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Discussion Starter #1
Alright, so I've tried and search for any similar problems, but can't seem to find anything that points to what I'm experiencing atm. Also, I apologize if this has already been discussed or I've posted this in the wrong place!

So! The problems I'm having is on a 1994 Ford Probe GT, 2.5l V6, the KL engine. Sometime ago I started to hear this really loud, pronounced hissing noise everytime I released the gas pedal while driving. Like, it's really loud, can hear it so well when the car is slowing down from around 3000 to 1500-ish RPMs. It's a constent hissing noise and gets gratualy lower and less adouible as the car slows down til you basicly can't hear it from inside the cab anymore, usuly below 1500 RPMs or so (the noise slows down with the RPMs by the looks of it). You can hear it while stationary too when revving it, I'll just let the video explain it, got a mountain next to me so got some nice echo to help with the audibility. The video is right here!
Also, as you can hear, when I hit 3000-ish RPMs and release the gas, you can hear something that kinda sounds like a grinding noise too? Only at this higher RPM tho, also not something I've heard before just recently. (I have taken the interior panels apart and got a hollowed out cat, so I might just be paranoid at this point x3).

So today I went under the hood again beacuse the car had started to act up a lil more than usual (more on this later, it might not be related to this). I managed to hear a faint hissing noise from somewhere behind or phraps on the intake manifold (more on the middle to the right side when looking at the car from the front). My best guess would be either some sort of vacuum leak with one of those vacuum hoses behind their, or maybe a bad intake manifold gasket? Can only hear this faint hissing when the car is on! As for the grinding noise? Assuming that's not normal.. I imagine some internal engine problems, not sure what, bearings?

Now, I don't know if this might be related to this or not, but might be worth mentioning. The car is leaking oil from both valve cover gaskets, front one being the worst one. Also last time I checked, it had engin codes for the EGR and both oxygen sensors (I've orderd these and will replace them). For the EGR however I can't seem to find the EGR valve/solinoid? Isn't it supposed to look like a metal mushroom? Read they supposed to be behind and under the intake manifold, but can't see them. Unless previos owner took it off and didn't get the computer re-tuned or is it the VRIS solinoids that's the problem?

Do hope I can get some help with this! I'm just a newbie, but have to start somewhere, right?
Thanks and best regards!
 

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The EGR valve is pretty hidden under the throttle body. I listened to your video. I definitely hear the hiss - immediately after you let off throttle almost like a blowoff valve.

I don't hear anything that sounds like bad grinding though, if that helps any.

I'd guess it's vacuum related but if your EGR valve is missing, you're going to have some non-standard vacuum routing.

Here's a picture of the EGR on a 2.0 if that helps you identify it! It will look the same, just might be in a slightly different spot.

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Discussion Starter #3
This does help! Just looked and turns out it still has the EGR valve, now is it better to just get an EGR delete and get it tuned out of the computer? Or should I just replace this old one? It's gonna be a pain in the ass to get too regardless tho. x3

Also, for that grinding-ish noise, it's not bad nor loud. But might have been amplified cuz of echos and no sound isulation in the car. But vaccume leaks wouldn't couse such a sound right? In combinations with oil leaks? Just thinking to myself here, it might be making that sound cuz of it, something in the engin not getting enough lubrication, might be completly wrong here, just a thought. The car has only gone 155000 kms (96300-ish miles). It does also smoke quait a bit white-ish smoke when revving it consistently at higher RPMs, like up to 3000 or higher. But looks more like white smoke rather than white with blue-ish tint to it.

Thanks regardless! Any help is better than none!
 

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This does help! Just looked and turns out it still has the EGR valve, now is it better to just get an EGR delete and get it tuned out of the computer? Or should I just replace this old one? It's gonna be a pain in the ass to get too regardless tho. x3
I don't think you can get it tuned out of the stock computer, so unless you're running aftermarket, you'll probably end up with a CEL. For mine, I ended up taking off the EGR valve, throttle body and idle air control valve to clean them and tried to get everything back to as stock as possible. (I took that picture when I'd found one of the vaccuum lines was unplugged and fixed it) It is certainly a pain in the ass to get to... that's the main good thing about the i4 - more room to work. (and maybe someday more room for a turbo kit~)

Also, for that grinding-ish noise, it's not bad nor loud. But might have been amplified cuz of echos and no sound isulation in the car. But vaccume leaks wouldn't couse such a sound right? In combinations with oil leaks? Just thinking to myself here, it might be making that sound cuz of it, something in the engin not getting enough lubrication, might be completly wrong here, just a thought.
To my understanding, the oil leaks won't actually cause a problem unless you also run low on oil... so if you're checking your oil level and keeping it above low, it won't prevent the engine from getting enough lubrication. If you're hearing the grinding at the same time you're hearing the hiss, I would honestly suspect the motor mounts.... the engine shifts when you go from on to off throttle, which could cause the sound. Unfortunately that's just a guess... you could try manually opening and closing the throttle at the throttle body so you can see if the engine is shifting at all?
 

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Discussion Starter #5
I'll have to see what I do with the EGR, I'll probs wait till I get the oil leaks and O2 sensors sorted out. But probably an important thing I forgot to mention now when I think of it.. Hissing noise, can that come from an exhaust leak? At least around the manifolds? Or worst case, cracked block/head or head gasket? I'm asking cuz if I push the car a lil in the higher RPMs when driving (driving a lil hard), I'll get the smell of exhaust in the cab, and hint of burnt oil (most likely duo being burned on the manifold). Wouldn't say it's an extreme amount nor smell, but enough to where it's quite noticeable. That would also maybe explain what's going on in this picture? Seeing how it looks like oil is being sprayed around there. I'm thinking bad exhaust manifold gasket? Or what are the chances of it being a cracked right there?
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This is a picture right after a drive, I can show more if needed.

Thanks!
 

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I'm having trouble orienting myself, and I am no expert, so I'm not sure... but to me, that looks like a valve cover gasket leak, since all the drips are coming from up top. Valve cover gasket leaks tend to make a huge mess and since they're coming from the very top of the engine, they make it hard to see what other problems might be there. My engine was absolutely covered with oil when I got it. I replaced the valve cover gasket, cleaned stuff up and found it was also leaking behind the timing cover (ended up being cam and front main seals).

The only real place for a leak above the exhaust manifold is the valve cover gasket, so that's certainly a problem (and would result in the burned oil smell, once the manifold heats up). Beyond that, you may be good or you may track down other problems once the first one's licked.

The oil leak is probably not what's causing your hissing sound... that's more likely a vacuum leak of some sort. When I listened to your clip (I'm at work now so working on memory), I didn't think it sounded like an exhaust leak, so more likely on the vacuum side. On the v6 it's probably a bit harder, but I ended up tracing all my vacuum lines by hand looking for cracks or other potential leaks when I found that my EGR had been unplugged by the prior owner, which was causing some trouble.
 

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Discussion Starter #7
I'll take a look at all my vaccume lines, or at least try to when I get the O2 sensors and my RTV Silicone Sealent. Is there anything I should keep in mind or any tips to finding potential vaccume leaks that can make the job a lil easier?
Also yeh, valve cover gasket is what I determined was the problem as well for the oil leaks. But also wondering if there could be a hissing type sound if let's say the exhaust manifold gasket is bad/cracket? Seeing how I do get some exhaust along with hint of burnt oil smell in the cab when pushing the car a bit. Wouldn't that maybe indicate a exhaust leak upfront somewhere?

Still waiting for my parts, hopefully I have them before weekend. I could've fixed the oil leak on the one vavle cover by now, but I wanna use quality rtv sealent along with the gasket.
Thanks for the help once again! I do appreciate it. (y)
 

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I don't know a ton on finding vacuum leaks. All I've done is follow each line by hand, feel for cracks or potential damage or bad connections. There are smoke machines you can use to inject smoke and see where it comes out, but I've only seen those used on YouTube.

It's possible that there's an exhaust leak (these cars are old and there's the potential for a lot of problems), but... if you're only getting the smell after you get the engine good and hot, it's probably just the spilled oil burning off. I'd imagine that if it were an exhaust leak, you would get the exhaust even at idle or as soon as you get it up to high enough RPM to create some pressure in the system.

I still think it's on the intake side since it happens after the throttle is closed, there shouldn't be much in the way of pressure in the exhaust system at that point.
 

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Discussion Starter #9
Yeah alright. I'll have a look around when I get my stuff and give an update here once I've gotten some of it fixed. Thanks!
 

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Alright, so, I don't seem to manage to figure out that hissing noise. So I've orderd an appointment at a workshop, told them to just go thru the whole car, do compression tests, check if the head gasket is good, look at that hissing noise and just generly see whats wrong. It also does seem to leak more oil on the backside (thowards the firewall) than I first thought. For the front valve cover, it doesn't seem to be leaking anymore after I fixed it. But haven't gone for a good drive yet. As well as I'm pretty sure the drive axle is on it's way out now too along with the oilpressure not seeming right. Been down very low on the gade in the dash, like more than usual which I can only think is linked to the potential vacuum leaks? Or phraps oil pressure sending unit?

I'll hopefully know more on the 11th next month, after the car has been at the workshop for a check.
 

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That'll definitely help. Someone who (presumably) knows what they're doing and can get hands on will no doubt give you much better answers. I hope your tech finds the answer quickly and cheaply!

I know it sucks to have it sit there while but having professional eyes on will definitely be a great place to start.

Mine's been hibernating a couple weeks while I took care of some other projects, hopefully this weekend I can get it back up and running.
 
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