Mystery Engine Trouble. Halp, mt.net!
 

The timing belt in my beater Miata shit the bed a few weeks ago. The valve seals have always sucked in this motor so I swapped on a spare NA8 head that I had laying around along with a Fel-Pro MLS head gasket (it's a beater, don't judge me) and a fresh Gates timing belt/ roller kit from 949. I got it all together this weekend, and before I put the rad in/ filled it with coolant I unhooked the injectors and spun the motor over until I got 30psi oil pressure, then hooked everything up and it fired right up, but it idles pretty poorly, billows oil smoke, and has a weird misfire/ artificial rev limit at ~3200rpm. The rev limit/ misfire may get worse with temp. I haven't let it run long enough to be certain of this. I'm sure I'm missing something obvious here, but I can't put my finger on it.



Known knowns:

-94 Miata
-Former project, current daily beater
-~120k on bottom end
-Compression is 190, 185, 185, 190
-Mystery meat head (spare; "came from a running car"; has been in a rubbermaid tote in my shop for 2+ years; possible problem?)
-Fel-Pro MLS head gasket (Possible problem?)
-Block deck was slightly rusty around the water jacket holes, but around the cylinders was fine
-750cc RC injectors
-MSPNP
-Re-used intake and exhaust manifold gaskets
-New valve cover gaskets
-Lifters are quiet
-Good oil pressure
-Cams are timed correctly
-Didn't make much power, but ran ok before timing belt broke
-Haven't filled cooling system yet (smoke isn't coolant)
-Have only run the car for short periods due to having not filled the cooling system
-Plugs were slightly damp with oil when removed
-Coils pass multimeter tests (were a low between the pins that should be isolated, but were even across the board; I don't think they could account for the oil smoke)


Known unknowns:

-Head is mystery meat
-Haven't set base ignition timing yet
-Fuel/ ignition maps haven't been touched since 2011
-LC-1 wideband hasn't been calibrated recently (O2 feedback is disabled in MS)



If the compression numbers weren't so even I would think that the head gasket had to be the problem. This is my noob face. Somebody halp.

check plug gaps, CAS, cam gears timing belt

This wont fix the massive burning oil problem.

Do you own a leakdown tester OP?

This. I'd put new plugs too.


Might be oil spilled from removing/installing the new cylinder head being burned on startup. He said it only ran a little bit.

Plugs were replaced with the head. CAS signal looks perfect in Tuner Studio. Cam gears and timing belt are fine. I don't have a leakdown tester, but should really break down and buy one. The engine has been run for ~10 minutes now in short increments, so it should have cleared any residual oil in the cylinders long ago.

I did set the base ignition timing and calibrated the LC1 (previous owner didn't wire the button/LED into the calibration wire, so I wired up a stand alone button/LED/ ground loop pigtail and a spade connector in the engine bay to do the free air calibration). The engine was running super rich, like 9.5:1 down to off the scale rich. I have no explanation as to why this is, as the car ran fine before with the same maps (and if it picked up cranking compression from replacing the head it would run leaner, correct?).

As a stopgap, I let VE Analyze Live lean the maps out from the O2 sensor data, and the car seems to be running better. Tonight after work I'll fill the cooling system, try to find an appropriate map, and try to drive it around some and maybe lean the map out some more.

Possibly you switched the supply and return fuel lines, thus causing fuel pressure to shoot up causing all these issues?

You say you replaced the head...how do you know the replacement is any good?

I don't think swapping the lines would cause the pressure to spike. I think it would cause the pressure to drop dramatically and/ or be wildly erratic.

I don't know for certain. Though the guy I got it from said it came from a good running car.

Also, the lifters are nice and quiet, which implies that it has led an easy life.

Also (2), I can't think of any way that the head could be damaged that would produce these symptoms and still show excellent cranking compression.

Also (3), since it makes excellent compression, this implies that the things that touch fire are at least somewhat healthy.

I worked late, didn't get to the shop until 6:45, put in the belts/ water pump pulley/ rad/ hoses, spent half an hour bending the lower hook mounts so that the bobbins on the radiator actually fit into them correctly, poured the first gallon of coolant in, and realized that the drain plug in the rad was MIA.

Then I rage quit. I won't have time to mess with it today. I'll try to let you guys know more tomorrow.

I've done that one once or twice. That or left the lower radiator hose off.

Coolant.......all over the shoes. Motherfucker.

http://25.media.tumblr.com/58324d508...72puo1_400.gif

I think I've been chasing an intermittent short in the MS this entire time.

Last night I filled the cooling system, smoothed the maps out to the apparent new baseline, and drove it around the parking lot some. After about 5 laps around the parking lot everything just went to shit, the dash in Tunerstudio lit up like a Christmas tree, and the motor quit and refused to relight. As I was pushing it back into the shop I noticed that the fuel pump was cycling, and the injectors (or some injectors?) were stuck open and just blasting fuel. I turned the key to 'ACC' and played with the MS some more once I got it into the shop, and noticed that the 'Battery Voltage' gauge on the TS dash was showing TPS%, not battery voltage. Also, Tunerstudio shows the "You have an error in your settings, and the MS doesn't know what to do about it" error some times, and I couldn't figure out either what the error was, or what was making the dialog box go away.

Thus my conclusion that there is an intermittent short in the MSPNP. Thoughts?

I monkeyed with it all weekend, and autotuned it/ tweaked the maps extensively, and I'm pretty convinced it's a problem with the MS. Occasionally communication from the MS will just go stupid, and show nonsense values (MAP locks to an arbitrary value, and rpm varies cyclically, for example). Also, at cruising load, it has a dead miss at a handful of particular rpm values (~3400 and ~3900 in particular; 3400 is an RPM column value in Fuel Map #1, but 3900 is not) that gets worse as CLT goes up/ as drive time goes up (and also may to be sensitive to bumps). This miss isn't present when free reving, and is either less present, or just less noticeable at wide open throttle. The wideband reads dead rich on each miss.

I'm pretty convinced that there's an issue either with an intermittent short in the MS or possibly someplace in the harness that is excited by the vibration frequencies associated with those rpm points.

Anybody have opinions?