check engine light

[Bubba13]

 On my second truck that I have for my daily driver,( 96 gmc sanoma, 2.2 4 cyl. ) The check engine light went on just shortly after the engine started tapping, not a knock but heavier than a tick. the oil pressure before all this was normal, 20 lbs at idle and 40 on hwy. Now once warm, the oil pressure is 20 hwy and 5 ish at idle. I use mobile clean 5000 oil with a can of Restore in it. The engine light code is " number 4 cyl missfire detected" It's been too cold here to attempt working on it yet. Yea I know it's later than 87 but there has to be some diverse mechanics on here to help. Any ideas will help.

[TexasRed]

Probably time for a tune up, plugs and wires.

[Bubba13]

changed plugs, still tapping. Also left old plug in block, attached new plug into boot , grounded to block, started engine, have spark, but engine doesnt sound different even with plug there.

[frogman68]

Do a compression test

[VileZambonie]

Unplug the injector connector and see if it has injector pulse using a test light

[Bubba13]

sorry, it has a tbi

[choptop]

Almost sounds like a weak coil. Does it have the four pac coil or just the single. You can have a spark outside like you tested, but if it is weak, it wont fire under compression.

[VileZambonie]

sorry, it has a tbi

You might wanna double check that. You should have SFI not TBI.

Are you hearing a mechanical noise with no load on the engine?

[KoolerSL2]

you said 2.2?
almost every 2.2 i see breaks the timing tensioner, which in turn makes a tap louder than a lifter but quieter than a rod.
id check that first.

[69byrd]

I had a 97 s-10 with a 2.2 and it done exactly what Chris said, so you might want to check the timing tensioner.

[Slade]

Just an observation but I would be very concerned about any engine with only 5lbs. of oil pressure.