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Old 07-29-2010, 03:06 PM   #1
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Default NA power loss problem

I recently bought a 94 miata w/124k miles.

i test drove it for about 15-20 minutes, car ran fine, no problems whatsoever.

then on the way home it started loosing power sometimes.

next day, I put new spark plugs in it, new spark plug wires, did a coolant flush + new thermostat.

Car does this after about 30 minutes of driving, just randomly will start to bogg?

When I press the accelerator it boggs it down instead of accelerating.

Car sat for over a year before I bought it, timing is good.

I was thinking bad fuel pump? I have a walbro 255 sitting around, can I throw that in or will it be too much for a stock car?

If anybody has ideas, please let me know.
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Old 07-29-2010, 04:28 PM   #2
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Look at all the hoses,does it start ok?, try a compression test. It could just be injectors cloged up. Try going to a junk yard try to find a 7mge or 2jz motor both are supra engines you can also find that motor in a cressada. Or depending on how much boost your running get rx7 injectors.
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Old 07-29-2010, 04:34 PM   #3
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its not boosted. comp test 190-185-190-190
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Old 07-29-2010, 05:25 PM   #4
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Walbro 255 will overwhelm your stock Fuel Pressure Regulator.

Open your air filter box, clean the **** out of your air filter/replace.

Go to auto parts store, buy "mass air flow sensor cleaner", empty a can of it onto your MAF.

Replace the gummed up cat.
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Old 07-29-2010, 05:40 PM   #5
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Originally Posted by fooger03 View Post
Walbro 255 will overwhelm your stock Fuel Pressure Regulator.

Open your air filter box, clean the **** out of your air filter/replace.

Go to auto parts store, buy "mass air flow sensor cleaner", empty a can of it onto your MAF.

Replace the gummed up cat.

Air filter replaced, did it to the MAF. I'll take the cat out.

I have a stock 99 eexhaust, will that fit?
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Old 07-29-2010, 08:19 PM   #6
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nothing helped... any other ideas?
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Old 07-30-2010, 03:01 AM   #7
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did you try injectors? and replace the cat?
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Old 07-30-2010, 03:52 AM   #8
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I had a similar problem with an old chevy truck. Very different vehicle, yes, but the issue was the coolant temperature sensor, which was reading a constant -40*. It ran ok while cold, but once it warmed up and the actual coolant temperature varied greatly from -40*, it'd cut out. Might want to check it, it's way on the back of the head, where it's impossible to see or replace.
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Old 07-30-2010, 08:03 AM   #9
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^- if it is indeed this (you'll not see the temp gauge move) you may as well replace he heater core hoses while you're back there, the CAS tends to drip on one if yours is leaking at all, and eventually they get hard and rupture.

Edit for more- The heater core tubes are VERY THIN and made of brass. I HIGHLY suggest you use a razor to cut them and remove them that way, else you risk crushing or squaring one out while removing it, not a pleasant thing to fix.
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Old 07-30-2010, 09:18 AM   #10
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^- if it is indeed this (you'll not see the temp gauge move)

Unfortunately, this isn't true. The 1994 miata has 2 engine temp sensors. One feeds the ECU, and one feeds the dash gauge. They both come off of the heater core plate area at the rear of the head. The big one (and the important one as far as your ECU is concerned) is connected to the actual 'block off' plate that your heater core hose comes out of. The smaller gauge sensor is actually mounted just forward of the plate to the driver's side. Between the EGR pipe and the CAS, it a real PITA to get to either of them.
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Old 07-30-2010, 10:06 AM   #11
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I have a spare CAS for my 99 (its of a 97) so I'll throw that on, (i've been told that might be the issue). I have to take the CAS out anyway since it's leaking a tiny bit of oil from around it.
My coolant ttemp gauge goes from 0 to about 1/3 up the gauge but one day i saw the coolant bubbling for a minute and the gauge was still at 1/3 up. Then I replaced the thermostat and did a coolant flush, it doesn't get as hot.

I'll replace both temp sensors.

EDIT @ 1153EST:
I am going to the parts store to pick up the temp sensors. if that doesn't help. I'm going to my parents house and taking my CAS off the 99 and throwing it on this engine.

Last edited by Dhaark; 07-30-2010 at 12:54 PM.
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Old 07-30-2010, 01:00 PM   #12
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Throwing money at the car in order to replace parts that you aren't sure need replaced is going to quickly get expensive...if it hasn't already.

^^This is what dealerships and many unaffiliated auto repair shops do, and is one reason why nobody trusts car repair shops anymore. They run codes, then replace sensors. When the same code comes back, it's not their fault - and something else needs replaced...generally it's the $300 part they replace first, then after they replace the $200 part, the $100 part, and the $50 part, and charge labor for pulling the engine twice to replace 2 of those parts, they realize that it was the $3 part sitting on top of the fender well...

...are they going to unreplace the expensive parts, and give me my money back... hell no.
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Old 07-30-2010, 01:04 PM   #13
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Quote:
Originally Posted by fooger03 View Post
Throwing money at the car in order to replace parts that you aren't sure need replaced is going to quickly get expensive...if it hasn't already.

^^This is what dealerships and many unaffiliated auto repair shops do, and is one reason why nobody trusts car repair shops anymore. They run codes, then replace sensors. When the same code comes back, it's not their fault - and something else needs replaced...generally it's the $300 part they replace first, then after they replace the $200 part, the $100 part, and the $50 part, and charge labor for pulling the engine twice to replace 2 of those parts, they realize that it was the $3 part sitting on top of the fender well...

...are they going to unreplace the expensive parts, and give me my money back... hell no.
You are correct, the temp sensor is $13x2=$26, not a big deal. CAS I have a spare, I also have my fuel pump off the 99 (stock fuel pump that was put in 200 miles before I took the car apart, so i know it works, hopefully still does).

It needed the filters, plugs, wires done anyway. I need to pull the CAS to replace the o-ring around it anyway.

I just need this thing to work properly
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Old 07-30-2010, 01:06 PM   #14
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crap is frustrating, isn't it?
the temp sensors shouldn't be identical. I would have expected the ECU sensor to cost a bit more than the gauge sensor
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Old 07-30-2010, 01:44 PM   #15
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crap is frustrating, isn't it?
the temp sensors shouldn't be identical. I would have expected the ECU sensor to cost a bit more than the gauge sensor

Autozone has them for $13.99 each. they are different but cost the same.
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Old 08-01-2010, 09:19 PM   #16
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So today, I did a few things on the car, replaced the heater core hoses, coolant temp sensor for both the ECU and gauge, PLUGGED the coils in all the way so they are not loose anymore, took the valve cover off (the bolts were not even finger tight), replaced the CAS seal that turned into plastic and was cracked in half.

I'll put the valve cover back in place tomorrow once the paint dries on it.
I also have a new VCG sitting here waiting, I replaced the vacuum hoses that go to the valve cover on the right and from the intake manifold to the PCV valve.

I'll do a coolant flush again tomorrow and take it for a test drive.
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Old 08-03-2010, 11:54 AM   #17
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Took the car out for an hour, no bogging yet. I'm taking it out again today for some more driving, we'll see how it goes. I think it might have been the coolant temp sensor that died and maybe was reading -40F so when cold it had the right amount of gas but when warm it was too rich?
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Old 08-03-2010, 11:56 AM   #18
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Say it.
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Old 08-03-2010, 12:07 PM   #19
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Say it.
You might have been right.
we'll see after todays run.
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Old 08-04-2010, 10:15 AM   #20
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So I think it was a mixture between the coils not being plugged in all the way and the coolant temp sensor. Yesterday, after a ~100 mile drive through some twisty roads, it did not bog or anything.
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