Bad Miata Engine/exhaust problem

:?: I am new to the forum so please bear with me. I race superbikes and bought this 93 Miata for my Fiance so she could go on the track too. It belonged to a guy named Andre befor I bought it. He told me about this club and Autocross.

It sat in a shop getting body work repaired for a month. When I picked it up it was running rough under 3000rpm. It felt like a clogged or gummy fuel injection system. So I added a can of B12 Chemtool and took it for a drive. As I was coming home the problem begin to get worse. Buy the time I was turning into my neighborhood it sounded like it was only firing on two cylinders. I try to limp it down the ally and I get a series of backfires. The last one came with a loud hiss and power suddenly came back. But I obviously have seperated my exhaust somewhere.

Now it runs but it is not running smooth. It also has exhaust coming out of the bottom of the catalitic converter. Besides having 106,000 miles it really is tip top and well taken care of engine. I checked all the wires but it really feels like it is only firing on 3.

Anybody have any Ideas where to start? Did I melt the catalitic converter? Did it collapse? I still have compression in all my cylinders no leaks or holes. No oil burning.

Could the cat be clogged?

I would start by trying a test pipe to replace the cat and eliminate that as a problem. You can get them on ebay for $30ish bucks and it will tell you if this is your problem.

The next step would be to try a set of injectors (30-40 on ebay or locally).

Try the test pipe and then the injectors and go from there.

You can pull the plug wires one at a time to see if one isnt firing. The idle will get rough if it is firing and it will remain unchanged if it isnt firing. Careful not to shock yourself. You can do the same with diconnecting the injectors one at a time to find one bad injector.


Chris

Check your plug wires on both ends. I've had one slip off of the coil-pack (back by the firewall) and exhibit the symptoms you're having.

Yup... Clogged cat... Had that same thing happen on 2 different Jeeps.

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Originally Posted by sammm

Check your plug wires on both ends. I've had one slip off of the coil-pack (back by the firewall) and exhibit the symptoms you're having.

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Yep I'm thinking plugs and wires also Miatas tend to eat up wires pretty quick.

Didn't happen to be any liquid down the plugholes was there, if the body shop cleaned the engine compartment it could cause issues if you fill them with water as I have done it myself!

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Originally Posted by POS Racing

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Originally Posted by sammm

Check your plug wires on both ends. I've had one slip off of the coil-pack (back by the firewall) and exhibit the symptoms you're having.

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Yep I'm thinking plugs and wires also Miatas tend to eat up wires pretty quick.

Didn't happen to be any liquid down the plugholes was there, if the body shop cleaned the engine compartment it could cause issues if you fill them with water as I have done it myself!

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I did the same when attempting to clean my engine bay once...

I'm in Frisco, if you'd like to meet somewhere, we may able to figure it out. Just drop me a PM.

I did find water in the plug holes. Especially #4 It had mixed with oil and was milky. And a couple of them had started working themselves off the connection at the fire wall. It has a very slow head gasket leak and a slow rear main as well. I was going to fix those later on but I guess since I have got everything to do I might as well fix it all at once.

I still have the same problem so I am going to go with the Cat. I think it is the problem.

How many miles do people normally get on these cars? Little inline 4 like this should last at least 250,000 to 350,000 miles.

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Originally Posted by Crash Crain

Little inline 4 like this should last at least 250,000 to 350,000 miles.

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It's just broke-in in at the mileage! :wink: Seriously, 150k-200k miles without major work is not unheard of. Replacement engines are cheap if it comes to that.

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Originally Posted by POS Racing

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Originally Posted by sammm

Check your plug wires on both ends. I've had one slip off of the coil-pack (back by the firewall) and exhibit the symptoms you're having.

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Yep I'm thinking plugs and wires also Miatas tend to eat up wires pretty quick.

Didn't happen to be any liquid down the plugholes was there, if the body shop cleaned the engine compartment it could cause issues if you fill them with water as I have done it myself!

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I had the same thing happen to me after picking my car up from the body shop once. The body shop had pressure washed the engine bay, and one of theplugs had gotten wet. It sounded like it was only firing on three cylinders because it was. :?

In my case unfortunately replacing plugs and wires didn't solve the problem, because running it on only three cylinders had fouled the cat.
Still, replacing the plugs and wires is an inexpensive place to start, and might solve the problem

Ataim has an extra cat for a 1.6 car. PM him or I if you want it. I would be much cheaper that way just incase that wasn't it. Oh.......and welcome to the board!

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Originally Posted by Crash Crain

I did find water in the plug holes. Especially #4 It had mixed with oil and was milky

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:idea: You have found your problem. :idea:

My cat failed at about 110k on my 92 B&T. It broke up and rattled like hell.

I replaced it with a free-flow cat and could tell a HUGE difference in the way the car ran.

Hope the new owner is taking good care of it. :( I sold it when we got Robin her Mazda 3.

RJ

Where did you get the cat and how Much$. I figured that when this engine finally needed to be replaced I was going to change alot on the car and the Input/output was high on the list.

I got it changed out at a place in Lewisville. They've done other exhaust work for me before. Not the cheapest place but they do very good work.

The free-flow cat was $249 installed. I could've gotten a cheaper one but the free-flow does make a performance difference.

You should at a minimum replace the valve cover gasket (the source of your leaks), spark plugs, and spark plug wires at the same time.

This way you avoid the problems that probably killed the cat.

There are instructions on the pointy board in the garage section that will help you in replacing the plugs, wires, and gasket. Those are easy items.

RJ

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Originally Posted by SPEEDRACER

Ataim has an extra cat for a 1.6 car. PM him or I if you want it. I would be much cheaper that way just incase that wasn't it. Oh.......and welcome to the board!

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Crash...before you buy new, see the post above!

YES!

No reason to buy a new one if you can get one that works fine ;)

Just be VERY careful when under the car... chock the wheels and use jack stands.

You will want to coat the bolts that hold the cat on with PB Blaster and NOT WD-40. You may need to use air tools to break those bolts free.

RJ

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Originally Posted by channelmaniac

You should at a minimum replace the valve cover gasket (the source of your leaks), spark plugs, and spark plug wires at the same time.RJ

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Make sure to blow out all of the crud that lives in the bottem of the spark pug holes. On the 1.8 I had all kings of crape in there, It took about 2 minutes on each plug with an air compressor to clean them out. But I was wanting to make sure that it was completely clean (the valve cover had borken and had metal parts all over the place.)

What are the torque Values on the bolts on the valve cover?

Small Something like 11 ft/lbs, you can crack the valve cover with too much.

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Originally Posted by Crash Crain

What are the torque Values on the bolts on the valve cover?

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Link to :batman: board torque specs list

According to that link, the cam cover bolts are 43-78 in-lbs.

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Originally Posted by altiain

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Originally Posted by Crash Crain

What are the torque Values on the bolts on the valve cover?

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Link to :batman: board torque specs list

According to that link, the cam cover bolts are 43-78 in-lbs.

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Wow! Thats not much more than finger tight!

BTW, here's a link to a step-by-step guide on replacing the cam cover, and here's a diagram of the correct order to tighten the bolts in:

http://www.miata.net/garage/valvecover/torque.jpg

Might I add that I would be willing to bet that your rear main seal is not leaking, but in fact that it is your CAS oil seal. This is located on the back of the head on the passenger side for 1.6 cars. Put your hand down there and see if you can feel any oil leaking.

That O-ring is about a 5 minute fix with the valve cover off... about 8 to 10 with it on.

RJ

You guys are great. You are right about the O ring as well. I am planning on working on her this weekend.

Myself and Service king are in a disagreement of the problem they have caused. After they fried the eletrical system on my Fiance's suv while replacing a tail light housing, they have now agreed that they may be at fault. It is being looked at now by a mechanic. I told the mechanic that If service king doesn't pay to have it all fixed than I will have to take them to court. It will be alot easier to prove now that they srewed up two of my vehicles not even two weeks apart. I might have the shop it's at put a new Cat on it while it's there just so I won't have to lift it and crawl under it. The valve cover gasket, O ring and wires i can do myself.

Thanks for all the info. Your information has saved me great amounts of time and money.