Vacuum Leak I think!?!? Or Failed Valve?

9

97MarkVIIILSC

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Hi Everyone. I figure this would be a good time to start posting.

I have a 97 Mark VIII with 136K on the clock.. well maintained and engine ran smooth UNTIL a few days ago, when i noticed my mileage would literally take a DUMP at red lights... It was like watching a New Years countdown. On the highway its fine and runs smooth, but at idle it seems to SLIGHTLY choke...almost rhythmically. every few seconds a slight bog.. nothing substantial, but with the hood popped you can barely hear and the engine shake with it. If i pull on the throttle body it sounds fine, appears to breathe ok as well.. but on idle, its a slight struggle. I'll make a video later if it helps. Any thoughts on this guys?

Thanks!
 
Before you dump thousands into it like I did take the step I should have taken from the start.

Buy a can of carb cleaner and spray all along the intake manifold gasket (with the car running of course). Have someone sit in the drivers seat. Ask them if the RPM's drop while you're spraying it. Spray one area at a time so you can pinpoint your leak.

You probably will be able to tell the difference yourself without someone sitting in the drivers seat, but I'm a big believer in two heads are better than one. This is how I found my intake manifold leak...I had similar issues to what you have.
 
ripped camel said:
Before you dump thousands into it like I did take the step I should have taken from the start.

Buy a can of carb cleaner and spray all along the intake manifold gasket (with the car running of course). Have someone sit in the drivers seat. Ask them if the RPM's drop while you're spraying it. Spray one area at a time so you can pinpoint your leak.

You probably will be able to tell the difference yourself without someone sitting in the drivers seat, but I'm a big believer in two heads are better than one. This is how I found my intake manifold leak...I had similar issues to what you have.
Click to expand...

Awesome - thanks. I had a feeling my intake manifold was leaking coolant. my brother who is very mechanically inclined told me that its common for these engines. I am not sure how true that is or isnt... but maybe I can tackle 2 birds with one stone?

Ripped.. If i remember correctly, didnt you have some special tool for working on your engine :D
 
97MarkVIIILSC said:
Awesome - thanks. I had a feeling my intake manifold was leaking coolant. my brother who is very mechanically inclined told me that its common for these engines. I am not sure how true that is or isnt... but maybe I can tackle 2 birds with one stone?

Ripped.. If i remember correctly, didnt you have some special tool for working on your engine :D
Click to expand...

tell your brother he is wrong the 4.6 SOHC has the leaky intake
 
97MarkVIIILSC said:
Awesome - thanks. I had a feeling my intake manifold was leaking coolant. my brother who is very mechanically inclined told me that its common for these engines. I am not sure how true that is or isnt... but maybe I can tackle 2 birds with one stone?
Click to expand...

And, there are no coolant passages in the DOHC intake.
 
DLF said:
And, there are no coolant passages in the DOHC intake.
Click to expand...

I was smelling coolant so i figured it made sense.

So, when I leave work I am going to spray down the gasket on the intake manifold to check for leaks. The car hasnt been as responsive as it normally is.

So, I am guessing no matter what, Its going to need the gasket replaced. On the off hand its not the intake, anywhere else I should check for a leak?
 
You can't guess you need to know.


FWIW these cars are known for bad water pumps, a gasket above your oil filter leaking coolant, and coils going bad ...start there.
 
ford nut said:
You can't guess you need to know.


FWIW these cars are known for bad water pumps, a gasket above your oil filter leaking coolant, and coils going bad ...start there.
Click to expand...

Well I dont see any drips, nor does it ever appear to be low- and the car alwyas runs at perfect temp.. so its probably nothing.

As for the Compression/Vacuum issue.. Im going to have to tackle this tonihgt...c ant take the crappy mileage!
 
ripped camel said:
Before you dump thousands into it like I did take the step I should have taken from the start.

Buy a can of carb cleaner and spray all along the intake manifold gasket (with the car running of course). Have someone sit in the drivers seat. Ask them if the RPM's drop while you're spraying it. Spray one area at a time so you can pinpoint your leak.

You probably will be able to tell the difference yourself without someone sitting in the drivers seat, but I'm a big believer in two heads are better than one. This is how I found my intake manifold leak...I had similar issues to what you have.
Click to expand...

You stop giving people advice right now young man!

Do not spray "Carb Cleaner" into that intake!!! You can either buy a vacuum test gauge for around $6 at Sears and always have a way to check leaks, or you can spend $4 on a can of "throttle body cleaner/ MAS safe!!" and clean the MAF as well as checking for leaks. You won't use a full can checking for leaks, so the remainder won't be wasted, you can not clean the MAF with Carb Clear it will ruin it

also, don't think it may be just a vacuum leak, mine has the same symptoms as yours and I have a blown head gasket, slight miss at idle, still runs smooth with load. Once I blow the water out of the piston it runs great lol

pull your plugs, check how they are burning, that will tell you ( or us if you take pics, and please label each plug according to cylinder)how the engine is burning, normally it will be a slight grey on the tips...
Look in the bore with a flash light, check piston tops for rust, or evident coolant, carbon build up ect ect

you said you don't have a leaky coolant, or can't find the leak? How often are you adding coolant if ever. A blown head gasket would explain irratic idle with scent of coolant
 
Sapperfire said:
You stop giving people advice right now young man!

Do not spray "Carb Cleaner" into that intake!!! You can either buy a vacuum test gauge for around $6 at Sears and always have a way to check leaks, or you can spend $4 on a can of "throttle body cleaner/ MAS safe!!" and clean the MAF as well as checking for leaks. You won't use a full can checking for leaks, so the remainder won't be wasted, you can not clean the MAF with Carb Clear it will ruin it
Click to expand...

Thanks for clarifying that!! Now, how will I be able to spot a leak with the throttle body cleaner? Will it seep out or something?

I seafoamed the car not too long ago by running it thru the intake..(PCV) I wouldnt expect it to need a cleaning again, but def want to find the leak!
 
As the engine is idling, it's pulling vacuum, when there is a leak it pulls from there as well...the cleaner is a combustable, it will make the engine rev as it sucks it into the intake


A can of Nitrous Oxide into the intake will make it rev ALOT

since you asked about it seeping out, I'm guessing you've never seen this process done...take the can and stick the straw in it..spray around the intake
manifold gasket, above the lower plenum, spray around vacuum hoses at ends, check for cracks in hoses, there's a T cluster on the driver side at firewall that rots out check there, and the oil blow off
 
Sapperfire said:
As the engine is idling, it's pulling vacuum, when there is a leak it pulls from there as well...the cleaner is a combustable, it will make the engine rev as it sucks it into the intake
Click to expand...

ahhh ok, so I want to spray around the gasket with this...?

This might be a stupid question - but do I run the risk of blowing up my engine, or atleast having this :q:q:q:q catch fire ontop of it?
 
I'm having a similar idle problem, still haven't figured it out.
 
Sapperfire said:
there's a T cluster on the driver side at firewall that rots out check there, and the oil blow off
Click to expand...

This isnt the same T im thinking, hwoever coming off the intake there is a T, with 2 hoses, approx 3 inches long each that come off of it. One of these had rotted/collapsed, so I replaced them, but now the T itself appears to be rotting a bit. I should check there.
 
Yeah, uh, replace all rotting things.

Just spray a little, no you won't blow the motor up like that.. You can open the hood, pull the intake off, remove all fuel from tank, spray throttle body cleaner ditrectly into the throttle body and have the vehicle driven shirt distances without gas...I've had to do it with cars in my parking lot that had bad fuel
systems

it's perfectly safe to spray a bunch, but it won't require it to find a leak
 
Wow people, guy has a SLIGHT stumble at idle but is not indicating a miss under acceleration. He also says its every few seconds when it stumbles. That is more then likely the IAC.

Also for finding vac leaks on the lower plenum stuff like throttle or MAF cleaner wont do chit. Starting spray is what you need but I don't tell non mechanically inclined people to use it because of the explosion/fire possibilities, more so for people that would spray it on so much that it pools. Just a couple split second taps of the nozzle around the injectors is enough to check. Really though that don't always work on our cars because when the intake gasket fails it fails in the middle pointing at the valley.


And no, your brother got the SOHC and DOHC motors confused. DOHC never had a coolant leak from the intake as there is no coolant in them. Plus the line that runs between the valley behind the water pump don't leak. I cant remember a single person ever having a leak there.


Oh yeah, another thing that can cause a rhythmic miss at idle are bad coils/coil boots. You can check the boots for cracks pretty easily.
 
LaserSVT said:
Wow people, guy has a SLIGHT stumble at idle but is not indicating a miss under acceleration. He also says its every few seconds when it stumbles. That is more then likely the IAC.

Oh yeah, another thing that can cause a rhythmic miss at idle are bad coils/coil boots. You can check the boots for cracks pretty easily.
Click to expand...

When you refer to Coils, do you mean spark plugs and the rubber boot surrounding them?

Im going to make a video when I leave to see if that helps identify this better.

Thanks for all the advice. I am sure with all you guys help Ill get to the bottom of this!
 
You have a 97, you have the COP "Coil over Plug" each plug has it's own coil...the coil is the entire part that's plugged into the spark plug

and now the main question...is your CEL on?
 
Check the fire of the coil, unplug one, see if engine idles the same or worse, if it stays the same unplugged, it's bad...check with spark plug incerted in tip and lay it off to the side to confirm
you know, turn car off, remove plug, with engine cool, stick
it back in the coil, crank car and see if it's sparking, check for proper gap
 
Carb cleaner sprayed around my intake manifold gasket almost stalled the car out because it was sucking into the engine. That stuff is only $3 at advance..not really breaking the bank. Wish I would have checked that first before hunting for failed sensors and fuel stuff! So that proves the gasket is leaking, because carb cleaner sucking into the intake will stall out the engine or attempt too.

The MAF is nowhere near the intake manifold so it won't harm it when spraying carb cleaner on the intake manifold to hunt for leaks. Yes you should only spray MAF or Electrical contact cleaner on the MAF, but why waste an expensive product like that on a gasket? Carb cleaner is good too have anyway to clean parts when toying with the car.

My point was spend the $3 on the carb cleaner, spray around the manifold gasket to see if it starts stalling out, if so problem solved. That is a quick easy thing to check. Hunting for failed sensors before trying the simple things first will result in a ton of wasted time and money...

Btw, yeah that was me with the special tool...hence my sig saying "Dead On" hammer mod...
 
I made a video last night, but too much noise to distinquish what I was talking about, and realisitically it wasnt all that noticeable anyways. It seems like it was really just that day... odd.

This weekend Ill change out the plugs, and check the coils/boots. hopefully will find my problem there!
 
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