Diagnosing a misfire on cylinder 6

[Tony Fritts]

ok so I am working on a vg30e in my wifes minivan (1997 mercury villager/nissan quest which her parents gave us). It has a cylinder 6 miss fire code. My first novice step was to check this plugs. Who knows how old these where and 2 where seized in the head so this turend into my longest spark plug change ever since I had to pull the heads and take them to a machine shop to get the plugs out (and exhaust studs which where broken).

I finally got the car back together and its still missing on 6. The additional information I have is
1- the ignition cap and rotor are new as well as the wires (the are cheap ones but very new)
2- when I hook up a vacuum to the intake is a very steady 17 (as I understand it staying steady is the good thing here)
3- The noid light lights up so the injector is getting voltage
4- Since I got to step 3 I thought it might be an issue with the fuel injector so I bought a new one, so odds are this part is good since its new. I guess I could buy a pulser and a fuel pressure tester but do not have that to verify its actually injecting
5- I checked the O2 sensor has been replaced by someone before me but nto sure how long ago. The wires on it look pretty new but thats not exactly proof of anything.
6- It smells rich when you get out (maybe this also indicates an exhaust leak?)
7- plug 6 was not a good brown color but was black. it was not heavily black and the black wiped right off with a shop rag.

I am somewhat stuck, it feels like its either bad o2 sensors, exhaust leak, or computer based on my limited diagnosis ability. I have no clue how to find/deal with an exhaust leak, the computer is about $120 and both 02 sensors are about $70 a piece. I have already dumped way more time and money into this then I meant to (pulling heads, new gasket kit, new head bolts) so was looking for other tests I should perform or any gut instincts from some of you more experienced mechanics that might keep me from being a parts replacer 🙂

Topic

[dave]

1997 mercury villager/nissan quest

plug 6 was not a good brown color but was black

Perform a compression test on cylinder #6 and a known good cylinder.

[video]http://www.youtube.com/watch?v=X_tbksFYhl4[/video]

[Tony Fritts]

I will pick one up tomorrow and let you know the results, if nothing else this project is helping me build out my tool set.

Thanks

[college man]

Don’t replace the o2 sensor. With your dvom ohm out
the injectors should be 11-18 ohms.Pick up a spark
tester and verify a good spark to #6 cylinder. Try
unplugging injector 6 to see if the
idle changes.

[Tony Fritts]

OK so here is some more information
Compression Test:

test	1	2	3	4	5	6
dry	170	160	165	160	165	155
wet	185	180	167	180	170	170

This is the first time I did this so I guessed on the right process based off Eric’s video. For my motor it seemd to take about 6 or 7 rotations to build up full pressure.

As reguards to the other question I only tested the 3 injectors on the front since is a sideways facing v

injector	ohms
2	13
4	13
6	12.7

Not sure if the fact that I have replaced the injector for #6 could be the cause of this difference or if its an indication of something else.

I did put an inline spark tester infront of #6 and it is seeing spark

Oddly after all that information when I pull the injector plug for #6 while its idling it does not really change the idle. I tested both 2 and 4 and when pulled you noticed an instant change in idle but #6 does not have any change or if it does its very slight.

[Tony Fritts]

Ok so I have found an issue, not sure if its the only problem as I have to order the parts. apparently when I installed the new injector their was a bit of the old gasket left in side the fuel rail. did damage to the middle o-ring when I installed it. I discovered it since a friend suggested I swap #6 and #4 injector to see if the problem tracked with the injector or with the cylinder. no one stocks the o-rings of course so I have to wait so will not know for a few days if this was the only problem or just one in the mix.

[Tony Fritts]

Question,
If I checked out one of those big o-ring kits do you think I could use those on a fuel injector? Of course assuming the are the correct size but did not know if a generic O-ring would go bad around a fuel injector. I do not mind paying for the injector specific ones but it will be a few days before any of the local could get me one and wanted to try and fix it this weekend.

Thanks

[college man]

since we have spark on #6 and injector #6 was replaced.
When you used the noid light to see injector pulse.was the
light flashing rapidly? I think the next step here is to start
spraying around the intake gasket around #6.

[college man]

[quote=”fullobs” post=65058]Question,
If I checked out one of those big o-ring kits do you think I could use those on a fuel injector? Of course assuming the are the correct size but did not know if a generic O-ring would go bad around a fuel injector. I do not mind paying for the injector specific ones but it will be a few days before any of the local could get me one and wanted to try and fix it this weekend.

Thanks[/quote]

spray around the injector/O ring with water or carb spray.

[Tony Fritts]

Spraying around the injector did not make any difference though I did not really think it would as the upper gasket was fine it was the lower and middle gaskets that where damaged. I did wait for the specific O-rings to get in and it did seem to resolve the issue. From what I can tell that injector was just leaking down into the cylinder slowly but constantly which was throwing off the mixture as would be expected. Also probably explained why it had become so hard to start as that seems to have resolved its self as well.

Thanks for all the tips

[college man]

Thanks for the update and the fix. 🙂

[Author]

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