrench an addition 1/4 turn, this compresses the washer on the spark plug. But keep in mind that that washer only gets compressed once.

 

Call around your area. A large mechanics operation could have a "fiber optic" viewer. You might check other local businesses like a specialty camara store.

Another way might be to stick a magnet down the hole. Since the block is aluminum and the plug tip steel. It could still be banging around in there. Which is also another reason to NOT use the car until you have your answer.

 

Hey, tell me if you get this fixed. I have the EXACT same symptoms as you do, but my spark plugs were perfectly fine(it all happened after I changed my spark plugs). About 200mi later, an injector failed, and it cost $600 to get it replaced(couldn't affored the extra $500 for all 6). But it's still running like that! I'm sure I'm damaging the other injectors by just running it, and I would really like to know what the cause of the problem is, becuase I have a strong feeling, the other injectors are still getting stressed, and don't have long left on them, and I'd like to prolong them as long as possible, but they feel like they're getting worse(something is still harming them!). I think something needs to be adjusted, or checked, or something is in there when I put in the spark plugs(replaced them /w NGK v-tips right afterwards, originally had NGK coppers).

Any idea's that the mechanic wouldn't laugh at? He said there's no way of predicing which injector is going to fail, but the car's still running rough , which caused an injector to go last time.