How long should a compression and leak down test take?

[nikohl]

Hey guys,

Total noob here. Have a purchase agreement for a 996tt pending PPI. How long should a compression and leakdown test take? Visited two reputable garages today and one garage told me 1.5 hours and the other told me 4 hours.

Thanks in advance.

[RFM]

You mai count 4 hours for a Turbo, 1,5 hours for a Carrera.

[JFP in PA]

Hey guys,

Total noob here. Have a purchase agreement for a 996tt pending PPI. How long should a compression and leakdown test take? Visited two reputable garages today and one garage told me 1.5 hours and the other told me 4 hours.

Thanks in advance.

The time quote is a fair estimate, depending upon which model the car; if yours is a Turbo, four hours is correct.

[White987S]

Pay a little extra and have new plugs put in. Ask for the old plugs back.

[nikohl]

Thanks guys. I've heard 4 hours from all the forums, but this very reputable garage told me 1.5 hours on a turbo. Should I go with them? I'll be there when it goes down.

[JFP in PA]

Knowing what this job takes, I would ask them to reaffirm their quote and pricing so they can't come back on you later. On the Turbo, there is simply too much stuff in the way to get this done in 1.5 hours.........

[nikohl]

Knowing what this job takes, I would ask them to reaffirm their quote and pricing so they can't come back on you later. On the Turbo, there is simply too much stuff in the way to get this done in 1.5 hours.........

Thanks JFP. Are you an experienced tech? Just trying to get a feel for tech experience.

[nikohl]

Oh, also guys should this be done on a cold engine, warm engine or once both?

[JFP in PA]

Knowing what this job takes, I would ask them to reaffirm their quote and pricing so they can't come back on you later. On the Turbo, there is simply too much stuff in the way to get this done in 1.5 hours.........

Thanks JFP. Are you an experienced tech? Just trying to get a feel for tech experience.

I am the owner of an independent shop.

[JFP in PA]

Oh, also guys should this be done on a cold engine, warm engine or once both?

Ideally, the engine should have heat in it, but from a practical stand point, with the amount time required to get the car ready to do a leak down, it will be warm at best.

[nikohl]

Oh, also guys should this be done on a cold engine, warm engine or once both?

Ideally, the engine should have heat in it, but from a practical stand point, with the amount time required to get the car ready to do a leak down, it will be warm at best.

Thanks for both answers JFP. Called the shop and they re-affirmed the quote. They said they wouldn't charge me more than the 1.5 hours and I will be there for the test, so I'll report back. An independent 3rd garage told me both are excellent and very honest, so either is fine. All else being equal, I'll take the less expensive one and also see how long it really takes.

Btw, this shop showed me where the cylinders were on the car and they would go through the bottom of the car and remove a plate where the cylinders are. He admitted that they are a bit hard to get to, but he's done it himself many times. Guess we'll see...

[JFP in PA]

On a normally aspirated 996, there is a heat shield cover plate over the coil packs that needs to come out so the packs and plugs can be removed. With the Turbo, there is a lot more stuff in the way due to all the "plumbing" for the turbo which further complicates the issue and takes a lot more time. If they are willing to do it for the time quoted, more power to you.

For reference purposes, here are the steps involved to do a normal plug change from a pretty good DIY write up:

Spark Plug Removal Prep

1. Jack up car, put stands under the rear jack points. Remove rear wheels.

2. Remove taillight assembly: 2 phillips screws.

3. Remove bumperettes: remove access plug, loosen size 40 torx from below 2 turns, pivots upward

4. Remove rear only wheel well liner: several torx and 2 plastic 10mm nuts (easy to strip when reinstalling)

5. Remove rear bumper cover: 4 phillips on top, 2 phillips on bottom, 4 torx on bottom, 2 torx in the wheel well. Its easy to scratch when removed. Slide off with a helper so you don't scratch the paint. Unplug the wires.

6. Remove center rear heat shield: 3 10 mm bolts, 2 screws. Using compressed air, if available, thoroughly blow all the dirt and debris off the intercoolers, engine, wheel well, brakes, etc.

Remove the intercooler with brackets

7. Disconnect the big hoses where they plug into the intercooler. Pull/pry with a screwdriver, the center of the hose retaining wire clips back far enough to release the hoses. Pull/wiggle the hoses out of the intercooler. It may be easier to remove the upper 2 hoses completely. Mark the inner and outer ends of the upper hoses or note where the arrows are to aid reassembly. Inspect the hose O-rings. The manual says to replace the O-rings, but I don't know if that's really necessary.

8. On each side remove 5 13 mm nuts/bolts holding on the intercooler brackets. Remove bottom 2 sheetmetal nuts attaching the bottom of the side heat shields. Pull the heat shield off the studs. Slide the intercooler assembly forward about an inch then remove it.

9. Bend the shields upward. Leave top heatshield attachment nuts on.

Remove the coils

10. Remove the heat shield attached to the head. Unclip the O2 sensor wires from it and let the shield slide down out of the way.

11. Driver side remove the waste gate vac hose and the pressure sensor(?) hose next to it.

12. Remove all the coil retaining allen head bolts.

13. Unclip all 6 coil wires. (I couldn't get the coils back on with the wires attached)

14. Remove the coils, it may be a little difficult to maneuver them out.

15. Using long extensions remove the spark plugs.

Visually inspect the new plugs prior to installation. Gap is about .8 mm (.032"), NOT 1.6 mm as the shop manual states. I wouldn't try to adjust them if the gap looks reasonably close. Mine were about .025 -.032". I had a new damaged plug that had the side electrode bent.

Visually inspect the coils. Pull off the rubber boots and look for any cracks or carbon tracking. Try to keep the rubber boots very clean to avoid carbon tracking. Put a small amount of anti-seize on the inner 1/2 of the spark plug threads. You don't want any grease or fingerprints on the ceramic, rubber boots, or in the spark plug recess in the head.

Spark Plug Installation

Install the plugs

1. Install the plugs. They should easily screw in by hand. Torque to 22 ftlb. (29.8 Nm)

2. Put the coils in place. Attach the coil wires prior to installing the coil bolts. Make sure the wires 'click' into the coils before you pull the little rubber boots down. Space is limited. Install the coil bolts with a SMALL amount of anti-seize. Torque to 7 ftlbs. (9.6 Nm)

3. Install the heat shield to the head with a little anti-seize. Torque to 7 ftlbs. (9.6 Nm) You may need to use a u-joint socket on 1 of the bolts. Clip the O2 sensor wires and vac hoses back on to the heat shields. Reinstall the 2 vac hoses on the driver side. Check for any loose/disconnected wires or vacuum hoses.

4. Bend the side heat shields back down.

Intercooler install

5. Check that the intercooler hose retaining wire clips are fully in position at the bottom of their grooves. Blow out the intercooler inside and out with compressed air. Make sure the intercooler hose inlet and outlet sealing surfaces are clean and smooth.

6. Carefully reposition the intercooler assembly on the car. Be careful not to scratch the paint. Push it rearward and install the nuts/bolts. Torque to 17 ftlb. (23 Nm) Tighten the side heat shield sheet metal nuts. Install the intercooler hoses. The hose ends should audibly click into place.

7. Reinstall the center rear heat shield.

8. With a helper reinstall the bumper cover. Remember to reconnect the wire. Install the screws loosely. Before you tighten it down position the wheel well liner and loosely install it's screws. Push the bumper cover and wheel well liner into position and tighten. (It was difficult to get the wheel well liner into position with the bumper cover fully tightened.) Do not overtighten the plastic nuts and strip the threads.

9. Reinstall the bumperettes. Engage the top groove and pivot them down, retighten the bolt.

10. Reinstall the taillight assembly.

11. Reinstall the rear wheels and torque to 96 ftlb. (130 Nm).

Book quoted time for above with leak down: 4 hours. Some dealers actually prefer to drop the engine down to do this rather than move everything in the way.

[nikohl]

On a normally aspirated 996, there is a heat shield cover plate over the coil packs that needs to come out so the packs and plugs can be removed. With the Turbo, there is a lot more stuff in the way due to all the "plumbing" for the turbo which further complicates the issue and takes a lot more time. If they are willing to do it for the time quoted, more power to you.For reference purposes, here are the steps involved to do a normal plug change from a pretty good DIY write up:Spark Plug Removal Prep1. Jack up car, put stands under the rear jack points. Remove rear wheels.2. Remove taillight assembly: 2 phillips screws.3. Remove bumperettes: remove access plug, loosen size 40 torx from below 2 turns, pivots upward4. Remove rear only wheel well liner: several torx and 2 plastic 10mm nuts (easy to strip when reinstalling)5. Remove rear bumper cover: 4 phillips on top, 2 phillips on bottom, 4 torx on bottom, 2 torx in the wheel well. Its easy to scratch when removed. Slide off with a helper so you don't scratch the paint. Unplug the wires.6. Remove center rear heat shield: 3 10 mm bolts, 2 screws. Using compressed air, if available, thoroughly blow all the dirt and debris off the intercoolers, engine, wheel well, brakes, etc.Remove the intercooler with brackets7. Disconnect the big hoses where they plug into the intercooler. Pull/pry with a screwdriver, the center of the hose retaining wire clips back far enough to release the hoses. Pull/wiggle the hoses out of the intercooler. It may be easier to remove the upper 2 hoses completely. Mark the inner and outer ends of the upper hoses or note where the arrows are to aid reassembly. Inspect the hose O-rings. The manual says to replace the O-rings, but I don't know if that's really necessary.8. On each side remove 5 13 mm nuts/bolts holding on the intercooler brackets. Remove bottom 2 sheetmetal nuts attaching the bottom of the side heat shields. Pull the heat shield off the studs. Slide the intercooler assembly forward about an inch then remove it.9. Bend the shields upward. Leave top heatshield attachment nuts on.Remove the coils10. Remove the heat shield attached to the head. Unclip the O2 sensor wires from it and let the shield slide down out of the way.11. Driver side remove the waste gate vac hose and the pressure sensor(?) hose next to it.12. Remove all the coil retaining allen head bolts.13. Unclip all 6 coil wires. (I couldn't get the coils back on with the wires attached)14. Remove the coils, it may be a little difficult to maneuver them out.15. Using long extensions remove the spark plugs.Visually inspect the new plugs prior to installation. Gap is about .8 mm (.032"), NOT 1.6 mm as the shop manual states. I wouldn't try to adjust them if the gap looks reasonably close. Mine were about .025 -.032". I had a new damaged plug that had the side electrode bent.Visually inspect the coils. Pull off the rubber boots and look for any cracks or carbon tracking. Try to keep the rubber boots very clean to avoid carbon tracking. Put a small amount of anti-seize on the inner 1/2 of the spark plug threads. You don't want any grease or fingerprints on the ceramic, rubber boots, or in the spark plug recess in the head.Spark Plug InstallationInstall the plugs1. Install the plugs. They should easily screw in by hand. Torque to 22 ftlb. (29.8 Nm)2. Put the coils in place. Attach the coil wires prior to installing the coil bolts. Make sure the wires 'click' into the coils before you pull the little rubber boots down. Space is limited. Install the coil bolts with a SMALL amount of anti-seize. Torque to 7 ftlbs. (9.6 Nm)3. Install the heat shield to the head with a little anti-seize. Torque to 7 ftlbs. (9.6 Nm) You may need to use a u-joint socket on 1 of the bolts. Clip the O2 sensor wires and vac hoses back on to the heat shields. Reinstall the 2 vac hoses on the driver side. Check for any loose/disconnected wires or vacuum hoses.4. Bend the side heat shields back down.Intercooler install5. Check that the intercooler hose retaining wire clips are fully in position at the bottom of their grooves. Blow out the intercooler inside and out with compressed air. Make sure the intercooler hose inlet and outlet sealing surfaces are clean and smooth.6. Carefully reposition the intercooler assembly on the car. Be careful not to scratch the paint. Push it rearward and install the nuts/bolts. Torque to 17 ftlb. (23 Nm) Tighten the side heat shield sheet metal nuts. Install the intercooler hoses. The hose ends should audibly click into place.7. Reinstall the center rear heat shield.8. With a helper reinstall the bumper cover. Remember to reconnect the wire. Install the screws loosely. Before you tighten it down position the wheel well liner and loosely install it's screws. Push the bumper cover and wheel well liner into position and tighten. (It was difficult to get the wheel well liner into position with the bumper cover fully tightened.) Do not overtighten the plastic nuts and strip the threads.9. Reinstall the bumperettes. Engage the top groove and pivot them down, retighten the bolt.10. Reinstall the taillight assembly.11. Reinstall the rear wheels and torque to 96 ftlb. (130 Nm).Book quoted time for above with leak down: 4 hours. Some dealers actually prefer to drop the engine down to do this rather than move everything in the way.

This is awesome.

[Loren]

JFP in PA is absolutely right - my best time ever on a 996TT spark plug change was 3 hours with a good helper.

Removing the intercoolers takes the most time as I recall.