Full throttle randomly feels like the brakes were applied, not sure why?
 

So when I'm driving my 2001 Miata (stock ECU/engine/intake/injectors) and at full throttle, usually from 2800-5700 rpm ish, the car will suddenly stop accellerating as though I'd hit the brakes.

When it happens, the exhaust note somehow sounds hollow. I'll then let off the gas and it'll be fine.

This only happens at full throttle, so I'm not sure why.

Judging by the age and miliage (149k) of the vehicle, I'm thinking it could be:

Fuel pump going out: Doesn't seem likely, my last pump went out and the car just wouldn't start.

Injectors issue: Not sure why or what.

VVT failure: Given the rpm, it could be this instead of a MBT related issue.

Spark blowout: New coils, wire and plugs 4k miles ago. Seems unlikely.

Engine blown: Not sure how this would feel like that, but given the amount of redline/full throttle use (pretty much any time, all the time) and milage, could be. Car has been running lean for a while as I wait for an ECU.

So, not sure. I need to keep driving, so I'll see if it gets worse, but I'd really appreciate help with fixing my daily driver.

At 150k, I'd start at the pump. It's the easiest to get to and the cheapest of the bunch. Fuel pumps fail funny. Sometimes it's just dead one morning, sometimes they cause fun drivability issues that make you pull out your hair chasing the ignition system. Sometimes they die in the shop while you're getting an oil change.

I'd also double check everything on the coils wires and plugs, since you touched them last. It's also dead easy to do a leakdown test with the plugs out, which will answer your questions about blown motor.

My fuel pump would cause the mixture to go lean under acceleration but would cruise fine. Sound familiar?

Sounds about right. Ordered fuel pump yesterday, should be in tomorrow. Will post results.

I had the same failure mode. I'd get a wicked stumble on acceleration that I improperly diagnosed as the FPR going out. Fuel pump fixed it.

I've got a used 190HP somewhere in the garage if you want to give it a go, shoot me a PM. Nevermind, sounds like you've got one on the way

Thanks for the offer, but denso + filter from rock auto is here tomorrow. :)

Damn. Still happening with a new pump.

Sock on the old one was ripped. Maybe it killed the new fuel filter?

I need to check my plugs.

Ecu just came in, tempted to throw on the wideband and MS3E to see what's going on but don't want to change things and make troubleshooting worse.

Any ideas?

Verify pressure? It's a little harder to do on an NB because it does not have the convenient hose clamp connections for the fuel lines like on an NA but it can be done.

I've got access to a couple spare NB in-tank regulators if you need one.

Would the ms3 have a read on fuel pressure?

There is no stock fuel pressure sensor so unless you add an aftermarket one, I'd say no. :(

What would be the symptoms of a failing in tank regulator? If you think it's a good thing to replace, I'll definitely buy one off you!

I'd imagine it would not be able to keep up with demand and go lean under accel, maybe getting lazy or something? New filter and pump leaves regulator and injectors. I'd be happy to loan you a stock reg for the sake of troubleshooting this, can't guarantee it'll solve anything though.

You have a wideband for that MS, right? Install it and see what happens when you go WOT and get the stumble. All it will cost you is a bung and maybe $20 if you don't have access to a welder.

Yeah,I have a wb, was thinking of installing the lot to get all the readings but it could make troubleshooting a nightmare.

I'll get that regulator from you though?

Just checked the spark plugs. They look good. Perhaps a touch lean, but definitely nothing that should be causing spark blowout.

I'm stumped. Up next would be maybe a new fuel filter? The one on there is only about 2k miles old, though, but I do run down to E on the gas and the fuel pump had a torn sock, so I'm not sure. Fuel injectors, maybe? Fuel pressure regulator? This is my daily, so I'm anxious about it all.

Alright, this is interesting.

Checked codes, have misses and inconsistent cam/crank signal.

Replaced cam sensor, idles much better, still locks up while accelerating.

So I pull the crank position sensor, and I'm trying to get the new one gapped properly...

And all the four nubs are a different length from the sensor. I've read that means the trigger wheel is broken. That I did not expect.

Will the crank sensor work fine with some scoring (plastic scratching) from the trigger wheel?

Trigger wheel isn't plastic.

I believe Erin is saying the trigger wheel cut into the crank sensor.

That's... a problem. Do you have access to another trigger wheel and sensor? I know the sensors are not exactly cheap.

Hmm. It's hall effect VR sensor, which works by having the trigger wheel teeth disrupt a magnetic field. If it hasn't broken through the plastic I'd try it with a different wheel and see if it doesn't work. If the scratches are superficial, it should still work. There might be a problem if enough plastic has been damaged to affect measuring the proper gap.

Now the question is why that happened. Was the single bolt holding the sensor loose, allowing it to move and make contact with the wheel? Or do you have a bearing problem allowing the front of the crank to move around?

If you're ready to go MS3, you might just want to get the 1.6l Protege 36-1 wheel to replace the stock four tooth. Not on VVT.

I'm... well aware of that. What an odd comment.

It's actually a VR sensor with a built in conditioner, not a hall sensor, which is an important distinction in this case.

The sensor is unlikely to be damaged by having a 1-2mm gouge in it from the wheel. The electronics are located back within it some distance, the visible tip is just steel.

That said, your problem certainly sounds electronic rather than mechanical, and the NB cam sensor is notorious, with the crank sensor slightly less so.

Yes, my problem sounds electronic.

But if there's a sensor, and four prongs, and they're all a different distance, that cannot be right. Look at any trigger wheel. All prongs are supposed to be the same distance.

You mean the gap between the sensor and the tooth is different for each of the four teeth at it passes by the sensor?

If so then yeah, that's a problem. One I've never seen, in fact.

I'm...well aware of that. What an odd comment.

Yeah, just checked it again. At least one of the nubs is noticably further away from the sensor than the other.

Put a 21mm ratchet on the pulley, and couldn't really get it to turn that much, but didn't feel wobbly. There some better way to test for wobbles?

Sensor gap errors cause massive, undriveable misfires at a repeatable RPM independent of throttle application.

Well, not sure my regulator is going to help. Sounds like Andrew has your number there.

I'm not so sure. At first the breakup was just at WOT, but now it's starting to happen at cruise as well. I'll probably try gapping the sensor once more, making sure it's a credit card's width out from the furthest prong, after clearing codes.

Swap MS3 in, test?

I haven't wanted to swap in the MS3, I'm not quite sure what to do with it as per the last PM.

Install the WB to see how AFR reacts during the stumble. Might help explain if its fuel, spark, sensory..

Install MS after and log, that should reveal sensor issues.

Checked, the crank doesn't seem wobbly, and the nut seems to be on there decently. Put a prybar on it a touch and saw the timing disk flex but nothing else moved. All seems solid.

If you were down here in Tucson I'd have a spare four tooth wheel you could use for diag. Maybe try calling Mike's Place? It's just weird that yours got damaged somehow.

Yeah, I could have just been imagining it. I'm not good with spacial relationships. Just gapped it all again, and seems like it should be working, but now it's not starting. Might have the gap a little too far now.

Codes are:

P0031
P0037
P0128
P0134
P0300
P0301
P0304
P1345

The second O2 sensor makes sense, I've removed the one that just checks up on the cat.

However, it says sensor 1 isn't active, which I thought was the primary O2 sensor. Odd.

P1345 is what I've been operating off, with putting in a new cam and crank sensor.

Well, I wasn't imagining the gap distance changing. I gapped it just so a credit card (my .030 feeler gauge) just had a bit of tension, then turned the crank... and the next prong scraped into the plastic of the sensor again. So I found the longest prong, set it so it just barely doesn't hit that one, and tried to start... no start.

What is the difference in length between the shortest and the longest tooth?

Right now, it's gapped so:

2x teeth ~.005 gap
1x tooth ~.01 gap
1x tooth ~.08 gap

Which is well outside of the .029-.059 gap spec.

Okay, just gapped it to ~.025 from one of the 3 longer teeth, and it's at least starting again. Time to see what happens.

Edit: What happened is that the O2 heater errors are back, as is P0300 random misfire and P1345 crank/cam signal data error.

The O2 codes are probably because you have one of them unplugged.

The Random Misfire and Crank/Cam code are probably due to your trigger wheel. I'm guessing that it's only seeing three out of four pulses per revolution because of the worn down nub being .07 shorter than the others, and the spec for gap is only .03 wide (.059 - .029).

Either get another 4 tooth wheel from Mike's Place or Mazda, or get the 36-1 Trigger wheel from a 1.6L Protege from the dealer, and install your MS3.

Will you people stop STOP advising others to install a 36-1 trigger wheel with an MS3, especially on a 01-05? It doesn't work.

So yeah, it's all wobbly. Had some friends take a video for me. Looks like I'll be pulling apart the front of my engine.

Reverant, which trigger wheel should I go with then? I was about to order a supermiata pulley. 12?

My bad. Didn't know that. Sorry.

Holy shit! I hope your crank keyway isn't too trashed :noes:

That pulley movement doesn't look good, ouch.

Only the FM 36-2 trigger wheel will allow full sequential and VVT to work properly with an MS3.

Ah, so it looks like I'll be ordering an ATI damper then. Had no idea 12 tooth wheels wouldn't do VVT/sequential.

Couldn't you just install FM's trigger wheel behind the Supermiata dampener?

Edit: Nope. Special trigger wheel.

Yeah, can't do that. And 949 can't grind off a tooth for me. Not sure which way to go now.

Wait, how does the number of teeth on the crank angle determine if you can do sequential and VVT on a MS3?

e:

https://www.miataturbo.net/attachmen...ine=1395846547

It has mostly to do with software configuration and the unusual pattern produced by the camshaft in the NB.

In theory, any crankwheel can be made to work with any engine configuration. In reality, there are certain practical limitations to how freely the software can be configured to deal with unusual or irregular OEM patterns.

Because the NB cam puts out a really odd pattern, the software config to run an NB engine has to be hard-coded. That hard-coding assumes an OEM crankwheel. (I believe that there's also now an option to deal with one of the common aftermarket wheels- can't recall if it's the 36-1, the 36-2 or the 12. Been a while since I looked.)

Okay, so update. Went to break the crank pulley bolt... and it just loosened immediately. Like, 10 ft/lbs.

Should I tear into things, inspect for damage, or just tighten it up and try to go?

EDIT: Tried tightening it. Only about a quarter turn before I run into one thing or another, but it snaps back. It's like tightening rubber. Turn it 90 degrees, and it just ends back at the original location.

What are you using to hold the crankshaft in place while tightening the bolt? Your description sounds a bit like what happens when you try to tighten the bolt against the transmission with the parking brake set. There's a fair bit of play in the overall driveline.

It's been a while since I did this, but I seem to recall that it's easier to do it that way from underneath, with the sway bar removed. More freedom to turn the wrench.

That's what I figured, yeah. It's ebrake, on ground, in sixth. Taking up slack. I'll see about turning it further.

Also, putting the transmission in 5th gear with decrease the amount of slack just a bit, since 5th gear isn't literally a gear, it's just the position where the input shaft is locked to the output shaft.

(On a 5 speed, 4th is the not-a-gear.)

Correct me if I'm wrong, but aren't you compressing the springs in the clutch disk?

If you have time, it might be worth ordering up a crankshaft holding/fixture tool:

https://www.miataturbo.net/attachmen...ine=1406395574
Rennenmetal.com

https://www.miataturbo.net/attachmen...ine=1406395574
Flyin' Miata : Miscellaneous : Tools : Flyin` Miata crank bolt tool/crank holder

Or you could do something somewhat controversial like use the "rope trick" to lock the crank in place.