Its kinda on topic because this is the car I am drivign while I restore my 77 bus and my 74 914....

After my $150 tune-up (cap,rotor,plugs,wires,air filter, replacing cracked hoses) I still get a P0300 error (only error showing) when I book it going highway speeds.

Three things Im wondering:

*Do plugs for *new* cars come pre-gapped? If not, would this error occur from having the plugs gapped incorrectly?

*This engine does consume a little bit of coolant/water. I know what this means, and I'm trying to avoid facing the music......would a prematurely failed head gasket cause misfires (burning some coolant in combustion chambers--no bubbling from radiator when running engine though)

*Are distributors on these import cars have a high wear rate? I can't seem to find individual parts for these distributors, and the dizzy's themselves are almost 300 bucks a pop (heard from a buddy of mine that import dizzy's suck). I'd rather do some diagnostics to find out WHY this is happening instead of throwing parts at this car.

I appreciate everybody's help here, I've been trying for some time to find some answers, i'm getting desperate.


Its driving me nuts



Thanks

Have you determined what the code is for?

P0300 is a random misfire code. If the system could identify which cyl is misfiring you would also have P0300(X) with X being the cyl #. Do you have freeze frame data to be sure it is happening on the highway?



Wrong plug gap or bad head gaskets can cause misfires. Never assume a new plug is gapped correctly. Worn distributors are more of a problem in cars with points, is there play in the shaft? Does the car run OK, does the misfire set the CEL? If not there may be no freeze frame data. It's not uncommon to have random sporadic codes stored without a performance problem.

Hey Ed, I missed you not being at the Hershey swap Dont be such a stranger.

Thank you all for responding.

A buddy of mine owns a shop, my car apparently doesnt have freezeframe data for the light. the CEL blinks (indicating a misfire) then sets the CEL solid on.

My code reader says P0300 and my book says P0300 is a Multiple/Random Misfire.

I put new plugs in to attempt to fix this issue (popped P0300 error before I touched the car) still doing it. I'll check the gap (doesnt take long)

I'm thinking any failing sensor would also show on the CEL information as a code, so i'm thinking its something the car doesnt know about.

Water/coolant burning would cuase a misfire, but im thinking i would see something to indicate the water is getting contaminated

No side to side play in the shaft, and apparently one cant get a replacement coil for my distributor, and the dizzy is 300 bucks.

While I enjoy something that runs, I know if I ignore this, it will bite me soon enough.

The guy at the shop (buddy of mine) says it could be the crank sensor, but wouldnt that accompany the misfire code?

Car only has 78k miles, I love the car, but hate how smart OBD II is.

I'm beginning to regret getting this car, but I know this is goign to be something easy enough to replace.

Wouldn't the combustion pressure prevent coolant leaks INTO the cylinder?

When cold, it runs normal, when it warms up, it feels like it hesitates while on the highway, every few seconds.....

doesnt pop a code then, it pops a CEL (blinking, then solid) @ highway speed under load.

Wouldnt the computer be able to tune out minor fluctuations in Af mixtures?

Could it be a TPS thats failing wihtout popping a CEL code for that item

My '96 Saab had the ole ramdom misfire. I think it was running lean, because every cylinder had its own coil, so I thought it was unlikely to be an ignition problem, or it would have shown up on a specific cylinder, and not random.

I tried everything, including a new set of used injectors that I had cleaned and calibrated before installing them. Then a clue surfaced. The light went off when it got really cold that winter, and stayed off until March. So I replaced the air temp sensor. On my Saab, it screwed into the throttle housing casting upstream from the throttle plate. It cost me $68 at the Saab dealer. Even though the old one tested OK, hot and cold resistance wise, the new one fixed it. About 3 days later, the light went out, and this time it stayed out.

'96 was a tough year for OBD II. I think it was the first year, and it tried to hold the engine to a higher standard than its design necessarily could hold to, in my opinion and experience.

Good luck.

What fuel does the manual recommend? I've had a few Mazdas in the past and they said to use 91 octane or better.

First things first Did you clear the code after the tune up?
other sources for misfire
bad or dirty injectors
fuel pressure problems
oil leak into distributor can affect it
ignitors or control modules can go bad
head gasket leaks


Do you notice the misfire after the tune up?

During my years as a driveability tech (GM, Audi,Porch,Mazda,LandRover,Shaguar) the P0300 became known as the random harassment code. There is live data and missfire counts per cyl available, however it requires a Star tester or Mazda specific interface. Both of these units are made by Hickok mfg. The most common cause of this code that I saw was due to arcing through the spark plug boot inside the cam cover wells. There was no way to see this other than a very small white witness mark on the boot. Missfire counts on the scan tool usually only appeared under load and usually not enough to set specific cylinder. I hope this helps, I have a large journal of notes but I cant seem to locate them in the very large pile of junk that I brought home after leaving corporate automotive Larry

Did you think about getting a new muffler for the car?

As another former Drive-ability tech will agree to the above, I would also add the basic concept is simply put any unexpected slow down of your crankshaft revolution as seen by input sensors then seen by the engine computer as unacceptable.
That covers a lot of ground as the engineers of the software must have found out the hard way.

In doing a quick search the most common problem seems to be the ignition coil, maybe its skewed or has a ugly carbon track but that's most likely.

I did see an EGR and a waisted set of main bearings the cause as well, my money is n the ignition coil based on your info. and the parts you have since replaced.
John

The misfiring (more of a hesitation) can be felt only on highway speeds...did not go away after a full tuneup.

I bought a code reader, and cleared all codes after my tuneup.

Could a failing crankshaft position sensor and/or harmonic balancer cause misfires WIHOUT the computer throwing a CEL?

I *REALLY* appreciate the responses! !

By the way, is the ignition coil a seperate part? (1996s had the coil IN the dizzy, cant seem to find a standalone replacement coil and a replacement dizzy is 300 bucks)

does your year car share parts/interchange with ford? i seem to remember a "joint venture". you may have to suck it up and spring for a trip to the dealer. how much did you pay for this car britt?

k

I havent checked with Ford interchanges, I paid $2400.

gets 30MPG on highway, starts everyday--and its my GF's parents whom were sellign the car, so they accepted payments!

I may have to go to the dealer, I dont think it'll be that much for one coil....

Sorry for the long rambling diatribe just thinking out loud

Highway speeds,
Normally at highway speeds you are at a light load situation, soft on the throttle. Consequently your EFI is ratcheting down your fuel mixture as lean as it can. During those times, lean A/F the amount of voltage needed to fire spark plugs goes up and if theres any flaws in the plug wires, or coil insulation, including for example the plastic in-which your coil is held together with can be skewed with carbon tracks / paths to ground for that higher ignition voltage. So if you give it just a little more throttle that increased the electrical pressure and could cause a misfire. A small one but the system will pick it up.

I would take a look at the coil , now I have no idea how it laid out so I can't help you there but If you can clean up the coil tower and put something like WD 40 on it maybe it will stop the misfire, on the other hand to make it worse and help isolate the problem you can spray some water, better salted on the coil wire and drive the car. If there is a problem the salted water from a spray bottle will likely make it worse, thus helping you narrow down the problem.
The crank sensor and the balancer can cause a misfire but I don't see your point? If you have a misfire and a check engine light, its being seen.
Well, if the balancer is wobbling that can cause the system to see a change in relative crankshaft rotational speed and may set a code as well... Normally when theres a misfire theres a code set.. However thinking further since the crank sensor is the first thing many times the EFI looks at when first starting an engine and acts as a rpm reference, often a car won't start, however crank fine just not fire and wont set a code, but I can't say once the engine is running is it likely to cause a hesitation which would be likely related to your problem, could be however in your case there is a code being set..

Which engine you got? Is it a DX or EX?

1.5

I was late to work and was zoom zooming to work....

No blinking light this time, i did not clear my codes from earlier, but it should blink when misfiring

Coil isnt a FLAPS item--they push the 300 dizzy.

Coil would probably be a dealer item, along with my door lock switch.

Next part is coil?

Is that the consensus?