1995 SL1 Cylinder 2 Misfire
 

1995 SL1 had blown head. I replaced the head and have a problem with misfiring on cylinder 2. It may have been there before I rebuilt the head, but I don't know for sure. Here is what I have done:
compression test on all cylinders checks out
new plugs
swapped plug wires between 2 and 3. In each case 3 fires fine and 2 doesn't fire.
swapped fuel injectors between 2 and 3. In each case 3 fires fine and 2 doesn't fire.

Got desperate and pulled plug on 2 and turned engine over for a quick second. Did not smell gas coming from spark plug hole.

I'm running out of things to check. I'm thinking of swapping the coils around to see if that does anything. And pulling valve cover off to see if the intake valve appears to be opening. Otherwise I'm stumped. Could it be that the #2 injector wire does not have current - though I did the screwdriver microphone test and it sounds like it is ticking. Any ideas would be appreciated.

Oh yeah, Engine starts right up, idles around 600 rpms. Drives, though with reduced power and has the expected spudder with one cylinder not firing.

If the compression is good, the valves are working. But having said that, if one of the valves was barely opening, it would not show up on a compression test because the engine is turning so slowly compared to a running engine.

The first thing to do is to pull the #2 spark plug wire and stick a spare spark plug in it and lay it on the engine. Then have someone crank the engine and look for a spark. If you don't get a spark, then you have a bad coil.

I checked spark also. Arcs like crazy when you pull the plug wire. Compression is about 180 on each cylinder. Is there any way the intake valve is not opening? Seems like if I have spark and compression the only thing that might be missing is fuel.

Sounds like you've got a short in the injector wire on #2 to me. Check the harness very carefully and see if some insulation is worn off and grounding it. If not, check the pins in the plug on the connector and make sure one of them isn't messed up.

Tried pulling the injector plug and putting a volt meter on it while the engine was running. Since I have no idea of what the voltage should be I didn't have a lot to go on. Volt meter was around 6 - 8 volts on two different injector plugs.

The easiest way to check the plug at the injector is to get a noid light from your local auto parts store. Plug it in and start the engine. If the light flashes on and off, then it's receiving proper voltage. If it doesn't come on at all or just stays on, then you've got a wiring problem. If not that, then I don't have any other suggestions. According to my Haynes manual, the resistance on your injectors at the connector with the engine off should be 1.5 to.2.5 ohms.

Just because an injector is getting the correct signal, it does not mean that it is injecting fuel. It could be clogged or mechanically broken. You could try swapping injectors.

I think he already did -- though I'd like to know how he was figuring out which cyl was misfiring. ODBI isn't all that helpful for isolating things to a particuar cyl.

Were you determining the bad cyl based on pulling off the plug wire/nothing changes?

Solved - by process of elimination, and fortunate observation. Long story...

Eliminated fuel injector
Eliminated fuel injector harness
Eliminated valves and timing
Eliminated compression
Got stung on spark...

Bought all new plugs and installed during rebuild. I checked spark on all the plugs, so I thought, but here is what happened.

Through all the messing around I broke a plug and yesterday had to buy another one for cylinder 1. I pulled the broken plug, pulled the plug on #2 and put it into #1. Then put the broken plug into #2 just to plug the hole. Put new plug into #2 wire, laid on front of car and started engine. Was sparking fine. Just confirmed that I had gas, had compression, and had spark. Yeah, thought I already knew that! Removed broken plug and put new plug into #2 and reconnected. Now cylinder #2 is firing fine! Huh??? But guess what, now #1 wasn't firing. Ah, I just put the plug that was in #2 into #1. Pulled plug on #1, put broken plug into #1. Put the offending plug into #1 wire, laid the plug and wire on the front of the car and started engine. Appeared that the plug was sparking, BUT what was happening was electricity was arcing out of the plug boot onto the metal and back to the plug tip. Sure looked like the plug was working but when I put the wire and plug onto a piece of rubber, no spark at all. Total frustration. Spent two evenings diagnosing a bad plug. Went and bought new plugs and new plug wires, reassembled and runs perfect.

Kudos Keith - you nailed it even though I thought I already had that factor eliminated. So, I learned that if I am going to check spark I need to get it off of a metal surface and onto some rubber.

Glad to hear you got it figured out and it WAS actually something simple. Happy motoring.