Adamasher

Hello everyone, first thread here so I apologize if it’s in the wrong category. My MazdaSpeed Miata will buck with anything more than 50% throttle. Almost sounds like a rev limiter. Any of you experienced this? Also unrelated note the car is coming up in 250k miles so I want to do a few maintenance items. I didn’t own the car at 200k and I don’t think it got the timing stuff so I’m definitely doing that with and oil change and fuel filters. Is there anything else I should do at the same time?

curly

iTrader: (25)

What kind of mods are done to the car? At 250k, it would have needed multiple timing belts, possible turbo rebuild, injector service, fuel pump replacement, multiple fuel filters, the list goes on. 250k in a MSM is a lot. I've worked on a dozen or so of them, and if you multiplied their mileage by 1.5-2, you'd have a regular NB2 in the same condition. Nothing that can't be fixed, but the heat of the turbo and relatively complicated engine bays shade tree mechanics are less likely to touch increase the general wear and tear on them.

Adamasher

Only mods to engine are little enchilada from FM. I’m assuming it’s had at least one timing belt. I just replaced the fuel pump this year.

I would like to do everything I can at this service interval to help my baby live as long as possible. Any ideas on the bucking issue?

curly

iTrader: (25)

You're going to want to start with a hand held OBD2 scanner. Plug in and check for stored or pending codes. Then look at live data and see if any sensor aren't reading right. Coolant should be ~200 when hot, TPS should read 0-100%, AIT should be ambient when cold, 100ish when hot, check maf flow, list goes on.

With the stock ECU it'll be sensitive to air leaks, so you could figure out how to smoke test it for leaks. After that I'd be checking fuel pressure and injector condition, as a mechanic "I just replaced the fuel pump this year" is usually a giant red flag.


That's some general diag suggestions without seeing the car in person.

Z_WAAAAAZ

Curly's right. There's a ton of maintenance items needing to be done on one of these vehicles at that mileage.

However, buckling with a rev limiter-type feeling at heavy throttle screams ignition misfire. For some reason, early 2000s OBDII-equipped cars have a hard time identifying ignition misfires related to heavy engine load, so it's not uncommon to have an issue like this but no check engine light or trouble codes in the system.

Long story short, I'd start by checking the spark plugs and then go from there. Wouldn't surprise me if they're excessively worn. If they look alright, one or more ignition coils or spark plug wires could be at fault too.

But also, listen to Curly's advice on the maintenance lol.

SimBa

My bet is spark plugs as well. My old ford escort used to foul them out pretty quickly and the main symptom was stumbling if I gave it too much throttle, especially getting onto the freeway.

Plugs, wires, fluids, etc... would be on my list for a new-to-me car.

Adamasher

I did the plugs and coils, did the fuel pump because the old one was getting hot and turning off, it was a no name brand replacement. My best guess is the timing belt maybe loose, or crank or cam sensor. My data tool doesn’t show cam and crank data and I don’t think the NB even has electric timing that can be read with a scanner but I could be wrong. Any thoughts on that?

curly

iTrader: (25)

Oh yeah, kept thinking injectors and forgot spark, but sounds like you did those recently.

OBD2 scanner will show ignition advance, and if you see RPM you're seeing the crank sensor. You can check sensor gap fairly quickly. You could hit the "rev limiter" you're experiencing and see if RPM data disappears. You'd have to stay in it a while, since most OBD2 scanners are pretty slow to respond. I have some nice ones at work that log so I can just go drive it then look at the data, flooring it while staring at a scanner is asking for trouble.

Basically what I'm saying is get a Link pnp and ID1050x injectors.