Okay, the CEL on my 99 Miata came on the other day. Car ran/runs fine, but took it to get the codes read. Here's what we found:
Oxygen sensor
Bank 1 sensor 2 no activity
Bank 1 system too lean
Cylinder one misfire
Egr flow Insufficient
Evap system no flow
Fuel restriction indicator
Where do you start when you have all this and the car runs fine? And I've got to tell you guys that for being the "answer", this has been one of the most problematic cars I've ever owned.
If not wiring then fuel would be my next suspect.
I'm away from my manuals, otherwise I'd ask for actual numbers. If it does have a fuel flow problem, that would explain a few of the codes. Check your pressure.
They could be unrelated problems, too. Do you know if any of those are pre-existing? They do foul their EGR pipes occasionally.
The 1999 seems to have more little problems than other years.
In reply to Keith Tanner:
No, I don't know if any are pre-existing. I told my son to have them reset them the last time he took it in, and he said he did, but some of old codes are still there (o2 sensor and cyl 1 codes), so I don't know. I did drive the car and it drives fine, no problems at all. ???
I can tell you a few things:
Bank 1 Sensor 2 No Activity: Most likely = cat O2 sensor dead, less likely = pigtail is unplugged, least likely = chafed wiring. In any case its almost certainly unrelated to the other codes, and should have zero affect on engine performance.
The first place to look for the EGR Insufficient Flow is actually the DPFE (at least on a Ford, 9 times out of 10 the EGR valve is functioning just fine, but the DPFE has gone bad, giving a false Insufficient EGR Flow feedback to the computer). HOWEVER, the Misfire #1 can be caused by genuine insufficient EGR flow (either from carbon blockage or a bad valve) which will also cause a Lean code because the oxygen didn't get used up. DOUBLE HOWEVER, a real Fuel Restriction can also cause the Bank 1 Lean code, and given what I have heard about Miata cylinder head castings, the fuel/air distribution to a given cylinder (#1 in this case) could be just inferior enough in quality to the other three to only cause #1 to misfire.
I would start with the easy thing first: check the Cat O2 sensor pigtail (plug), then put a meter on the four wires for the Cat O2 sensor itself and check for voltage on both the pre-heat wires and the feedback wires. If either pre-heat or feedback circuit is dead, the Cat sensor needs to be replaced. Or, you could just replace the sensor first, since they all go bad eventually and see if that fixes the Bank 1 Sensor 2 issue.
Best guess on the EGR code is a bad DPFE sensor.
Best guess for the lean code and #1 misfire code is that they are related to the fuel restriction issue.
Vacuum leaks
iceracer wrote: Vacuum leaks
Touche', at least for the misfire/lean code stuff
(on a real computer, now can type)
Yeah, the dead rear O2 sensor won't affect drivability, it's an emissions test fail.
The DPFE (had to look that up) is rarely the problem with 1999 Miatas, a clogged up EGR pipe is far more common.
What's the actual code for the last one? It's not one I'm familiar with, and the manuals will tell us what trips it.
In reply to Keith Tanner:
Unfortunately he only wrote down the descriptions. I'm going to have him go back and get them read again, and then have them reset to see what's new and what's old. I'll report back...
I'm betting clogged EGR pipe too. Mine will occasionally throw a code and I'm betting its that. I did a fair bit of research on this, and the EGR pipe can cause all sorts of issues when its gunked up.
Might as well do plugs and wires on your car if its been awhile though.
I'd start with the most serious problem- cyl one misfire. These cars have a problem with coils, and I've had to change mine. Could be that. Or a partially plugged injector- but I'd figure a coil may be going out.
The plugged EGR will not cause the exhaust errors- just plugged EGR. That has to be very cleaned out- which I need to do, too.
The misfire, especially if it's not often, can cause a lean code (assuming there are no leaks). FWIW, it does not take much of a leak to really mess things up- so inspecting the intake plastic is a free thing to do.
That seems to be the first one that needs looked at.
In reply to alfadriver:
Car runs fine. There really isn't any cyl one misfire. I already checked all that out, and it has new coils, wires and plugs.
I told my son to get the codes checked again, write down the numbers and get them reset. Before he was able to go to the parts store the check engine light went out. Waddyathinkthatmeens?
Some codes will reset themselves if the problem goes away, some will not.
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