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Intake Manifold Oil Leak


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#1 BKLounge445

BKLounge445

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  • Gender:Male
  • Year: 1995
  • Make:Pontiac
  • Model: Formula
  • Engine:Lt1
  • Transmission:Auto, 4.10
  • Modifications:
    4.10 Gears, Flowmasters, K&N Filter (soon to be replaced)

Posted 06 June 2010 - 11:31 PM

I just bought a 1995 Firebird Formula yesterday morning. I do have to say that I am in love with this car, even with the work I know they require. First off, it has an oil leak. I am fairly certain that it is the Intake Manifold Gasket. You can see oil trailing down the engine block and it runs down my exhaust till about the middle of the car. At first I thought it was burning oil but then I realized it was just leaking on the exhaust and burning there. I am not 100% sure that the leak is the Intake Manifold, that just seems to be the most common and probable source. I bought a new gasket to put on and I was wondering if anyone could tell me how long and how involved it will be to put it on. And I do know that once I get it on it has to sit for 24 hours. Also, what should I do if that is not the leak? I don't know where else it would be. I am new to the forums and love it so far. Thanks for the help!

#2 Me Too

Me Too

    1st Class Tech

  • Members
  • 824 posts
  • Gender:Male
  • Location:Virginia
  • Interests:Good music, audio video stuff, our art collection, watches, cars, cycling and electronic design.
  • Year: 1994
  • Make:Pontiac
  • Model: Formula
  • Engine:Modified LT1
  • Transmission:6spd
  • Modifications:
    6spd manual transmission, with 3.42 diff. Fully ported and polished heads, big valves, Titanium retainers, AFR Hydra Rev Kit, Crane 1.6 roller rockers, Extrude Honed exhaust manifolds, K&N filter, air foil, OBDII PCM, teflon coated air intake, flow bench corrected intake and exhaust passages, ported and polished intake manifold, everything port matched. Custom, high output, dual diode bridge alternator. Borla Exhaust system. LT4 clutch and hydraulic clutch release unit. Custom driveshaft. KYB AGX shocks. X-Brace. Cross drilled brake rotors. One of only two verified 1LE Firebirds made in 1994. Engine has 6,600 rpm shift limit. Green with gray leather interior and all factory options.

    That's the good news, bad news is that I no longer own the car.

Posted 07 June 2010 - 12:30 AM

The most common failures are the end rail gaskets, made of non-silicon rtv, and then the bolts loosening and oil leaking that way. Also, any oil leak is also a vacuum leak and these cars do not tolerate vacuum leaks, so expect it to run somewhat better when the leaks are fixed.

It's not hard to do. However, you will need one really special tool to make the job easy and that is a very thin open end, 9/16 ths wrench or 14 mm (both will fit). The problem encountered when removing the intake manifold is that several of the bolts are studs with a nut on top to hold little bits of smog equipment and other things. When you try to undo the 14mm nut on top to remove the equipment that you can remove the bolt, the whole thing starts to unscrew--unfortunately, the equipment on top then gets caught and the bolt cannot be removed. So, you need the thin wrench (like a bicycle cone wrench...they are available in this size and can be bought at any bicycle store) to hold the bolt still while the top jam nut is removed. Hope you got that, if not, you will when you try to remove one or all of them (I think 3 are like this).

For gaskets, try Phelpro--they include the special rtv, and the fiber gaskets seal pefectly. The trick on the rtv is to install according to the instructions and then let it semi-harden for about 45 minutes or so--then put the intake down onto the valley absolutely perfect the first time--do not move it once it is set in place (don't make any mistakes, if you do, then re-do the rtv and get it right the 2nd time), so make sure it goes down perfectly straight. Then bolt it down and torque in two passes to 34 ft lbs. The torque on the nuts that were just mentioned is maybe 2 or 3 lbs, never more than 5 lbs. The torque on the throttle body is 10 ft lbs.

Be really, really careful when sealing the rubber elbow onto the throttle body, it tends to get caught under the throttlebody and rips when it is tightened down. When tightening the gear clamp for the elbow, only tighten just enough to hold it in place, if the rubber puckers, it is too tight.

Do not use silicone based lubricant on anything--don't use it on the rubber elbow to make it easier to slide onto the throttle body. A word of warning, do not be tempted to set the idle speed using that adjuster screw that is now visible on the side of the throttlebody. It is not an idle adjuster, it is the mixture control screw and the slightest change will greatly affect the way the engine runs, to the point that the PCM cannot compensate for the change.

If you need any help beyond this...just post your questions.

Have fun.

#3 BKLounge445

BKLounge445

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  • Members
  • 9 posts
  • Gender:Male
  • Year: 1995
  • Make:Pontiac
  • Model: Formula
  • Engine:Lt1
  • Transmission:Auto, 4.10
  • Modifications:
    4.10 Gears, Flowmasters, K&N Filter (soon to be replaced)

Posted 07 June 2010 - 12:34 AM

Thank you so much for the help! I will be sure to check for more leaks after this gasket is installed. I am going to put it on tomorrow or Tuesday so if I run into any problems I will be sure to post them. Thanks!

#4 Me Too

Me Too

    1st Class Tech

  • Members
  • 824 posts
  • Gender:Male
  • Location:Virginia
  • Interests:Good music, audio video stuff, our art collection, watches, cars, cycling and electronic design.
  • Year: 1994
  • Make:Pontiac
  • Model: Formula
  • Engine:Modified LT1
  • Transmission:6spd
  • Modifications:
    6spd manual transmission, with 3.42 diff. Fully ported and polished heads, big valves, Titanium retainers, AFR Hydra Rev Kit, Crane 1.6 roller rockers, Extrude Honed exhaust manifolds, K&N filter, air foil, OBDII PCM, teflon coated air intake, flow bench corrected intake and exhaust passages, ported and polished intake manifold, everything port matched. Custom, high output, dual diode bridge alternator. Borla Exhaust system. LT4 clutch and hydraulic clutch release unit. Custom driveshaft. KYB AGX shocks. X-Brace. Cross drilled brake rotors. One of only two verified 1LE Firebirds made in 1994. Engine has 6,600 rpm shift limit. Green with gray leather interior and all factory options.

    That's the good news, bad news is that I no longer own the car.

Posted 07 June 2010 - 12:47 PM

You are welcome. This is everything that I could find on vacuum leaks and wrote this paper. These engines are very susceptable to any vacuum leak and the PCM can not compensate for it. Vacuum leaks change instantly with the throttle opening. However, the O2 sensors can't change as fast. Therefore, the PCM is always trying to catch up and the result is a bad running engine. You can copy and paste it to a Word document, then keep it in a file on your computer. If you find anything else, just drop me a note and it will be included.

VACUUM LEAKS & the LT1

Copyright 2004 by Charles O’Toole

This tech article applies to 1993-1997 Firebird, Corvette and Camaro, including the Impala SS and other automobiles with the LT1 series engine. There is some applicability to the LS1 series of engines and V6s with similar engine management controls.

The LT1 engine is very susceptible to vacuum leaks caused by failures of both vacuum hoses and vacuum control solenoids. The following parts should be checked for a vacuum seal, replaced as needed and definitely replaced after several years of use. The actual age of replacement depends on operating conditions, since hoses and parts fail more quickly with high engine heat and in hot areas of the US (Southwest and Southeast).

1. Check these vacuum hoses and fittings:
a. Two vacuum lines, one going into and one leaving the Vapor Canister Control Solenoid (Right side of the intake manifold).
b. Vacuum line from the EGR Control Solenoid to the EGR and left-hand side of the intake manifold. This line has a common connection at the EGR Control Solenoid.
c. Large, ½” hose leading from the throttle body to the rear of the right side valve cover. Also, replace the plastic elbow—newest design has a small “catch” to retain the elbow in the valve cover grommet. Replace the grommet in the valve cover.
d. If the PCV valve is over 10,000 miles old, replace it with a quality all metal or GM part. Replace the molded, curved ½” hose and the rubber grommet in the intake manifold that the PCV valve fits into. Shaking is not a valid test--the PCV Valve is a calibrated air leak.
e. Check that the EGR valve is holding a vacuum.
f. Replace both the EGR and Vapor Canister Control Solenoids. These parts wear out rapidly in dusty conditions and are huge vacuum leaks.
g. Jack up the left rear of the car (Firebird and Camaro), remove the left rear tire and locate the plastic access plate for the Vapor Canister. Remove the small plastic screw with a #2 philips screw driver and the 7 or 8mm bolt and remove the access cover. Check all vacuum fittings and hoses to and from the Vapor Canister. The hoses can dry out and crack, also the nylon vacuum line from the Control Solenoid (right-hand side of the intake manifold) to the Vapor Canister, has a ¼” X 1” rubber hose glued to the end. The glue deteriorates and the rubber connecting hose separates and allows a vacuum leak.
h. The rubber elbow that joins the MAF and throttle Body. These two joints are responsible for most of the vacuum leaks on the LT1. The rubber seal and worm gear clamps can be damaged by incorrect installation. Remove and check the clamp for distortion and nicks, and check the elbow for tears and deterioration. If it is old, replace it and install the new one carefully to ensure a perfect fit. Grease the worm gear to prevent damage when tightening and do not overtighten. (Caution) Do not use silicone grease to ease the elbow onto the throttle body. Check that the small, stainless steel, ¼” tab at the worm gear is not gouging into the rubber seal at the MAF or throttle body—gouging causes a vacuum leak. If it does gouge the seal, bend it up slightly. If the clamp and/or elbow are damaged, they must be replaced. It is impossible to obtain a vacuum tight seal with parts that are damaged.
i. The idle inlet passageway/hot coolant throttle body heater on the underside of the throttle body can cause a vacuum leak. There are several torx screws that come loose, tighten snuggly and use locktite.
j. The black plastic plate on top of the throttle body is a notorious vacuum leak. Replace the plate with one made of aluminum and a thick paper gasket or buy a new, plastic plate. Be careful to not distort the plastic plate when tightening. Use locktite.
k. HVAC fitting at the right-hand side of the intake manifold and the fuel pressure relief valve vacuum hose located on the right-hand side of the intake manifold. Be careful that the the hoses are on the correct fitting.
l. Throttle body to intake manifold gasket—torque to 10-ft lbs. and use locktite.
m. The MAP sensor has a rubber seal on the underside. This seal can be lost during replacement or can tear—it is available separately from the MAP.
n. The intake manifold has two vulnerable areas—the intake gaskets and the end rails. The intake manifold bolts should be torqued to 34-ft lbs. in two passes. If re-torquing fails to solve the problem then the gaskets should be replaced. The other problem is oil leakage from the intake manifold end rails. If oil is leaking out, then air is also leaking in, since the PCV valve puts the interior of the engine under a vacuum. All air entering the PCV system must be metered through the MAF. A vacuum leak, even an oil leak, allows air into the system that is not MAF metered air. The same can be said for all oil seals throughout the engine.
o. Power brake canister vacuum hose from the left side of the intake manifold to the power brake booster.
p. The Idle Air Control Solenoid and the Throttle Position Sensor can come loose, use locktite on the Torx screws.
q. It is possible for a loose exhaust header bolt to allow an air leak into the exhaust system. This leak affects the hydrocarbon/O2 balance that is read by the O2 sensors. A leak of this type would cause the engine to run rich rather than lean as the ECM/PCM compensates by modifying injector dwell. Use GM part # 12346004, Teflon pipe sealant (for high heat), or Locktite 272 (hi heat) to lock the exhaust manifold bolts into the head.
r. On 95-97 LT1s check that the distributor is vacuum tight and the vacuum lines to and from the distributor cap have not deteriorated.
s. Replace the o-ring on the oil filler cap and the extension. O-rings are available at Ace Hardware for about 50 cents. Remember all air entering the engine for the PCV system must first go through the MAF, any air leaks, even past an o-ring on the oil filler cap is a vacuum leak!

This is a living document, please let me know if there is something that should be included.






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