1999 jeep cherokee auto 211k developed mystery coolant leak.
-Oil is normal in color.
- Milk shake under oil fill cap.
-Failed a calorimetry test (block test).

Headgasket replaced. Head and block deck checked for warp. Everything was reassembled with a failure to start due to a distributor index sensor with a p0340. I must have damaged it while replacing the motor mount. Replaced it and starts right up. The next morning it fails to start this time with no codes. Will crank and fire off a cylinder but it's infrequent and weak. Plugs removed and visualized during cranking. All have a good looking blue white spark.
With engine at TDC end of compression stroke and the distributor cap and sensor removed the indexing hole is aligned. Distributor button is in the 5 o'clock position. Timing was not disturbed while replacing the head but still verified. Charged the battery all morning and let it crank over for about 15 seconds which got it to stubble to life. Runs great comes up to temp drives fine. No feeling of loss of power. Changed out the battery with a known good 1 month old battery. Waited 2 hours before The next start attempt and it's failure to start again. When it's hot it can be turned off and back on multiple times.The next step in my head is compression check and spark plug gap.

I have missed something.

 

Well, an engine needs air, fuel and spark. So, with spark believed to be good, then in the cheap and easy theme, check for bunged air supply (ya I understand unlikely) and then fuel pressure. Pump should run for a couple seconds at key-on to prime/pressurize system and then during start and into run. And for that matter, bad fuel. Bad fuel can be hard start but run ok when engine warmed up.....?

Good luck!
Tim

 

I think my issues are over lapping and independent of the head gasket change. Plugs were changed to factory spec, cap replaced with brass terminals, plugs replaced with factory spec. Just for fun I cleaned the IAC valve. It starts which is great. Lets see what it does with a cold soak.

 

Looking at this from another angle I think I have made a rookie mistake. If we take the air-fuel-spark-timing-compression diagnostic approach, which is how I was taught, I went through all 5 factors which should result in a running engine. Unfortunetly I made some assumptions about air and fuel. There also was a temperature difference of more than 50 degrees, 65 down to 12, from starting this repair and reassembly which may or may not have been a factor. The tune up parts were due to be done and cheap. But the main issue appears to have been the IAC valve. But wait I had opened the throttle to WOT while cranking over taking the IAC out of the question and commanding the PCM to clear a flood condition. After letting the engine dry out it would only start with throttle. I didnt clear the engine for long enough and had a dirty/questionable IAC.

Lessons relearned. Follow the algorithm and don't assume.

 

Cummins93,

Sounds like you already have a pretty good head for this type of thing. Glad you retraced your steps and found it.

I like Shrodinger's Box (he makes diagnostic videos on youtube) approach to a cranking no-start (similar to how you were taught):

Acronym FASTTEC:
Fuel
Air
Spark
Timing (ignition)
Timing (cam/crank)
Exhaust
Compression

They are ordered to help decrease troubleshooting time based on probability and overlapping concerns (though it doesn't always work out that way). For example, if you had a specific reason to suspect a compression problem, you may opt to start with that. But his take is that if you are going in with no prior information about the failure, this order -generally- works out faster (but not always).