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-   -   Down on power, diagnosis? (https://www.miataturbo.net/general-miata-chat-9/down-power-diagnosis-25820/)

pdexta 09-09-2008 01:33 PM

Down on power, diagnosis?
 
First off, yeah, I know it's a stock Miata, they're all slow but this one seems excessively slow :fawk:

I just bought a '99 Miata, it's got a few little issues I'm working on patching up and was hoping to get some advice. The car was supposedly in perfect working condition. When I take it out for a testdrive it feels very sluggish, it gets progressively worse to the point it'll barely operate under it's own power. I pull over call to get picked by the lady at the dealership. Ultimately it's diagnosed as a clogged cat. We end up working out a deal on the car; they don't want to drop the money on a cat and I don't mind living without one. I buy the car, take out the midpipe and pour out the remnants of the cat and the car runs a 1000 times better.

I get the feeling the car is still a bit down on power though, especially at higher RPMS. I've got a friend with a stock '99 that I'm going to line up with tomorrow and find out for sure, but the butt dyno says the car is a bit slower than my '90 was when it was stock and I know that's not right. I've searched and come across a few possibilities; fuel filter, coil pack, plug wires (already did plugs) and just wanted to get some opinions before I started aimlessly throwing parts at it.

So anyone have any tips for me? What would you try first? Thanks for any (useful) advise you guys can contribute.

Fireindc 09-09-2008 01:51 PM

Basic tune up? Plugs/wires. Definately an oil change, is it throwing any CEL's? Check that, possibly an 02.

How many miles? Maybe run some water/seafoam through a vac line and clean out the heads. (if you dont know how to do this research before running water through your intake manifold.)

After all that.. leakdown test? Unlikely but possible somethings not right internally.

Joe Perez 09-09-2008 02:03 PM

Well, if it wasn't throwing codes before, it will be now. :D

Seriously, though. The failed cat seems to me like a symptom, rather than root cause. Cats don't just die like that. When I pulled the (apparently original) stock cat off my '92 about three years ago, it looked just fine and dandy inside.

Something else is wrong with that engine. It's either running far too rich, or the ignition is massively retarded, or, well, who the hell knows. Could even be that whatever was wrong has been repaired, but that they failed to replace the cat which perished as a result.

First things first, though. Take that car down to PepBoys and have 'em pull the codes. I'd expect a P0420 / P0421 (catalyst efficiency), but what else does the ECU have to say?

pdexta 09-09-2008 03:33 PM

Forgot to mention, no codes at all. Which I thought was kinda odd for having no cat. Maybe someone disabled the bulb, I'm sure they'll think I'm nuts getting a code read when it's not showing a code but I'll get it pulled and get back to you guys. Ahhh, looks like I just bought another money pit :(

*Edit: Joe, just realized you're from Port Charlotte. Do you guys ever get together for any meets? Anyway :wavey: to a local.

99NBMia 09-09-2008 03:37 PM


Originally Posted by Joe Perez (Post 306173)
Seriously, though. The failed cat seems to me like a symptom, rather than root cause. Cats don't just die like that. When I pulled the (apparently original) stock cat off my '92 about three years ago, it looked just fine and dandy inside.

True, my brother's car ran good when it was first boosted but about 1 month later the car ran horrible. I mean stock NAs could easily own it...he one day pulled the cat only to find a big wad clogging the exhaust. This was most likely due to him running cautiously rich at first...that motor has something wrong, my guess would be wires/plugs/coils...sounds spark related. :)


Originally Posted by pdexta (Post 306221)
Forgot to mention, no codes at all. Which I thought was kinda odd for having no cat. Maybe someone disabled the bulb, I'm sure they'll think I'm nuts getting a code read when it's not showing a code but I'll get it pulled and get back to you guys. Ahhh, looks like I just bought another money pit :(

My best investment for my 99 was my scanguage 2.

Ben 09-09-2008 04:12 PM

CA car or Federal? Which cat was clogged? If CA, CA car does not monitor "main" cat, only precat. Possible both were bad, and easy to overlook the CA precat in that god awful exhaust mani if you're not expecting to find it.

Coil packs on those things suck, it's likely toast and the cause of the cat failing. Watch for a misfire code.

Joe Perez 09-09-2008 04:13 PM


Originally Posted by pdexta (Post 306221)
Forgot to mention, no codes at all. Which I thought was kinda odd for having no cat. Maybe someone disabled the bulb,

Easy enough to tell- does it come on for a couple seconds when you furst turn the key?


Ahhh, looks like I just bought another money pit :(
Nah, just install a turbo and a MegaSquirt and all will be well. :D


*Edit: Joe, just realized you're from Port Charlotte. Do you guys ever get together for any meets?
Fuck if I know. I've been living in SoCal for the past four years, just moved back here about a week ago, and I already hate the weather and miss the good roads back west. Florida sucks my balls.

Stein 09-09-2008 04:41 PM

Failed cat is often caused by bad coil pack on a 99.

EDIT, Whoa, I see Ben already caught this one.

99NBMia 09-09-2008 06:38 PM

OP I actually have two working 99 coil packs, if it turns out you need one lmk.:)

pdexta 09-09-2008 10:20 PM


Originally Posted by 99NBMia (Post 306290)
OP I actually have two working 99 coil packs, if it turns out you need one lmk.:)

PM'd. Thanks for the offer. I'm assuming that's what it is. I swapped some new plug wires off my other car and it seemed to help a bit but there's definitely something else going on.

I'm not sure if my car is a cali car or not, I found the emissions sticker under the hood that says: "Conforms to US EPA regulations". I don't see any canister off the exhaust manifold but I guess it's hidden under the heatshield anyway. I'm kinda thinking it is a Cali car since the check engine light isn't on (definitely comes on when i turn the key though) and the cat is definitely out. Maybe that heat shield needs to come out to get a better look.

Ben 09-10-2008 08:13 AM

What is the VIN?
Does the CEL illuminate with the other lamps when you roll the key to IGN?

pdexta 09-10-2008 08:38 AM

The VIN is JM1NB3533X0131132.

The CEL light does come on with the other lights when you turn the key.

Torkel 09-10-2008 08:42 AM

Congrats to buying a -99, the best year Miata ever made!! It is easy to spot if your car is a Cali or a standard. The Cali has an extra small cat just below the manifold, while the standard car just has a descending pipe. Judging from the sticker, your car probably is a standard.

The lacking of CAT should make your car produce a CEL. To start with regular maintenance, such as oil change, plugs and filters is a good advice. Mobil 1 10x30 or 10x40 is recommended for the Miata engine.

Also as mentioned: The coilpacks on our cars are known to be weak and fail and this often causes a CAT failure. But they typically either work or don’t, not slowly failing and causing the engine to loose power and if they fail, a CEL for misfire is typically present.

Did the previous owner doodle around with the intake? I have seen a car with a failed PVC valve in combination with a breather on the crankcase (instead of the normal line to the intake) suck so much oil into its intake that it ran terrible on higher rpms. PVC valves are about $6. Change it to be sure.

pdexta 09-10-2008 08:54 AM

Thanks for the advise, I'll pull the intake off tonight and see what it looks like inside. The car is completely stock and I haven't seen any signs that it's been modded, but it is a 9 year old car, no telling what it's actually been though.

Ben 09-10-2008 09:35 AM

Federal car

Torkel 09-10-2008 11:22 AM


Originally Posted by pdexta (Post 306512)
Thanks for the advise, I'll pull the intake off tonight and see what it looks like inside. The car is completely stock and I haven't seen any signs that it's been modded, but it is a 9 year old car, no telling what it's actually been though.

No need to pull the intake manifold before you answer: does it have a aftermarket intake?

pdexta 09-10-2008 03:01 PM


Originally Posted by Torkel (Post 306573)
No need to pull the intake manifold before you answer: does it have a aftermarket intake?

Nope, she's all stock.


Originally Posted by Ben (Post 306527)
Federal car

Woo hoo, some good news! Thank you sir.


99NBMia is sending me a coil pack so hopefully that takes care of the problem. Oh and the car has 105k miles on it, just noticed it was asked earlier and I overlooked it.

pdexta 09-21-2008 04:17 PM

Figured I'd go ahead and bump this with an update. Still trying to diagnose the problem. I'm getting around 19-20mpg, car is noticeably slower than it should be, especially over 5500rpms. In a similar commute I use to get 24-25mpg in my stock '90 miata. So far I've done: oil change, new spark plugs, new coilpack, new plug wires, and new fuel filter. I also seafoamed the intake and gas, it smoked after I did the intake but not too much and certainly nothing like I've seen some cars do. There was no change in the car from anything I've done to it. The air filter looks brand new. I pulled the intake off and it's perfectly clean.

I did a compression check and got 150, 145, 145, 150. Those numbers seemed a bit low, so I tested it on another car that I'd done previously with another gauge and numbers were ~25psi lower than the previous test a couple months ago, I'm guessing the gauge just reads a bit low.

I'm pretty much out of ideas at this point. I thought about hooking up a wideband to it to see if it's running abnormally rich or lean, but beyond that I have no idea what to do. I'm about ready to go buy some Vtec and type R stickers to see if I can pick up some power from those.

KPLAFIN 09-21-2008 04:55 PM


Originally Posted by pdexta (Post 310690)
I have no idea what to do. I'm about ready to go buy some Vtec and type R stickers to see if I can pick up some power from those.

You just made my sig :bigtu:

greddymx5 09-21-2008 05:31 PM

Maybe crank related... I have a 99 engine in my car that had a bad crankshaft...Loses a lot off power...

http://www.miata.net/garage/crankshaft.html

http://www.miataclub.org/orlando/94crank/

http://www.miata.net/garage/hsue/LoctiteCrank1.html

pdexta 09-21-2008 06:04 PM


Originally Posted by greddymx5 (Post 310703)
Maybe crank related... I have a 99 engine in my car that had a bad crankshaft...Loses a lot off power...

http://www.miata.net/garage/crankshaft.html

http://www.miataclub.org/orlando/94crank/

http://www.miata.net/garage/hsue/LoctiteCrank1.html

Wow, I hope you're wrong! PM'd with a few questions. Thanks so much for the help.

patsmx5 09-21-2008 06:05 PM

Try installing BRK5 NGK spark plugs gapped at .020" and see if that does it. If it does, you have a weak coil pack.

greddymx5 09-21-2008 06:39 PM


Originally Posted by pdexta (Post 310712)
Wow, I hope you're wrong! PM'd with a few questions. Thanks so much for the help.


I could be right... The change off timing will cause a great difference in exhaust temps. causing the cat to go deffect...

If the engine throws a cell from the emptied cat (what should happen) you can try to take the last lambda sonde out off the exhaust and plug the hole.
As the 1st sensor sees bad air and the 2nd ambient air this could work.(normally it measures the diff created by the cat)
(as long as it trows no cell don't bother this)

patsmx5 09-21-2008 06:44 PM

Cam timing could be off too. My exhaust cam was a tooth off when I bought the car cause it "has a new timing belt". After a few days I pulled it down and put another new TB, and found the old one was installed wrong. The exhaust cam was a tooth off, and fixing it made a difference in power on top end.

greddymx5 09-21-2008 07:02 PM

Yep, this also is a good one..

Rotate the engine until timing mark (down) is spot on.
http://www.miata.net/garage/images/TBELT5.JPG

Check the marks (highlighted in white below here) There must be 19 teeth of the timing beld between them.
http://www.miata.net/garage/images/TBELT6.JPG

pdexta 09-22-2008 03:48 PM

I pulled the valve cover today. The cams are 19 teeth of timing apart, thanks for the tip. I put a timing light on it and it looked like it was jumping back and forth between 10 and 11 degrees before tdc. I've been running premium in it, if that makes a difference (I read that '99s didn't have adjustable timing and they adjust timing based on a knock sensor... I think that's right anyway). I didn't want to dig any deeper into it today as I need to get to work tomorrow.

I gotta make this some kinda contest or something... Whoever correctly identifies the problem will get a bright shiny new Flyin' Miata 1.6 -> 1.8 throttle body adapter, shipped directly to their door!!! Ohhhh! Ahhhh!

greddymx5 09-22-2008 05:52 PM


Originally Posted by greddymx5 (Post 310733)
Rotate the engine until timing mark (down) is spot on.
http://www.miata.net/garage/images/TBELT5.JPG

Did you move the crank to see the timing mark on the gear???Or did you only see the top gears?? (gear is located behind the plastic covers...You only need to remove the top cover and shine a light inside to see the gear.)

If you saw the bottem gear on time,top gear on time, timing should be spot on... Meaning both (above) pics will be on time. But this doesn't mean the keyhole is ok ....
Pull out 1 sparkplug (key out, handbrake on, gear in neutral.)

Find out what the top point off the engine (cyl 1) is (You can use a socket extention in the sparkplug hole. Youll need the highest point.
The gear must be spot on TDC http://www.miata.net/garage/images/TBELT5.JPG

If this is ok, timing is not the issue.

Do not look at the pulley & timing adjustment mark on the plastic cover.. It is useless for this...


Next thing is spark plugs/ wires and fuel filter.

greddymx5 09-22-2008 06:07 PM

QUOTE: it looked like it was jumping back and forth between 10 and 11 degrees before tdc.

You must connect TEN and GND to see a stable and correct timing mark...
Only the 99+ have no scematics anymore in the diagnostic connector.
See this page:http://www.miata.net/garage/ignition.html#timing



QUOTE: they adjust timing based on a knock sensor...

No they reduce timing only when knock occurs. On hot days, heavy engine loads, low rpm/full trottle this can happen.
It's a savety device.


[/QUOTE]

patsmx5 09-22-2008 06:09 PM

99's have two marks on the balancer. Align them with 0 and 10* on the plastic cover and that puts the motor at TDC on #1. Couldn't hurt to verify that it's right with an extension in the spark plug hole, but either way there's no reason to pull any TB covers.

I said it's the plugs. Change them to NGK's and set to .020.

pdexta 09-22-2008 06:11 PM

I only looked at the top gears. I didn't know how far I had to go pulling stuff off to see the lower gear and didn't want to pull apart my daily driver on a work night. Plugs, wires, and fuel filter have already been replaced so they aren't the problem. I think I'm going to hold off on the lower pulley until next weekend. I don't want to end up trying to replace the timing belt when I have to work the next morning.

patsmx5 09-22-2008 06:13 PM

Did you use NGK spark plugs? What gap did you set them to? What brand wires did you use? Just cause you replaced them with something doesn't mean it's not that. These motors are pickey about some things. My motor doesn't run right on Champion plugs. Dunno why, but it likes NGKs.

pdexta 09-22-2008 06:18 PM


Originally Posted by patsmx5 (Post 311117)
I said it's the plugs. Change them to NGK's and set to .020.

Plugs have been changed from NGK's to new Iridium NGK's. I gapped them closer to .040, as everyone else seemed to suggest. You're suggestion to gap them to .020 seemed to be in order to diagnose weak coils, which have already been replaced so that is not the issue. Are you suggesting that the plugs are simply gapped to wide? Or did you miss that the coils have already been replaced?

pdexta 09-22-2008 06:21 PM


Originally Posted by patsmx5 (Post 311125)
Did you use NGK spark plugs? What gap did you set them to? What brand wires did you use? Just cause you replaced them with something doesn't mean it's not that. These motors are pickey about some things. My motor doesn't run right on Champion plugs. Dunno why, but it likes NGKs.

Plugs are NGK Iridium gapped to .040. Wires are Magnecor 8.5mm competition wires.

patsmx5 09-22-2008 06:27 PM

Put regular plugs in it and gap them to .020 and I bet your problem goes away. Try it. It's cheap. I suggest running regular plugs all the time anyways. It doesn't call for Iridiums. Don't use em. Less gap won't hurt anything and if you have a miss at higher RPMs, then less gap will fix it. I know you said you "swapped" coils. Doesn't mean you fixed anything. 99's are known to have weak coils. Swapping around weak coils is just moving a problem around, not fixing it.

greddymx5 09-22-2008 06:29 PM


Originally Posted by patsmx5 (Post 311117)
99's have two marks on the balancer. Align them with 0 and 10* on the plastic cover and that puts the motor at TDC on #1. Couldn't hurt to verify that it's right with an extension in the spark plug hole, but either way there's no reason to pull any TB covers.

I said it's the plugs. Change them to NGK's and set to .020.


Off topic...
Good to know.. i have a 95 block with a 99 head... And only 1 timing mark at 10 degrees... None at 0... I did not know for 99+ models.

pdexta 09-22-2008 06:47 PM


Originally Posted by patsmx5 (Post 311136)
Put regular plugs in it and gap them to .020 and I bet your problem goes away. Try it. It's cheap. I suggest running regular plugs all the time anyways. It doesn't call for Iridiums. Don't use em. Less gap won't hurt anything and if you have a miss at higher RPMs, then less gap will fix it. I know you said you "swapped" coils. Doesn't mean you fixed anything. 99's are known to have weak coils. Swapping around weak coils is just moving a problem around, not fixing it.

Alright, I'll be back in 20 min and let ya know what happened. :wavey:

pdexta 09-22-2008 07:14 PM

Switched back to the old plugs, gapped to .020 and took it for a spin. I thought it helped a little bit at first but I think it was just me being optimistic. Still feels like the car falls flat on it's face in higher RPMs, barely accelerating at all. I guess it could still be the coils, I'll PM the guy I bought the coils from and see if I can get a little history on them.

Thanks again to everyone helping. I love you guys.

patsmx5 09-22-2008 07:16 PM

You know, if the main cat was plugged, the pre cat may be plugged too. It's built into the manifold. Have you punched it out yet? If the main one died surely the pre cat is done.

pdexta 09-22-2008 07:34 PM


Originally Posted by patsmx5 (Post 311154)
You know, if the main cat was plugged, the pre cat may be plugged too. It's built into the manifold. Have you punched it out yet? If the main one died surely the pre cat is done.

Wow, I didn't know there was one... I thought that was only on the Cali cars?

patsmx5 09-22-2008 07:43 PM

I think all 99's had the pre cat. Mine did and it's not a cali car. It's called "the boat anchor". That huge cast iron manifold has a pre cat built into it. Double check, but I'm 99% sure all NB's have a pre cat.

pdexta 09-23-2008 04:08 PM


Originally Posted by patsmx5 (Post 311162)
I think all 99's had the pre cat. Mine did and it's not a cali car. It's called "the boat anchor". That huge cast iron manifold has a pre cat built into it. Double check, but I'm 99% sure all NB's have a pre cat.

Can anyone confirm that all '99's had a precat in the exhaust manifold? I was under the impression that was essentially the difference in a cali car and a 49 state car. I'm gonna be hella unhappy if I go to the trouble of pulling the manifold out for nothing.

patsmx5 09-23-2008 04:12 PM

Probably not worth much, but IIRC, cali cars have 3 O2 sensors and non cali cars had 2. I'll look up the pre cat shit real quick...


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