NB RUnning Poorly...any ideas?

[hamish71]

Its not the cat...or any exhaust restriction. Swapped in a whole new system just to test it...and made no difference.

[hamish71]

OK, the car is now running very cleanly, starts great, idles perfect, but it still has a massive flatspot from 3000 to about 52/5300 rpm. I am convinced it is timing, somehow, and want to be able to check the operation of the Cam Angle Sensor, the VVT Actuator solenoid. I also found a thread on the big forum where a guy suggested, for a similar problem, checking the OCV as follows. ....anyone care to describe in detail how to do steps 1 and 2 of this:

Guessing here - maybe your VVT is not responding. That would give the symptoms you describe.
(1) check the filter in the top of the oil control valve (OCV) is not blocked
(2) check the actuator in the oil control valve solenoid operates when 12 V is applied (ie. take it out and watch it)
(3) check you have decent wiring to the OCV solenoid (maybe cam sensor too)
(4) take apart the VVT mechanism, clean it, and make sure all the working parts are free to move (especially the startup locking piston)
(5) long shot this one - do you have decent oil pressure? - no clogged filter, properly opening bypass etc?

[hamish71]

OK....worked out how to pull the OCV and clean it myself...and whilst I was there cleaned the Cam Angle Sensor, and the VVT SOlenoid....about to drive home, so will post if it works....or not.

[hamish71]

Ok, as above, cleaned the CAS, and the OCV. Drove home....problem still there. Flat spot until 6000, then takes off...I am convinced it is timing related...

Jut ran 12v aacross the solenoid as well (VVT Actuator), and it \"appears\" to work correctly.

So, am thinking will try a CAS swap as soon as possible...

[JBT]

What was/is the timing setting showing on the crankshaft pulley with a timing light?

[hamish71]

Checked the timing marks last week....it had jumped a tooth. Have corrected this, but it has made no difference to the flatspot.
I dont have a timing light to check it in operation.

[JBT]

I think it would be worthwhile checking that to start with, otherwise you're shooting in the dark.

[Garry]

I've heard stories of the lobe on the camshaft that triggers the cam shaft position sensor turning on the shaft. It's only a press fit and it's not keyed to the camshaft. Unlikely that it's moved but it doesn't need to move very far to upset things.

[hamish71]

OK, as of today, I can state it is not the Cam Angle Sensor, and it is not the VVT actuating solenoid. Have swapped these parts in and it has made no difference. I am convinced it is time related, so, I am guessing it is time to pull the valve cover off and check the vvt actuation system itself.

[JBT]

Why don't you get someone with a timing light to check the basic timing advance first to completely eliminate that possibility?

[Steampunk]

I found this when I googled Miata.net for timing issues: (sorry if someone has posted something similar)

Uneven Running

If your Miata is running unevenly, sometimes stalling, sometimes hesitating, there could be another problem. Your timing belt may have jumped a tooth or worse, your crank shaft may be broken.

An easy way to check is, pull #1 spark plug, and drop the dipstick down the hole. Turn the motor by hand and watch the dipstick until it peaks at top dead center. This will tell you the crank shaft is at TDC. Now check to see where the timing mark on the crank pulley lines up. If it is to the left of 0, then the key way may be worn or the timing belt may have jumped a tooth (or was improperly installed). In either case, you need to pull off the timing belt. While its off, check the keyway on the crank nose.

There is another possible cause for hesitation and poor idling:

Water in the engine - if you clean the engine bay with a pressure hose and spray the top of the engine block, you may have troubles. The rubber seals on top of the spark plugs aren't so great, so some water can seep into the cylinders, particularly the no. 1 cylinder. Once it dries out, everything should be fine. You may need to blast the water out with high pressure air.

http://www.miata.net/garage/ignition.html

[JBT]

An easy way to check is, pull #1 spark plug, and drop the dipstick down the hole. Turn the motor by hand and watch the dipstick until it peaks at top dead center. This will tell you the crank shaft is at TDC. Now check to see where the timing mark on the crank pulley lines up. If it is to the left of 0, then the key way may be worn or the timing belt may have jumped a tooth (or was improperly installed).

Actually, that TDC test will only check the pulley/crankshaft relationship. The timing belt could be non-existent and the pulley and crank will still turn together. You need to physically inspect the cam timing marks (remove cam cover etc.) to check the timing belt is correctly fitted.

[hamish71]

OK....
So having verified the timing, changed/checked all the sensors, the coils, and the leads, I am thinking I am just going to go ahead with the rebuild. WHilst doing so, I will examine the vvt actuator inside the valve cover, check the injectors (cant see it being fuel flow, but I will get them flow tested anyway), check the fuel pump for pressure....and other wise, gut the engine, macine it, put in all the new parts.

[hamish71]

The Saga Continues.....

I had the manifold off, and the narrower passages were completely blocked. Cleaned these, and the throttle body, and have found a significant improvement in overall power...BUT...

It still stumbles at 3000, and then seems to find itself at 5700 ish. It like it \"comes on boost\"...not snap sudden...but sudden all the same.

[Craig]

Could it be an SVT related issue? When's that supposed to kick in?

Isn't there a solenoid in the intake that adjusts the intake, or was that the NB8A?