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1997 - P0300 and hot plugs.

3K views 14 replies 7 participants last post by  nattanont 
#1 ·
I'm tossing this out there because I ain't really such a hot mechanic (gasp). Go ahead and tell me to search n00b, but I couldn't find my particular situation described.

'97, stock everything. I got a P0300 (random/multiple misfire) the other night romping on the car a little (maybe a lot). It's still a solid CEL and hasn't flashed at me again. The car is running perfectly fine. I haven't done really any diagnostic stuff, but I did check the plugs, and they're gray/white. So.. fuel something? Unrelated to the P0300? I'd appreciate it if you guys could point me in the right direction. Some things:

-I read the service bulletin from 1998 or so about either needing to readjust the crank angle sensor or replace the ECU (**** me) on 97s. Haven't checked the sensor yet or gotten freeze frame data for the code.

-I plan to check/set if necessary the timing, but I haven't tried it yet because my Haynes manual indicates that there's a special procedure requiring special equipment to set the timing on 97s. I can't find any more info. WTF they talking about?

-My plugs are NGK Iridium stock equivalents, and I've heard tell that Iridiums suck somehow. The plugs and wires are relatively fresh. Could the hot plugs be a symptom of that particular plug? And if I spend a lot of time on the highway and running the car hard, should I bother switching to a colder plug?

Anyways, there's a big dump of questions and bullshit. I haven't had much time to crack into the car and I'm about ready to take it to a real grownup mechanic. Any help would be appreciated. Thanks dudes.
 
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#3 ·
Reading plugs is really more of an art than many people think. They show your LAST ENGINE CONDITION. This is very important. If you pull out a plug after idling for a while and pulling slowly into your garage, the plugs will show your engine condition at idle. If you run down a 1/4 mile and kill the engine right at the end of the track and coast to a stop, you'll be able to see on your plugs how the engine was running at xxxx rpms at xx miles per hour.

Those shots of plugs dripping with oil after being pulled from an idling vehicle? Yeah, that shows a gross malfunction.

So. Onto your shitty fucking worthless 97 ecu. How I hate it. THAT ecu is the reason I bought a 95 the 2nd time around rather than another 97. I hate that fucking ecu.

p0300: Can be many things. It CAN be plugs and wires and often is. Grabbing some fresh NGK resistor type plugs (bkr 5e-11s? That's from memory) and known good wires might help. It might not. With plug wires, you usually get p0300 and po30x. General misfire and cylinder specific misfire.

That crank sensor can indeed cause the problem. It has to be gapped correctly. That's the gap between the tooth on the crank wheel and the sensor. This is easy to check and reset with a feeler gauge.

It seems to me that the rear O2 sensor can help trigger p0300s, but that's also usually paired with the code for the rear o2 sensor itself. But not always.

The EGR system can cause a p0300 problem! Of all the fucking things. I could swear at the ECU some more, but you get the idea. It's a piece of ****. Anyways, cleaning out the ports in the EGR valve and in the crossover pipe itself often help. Sometimes the ports in the intake manifold need a little cleaning too.

The fuel pressure regulator on the end of the fuel rail can also cause p0300s. Sometimes, it's just the little regulator itself. Sometimes, it's the electronic part with the wires plugged into it.

Annnd..... that's all I got off the top of my head. I struggled with p0300s for a long time too. I fixed it by installing a Link ECU and ignoring the problem till it was emissions test time.
 
#5 ·
till it was emissions test time.
There's the rub! It's this month.
I have a fresh set of NGK BKR5EGPs and I'll see if those do, uh, anything. The wires are NGKs and pretty new, so ideally they're fine. I'll check piddly stuff like the ground strap too FWIW. Rev, thank you so much for the essay. I'll see if I can get that stuff ticked off.
 
#8 ·
have you not tried reseting the code or Mil/cel?

or just disconnect the negative terminal on the battery for about 15-20 seconds.
should reset the ecu, and if it comes back then you know you have issues.
some ecu/ecms will store that in its memory till reset.

idk if this works on miatas, but on tons of other cars it does.
so i am assuming it would
 
#10 ·
I should have mentioned. I have TWO spare 97 ECUs sitting in my garage somewhere. You're welcome to borrow one or both if you need. As long as you return them. Or we could do convenient rent-to-own payment plans. :D

Resetting codes: That does not help. Because now you have your codes deleted, your freeze-frame deleted, and you have to re-pass the individual component tests before the ECU sets the ready code. And if you're indeed having a problem with your EGR system causing the p0300s, you'll NEVER get to the ready state. Been there. Got a teeshirt. I hate that teeshirt.
 
#13 ·
Well, this is just about the least helpful answer I could possibly give you, but I just consider the occasional P0300 a quirk of the car, unplug the battery, and carry on. It happens every few months.

I'm kinda trashy like that.

Sorry, man.
 
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