Spark & Gas - what else is needed? (please don't say compression)


#1

I figured I’d start a new thread asking a basic question rather than assuming I know anything (which I likely don’t!).

'98 Nissan Maxima had a check engine light come on and started running very rough. I took it to get a code read and came up with P0320 and P0325. I’m not worried about the 0325 since that’s a knock sensor. 0320 is a misfire on cylinder 2.

With the car idling, I pulled the power connector from coil pack 2 to see if it made a difference in the idle - nope. I did the same for the other cylinders, and each responded with a noticeable change in the idle, which was remedied when it was reconnected.

I moved the coil pack from #2 to #4 (swapping them) and the same problem existed - idle was rough and didn’t make a difference when I pulled the power on 2, but it did on all other coil packs. So, it seems the coil pack ins’t the problem since multiple packs don’t seem to make 2 work, but they work on other 4 and 6.

I then pulled the spark plug from cylinder 2, it was very black and looked in bad shape. I replaced it. Still no love.

I then put a spare plug in the coil and was able to see spark as the engine ran, so it seems that the coil pack at 2 is getting juice.

So, I have gas (big odor when the car is running - seems super rich)
I have spark

Still running very rough and the 0320 code remains.

Ideas of where to go next? I’m almost resigned to going to a shop and spending far more than I was hoping. I’m not sure what else I can do to determine, and alleviate the problem.


#2

In order for an internal combustion engine to run it needs these four things.

*Fuel

*Air

*Spark

*Compression.

Tester


#3

The missing element is oxygen from the air. The engine needs a fuel/air mixture and as you noted, the mixture does not have enough air. If your air filter is not clogged, I have no idea what causes this problem. In the old days, I would suggest a stuck float in the carburetor, but your car doesn’t have a carburetor. Our other regulars may be able to help you.


#4

Can you swap the #2 fuel injector with another one?


#5

Since you smell fuel, you may want to look at the injector

By the way, why haven’t you checked compression?

Years ago, my brother’s car had a hard time starting, and ran quite badly. It had low compression, due to valves that were out of adjustment. After doing the valve adjustment, all of his problems were resolved


#6

1998 model…Can we assume the mileage is north of 150K miles? The next step is to check the compression on that cylinder. A compression gauge is inexpensive or many auto-parts stores might have one they will loan you…A normal reading (throttle held wide open) is about 125-175 PSI .Give it three or four revolutions…Disable the ignition when doing this as you don’t want the engine to start…You might as well remove all the plugs and test them all while you are at it…

Should your #2 cylinder have normal compression, then the fuel injector becomes the prime suspect…Next would be a major malfunction in the valve gear like a broken rocker arm or badly worn cam lobe…


#7

I prefer a leak-down test.

A leak-down test tells you why the compression is low.

Tester


#8

I had ruled out the injector since I smell a strong presence of gas. Maybe that thinking is wrong. I’ll try to remove and clean/replace and also check the compression.

Thanks all - report to follow.


#9

Try pulling the new plug you put in cyl.2 and see if it’s wet with gas. Run the engine for a few seconds before doing this.


#10

Always run a compression test. A low cylinder can cause incomplete combustion which will cause that cylinder to run rich.
One would think that if this problem came on abruptly then compression would not be an issue but that’s not a given.

If an injector is hanging open for whatever reason the excess gasoline can keep the cylinder wall washed down. That can cause low compression and piston ring/cylinder wall wear.


#11

A strong presence of gas suggests a bad injector. It’s either not closing properly (leaking) or not spraying cleanly.

One item missing from everyone’s list is vaporization. Combustion happens only with those hydrocarbon molecules that are in direct contact with oxygen molecules. In properly vaporized fuel, there’s a lot of surface area per the volume of gas being injected, allowing lots of the fuel to combust near the top of the power stroke, and allowing pretty complete combustion in the short time that is the power stroke. If an injector is not spraying cleanly, if it’s splurting droplets out like when you squeeze a Windex bottle slowly. There’s much less surface area per volume, and can be too little surface area to burn through the droplets completely. The combustion will have to burn through the droplets like peeling the layers of an onion. If the orifice is worn in the injector, it also allows too much gas to get through. These manifestations create that strong gas smell you’re experiencing.

As 2 cents said, pull the spark plugs and see if any are wet with gas. If one is, either that cylinder has no spark or the injector is shot.


#12

If the spray pattern of an injector is badly compromised by dirt or whatever, the fuel stream can remain in a liquid form, like a shot from a squirt gun, and will not ignite properly in the combustion chamber.It WILL cause the catalytic converter to overheat as it tries to burn the raw fuel being pumped through the engine…In another injector failure mode, the “pintlle”, the little valve that closes the injector fails and a steady stream of fuel is injected into the engine flooding that cylinder…


#13

bump


#14

Why did you say “don’t say compression” ? You know the engine is getting both fuel, spark and timing because it runs. Deficiencies in any of those would kill all the cylinders and you know cylinder 2 is getting spark because a plug hooked to the wire fires outside the engine. You know #2 is getting fuel because the plug is wet.
This only leaves an injector flooding the cylinder with a stream of fuel pr compression caused by bad valves, valves , rings or a hole in the piston. The bad valves anything that would cause the valves to not open or seat.


#15

The no compression thing was a hopeful wish, since I would think that would be the most expensive thing to fix.

An update: I pulled the front 3 injectors (2-the failing cylinder, 4 and 6).

2 looks very much different from 4 and 6, in the sense that there’s a spacer or something at the end that’s missing. I’m not sure if that would impact the flow of gas, but it’s there for a reason so I’m assuming its absence is a bad thing.

Anyway, I’ll pick up 3 new injectors tomorrow.

Thanks for all the comments - more, please, as necessary.


#16

I’d suggest you pick up all new injectors rather than three.
Let us know how you make out. We can be long winded, but we actually do care.


#17

If the one cylinder is the only problem then why not just get a full injector seal kit and give that a shot?

It could be that the entire problem is due to an air leak because of the missing spacer. A seal kit is probably 20 bucks for all of the injectors. A full set of injectors will be ouch…


#18

Then just buy one single injector . . .


#19

The injectors fail in different ways, some stay open and let way too much fuel out. Too bad the code won’t say why there is a misfire.


#20

So I replaced two injectors (which had noticeable damage) and fired the car up. Ran smoother, it seems, though really hard to tell without taking it for a spin. As with my first test in the original post, I unplugged the coil pack and this time I did hear a noticeable difference in the idle.

However, within 30 seconds, white smoke started billowing out the exhaust. Bummer.

I checked the box under the dash that manifests codes via a flashing check engine light. To be clear, the check engine light isn’t flashing - when it’s put in a test mode of sorts, (I think it’s called an ECU) it will flash the codes.

I’m getting 0304 which is defined as knock sensor
0701 which is multiple cylinder misfires (no duh! - lol)
0201 which is ignition signal circuit

I’m up for the challenge, but I just don’t know that I have the ability to completely diagnose and fix the problem. Time to throw in the towel?