SOLVED: Half-power, bucking, 500rpm idle, won't rev past ~5K

[Kershaw]

Yeah, I would be swapping everything from the good running e30 to the bad running one 1 thing at a time.

[hwy84]

Did you check the ECU? What are the odds its an 027 ECU from an ETA and hence the 5500 rpm rev-limiter? It sounds like you may have an eta/seta block with an i head and that might be the cause of your issues.

ECU is a 153. Swapped it with a known good 173 from the good car - no change.

That said - it could be a poorly done e2i swap. That would explain the low compression and power for sure. I am embarrassed to say I don't know if there is any external way to differentiate... is there a telltale sign? I looked at the pistons, with an endoscope, and can only see a partial view. Look like i or seta, but don't look like regular eta.

Yeah, I would be swapping everything from the good running e30 to the bad running one 1 thing at a time.

Yup. That's been the procedure. So far nothing has made a meaningful difference. I am beginning to suspect that something internal is just plain wrong, or the harness is shorting out/has broken wires. The sensors all test good, and have been swapped with other good sensors, and no change.

Good times.

[itsonlygeorge]

There is no way to differentiate between blocks as they have the same casting. You can decode the serial number on the block but it doesn't have any info on 2.7 or 2.5.

http://www.r3vlimited.com/board/showthread.php?t=72192

[hwy84]

There is no way to differentiate between blocks as they have the same casting. You can decode the serial number on the block but it doesn't have any info on 2.7 or 2.5.

http://www.r3vlimited.com/board/showthread.php?t=72192

As I suspected. Thanks.

[hwy84]

Getting somewhere - but not where I'd hoped.

At this point I am starting to think I just have a really tired M20B25 (slow and no torque), with an AFM that has two bad places in the track that make the surges.

Tonight I swapped in brand "new" rebuilt injectors, a new clean fuel filter, and new O2 sensor. Also got the valve cover gasket torqued appropriately so it doesn't leak oil.

Now the engine always pull all the way to redline. Still very slow up to 5,500 RPM, with two "surges" between 3K and 4K RPM, but is otherwise smooth. Decent top end still above 5,500 to redline.

Outside:

All that's left outside the motor is to swap the plug wires, and new plugs again, in case the ones from last week are too fouled to work well.

Inside:

I scoped the pistons - lots of carbon. Looks like black crystals growing off of the entirety of the piston tops. If the valves have equal amounts of carbon, they could potentially not seal against the seats, and explain some of the low compression.

Could also be a SETA cam. Don't know how I could tell. I'll investigate.

Next steps:

1. I'm going to diagnose the harness and sensors while running to eliminate those.
2. If those check out, I'm going to try some Ventil Sauber/Seafoam - though I don't have high hopes for those working to de-carbon the innards.
3. If that doesn't do it - I'll pay a shop to spend a couple hours making sure I didn't miss something
4. Then it's time to yank the motor.

Thoughts?

[mazzo]

Maybe it's time to refresh your AFM too?

[hwy84]

Just a quick update - my compression is fine. I didn't do the test properly before. I tested on a cold motor, with the throttle closed. Bonehead.

Warm motor, throttle open:

150
145
140
140
145
155

So that seems great. Swapped fuel pressure regulator for know good just in case, no change.

While I was testing the compression, I noticed the exhaust manifolds are extremely hot. Like, smoking hot. Could be my imagination, but it seems like they are way hotter than my other cars'.

I'm starting to think my spark timing is to blame here. I don't know how, but I'm gonna investigate the cps and toothed wheel even further.

[JinormusJ]

Hey HWY

Thanks for the PM earlier; looks like you've already tried a lot of things I mentioned in my reply. I didn't know what your level of knowledge was on these cars, but I'm glad you're making (some sort of) headway. Unfortunately, the problem with my former e30 was not nearly as bad as that video you posted: I honestly wouldn't know what to tell yo

But I'm in for the final result and you getting this sorted

Best of luck

[packratbimmer]

What injectors did you put in and are they cleaned? I would stick with stock 14 #-ers until resolved.

Have you thought about the CAT? Have you read the CAT temp fore and aft?

I did not read every line here, but you are not running platinum plugs I hope?

Good luck - seems like you are closing in on it...

[hwy84]

What injectors did you put in and are they cleaned? I would stick with stock 14 #-ers until resolved.

Have you thought about the CAT? Have you read the CAT temp fore and aft?

Using Ford Injectors, from the contour - a little higher flow, but within the trim of the ECU.

I am leaning heavily towards the cat, as you suggest. Im looking into that tonorrow...

The symptoms have changed a little over the last few days:

• Idle has more misses
• Pulling away from a stop requires at least 2k rpm, and a lot of clutch
• Acceleration is worse (crazy!)
• Throttle blips while idling will either kill the motor, or have no response - sometimes even full throttle won't make the rpm rise
• Occasional rattling from beneath the car
• More back popping on deceleration

Seems very clogged/broken cat to me.

We'll see!

[hwy84]

While it's weird to talk to myself, I will continue to do so. Heh.

Cut the cat out - it's clean as a whistle. Looks perfect.

Welded in a straight section of pipe - no change.

Next up: replace the harmonic balancer to see if it's just out of spec/weird/JB Welded enough to screw things up.

<sigh>

More updates as I have 'em.

[hwy84]

Failed woodruff key

I pulled the timing belt, and this time also removed the crank bolt. If you've read this far you may remember that the bolt had been only finger tight when I first inspected the crank position sensor and harmonic dampener/toothed wheel.

Seems as though the loose fit may have allowed too much play, allowing the gear to spin on the crank nose, bending/smashing the woodruff key, and damaging both keyways in the crank, and in the gear (see below).

For grins, I'm going to get a new key, and new gear. I'm hoping the keyway on the crank is still reasonable enough that with the bolt tightened to spec, and the tolerances tight on the key and gear, it will hold together and keep the timing correct. If not, I'll swap the block out for a good used unit, and keep my head and accessories...

Not the outcome I was hoping for - but I'm glad I found what appears to be the root cause.

[ak-]

Wow.

Lot's of work, but wish you luck.

[hwy84]

Wow.

Lot's of work, but wish you luck.

Thanks. Seems like I'll need it!

I started researching Belzona and Loctite 660 keyway repairs - some people even do it with JB Weld. Looks like it might be a real solution... at least a first step before I replace the block/crank.

Anyhow - I'll continue posting with my results - but it'll be a few days before the woodruff key and new gear arrive.

[hwy84]

Solved it!! Sweet sky above!!

The failed woodruff key was the culprit.

I bought a new key (less than a dollar!) and a used crank gear (40 bucks) with a good key slot.

I used loctite 660, with the corresponding accelerator to fill the wallowed area in the crank, and to hold the new key in place while I installed the new gear. The gear is stubborn, and takes some force to press onto the shaft, but once tapped on far enough,its easy to press on the rest of the way with the big ol' crank bolt. Basically followed the process detailed on miata.net - the first year miatas seem to eat their crank woodruff keys, and this is a proven repair for those. http://www.miata.net/garage/hsue/crank/loctite_3.htm

I also used loctite 680 on the crank bolt/washer/gear mating surfaces, to help keep the bolt from spinning loose ever again. Torqued to spec (304 ft/lbs).

Replaced the water pump, Timing belt, and pulley for good measure, made sure everything was lined up - crossed my fingers and....

She started right up!! Idled WAY high though - about 1800 rpm. I figured the DME had adapeted to advance the spark timing as much as possible to try to compensate for the retarded crank gear/toothed wheel before, so I just let it sit idling for about 5 minutes (used the time to bleed the coolant).

It figured itself out completely, stepping down from 1,800 to about 1500, to 1,000 to 650 over the 5 minutes.

Took her for a spin, and the power is all there!! No more hesitation, no more flat spots, no more anything. Just a smooth running m20!

I'm stoked as hell!

Bottom line - if your timing seems off, but your timing marks line up - check the woodruff key.

Hope this ordeal helps someone else in the future! I'm gonna go drive!