Symptoms of a blown/leaking intake gasket?

Discussion in 'Fox 5.0 Mustang Tech' started by 85_SS_302_Coupe, May 18, 2009.

  1. Lets just hear what everyone would list as symptoms of a blown or leaking intake gasket. I've got some major gremlins that i can't seem to narrow down and i want other peoples opinions to make sure I'M on the right track.

  2. spray carb cleaner around it and the RPM's will rise
  3. Crap i mean this for tech.

    Ok but what if it's out between cylinders and not around the edge of the intake? Or on the bottom side around the lifter valley?
  4. Loss of coolant: can go directly into oil, or go into pistons and burn up.

    Vaccume leaks causing idle issues.
  5. Could suck oil up and burn it if its on the bottom side.

  6. Exactly. My damn car will not idle. It'll fire up and run but ONLY if you're giving it gas. I've gone through the carb, i've adjusted the float level. It's getting gas and fuel. I've unplugged and pluged the brake booster to make sure that's not leaking, also the PCV and the vacuum advance (not a big deal because there shouldn't be advance at idle anyways). I've covered every carb source of a vacuum leak, and i've sprayed carb cleaner all over the place looking for it to suck in and change the RPM but nothing happens. I'm scratching my head and i'm totally lost as to what the problem could be. The only other thing i can think of is the intake gaskets because it definitely seems like a vacuum leak.

    I should note, there's no smoke so it's not burning coolant or oil. When you get it started it'll rev just like any other time and i've even drove it, but it will NOT idle. I did at once point get it to where it would idle if i cranked the curb idle screw in so it was about 1500rpm but if you did anything to cause idle to drop below that it would stall.
  7. Well there is only one way to tell.

    When you put the intake gaskets on did you take note of the gasket face that said HEAD SIDE. I am not sure if it really makes a difference but alot of them are marked that way.
  8. I don't ever recall seeing "head side" on a set of Felpro 1250s :shrug:

    The thing that is really bugging me is that it's ran all this time, probably at least 1k miles since the stroker went if i put them in wrong i would think this problem would've been here from the beginning...unless you're saying that putting them in wrong could've caused them to blow?
  9. Im not sure whats going on. I do know on the last set of felpros I installed that it was embossed in the gasket, right in the center HEAD SIDE.
  10. Well i'll find out because the only thing i can think of to do next is pull the intake and see.

    I've never been so stumped with my own car. I can't stand it.
  11. Im sure youll figgure it out.
  12. I saw the same thing when I did the intake gasket on my '84. Good thing, too, because until then, I was assuming that they were reversible and almost threw 'em on there wrong. :doh:

    I knew my intake gasket was crapping out only because I was getting oil loss from the top-end of the motor even after changing out the valve cover gaskets and cleaning the thing up. Most of the oil was coming from the upper-rear of the motor, and because it was higher up than the crank, I knew it wasn't a rear main seal issue. Stoopid old cork gaskets. :notnice:

    I wasn't getting any coolant sucked into the crankcase or coming out of the exhaust, though, and it ran perfectly fine. Interestingly enough, it still runs fine and isn't losing coolant or oil from the gasket, even though the passenger-front bolt on the intake snapped right off during the removal phase and I bolted it together with that bolt still missing. (If it does eventually leak there, though, I'll just have an excuse to upgrade to E7 heads. :D )
  13. There is no easy way to find vacuum leaks. It is a time consuming job that requires close inspection of each and very hose and connection.

    Small vacuum leaks may not show much change using a vacuum gauge. The range of "good readings" varies so much from engine to engine
    that it may be difficult to detect small leaks. Average readings seem to run 16"-18" inches at idle and 18"-21" at 1000 RPM. The only sure
    comparison is a reading taken when your car was performing at its best through all the RPM ranges and what it is doing now. Use one of
    the spare ports on the vacuum tree that is mounted on the firewall near the windshield wiper motor to connect the vacuum gauge.

    Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the
    engine will change speed.
    Avoid using flammable substitutes for the oil such as propane or throttle body cleaner. Flash fires can occur due to the heat and possible
    electrical sparks. Fire is an excellent hair removal agent, and no eyebrows is not cool...

    The vacuum line plumbing is old and brittle on many of these cars, so replacing the lines with new hose is a good plan. The common 1/8”
    and ¼” vacuum hose works well and isn’t expensive.

    Look for broken vacuum connections, damaged vacuum lines and hoses (don't forget the PVC valve and brake booster hoses).
    Check the brake booster and the rubber grommet that hold the vacuum check valve for damage.

    Diagram courtesy of Tmoss & Stang&2birds

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information
    Everyone should bookmark this site.

    Ignition switch wiring

    Fuel, alternator, A/C and ignition wiring

    Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

    Vacuum diagram 89-93 Mustangs

    HVAC vacuum diagram

    TFI module differences & pinout

    Fuse box layout
  14. i was having a similar problem, and i still am.

    But i did remove the intake and there was an intake leak from the lower intake to the head. Have you ever retorqued the intake? These motors are notorious for the intakes loosening up, and my engine builder was telling me depending on how thick the gasket is, you may have to retorque the intake a few times before it totally seats.

    My lower was a dead giveaway that it was leaking, i could see oil in the runners, but i was driving the car a good ammout of time wiht the vaccum leak, and it kept getting worse.

    Also, i use a black RTV sealant called "the right stuff" and that **** WORKS, the name sounds hokey, but buy a can and put a dab on your finger you 'll get it after that, its not as slick as regular RTV and its a much better seal. I put a healthy ammount of that stuff around the water jackets and the end rails, and this time on the intake ports i put a very thin layer of clear RTV just as insurance.
  15. did you plug the vacuum port on the back of your lower intake (if yours has one) :shrug:

    I forgot to plug mine when when I did mine and chased it for hours lol

    View attachment 257421
  16. Well...pulled the intake today and the gaskets looked almost like they did when they came out of the package. Still, i replaced them anyways (Felpro 1250s). I also replaced this weird little vacuum "tree" thing that originally came off the back of my stock EGR plate that i was using for the brake booster...because it had 2 little vacuum ports off the side and i just wanted to rule them out.

    Those two things together...and now it'll try to idle down around 1k-900rpm, but after a few minutes it'll still struggle down and start choking out unless you tap the gas. I also replaced the plugs for good measure. One thing my buddy tried was covering his hands over the carb while it tries to see if that would choke it down, thinking that if it did have some other vacuum leak then it should stay running right? It did choke down doing this...I even went so far as to pull out the screw in plugs in the intake that are for things i don't use (like extra temp gauge ports and vacuum ports) and retaped them to make sure they weren't leaking. I even bought another ignition module and swapped that in to see if it changed anything but it didn't.

    Now i'm really really really LOST. I've ruled out just about everything i can think of. Now that it's idling somewhat ok i took it for a drive, and one thing i did notice is that when the fan kicks on, the RPM drops very hard...which has always been typical even though i have a 3G and Yellow Top, but now when it kicks on the car instantly tries to die. So my next step is to have the alt tested and maybe by some miracle this whole thing is happening from weak spark or something....but i did try the old "pull the positive terminal" trick with the battery and the car DID stay running with it off so i don't know if this will lead to anything either.

    While i was driving it, there's NO loss is pulls hard as hell and goes clear to 6k with no problem at all except lack of traction.
  17. I hate to hear about these pesky little problems. Car is kool as hell, plenty powerful but wont idle to save its damn life. Its always somethin really stupid too. I had the same problem with the fan kickin on and tryin to kill the motor, it ended up bein my E-fan's power wire placement. We now run it straight off the battery and it doesnt do it anymore! Im gonna eventually run the wire into the cabin and to the fuse box but try runnin the power wire straight off the battery for a couple cycles and see if it helps any!
    Good luck!
  18. I'll have to look at it but i think we have it ran off the coil and then to the relay and then to the fan...i'll have to double check but i'll look into that and see if it helps. I'm also going right now to have my alt tested just to make sure it's up to par.

    By the way, where can i see pics of the '66? I always see it in your thread but i've never seen more of it :D
  19. I ran mine off the coil and the guy that tuned the car said NOOOOOO. He changed it over to the battery and it REALLY helped out. I have a relay as well but he said it didnt matter. Check into it for sure!!!

    As for the 66...I dont think i have much info about it, but Ill PM you a link to my Photobucket which has more pics.

  20. fel pro 1250's dont' say head side, they tell you to face the blue lining towards the intake. i just put mine on about 7 days ago