Cal Club Autocross Forums

Hi everyone,

Need some advice. Car is a 2000 Miata, and has a cylinder 3 misfire.

Things I've tried so far:
-New plugs & wires (old ones were only 10k old, #3 was wet and smelled like fuel)
-Switched #2 & #3 injectors, code stayed with #3
-New coil pack
-PCV valve has 5k on it
-Cleaned EGR valve 5k ago
-Unplugging MAF causes car to stumble or stall

The code originally appeared on a cold morning, and I cleared it after filling up with good gas and using a bottle of injector cleaner. It stayed off for about 3 days, and came back until the day after El Toro last weekend (about 250 miles of driving & 8 autocross runs). The car seemed to run fine and didn't seem like it was down on power. Cleared it a couple more times after trying the spark plugs, wires, & injectors, and it would come back on after about 15-30 miles. Now it comes back after about 15 seconds of resetting.

Going to borrow a friend's compression tester this afternoon and see if compression checks out, but if I end up ruling that out, what else could be causing only cylinder 3 to misfire? It's obviously getting fuel, as the plug was fairly wet. It appears to be getting spark, and the new coil pack, plugs, and wires didn't help. Oil doesn't appear milky, and I'm not losing coolant. I burn about a quart of oil every 1500-2000 miles.

Any ideas? Thanks!

My advice is to contact Steve at Gearhead's Garage...

http://www.gearheadsgarage.com/contact.html

Brian: You probably already know all this...it's gonna be process of elimination.

A code P0303 may mean that one or more of the following has happened:
Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back. If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Hope this helps.

When I had a P0300 last year, mine turned out to be a bad crankshaft pulley plate and crankshaft angle sensor after replacing a whole lot of parts that didn't solve the problem. Your error is more specific than mine, though.

From Ed's list:
Faulty spark plug or wire - Replaced, unlikely
Faulty coil (pack) - Replaced, unlikely
Faulty oxygen sensor(s) - Unlikely the code would be so consistantly on #3
Faulty fuel injector - Swapped, unlikely
Burned exhaust valve - Compression check should give indication on if its bad enough to not get the fuel lit (which would be consistant with wet plug)
Faulty catalytic converter(s) - Unlikely the code would be so consistantly on #3
Running out of fuel Unlikely the code would be so consistantly on #3
Poor compression - Same as burned valve
Defective computer - Hope not, but worth keeping in mind. I don't think the computer could cause a consistant single cyl error

A dropped intake valve could do this as well, but less likely than a bad exaust valve.

Let me know if you end up with a cheap engine to sell

Jay W

The verdict is in. Wet numbers were similar, so at least the problem is in the top end.

What do your plugs look like?

1, 2, & 4 all looked fine, but #3 was a darker brown and had more carbon build up than the rest. It was also wet. These plugs were pretty new, only about 5 months old.

Seafoamed the car earlier. It still ran rough for about 5 minutes afterward, and threw the code again. I cleared it, and drove around for about 4 miles, and it didn't come back. The idle seems to have smoothed out, and the exhaust doesn't smell strongly of fuel anymore. I'll do another compression test tomorrow, but it seems like it's a dirty valve. It's probably the oil consumption that's causing the carbon buildup. Not sure how it's getting into the cylinders though.

Aaaaand it's back. Off to the shop now I guess. I wish I had a garage so I could do these bigger jobs myself.

I've never done this on a car myself but a leak down test might help you locate if its an exhaust or intake valve. You hook an air compressor to your compression gauge to pressurize the cylinder and watch it leak. There are kits available with the fittings you need. You can then listen to hear if the air comes out the intake valve by listening in the air box. If you hear it come out the tail pipe its an exhaust valve. It works on motorcycles but I've never done it on a car. Bikes have shorter intake and exhaust lengths so you can hear it. Just an Idea.

Even if I were able to locate the leak, I don't think I'd be able to do anything about it. I'm limited to small jobs, since I park in a parking garage, and can't really leave the car taken apart for an extended period of time.

Has anyone had experience with Tri Point Engineering? They're like a mile from my place, and seem to work mostly on RX-7s, but do all Mazdas. I've read mixed reviews online, but wanted to get some opinions here too.

Brian Kelly wrote: Has anyone had experience with Tri Point Engineering? They're like a mile from my place, and seem to work mostly on RX-7s, but do all Mazdas. I've read mixed reviews online, but wanted to get some opinions here too.

Haven't actually had them work on anything of mine, but as people who I have raced with and know, I can recommend them.

Brian Kelly wrote:Even if I were able to locate the leak, I don't think I'd be able to do anything about it. I'm limited to small jobs, since I park in a parking garage, and can't really leave the car taken apart for an extended period of time.

Has anyone had experience with Tri Point Engineering? They're like a mile from my place, and seem to work mostly on RX-7s, but do all Mazdas. I've read mixed reviews online, but wanted to get some opinions here too.

They'll take care of you; they live and breath Mazda, including Miatas. They are under new ownership now and are trying to correct some customer relations issues due to the previous owner. See Sean or Jon and let them know what's up.

Dropped the car off with them tonight. I think I spoke with Scott (long haired guy, really nice). They're going to do a leakdown test and give me an update.

Tri point got around to the leakdown test last night, and sent me an email today.

Cylinders 1, 2, & 4 are good, and 3 is leaking through the intake valves. Their quote seems kind of high, and they really took their time getting around to the leakdown test, so I'll probably end up taking it somewhere else. Hopefully I can get it done by the next event, but if not, I may be looking for a codrive.

Brian Kelly wrote:Tri point got around to the leakdown test last night, and sent me an email today.

Cylinders 1, 2, & 4 are good, and 3 is leaking through the intake valves. Their quote seems kind of high, and they really took their time getting around to the leakdown test, so I'll probably end up taking it somewhere else. Hopefully I can get it done by the next event, but if not, I may be looking for a codrive.

What is their quote? I know you mentioned not having space to do the job, but if it were me, I'd try to pull the head myself and save a lot of labor money. God knows, there are plenty of "how to" resources available.

I'm with Ed, pulling the head is not that hard, and given the car needs a valve job at minimum, you could save yourself quite a bit of coin doing so.

They quoted me 12 hours of labor @ $100/hr, and $500 for machine work for the head. Called a couple other places that gave more reasonable quotes, so I'll probably send it elsewhere tomorrow.

I agree that doing the work myself would save me a lot of money, and I would love to do it myself, but I really don't have the time or the space. If I had a garage, I'd love to give it a try myself.

Jayson Woodruff wrote:Let me know if you end up with a cheap engine to sell

But yeah, that quote sounds like too many labor hours and although I don't know machine charges well, I wouldn't have guessed even half that number.

Jay W

Just another option: Headsonly.com has a pretty good reputation (I have one) and charges $350 for a rebuilt exchange. You can have the new head sitting there before you start and with a buddy get the whole job done in a short day. I think you have 30 days to return the core and they don't require an up-front core charge.

If you could get the rebuilt head and don't have a garage you could rent space at one. Here's an option.

http://www.urdreamgarage.com/

I've never used them, not connected in any way, etc. Good luck.

Bill Martin wrote:Just another option: Headsonly.com has a pretty good reputation (I have one) and charges $350 for a rebuilt exchange. You can have the new head sitting there before you start and with a buddy get the whole job done in a short day. I think you have 30 days to return the core and they don't require an up-front core charge.

Excellent idea. And it really is a quick job.

KJ Christopher wrote:

Bill Martin wrote:Just another option: Headsonly.com has a pretty good reputation (I have one) and charges $350 for a rebuilt exchange. You can have the new head sitting there before you start and with a buddy get the whole job done in a short day. I think you have 30 days to return the core and they don't require an up-front core charge.

Excellent idea. And it really is a quick job.

AND, you would want to do the class-legal clean-up milling of the head if it does not come with one.
So, here's an offer... call Stan Kowalski. He's in Riverside, near Corona/Norco. He's a fellow autocrosser. He has the space for YOU to work on it and I have a car hauler. For $100, I'll come get your car and haul it to Stan's garage if you don't have another way. He'll probably help you with the job, but you would need to talk with him. He's a Miata expert and has helped several other racers.

You guys are making it really hard to justify sending it to a shop. If I had a place with a private garage, there would be no question. I guess my biggest fear is not finishing the car and having to leave it in pieces overnight, or for several days if I have to order parts. I've never removed a head before, so I'm not really sure what to expect. SWMBO is already mad that I didn't send it to the shop after the first CEL.

That being said, does anyone know a good shop in the SFV that I could call for a quote? I'd prefer to take it somewhere semi local. I've spoken with the Miata Specialist shop in LA, and Japanese Auto Tech in N. Hollywood, and they both gave better quotes than Tri-Point.

As for Stan's shop, that would be perfect if I lived closer to Riverside. Also, looking at the inventory on headsonly's site, it looks like they only have the 1.8 NA heads, I didn't see any for an NB.

Also, THANK YOU to everyone who has weighed in! I really appreciate all the input and suggestions!