6 replies to this topic

[Tao]

'99 Miata....it developed a CIL, #3 cylinder misfire...........rough idle, obvious mis but with increased rpm or on the track there is no obvious mis or loss of power...........
I changed; plugs, wires, coil pack.......no change
All wires are sparking......all injectors are opening (heard with stethoscope), battery has good voltage static and running.
Next step is to remove, check and clean the injectors again (did this at the beginning of the season).

This does not appear to be the usual '99 misfire issue........any ideas?

[chris haldeman]

Intake and or exhaust valve lash has tightened up causing a low rpm miss fire. I've seen it many times. Car idles poorly especially when cold but revs out and seems ok on track. It's not 100% on track but better than at idle. Lash tightened up because valves are pulling into head and or degrading.

[chris haldeman]

Perform a leak down test before farther parts swapping

[Jim Drago]

Intake and or exhaust valve lash has tightened up causing a low rpm miss fire. I've seen it many times. Car idles poorly especially when cold but revs out and seems ok on track. It's not 100% on track but better than at idle. Lash tightened up because valves are pulling into head and or degrading.

I agree, leak it down

[davew]

I'm not an engine builder, but I agree with the 2 engine builders.

 

Basic engine theory is that you need 4 things to make an engine run; Air, fuel, spark, compression. Air is generally not an issue, you eliminated spark and fuel, that only leaves compression

[Tao]

thanks guys.......compression and leak down test will be done as soon as I get a good leak down tester.....the one I have from harbor freight sucks.

[LarryKing]

I thought the 4 things are suck, squeeze, bang, blow.