99 head swap backfires won't start
 

I swapped out my warped 96 head for a 99 head. I had the 99 head taken to a machine shop and had them shave.008 off to make sure it was straight. Then put it on the car. everything went smoothly with the installation except that we had to take about a 1/4 inch off the bottom of the passenger side chain cover mounting bracket(the stamped steel one that sits behind the cam gears).

Now the car will not start. And is back firing through the intake when cranking.

I really think that it is the ignition timing but i'm not sure of a great way to verify that it is sparking at TDC of compression stroke.

Ive tried moving the cam sensor to see if it would help. and it can stop the backfire, or it can cause a flame to shoot out of the throttle body depending on where it's positioned.

The car is a 92 with 96 block, 99 head, 90-93 MSPNP.

any advice would be appreciated.

Flip the ignition wires. Sounds like you've got the 1/4 plugs connected to the 2/3 coils and vise-versa.

The relative positions of the two coils are reversed on the 1.6 engine as compared to all of 94-00 1.8s.

It actually doesn't matter which coil is which, so long as the correct path of ECU wire -> coil -> plugs is maintained.



EDIT: just noticed that this was only a head swap, not an engine swap. Are the ignition wires hooked up the same as when this was working with the '96 head?

Did you install the timing belt correctly.?

I bet the cam gear on one of the cams is off. When crank is at tdc the front cam lobes on both cams should be pointed outwards.

(zack morris's phone)

Sounds familiar doesn't it lars....

I would check the cam timing.

Another vote for cam timing.

Cam timing.

We checked it a few times. The cam timing seems spot on.

How did you check it? Did you only check the belt for 19 teeth and E/I in the right place? Put it at TDC and take a picture of how the front cam lobes are pointed on both cams.

If you want to check ignition timing:

Disconnect the injector connectors.
Pull out the spark-plugs
Put the spark-plugs in the Spark-plug-connector and ground them to the engine block.
Now check timing with the timinglamp.

As for the cams: you can mount the cam-sprocket wrong. The wheel for the exhaust and intake are the same but they are mounted specificly for their function.
Check the manual.

We all think you're lying. ;) Photograph the cam gears with 19 teeth between the marks, photograph the cams with #1 lobes opposite facing at #1 TDC, and also confirm that #1 TDC is actually #1 TDC - don't use your balancer, use the crank pulley mark or stick a screwdriver in the #1 spark plug hole and rotate until it's at its peak.

The only other thing it could be is if you crossed the spark plug leads or the coil plugs (plugging the 1/4 coil harness into the 2/3 coil)

In for failed timing pics. Some one should figure out what it takes to time it to run the intake as exhaust and vise versa. I'm surprised some timing belt first timers havent stumbled upon it yet.

Thanks for the lack of confidence fellas, lol. Seriously hope you guys are right! I will go check and take pics.

we doubt because we care.

I doubt because of this. Seems?

https://www.miataturbo.net/attachmen...ine=1314366443
Crank
https://www.miataturbo.net/attachmen...ine=1314366443
Cams
http://i1176.photobucket.com/albums/...photos/009.jpg
Cylinder # 1 Lobes

Thanks fellas, guess I decided that it would be good to line them up without reading the letter on the stamped steel plate. Yay For Miata Turbo And All Those Who Doubted! Thanks Everyone!

Well, you did it wrong as we thought. you have E lined up with I on the intake side, and I lined up with E on the exhaust side...

when you do it correctly, I and E will point veritcally and you should have 19 belt teeth between those two marks. the Cam lobes will also point away from each other.

Epicly wrong that...

E = Exhaust, I = Intake, both point to 12 O'Clock whan the crank points to 12.

You'll be a pro next time.

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

Since you probably had the cam gears off, Make sure that the pin in the exhaust points to E and the pin in the Intake points to I.

When everything lines up, your first cam lobes should point outward, also.

that link describes it better.

I just point the pins to 12 O'clock, far less confusing.

Update: the car now starts.

But will only idle with the throttle cracked, Vacuum is low around 5 in hg, and its running around 10 A/F normally 12A/F at idle. the IAC is sucking what seems like a lot of air. If I plug the IAC and start it with the throttle cracked it pulls almost 10 in hg.

I will let the car cool down then try cam timing again? any other thoughts?

More pictures just in case, please.

I loved "We doubt because we care", hahaha!

okay I will tear into it again and send more pics

it's pretty easy. here's how the cam lobes are supposed to be on the first cylinder closest to the timing belt.
https://www.miataturbo.net/attachmen...ine=1314386721

https://www.miataturbo.net/attachmen...ine=1314395440
correct cam timing
https://www.miataturbo.net/attachmen...ine=1314395440
New plug, ran about 30 minutes

The car is running rich, has a low idle around 500R RPM, and has low vacuum around 5 In Hg. Any pointers?

Could be a tooth off?

Bent valve? lol j/k.

playing with the cam sensor position brought the idle way up and also brought the vacuum up to about 17 in Hg. Still quite not right but I will mess with it more on Sunday.

lol @ "we doubt because we care" :makeout:

Compression test to rule out the obvious, then reset your base timing.

I dont know if that mark on the wheel is just a scratch or an indicator mark but are you sure the cam is lined up correctly?

Reset MS and did base timing it runs pretty well now just need to iron out a few things with the tune and all should be good. Thanks again for everyone's help!