New [to me] shortblock
Timing = dead on
Compression = 187 | 183 | 181 | 185 (might have forgot WOT)
So I got my engine all squared away a few days ago and got brave enough to take it for a drive.
Smooth, no leaks, drove for about 15-20 miles around town.
Decided to drive it home on the highway, 30mile drive.
No problems, sustained 70mph, no signs of problems....datalog looks great.
Just as I'm about to pull off the highway I notice my legs are getting warm, stop at the stoplight and smell coolant...my radiator cap wasn't seated well and was dripping fluid. Temp gauge on MS = 173°F (actually 203°) fans kicked on as I fiddled with the cap.
Get back in the car and the idle is very lump, almost 3-cly like. Start to drive once I pull back in line at the next green light...car has no power, feels like 3-cly. Then "click", perfect again. Like an on/off switch, no power. Power back.
Drive to the next stoplight, lumpy idle again....green light, give it load, good again. Notice 17~Hg. (40kPa) of vacuum at idle. about 3~hg. low. (usually at 32kPa).
Park the car.
The day before I had trouble with the gasket on my IAC valve, so I decided to block the lines, incase somehow a small amount of coolant was injecting into the intake at idle. No dice.
Left it alone. Next day I got to drive it another 30miles back to the garage I work on it at. Started up perfectly, 3-cly syndrome again. Get on highway, overheats almost instantly. 230°F. Pull over. Thought about it in my head and considered a jumped tooth on the timing belt. Try to take off the valve cover and whatnot, but I have no luck in rotating the crank. Roadside assistance shows up and I put everything back together. Check my coolant, seems a tad low (but overflow is higher than usual). Refill the radiator.
Drive off. Starts to overheat within 2-3miles. Drive with heater on, sustained 220°F for the trip home in 87° weather (not fun BTW).
I suspect the timing belt at this point, however still looks dead on. 19 teeth between the marks at TDC. notice a little slack, so remove and redo, tension better.
Recheck the timing, had to adjust. makes me think it was off.
In the meantime I check the thermostat in boiling water. Opens at 180° as it should.
Burp the system. let it idle as I go through my software.
Idle gets lumpy vacuum low. Unplug the IAC and idle is normal again, 1020RPM, but at least smooth.
So I decide to take it around the block to see how it reacts. Coolant stays high 220°F, drives perfectly.
Get into a bit of boost to see how it reacts and backfires out of the exhaust.
Go back, check compression: 170 | 168 | 161 | 170
only thing I can think of at this point is the head and gasket??? at a loss.....help
I either got three problems or one really large one....not quite sure whats up. Idle valve had always been working prior, overheating sucks, and the backfire doesnt make sense. Unless for some reason I didnt have the crank at TDC when I aligned the cams.
log of backfire: http://www.miataturbo.net/braineack/...e/backfire.jpg