Stock 1.6 NA, no power, (less than normal :-)

Craig505 · Postby **Craig505** » Sat Jul 22, 2017 9:39 am

Hi all, My 1989 Eunos has lost a lot of power over a couple of weeks. So much that it's very difficult to get it off the line on an incline.
It started by being sluggish when cold, but would then come good as it warmed up. I put it down to old plugs and changed them when I got a the chance. No change, so replaced the leads, still no change, so replaced the coil pack as there was some evidence of tracking. Still no good.
It's gotten worse and is hardly driveable. Symptoms are loss of power as soon as you begins to release the clutch, almost as though the timing isn't advancing. I've checked, and reset it to the stock 10deg. When you do manage to get the clutch out there is no throttle response, with the engine just chugging over. With some coaxing up to 2500 - 3000 it then seems almost normal, revving out to about 5500. I've checked the a.f.m. and it's free to move. Next steps are to check the a.f.m temp sensor and do a compression test. Any other thoughts or advice that might be causing the issue?
Many thanks in advance.

Craig505 · Postby **Craig505** » Sat Jul 22, 2017 10:24 am

Forgot to mention, vacuum at idle sits at 325 mm Hg. Too low?

manga_blue · Postby **manga_blue** » Sat Jul 22, 2017 10:38 am

325 mm Hg is too low. Check for inlet manifold or vacuum hose leaks, including a missing bung at the back. PCV valve jammed open is another candidate. Your performance symptoms do point towards a leak somewhere.

Less likely, but still possible, is a slipped tooth on the timing belt.

slomo · Postby **slomo** » Sat Jul 22, 2017 9:32 pm

If your timing appears to change, then check for front pulley wobble. There may be signs of a loose pulley bolt or worn crank keyway.
Gradually getting worse over a shortish time is a typical sign of above.

Craig505 · Postby **Craig505** » Sat Jul 22, 2017 10:00 pm

Thanks for your help. I've checked for obvious leaks but can't find any, by the bung at the back do you mean the welch plug at the back of the manifold? The pcv valve seems to be ok, I've also bridged the afm temp sensor, with no change. The compression test has 150 psi across all cylinders.
Looks like I need to check the belt timing.
I do have a slight pulley wobble Slomo, I've been keeping an eye on it but now looks like the time to do something about it. :frown:

Cheers

manga_blue · Postby **manga_blue** » Sat Jul 22, 2017 10:22 pm

Craig505 wrote:I do have a slight pulley wobble Slomo, I've been keeping an eye on it but now looks like the time to do something about it.
Cheers

That's a bit of a worry. Check this out: https://www.google.com.au/search?q=snc+failure+site%3Amiata.net&rlz=1C1GGGE_enAU454AU454&oq=snc+failure+site%3Amiata.net&aqs=chrome..69i57.9287j0j7&sourceid=chrome&ie=UTF-8#q=snc+failure+site:miata.net&start=10

Craig505 · Postby **Craig505** » Sun Jul 23, 2017 7:20 am

yeah, I was aware of the s.n.c. issue before i bought the car, but it was too cheap to pass up.
I think ill be able to do a "fix" on it, as I have access to a machine shop.

I'll post up how I get on.

slomo · Postby **slomo** » Sun Jul 23, 2017 9:21 pm

Use the locktite repair with new bolt, key and sprocket. If caught early, the non drive side of the keyway is undamaged, and used to align sprocket and key when "glueing" with 660. Don't forget the bolt torque has been "increase/updated"
Refer total process and revised bolt torque on Miata,net. Replace the crank seal at the same time..

Craig505 · Postby **Craig505** » Mon Jul 31, 2017 6:44 am

Thanks for the assistance. I confirmed yesterday that the belt had jumped a tooth, retarding both cams. I was able to jump it back and retension by just removing the two top covers. It's a very temporary fix just to confirm that it had skipped, and to wait for the parts and time to do the job arrive

In the end it took about 3 hrs to get it sorted. Manifold vacuum is now back to 500mm/hg and the car is driveable again

Cheers