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Discussion Starter #1
Okay, we delved today to try and find the mysterious problem plaguing my new engine. Newly rebuilt, whatever.
FYI, it's a 1988 MX-6 Turbo. If you're reading this post, and dont' know what problems I'm referring to, please, read the post "Trouble with new engine" I don't want to repeat myself because this post is already REALLY long.
One thing we found out is that the EGR valve is not operating properly. After taking it off and using about 3 cans of B-12 and getting almost ALL the soot off, and making sure the diaphragm moves freely, it still doesn't work. No trouble codes or anything, but, if you put your finger on it and rev the engine, the diaphragm doesn't move a bit. However, if you remove the vacuum hose going to the airbox, and suck on it a little, the diaphragm moves just fine and the engine stalls. Any ideas? We cleaned out the little nipple that the hose goes on and it's fine. Just not getting any vacuum there. Also, after messing with stuff for a while, I turned up a trouble code 4. Crankshaft position sensor #2. I didn't know I had one sensor let alone two. Where would I find this so I can check it? My Haynes manual says nothing about it.
My water thermo sensor <I think that's what it is, it's at the bottom of the radiator near the drain plug> is new, but, I don't have the connector, it broke when removing the old one, and you can't get the connectors. It's not hooked up, but I don't think it'd make that big a deal. If I'm wrong, please correct me. And then go out and see which lead from the sensor goes where on the wiring harness, it's only two wires! The other thing is I'm pretty sure I have a bad seal on my turbo. Oil keeps mysteriously appearing on the housing and burning off, and whenever I've revved the engine, and the rpm's come down, smoke pours out of the tailpipe. Can't be valve seals because I just had the head rebuilt. Could that contribute to backfiring and loss of power at 4000 rpms?
I'm about at my wits end, but, for the sake of my marriage, I don't really wanna spend hella cash at a repair shop, if I can do it myself, and save money, the happier my wife, and consequently, myself, will be.
Thanks for everyone that responded on my earlier post. Just to let you know what I've tried that didn't work, here's the list:
Changed plugs, wires, cap and rotor. Changed out the distributor. Switched the VAF meter. Changed the EGR valve. Checked vacuum routing and hose fittings. Two hoses are somewhat loose, they slide right on and off with the clamps attached. Still looking into replacing those. Otherwise vacuum hoses look fine. Timing has been checked, set, rechecked, and reset and is as close to perfect as we could get it. Changed out the igniter. Put in a new coil, OEM style. Checked fuel pressure, it's 40 psi through all rpms. Fuel filter is new. PCV valve is new. Air filter is new, not that it would make a difference.
 

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I've been wanting to post, but not sure that I can really help.

Something that no one has mentioned, it may be your turbo. Your turbo may be going into an overboost condition, which will cut off the fuel to the motor, making it cough AND sputter as if something were wrong with the motor.

A friend of mine had a car like ours (he's the one who got me to liking MX6 GTs), and towards the end, the turbo was failing, going into over boost, and you'd loose power at your higher RPMs. The turbo should kick in at about 3250 rpms or so, and gain more boost on up. Since you already have a bad seal in the turbo (that you know), and since you don't have ANY back pressure, it would not surprise me if the turbo is going into an overboost condition, or "thinks" it is. You might try a Grainger valve, ask Anarchy34x about that. See what he has to say.

Just a thought. Good luck man. Hey, I'm from Odessa (born there), my Dad's side of the family still lives there.
 

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Discussion Starter #3
I never would have thought about overboost though because it never overboosted before, and the exhaust hasn't changed, just got the engine rebuilt.
Guess I need to buy a boost guage to find that out one way or another.

Heh, Odessa sucks, it's cool that you managed to escape :D
 

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I didn't want to say that about Odessa, but I am always trying to get my younger cousins out of there! I even offer to help. No offense, but I'm real glad to get out of there (we moved when I was like 3 or 4 yrs old). But I do like the Sandhills, and you're not too far from Beamount.

Well, with a rebuilt motor, and no back pressure for the turbo, it would not surprise me. I believe that Anarchy said that when he changed the intake on his (to a less restrictive intake), it was going into overboost, sometimes though, not all the time. Or maybe you should ask him.

Know any Gifford's in Odessa?
 

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Are you using the Haynes manual?! For god's sake, if you're going to spend all this time, get the factory shop manual (100 times more accurate and detailed) for your year car from the mazda dealer for about $90. You'll be glad you did.
 

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Magik8 has a point. When I used the Haynes Manual for my 1991 Nissan, it covered pretty much every Nissan\truck\SUV from 1983 to about 1994, EXCEPT my 1991. Sucked ass.

One time, I looked up manifold installation/removal. It said, "To remove manifold, unbolt everything attached to it, and unbolt it from the engine, and pull it off. Installation is the reverse."

I was hoping at least for some tips on how to Not break the manifold bolts, or something.
 

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Discussion Starter #7
I'm about to buy a factory service manual. I see your point completely.
As for overboost, I don't think so. I don't have a boost guage, but, a friend used to in his car. Turbos don't seem to build boost unless the engine is under a load, ie: the car is moving. If you're just sitting there revving it, it doesn't build much boost. I never have figured out why. The car doesn't just stumble if I'm accelerating, it does it when I'm just sitting there revving it, too.

And no, I don't know any Gifford's in Odessa. :)
 

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I could understand why a turbo wouldn't build much boost if it doesn't have a load. I'm not sure how to explain it, but without a load, there wouldn't be enough resistance to create a lot of pressure on the intake. Does that make sense? Without something "loading" the motor, all that air forced into the intake would be exhaled very quickly, not allowing pressure to build up.

It was just a thought though. Best of luck to you man. Have you ruled out the possibility of a poor rebuild?

Also, where are you driving this car with no exhaust?


[Edited by jiffy6969 on 03-05-2001 at 03:32 PM]
 

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Discussion Starter #9
No, the rebuild was good. Before we put the engine in, my friends father, who was a machinist for 25 years, checked all the tolerances and everything, and everything looked really good. He's the kind of person who finds fault with EVERYTHING, and he grudgingly admitted that it was a good rebuild.
As for the exhaust, I'm driving around good ol' Midland/Odessa. The cat is gutted, so, it still looks like there is one, and with all the mustangs and camaros around here, my exhaust, open as it is, isn't all that loud, comparatively. There is no emissions testing here yet.
I'm not gonna drive with the cat gutted forever, for you environmental types. It was broken inside, and very restrictive, so, I gutted it. I'm saving up for new exhaust including a muffler, cause it sounds RICEY now <bleh> and a high-flow cat.
My problem HAS to be electrical or vacuum related. It's probably a matter of some vacuum hose incorrectly routed. I'll let the mechanic figure it out though, I'm tired of screwing with it :(
 

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I don't blame you for being tired of screwing with it. yall are lucky you don't have emissions testing down there. It is really cool that you had someone take a look at it, particularly a meticulis machinest, he should know a good rebuild when he sees it.

Well, let us know what your mechanic finds out. You got me trying hard to figure this thing out (in my head) and I want to know the answer.
 

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Discussion Starter #11
Took it into the Mazda dealership today. We shall see. Hoping it's not too expensive... bleh.
 

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FYI---- EGR valve also works with a load. Revving engine will not (should not) open it. Thought I'd let you know.
 

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Discussion Starter #14
I didn't know about the egr, but, it makes sense...

As for the ECU, I hope it's not f-cked up, they're expensive, though the junkyard has one.

We shall see in a couple of days <keeping fingers crossed>


[Edited by TexasMX6GT on 03-07-2001 at 01:13 AM]
 
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