Misfire on Cylinder #2...Thoughts?

[5.0L Miata]

Hey All,

Well the car has been driven a tiny bit but I've been holding back getting out and enjoying it because I have a bad misfire.

Cylinder #2 is not firing at all. At idle if I pull the plug wire off the plug there is no change in the tone of the engine. I've pulled the plug and it is dark (they are all new plugs) and wet. I installed a used plug that I had lying around, thinking that perhaps it was just a bumb plug... and sure enough it began to run on all 8. I took it for a quick run, came back, washed the car, went to take it for another run and I was back on 7 cylinders again. No swapping plugs doesn't do anything...I have not been able to get it to run on 8 since.

Last night I installed another new plug, wires, cap, and rotor with no change. This is a stock 1988 5.0L with approx. 100k miles on it.

I did have the injectors out of the intake manifold for about a year and they were stored in a ziplock bag. Any chance that I have a stuck injector that is just dumping fuel into the cylinder...is that common at all? I guess I should also invest in a compression gauge and see where I'm at there. I really hope it's not a stuck valve or rings.

I do not see any odd smoke coming out of the tailpipe...although there is some black in the condensation coming out of the tailpipe.

Any words of wisdom?

5.0L Miata

 

[HISSIN50]

The 88's injectors were not so hot. You can run a cylinder balance test, which might be revealing (then again, you already know there is an issue there).

Have you tried gapping that plug a little tight and seeing how it does.

Good luck.

 

[90mustangGT]

Ok, well swap injectors and see what happens. Go from there, at least this will eliminate the injector theroy, or maby confirm it.

 

[BrutalStang]

i had a friend who had a misfire issue as well, his turned out to be the injectors as HISSIN50 and 90mustangGT have already suggested.

just thought i'd back it up

 

[PuterAmI]

Any chance that I have a stuck injector that is just dumping fuel into the cylinder...

Yep. I troubleshot an engine for a day until I went back to the basics.

Combustion needs four things - fuel, air, compression, and spark. Take away any of the four and you get a misfire.

Check compression with a gauge. Spark with a screwdriver or spark tester. Pretty sure you are getting air unless you are having serious problem with the intake valve or rocker. Last is fuel. You can swap the injector for another cylinder and see if it travels.

 

[5.0L Miata]

Thanks all...I've done the following:

1) New plugs, wires, rotor, and cap...tested for spark and have it at all cylinders.

2) Compression check with the following results:

Cylinder #1 - 160, 158
Cylinder #2 - 162, 162
Cylinder #3 - 158, 156
Cylinder #4 - 156, 145
Cylinder #5 - 145, 142

Then I stopped because my battery was dying. I think the battery issue could also have played into the results on the last run of #4 and all of #5. I'll test the rest tonight when I get home with a charged battery.

So I have spark, I have air, I have compression...I think the issue is that I have too much fuel. The plug in #2 is wet and I pulled the dip stick this morning and it smells a lot like gas. I wiped in on a paper towel and sure enough hardly any oil came off...I repeated and got the same results. I have a feeling that the injector must just be leaking fuel all of the time and flooding the cylinder and fouling the plug. Would this be a reasonable conclusion?

So I guess next steps are finding a used 19lb injector or two and changing the oil and filter.

Anything else? Any other suggestions before I move ahead?

Thanks again,

5.0L Miata

 

[tjm73]

...I think the issue is that I have too much fuel. The plug in #2 is wet and I pulled the dip stick this morning and it smells a lot like gas.

If you have fuel in the oilpan, the oil is garbage. Drain it all, change the oil filter and put new oil in the engine. Gasoline destroys the oils lubrication abilities. Turning it over a lot and/or running it with the contaminated oil will ruin the engine.

 

[5.0L Miata]

Yup...I'll be changing the oil before I fire it up again. Hopefully I haven't done any damage, but the compression #'s look good so I think I'm ok.

 

[PuterAmI]

Any other suggestions before I move ahead?

Swap the #2 injector to another place and see if the misfire goes to that cylinder. If so, you definitely have your culprit and you can go buy a new one, or find someone that has changed theirs out for bigger ones.

 

[HISSIN50]

Jrichker has a post about using a cup of soapy water and compressed air to test an injector (the injector has to be out of the car). Basically one uses the compressed air to mimic fuel pressure, and the soapy water (put the pintle end of the injector in the water) will make bubbles if the injector is bleeding.

Good luck.

 

[5.0L Miata]

Cool thanks. Too bad I'm a broke ass and can't afford an air compressor! I found some used one's for $20 a piece, so I'll try that out and see what I get.