Dunno why I see this problem but it's happened again... I fixed the keyway and replaced bottom cam pully and pully stack. Got the belt on rotated and checked 4 times to verify all was aligned, I even took a break in between two of the checks.. Car fired up and ran great. Then later same day getting on hwy I hear turbo spool massively and no power and engine dies - code reader shows same codes from previous belt slipage. I followed directions to the letter when reinstalling it (I was changing the water pump and the belt had only 8K on it so I didn't replace it). Everything was torqued properly with a good torque wrench and timing belt tension is set by the spring on the tensioner pully and had the 9-11mm deflection it should b/t the top two pulleys ??? So how the ### does this happen :-P

Maybe time to replace the cam pulleys ? get a fresh belt and have another go at it ? Only thing I can think of is they are slipping on the cams themselves? Engine has 140K, could also be time to find a new block ? Cheaper is better if it's not gonna slip again. Oh and the idler and tensioner pulleys free spin just fine? When the car died last night it overheated pretty well :-( Ended up trailering it home and got back at 2am ... after burning 7hrs in the garage on the car earlier same day = lame. Thoughts ? I've never hear of anyone having the belt slip like this ? FYI the keyway is def not an issue at this point - it's welded in and ground down and I had to tap the new crank pulley in (I seriously doubt it moved - but I haven't torn the car apart yet).

 

Bump - someone here has to have had timing slip ? I've talked the local Mazda dealer into simply installing a new belt/tensioner/tensioner spring/idler and cam pulleys (and new cam pulley bolts and main cam bolt) if I bring it in with the belt exposed (saving me $$$ on the job), I'm thinking leak down test while they have it. But still this shouldn't be happening ? I sprayed the crank pulley w/brake cleaner to make sure no oil etc was on it prior to installing .. My friend has suggested I could have #4 thrust bearing issue causing crank to move in and out and thus allowing slippage (but my VIN is out of the known range - may get dealer to verify that also). I don't want to drop 700$ on parts and labor if I end up with the same prob afterward (and of course dealer will not guarantee any work of this nature). This puts me close enough $$ wise to find a new block ? 140K seems like nothing for a miata motor tho ?? I'm only running 12psi and it has been very reliable for the last ~2yrs aside from normal maintenance items. What would you guys expect to get out of a conservatively boosted block ? I run safe (read conservative) timing / fuel - never any knock, never blows smoke - burns clean even ragging on it hard.

And yes I would do it but this would be the third weekend I've torn it down to the timing belt and I'm f$$$ing tired of doing it :-P

 

Update - tore it down to timing belt and wtf no slipage??? When it died I had massive turbo spool but no power and detonation followed the spool. I'm thinking exhaust valve stuck open ? Will do more diag tomorrow. In the mean time I'm shopping for a new block - any pointers on where to find one for reasonable ? I want a spare to build up when I take this one out.

 

Try doing a cylinder leak down test before tearing it down...you should be able to determine if you have any valve leakage.

 

Compression tested for sanity and held compression just fine, new plugs, wires and coil pack (they were all old anyway) and still no fire :-( All lifters moving as expected so not likely an issue there. It occasionally catches for a second or two and immediately dies. Keyway fix is so permanenet I cannot get the crank pully bolt off even using the starter so I seriously doubt there was any slip. Prob just coincidental I had the issue b4, fixed it and now have a new issue.Went back to oe ecu - no change (just to eliminate any possible probs there), verified exhaust flow (no blocked cat), charge piping looks fine (chased it all thru the bay to make sure nothing came off). WG and bypass valve are also fine (not stuck), IC looks ok also. Turbo is also fine. Thinking I may let the dealer have a crack at it now ? Any other suggestions welcome.
-B

 

NAs have a reputation for bad grounds...not sure about NBs. I started having intermittent "loss of power problems" (perhaps worsened when I started driving my '90 during Chicago winters) in winter of '07. Did all the usual stuff:
New plugs, new fuel filter, checked resistant of my plug wires, checked resistance of coil packs, adjusted fuel pressure up (BEGI RRFPR), monitored fuel pressure while driving with & without boost, still kept having intermittent problems.

Car died on the interstate one day last August (had fuel pressure guage and knew it wasn't a fuel problem) and it took me an hour to get it 10 miles home, bucking and stalling the entire way. I saw some info on Miata.net on ground problems, so I removed and cleaned every single electrical ground I could find from the trunk to the engine compartment. Took less than an hour and cured my intermittent "loss of power".

Also, see if you can borrow a code reader/scanner to look for any stored OBD-II codes (my 90 is OBD-I, so I don't have that option). Putting the car on a "scope" might also help pinpoint other ignition/electrical problems.

YMMV,

Mitch

 

Can you post the codes you pulled?? Did you goggle those specific codes with "Miata"?? Also, have you verified that you have fuel pressure when cranking and trying to start the car?? Have you tried a couple of shots of ether into the TB while cranking???

 

Will post the codes - I believe it was the cam angle sensor (generic crank angle sensor but upper sensor) I have replaced both of these last year fyi. I did check the motor ground near the turbo but will take a look at the trunk ground and post the codes. Oh and fuel pressure - I replaced the pump about 6 months ago and installed a guauge in the engine bay and there is pressure during cranking.
Thx for the suggestions,
-B

 

Check the wires crossing over the valve cover front next to the intake manifold. Have seen them rub through and short to ground.

 

Here's the FM writeup on this:

Troubleshooting ground problems.

Time for another one of TurboDog's Tech Tips from Flyin' Miata. On high mileage cars (so far only on 90-97 models) we've had a few exhibit some strange behaviour under acceleration or when shifting. The tacho needle drops, power falters for a second, then comes back on. There is a harness that goes from the chassis to the intake manifold on the passenger's side of the engine. This harness contains fuel injection wires, cam sensor wires, etc. Each time you accelerate, the engine rocks and tugs on this harness. Often wires will fatigue and break within the harness, causing intermittent problems. To test for this problem, start the car and start wiggling the wires trying to simulate the engine rock. If the tacho drops or engine falters, you've narrowed down your problem. You'll need to slit the covering over the harness and carefully examine the wires to find the offender(s). Good luck!

 

P0339 fyi - I found the problem - the main crank pulley (not timing pulley) sheared the section of the woodruf key that keeps it inline with the keyway, thus the car was not reading the proper time to fire based on signal (from those little annoying notches on the pulley stack) from the bottom crank angle sensor. Time for a new block :-( since a long block is less than a new cank and I can keep my existing head and have it ported :-) Will prob see if I can find a pro welding shop to weld the pully stack in place in the mean time since I've got upcomming house projects for the next two months and then go back to dropping in a new motor after that. Just need to line up the pulley with the woodruff key and have it mig'd in place (may as well have them mig the bolt in place too - the short block is now disposable as far as I['m concerned :-( (but needs a 240v mig for this to hold up for any period of time). Suckey - someone who changed the first timing belt undoubtedtly did not tourque the bolt to spec or replace the original woodruff key and end result is a keyway thats beyond repair (at least the chunk of woodruff key I mig'd in is sitting tight on the timing cam (lower pulley) and not going to move anywhere any time soon. I checked all of this today and it fired up then I turned on the A/C and that was the end of it - the load was enough to free spin the crank pulley stack and she died. Long story short - always replace your crank bolt, woodruff key and torque to correct specs and use plenty of locktight (red) and you prob won't have this issue. Thanks again for the suggestions.
-B

 

Damn, glad you found the problem but it is really ugly!! Can you please post pics of the sheared key and pulley???

 

Long nose locktite fix works. Check MNet for instructions.

 

I'm pondering that olderguy but I also filled in the gap on the keyway with a mig so no need for liquid metal part of that fix and I used a LOT of the red locktight - curious how do you pull the bottom (timing) pulley off ? A traditional puller will not fit due to the bottom surround of the engine ? Mine is also well locktighted in now but pbblaster seems to melt red locktight easily. I'll have to post my phone picts so you can see how bad the keyway was (don't have a great after pict unfortunately). Front of the keyway was gone - the good news is rear of the keyway was intact so it acted as a nice guide to hose clamp a key in place and fill along the edge (then remove key and grind - alot). But not sure how to get that timing pulley off ? It's really on there - any puller that is good for this ? Last time I removed it with a traditional puller it broke part of the outter lip (I've sense replaced the pulley).

 

There should be two small threaded jacking screw holes. If not, drilling and tapping a couple would probably be the easiest; but then you would be going for another pulley.

 

No such luck on the jacking screws but I'm gonna have one last go at it (new pulley, key and bolt) when I get parts (couple days), I'll try some small pry bars and no matter if I destroy the existing pulley (after all it's ~24$, pretty reasonable) but I like the tapping idea - may give that a go thx.
-B

 

A few picts showing the fun - I edited them down so they load quick and the quality sucks since I only had the camera on my phone for this. I'm finally a paid subscriber now since this is by far the best forum for turbo'd miatas

 

Fixed :-) Key problem here was not getting the proper clamping force on the crank bolt - due to old locktite residue etc (even torqued to 150'lbs the new pully boss was loose), I ran a tap thru w/pb blaster about 5 times (followed by a LOT of break cleaner) and got a new bolt and could finger thread it easily. Then scored the new woodruff key with emory and the keyway and used jbweld to fill the .05" gap that was left after the welding fix (it's not even worth it - I know the jbweld will turn to dust but why not - it was just to hold the assembly in line so I could get torque on the bolt). I replaced the timing belt again (in case I stretched it) and everything else timing related (incl front main seal) and put a **** ton of red locktite on that main bolt and torq'd it down to 130'lbs, 5 over spec - I don't wanna play with this again till I buy a new motor. I then let it sit for 2 days in the sun to let the locktite and jbweld cure (I've been driving a family loaner '95 corolla POS - for two %^#& weeks now so this was a hard 2 days to wait).

After the two days everything is golden, low end torque is back with a vengence, idle is happy, the pully stack spins with absolutely no visible wobble. Now I have to get back to that overheating thing... Ordered 2x12" slim fans you guys are running from siliconintakes and a 7x11x1 1/2" oil cooler from summit along with a lot of other sorely needed maint parts :-) Regardless she's back up and running hard. Lesson learned - Always tap that **** when you replace that crank bolt, and buy a new bolt! :-)

Oh and it took a half can of pb on the main bolt and on the crank timing gear + a full size crow bar and a sledge hammer to get that f%%%ng crank gear off.... Much fun. But PB does disovle red locktite fyi.

 

Glad to hear you got it all back together again! Also good to know that PB Blaster will dissolve red locktite. I've got to due a timing belt change soon on my short nose 1.6L and I'm torn between leaving the crank bolt "untouched" (you can do this on the 1.6) or taking it out, replacing it with new and a load of locktite.