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Discussion Starter · #1 ·
Ok. I have a really annoying problem. I have an '88 MX6GT with t-bird upgrade. car is running 15psi of boost. At pretty much anytime it feels like it the car just drops all acceleration. Any gear, any rpm. Seems to get worse with increased boost. Had it set at 12psi and it was not nearly this bad. Car runs very rich so I moved the boost up to 15psi to equal that out. Well, that and to go faster anyway. It seems like no fuel or no air is comin in when this happens. I can have the peddle to the floor and hold it there and it won't drop in rpm's but there is no power at all. If I let of the gas for a sec or two it comes back on. One note I've made is that my air flow meter is straight up, it may be closing on me, but I dunno why it would get worse with more boost. I have an a/f gauge and it reads rich right when it happens, then looks like it turns off, but not. It drops all the way to zero. Anyone ever have this happen before? it sucks when I'm trying to race someone and it happens, makes me look like I can't drive. I know I need new plugs and am investigating some now, any suggestions on those would help too. Please help, this sucks!
 

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You're hitting overboost man. The stock ECU cuts the timing and fuel whenever you exceed 12 psi for more than 3 seconds. Turn it down to 12. You'll have to get an upgraded ECU that eliminates the boost cut. If you do that, you'll have to upgrade the fuel pump and or injectors to go over 15 psi.
 

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Discussion Starter · #3 ·
Ok, the car already has a performance chip in it. The previous owner had boost set at 18psi, but had since removed aftermarket fuel pump (dunno why, dumb ass!) and turned boost back down to 12psi. And, boost only hits the 12psi when in 3rd or 4th gear, unsure of that one. It only hits 10psi (if I'm lucky) in 1st and 2nd. Since I turned boost up it has gotten worse. For the most part this only happens in 2nd or 3rd. Does happen in 4th and 5th too, but if I let off gas and then back on it won't do it again, that's what gets me. Once it has had it's problem it doesn't do it again. I took the car up to 140mph in 5th with boost at 12-13 and I had no problems at all. Is it still the cut, even with the chip? Don't ask me what kind, it was already in there when I bought it.
 

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Discussion Starter · #4 ·
Ok, I went ahead and turned boost back to less than 10psi. It was about 7-8. It still has the problem. I decided to see if it was the boost cut anyway, despite the perf. chip. It is really bad when I make a right turn. Go figure. It is almost a stutter at that point, on-off-on-off. Just about as fast as you can say that is how fast the power comes and goes. It's not stuttering like a misfire, just power, then none, then it's back again. Now, it jumps really fast from one to the other. If I hold down the gas (I basically don't have time to let go, it happens so fast now) it comes back. Do you think it may be a bad hose, connection, maybe the air flow meter? Sounds dumb, but aside from this the car runs great. I can hold boost once it gets the "cobwebs" out, it's just a matter of time. So I am doubting it being the ecu and the boost cut. It seems like something is loose or maybe a boost line or intake line has a hole or something. I'm gonna check out that last part tomorrow. I have some wiring that needs attention anyway, so while I'm under the hood I'll be lookin and making sure everything is good and tight.
On another note, how would I tell if this car came stock turbo? I can't tell due to not enough experience (yet) with this model. My previous car was a Protege (nice but slow as hell). And by the way, please don't tell me to look at the badging, I already did and it doesn't say GT anywhere, all that has been removed. All that's left is the Mazda MX6 emblems. All of the turbo stuff in it is not stock, and I would like to know if I can find out so when I'm ordering parts that require a description of either turbo or non I will know. If you can help me please do, it's no fun driving a car that "bucks", which is what it feels like. It's like hitting the gas hard, then off, then on, then off. It's really annoying, and somewhat pain in the back from all the back and forth crap. Thanks.
 
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Your problem just about sounds like lack fuel, like perhaps the fuel pump is failing or not putting out enough or the the fuel filter is restricted(clogged). Another possibility is a problem with the air flow meter.

Another possibility is the pcm could be picking up detonation and thus retarding the timing(mine does that), but it doesn't recover quickly like you said yours does.

MX6 GT models are ALL turboed. If it is not turboed then it is an LX. There is NO chance that the turbo was not oem on your car, as too many items would have to be exchanged.
 

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88MX6GT said:
how would I tell if this car came stock turbo? I can't tell due to not enough experience (yet) with this model. All of the turbo stuff in it is not stock, and I would like to know if I can find out so when I'm ordering parts that require a description of either turbo or non I will know.
If you really want to know check out the VIN. Any dealer could probably let you in on a lot of info about your car just by running the VIN.
 

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Sorry man, didn't know all that about the chip when I posted before, you didn't mention it or have it in your signature.
It may be lack of fuel, or an air leak somewhere. But.... Something like this happened to me, and I think it's too weird to happen to anyone else, but, you never know. I had my engine rebuilt, and I drove it for the break-in period, then stomped on it, expecting a rush of power again. Well, instead, after 4K rpms, it stuttered, kind of like what you're saying. I replaced every ignition component imaginable. It turned out one of the lifters was missing from one of the rocker arms, and it was valve float. Sounds crazy, but, if your ignition components are good, you're getting good fuel pressure, and there are no air leaks, then it's time to start looking at crazy stuff. You DID check all that other stuff, right?
 

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Discussion Starter · #8 ·
No problem tex. I didn't know if my mods would show up on the signature or not. I don't even know if I put any o here or not. I was tired. Anyway, whatever is wrong, it has basically rendered the car useless for now. I drove it (well, tried to) about 15 mins today going to my parents house. As long as I stay off full throttle, and only use like 1/3rd throttle, the car is fine, once it needs more air or fuel past that point it starts stuttering. Now, I thankfully got it to my parents house, it won't even run. It starts for a few secs with really low rpm's, barely enough to stutter and run, then shuts off. It has gotten so that all of a sudden it just won't let air in or something. I drove it to their house and twice it just idled and wuoldn't let me hit the gas at all. While it was doin that at their house I popped the hood and turned the throttle cable. It sounded like the air was being shut off when I did that, I heard a vaccuum sound for a sec, then nothing. I removed m air filter to get a look at my air flow meter, but now the car won't start at all. All I did was remove the filter, eft the plug intact and all. It does appear that the AFM has been messed with. The little black cap that is supposed to be sealed on top looks like it has had the sealant cut open and maybe had the black top removed before and then stuck back on. I did that with my Protege with mixed results, but nothing like this. On that case I just ripped out the plug (on accident) and had to go in and solder on a new sensor that I had broken off. So, now I am gonna mess with it tomorrow. I'll see if I can't get it started and watch the AFM, see if it does indeed close when I hit it. For the most part it has no problems when in neutral, only when in gear. When it doesn't want to run, that's when it has problems in neutral. I am also gonna be buying new plugs, wires, cap, rotor. All that fun stuff. I've had the car running for maybe a week and a half, all I have had money for/time to do is stick in Mobil1 oil and an oil filter. I need to try to find a shop that has a good set of plug wires in stock, but I will most likely have to order them and have them shipped here. I'll be going with NGK plugs or Bosch ones. Anyone have any suggestions as for a good plug for me? Once I get this thing fixed I'll be running 12-15psi again, and don't know if stock plugs are still ok or if I should go one heat range colder. I am expecting to find something dumb wrong, I don't feel it is serious, but it is enough to sideline my fun until I get it running again. I only asked if the car was a stock turbo cause there is a lot of stuff rigged under the hood. I have wires going all over the f'in place and none of them are neatly done, all are loose and dangling around. One more note/question. On what appears to be the boost solenoid (my experience with solenoids is strictly from an outboard motor background for boats) but it looks like one. There are 3 places to hook hoses up to. Only 2 of mine have hoses. Since the car is at my parents house I can't describe it now (d*mmit, I forgot what it looked like now), but if someone could tell me what all 3 are supposed to go to I can print it out and go look. I doubt stuff comes with an extra connection that goes nowhere. I have a bunch or wiring questions I will make a new thread about tomorrow, once I have had time to examine them and what they come from. Mostly I need to know where they are supposed to go. I have found 3-4 wires with spade connectors (all the female ends) that are not connected to anything. I can tell this car has been worked on my someone who was not a mechanic. My fanwire has been grounded so it runs constantly, which I don't mind, but the wire is too small and heats up really quick and will burn you if you touch it, so I've got my hands full on getting this car's engine bay organized. Time to invest in some good wire, probably 10 guage or so (once I see what sizes look like I'll know) and some good tie wraps for now. Once I have it all ok again I'll go for neatness, I just want them replaced and out of my way. They go everywhere. I'll take a pic of it and when I get it developed I'll show you what I had todeal with, it's one big mess. Thanks for all your help so far, and hopefully I can get some more good answers/help out of you for this car. I'm sure you'll try, just a matter f what is wrong and what you think s wrong, I"m not saying that you don't want to help. FYI, I had to make that clear.
 

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Well, to answer a couple of your questions that I'm knowledgable enough to answer.
Plug wires. You can get OEM NGK's at the Mazda dealer for about $22. Go with the NGK plugs from the dealer, too, they're cheaper by about $.50 than at a parts store. On the BCS, there is one hose coming off the compressor side of the turbo, one going to the wastegate actuator, and one little vacuum hose going to the pipe that goes from the turbo to the intercooler. As for the VAF, or AFM, I dunno what could be screwed up in there. I found an extra at a junkyard for pretty cheap, someone wants to buy it from me, but, if that doesn't go through I can sell it to you. Or you can find one at a junkyard probably.
Good luck man, hope you figure it out.
 
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If your power is only cutting out on the gas and you have full boost try half throttle so the boost isnt at full swing. Do you still have the same problem? It may or may not occur at lower boost but check all air tubes for tears, holes, or loose clamps. If theres a leak in the system (your air meter is vain air flow system) the door would swing all the way but with a leak the pressure sensor in the manifold cannot match the pressure it should calculate off the door swing and the turbo would overboost and the fuel and spark is cut off. This would be the reason your exhaust will read rich and then drop to zero. In letting of the gas when the problem occurs your TPS(throttle position sensor) goes from reading high voltage to low voltage and the door has already dropped down from full swing to closed.
 

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Discussion Starter · #12 ·
Ok. I dug into the car today and did some stuff. Still won't run, but I did get some stuff done that needed attention. Air flow meter has been opened up before, but all looks ok in there. I checked all hoses, clamps, everything, no holes, tears, nothing. Only area of interest is the TB tube. It looks like it may be split right where the tube attaches to the TB, but I couldn't tell. No, I did not take it off yet, that is tomorrow. The AFM's gate is opening all the way up, I made sure of that. I do have an AutoMeter Phantom series boost gauge, that reads vacuum on one side and boost on the other. It operates just like norman, I hit the gas and the vacuum decreases. I don't know if it is supposed to go down, but it heads towards boost. It has always done that in that way, so I am assuming it is normal (it's my first turbo car, so I don't have much for experience to go on (yet)). When I hit the gas (during the limited amount of time that the car will run) it just dies. If I tap it really fast is gets rpms up, but nothing like it should. If I stomp it it dies. One friend mentioned maybe my fuel pump s dead, or dying. Any thoughts on that one? I am planning an aftermarket one anyway, but right now my priority is getting it running again. Could it be fuel related? If so, what area? Like I said, maybe pump, or maybe bad injector? i doubt one bad injector would make a car inoperable, would it? After today I am leaning towards the thought it is fuel related. Everything I can see as far as air intake is concerned appears to be just fine. Other possibles: check valve? sensor? All are from friends, not my own thoughts. As I said, I'm thinking fuel delivery. Could it be ignition comonents are shot to hell? I took off all spark plugs, wires, dist. car/rotor and checked everything, nothing seemed wrong there. I am awaiting all new components that I just mentioned, I was just lookin anyway. New car, I always change those and oil when I buy a car (even if it is 3 weeks later:(( )
One more thing. I believe it was Tex who told me what the 3 hoses go to on the boost solenoid. Well, I found em all except the one that is supposed to go to the i/c piping. The solenoid is missing one hose, I am assuming it is that one. I have an HKS I/C pipe upgrade on the car and did not see a hose fitting, is there one on the HKS pipes? If so where is it? FYI -- I do have a BOV (unknown stock? or what) If you have any other suggestions please reply, any help is good help, no matter what. I'll be trying the TB hose tomorrow, gotta see if it is split or not. Thanks for all the help trying to help me.
 

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Wow, it kills me to read all these things someone did to your 6. Sounds like the previous owner raced it or he was a complete moron. Maybe it's a case where curiosity killed the cat. Previous owner had too much curiosity and unfortunately your car was the cat. Our cars are pretty damn nice from the factory... why do some people feel the need to modify and eek out every possible component for max power. It seems to me when people try to fiddle with things they kill the car's efficiency and make a huge mess. Sorry I don't have any real advice for ya but I hope everything works out and you are enjoying the process of fixing it up. I have a feeling I would faint if I had a look at the condition of things under your hood. Good luck.
 

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Losing power when turning to the right is a classic symptom of a fuel pump problem. Either the pick-up is clogged or it's on it's way out. If it's not the tb boot, which the symptoms sound like too, I'd definitely check the pump.
 

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Discussion Starter · #15 ·
2Rusty... I know what you mean man. My car is black with grey int. The car itself is beautiful inside and out, even , surprisingly, the engine area is clean, there ar just a bunch of wires pretty much laid everywhere. For exapmle, my O2 sensor wire is laid out right across the BOV, so when the BOV is activated that poor wire got toasted. I already fixed most of the wire stuff, but with the engine in and me not really knowing much about this stuff it does still look rather bad. It is better, I tried to rewire most of what I could out of the way and around the engine bay instead of over it.
Bruce: thanks for your input on the fuel pump. I actually have a new sending unit arriving today (not exactly what you meant I know, by my fuel gauge doesn't work) and once I find and decide on a fuel pump I'll be doin that too.Thanks again,
 

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Walbro make a couple of pumps that will fit. Either 190 or 255 lph flow. I don't have one, but apparently they're very good and cheaper than oem replacements. Should be able to get one for about $100.
 
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