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Weird Issue Setting Timing - Need Help!

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Best Answer bmarshall1 , 07-04-2014 08:19 AM

The timing and idle issue seems to be solved at this point.  For all of those who were pointing to a vacuum leak - give yourself a pat on the back.  The interesting thing is where I found the leak...

 

I took the upper manifold to replace a leaky injector ring and decided to test the VICS check valve, it is supposed to be a one way valve, but mine was open in both directions, possibly flowing air backwards and when it should not have been, perhaps giving the appearance of a vacuum leak.

 

While I can't say for certain this was the problem, I can tell you a new VICS check valve made all my problems go away.  The timing is steady, the idle smooth, and it will hold a partial 2000 RPM throttle.

 

THANK YOU everyone for all of your input!!  Miata people are a great resource and awesome community.

 

Bruce

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#1
bmarshall1

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I have a Mazdaspeed slotted timing wheel on my 99 and I am in the process of setting the timing.  From what I understand I should be using the mark in the timing wheel that is on the left and align that up with my desired advance (14 degree )

 

 I have the TEN and Gnd jumped, idle as close to 850 as possible (actually 900 is as low as I can get it, idle screw all the way in).  All electrics off, engine is warm but no fan running.

 

Here's my issue: I can get the timing to near 14 (it jumps around a bit +-3 degrees) but here's the part I do not understand - after a few minutes of running the timing reverts to 10 degrees and does not move, no jumping around, period.  Upon restart it back to jumping around14 for a few moments then reverts to 10 again. The timing wheel is not moving between attempts.

 

Any ideas?

 

My thoughts, motor too hot (computer locking down the timing), should i undo the TEN jumper for timing?  Any thoughts?

 

Thanks for any help.

 

Bruce



#2
bmarshall1

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OK, more symptoms have cropped up.

 

On a warm car, TEN and GND bridged, I can set the timing to any number above 10., it idles a bit high, but around 1000 is as low as it goes and I can hold the throttle at a steady 2000 rpm or blip it w/o any problems.  Once the car has ran for a few minutes (or moments) the timing drops to 10 degrees, the idles gets very smooth, and it will not hold a steady 2000, it starts to climb then shuts down to idle and cycles back and forth until I release the throttle, then it's back to idling fine.  It will go more than 1/4 throttle without issues though.

 

Otherwise good throttle response and seems to run good.

 

Any ideas?



#3
Bench Racer

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OK, more symptoms have cropped up.

 

On a warm car, TEN and GND bridged, I can set the timing to any number above 10., it idles a bit high, but around 1000 is as low as it goes and I can hold the throttle at a steady 2000 rpm or blip it w/o any problems. 

 

Once the car has ran for a few minutes (or moments) the timing drops to 10 degrees, the idles gets very smooth, and it will not hold a steady 2000, it starts to climb then shuts down to idle and cycles back and forth until I release the throttle, then it's back to idling fine.  It will go more than 1/4 throttle without issues though.

 

Otherwise good throttle response and seems to run good.

 

Any ideas?

Recent experience with my 1.6 Spec Miata.  Engine with throttle pedal held at 2,200 rpm oscillated back and forth to 1,700 rpm untill removing foot from pedal. After doing everything I could think of and find in the FSM including the throttle position switch checked ok to the FSM specs, I removed the electrical connector for the throttle position switch at the switch and thank you the oscillating stoped. Bought a new throttle position switch, issue solved. 

 

Well intended post. :bigsquaregrin:

 

EDIT:

With your engine cycling back and forth issue and your vaccum hose issue, be sure you do not have a vacuum leak issue causing the engine speed cycling issue.


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#4
bmarshall1

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Bench,

 

I have checked for open vacuum fittings and found none, and also did the brake cleaner test by spraying it around the manifold (no change in RPM).  At 1/8 or 1/4 throttle the oscillation goes from 600 to 2000 RPM, like it wants to die, then goes up then wants to return to idle.

 

I'm sure there is a very simple explanation but I have not found it.  I am thinking somewhere along the lines of bad  IAC, idle/air bleed screw (if the car even has one) or the TPS??

 

It was doing this before (I bought used) so I assume it's nothing I did during my tuneup/manifold cleaning.

 

I have also checked the IAC: when I unplug it the motor goes to a very low idle andtells me it's working.  I also checked the ohm resistance it's only slightly out of spec, but then again so is my street 99 and it runs fine.

:banghead:

 

Any ideas are welcome.



#5
Keith Andrews

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It sounds like you have 2 1999 Miata's.  Why not swap the suspected IAC and see if your problem goes away or moves to the other car.  Have you confirmed all the pulley bolts are tight?


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#6
bmarshall1

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Keith,

 

That will be one of my next steps (switching IACs).  Yes, all pulley bolts are tight.



#7
Keith Andrews

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Just swap throttle bodies for ease of narrowing down where the issue is or is not.  

 

Can't you also reference the other car for your vacuum lines?


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#8
bmarshall1

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I had already thought of that but my other car has a supercharger :)  so none of the lines run the same.

 

Heading out to the garage to take another look.  I was talking to one knowledgeable fellow and he mentioned that once the car reached a certain temp it would cycle back and forth between open and closed loop in the ecu, maybe a lead?  He also mentioned get a fuel/air gauge and look at the fuel mixtures when this happens.



#9
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 I was talking to one knowledgeable fellow and he mentioned that once the car reached a certain temp it would cycle back and forth between open and closed loop in the ecu, maybe a lead? 

When I was root causing my engine speed oscillating from 2,200 rpm to 1,700 rpm it was happening when the valve cover was warm, with the radiator cold. The after market temp gauge had not left the 140* minimal temp. When the engine was cold there was no oscillation. The 1.6 the ECU  is in open loop untill some temp is reached. When in open loop, the ECU receives no info from the thermosensor, the throttle position sensor and 1 or 2 more devices. Receives info from all devices after a specific temperature. 


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#10
Ron Alan

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Here is my understanding. If the needle is all the way in and you cannot get 800 RPMs you cannot set the timing. Odds are you have a vacuum leak. But in the meantime pinch off the idle control hose until the rpm's get to 800 then do again what you have already tried!

Ron

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#11
bmarshall1

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Ron,

I have not heard of an idle control hose, can you guide me to it on my 1.8 (99) and I will give it a try



#12
Ron Alan

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My apologies Bruce...from memory I was writing and the hose I spoke of is on the 1600...doh! But assuming the TB screw is adjusted all the way there is another adjustment on the rotating cam the throttle cable is attached to. Right on top of the TB where this is at is a 8mm nut with an Allen screw. You can adjust this also to lower the idle I believe...

Ron

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#13
bmarshall1

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✓  Best Answer

The timing and idle issue seems to be solved at this point.  For all of those who were pointing to a vacuum leak - give yourself a pat on the back.  The interesting thing is where I found the leak...

 

I took the upper manifold to replace a leaky injector ring and decided to test the VICS check valve, it is supposed to be a one way valve, but mine was open in both directions, possibly flowing air backwards and when it should not have been, perhaps giving the appearance of a vacuum leak.

 

While I can't say for certain this was the problem, I can tell you a new VICS check valve made all my problems go away.  The timing is steady, the idle smooth, and it will hold a partial 2000 RPM throttle.

 

THANK YOU everyone for all of your input!!  Miata people are a great resource and awesome community.

 

Bruce






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