420A What is causing loss of power/misfire?

[96WhiteEclipse]

So my 2g Eclipse GS is running rough. It ended up not shifting at all and engine was having idle issues. Replaced TPS and IAC. Engine idles and shifts great. Well, it sounds like it’s completely lost cylinder 3. I had a suspicion it might be spark plugs. I started the car and disconnect the wire to cylinder #3 and nothing changed. It still ran kinda rough like it was missing that cylinder. So instantly you would think it’s just a bad plug but after taking the plug out and connecting it to the wire and cranking the car the plug sparked normally. So if it’s not the plug would it be an injector? Could it have skipped a tooth in the timing? I need some help please and thank you

 

[CKOPOCT]

Yes... if the plug is firing normally then the cylinder is missing fuel, air, or compression. However, could still be a bad plug/ignition issue. Seeing spark doesn't necessarily mean the spark is strong enough when subjected to the environment in the combustion chamber. Was the spark blue or orange/yellow?

Skipped timing - no. Jumping time wouldn't affect just one cylinder... and if you jumped more than one tooth you'd be dealing with bent valves - which WOULD cause your issue, just in multiple cylinders.

Assuming the spark is there, is fine, and is in time, a lack of fuel is the most likely and easiest thing to point to. This could mean a bad injector. It could also mean the injector is fine but it isn't getting the signal it needs due to a wiring or connection problem. With the age of the car/components and the number of heat/freeze cycles the components have seen, definitely check the injector pigtail connectors. I know mine practically shattered when I went to remove them a few years ago on my '97.

'Twer I you I would swap parts around to see if I could pinpoint exactly what is failing where. Swap plug wires and see if the problem follows the swap or stays the same. Follows, bad plug wire. Stays the same, possibly a bad plug - but move on to the next paragraph. (Again, just because you see spark with the plug laying on the engine doesn't mean that spark will be strong enough to do its job under operating conditions.)

Pull the plug for #3 after running the engine for a minute. If #3 isn't firing at all the plug should be soaked with fuel. If it is soaked then you know the fuel system is working fine (back to possibly bad plug or a compression issue). If the plug is dry then no fuel is making it to #3. Inspect the wiring and connections for the injectors. If everything seems fine, swap injectors around and see if the problem follows or remains in #3. If it follows - bad injector. If it remains, it's a wiring/connection/signal problem.

Compression - if you've determined you need to check for compression then the next step is a compression test. You should see above 100 on all cylinders, and your numbers should be fairly consistent across. If #3 is significantly low then you need to do a leak down test to determine where your combustion chamber leak is.

Hope this helps.