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.