konakat

So I just did a vacuum test to try and track down my rough idle issue, and I have a pretty big leak, but not from where I would suspect. All of the air was coming out from where the dipstick tube connects to the block. I think I know what this means (head gasket), but wanted to get everyone else's opinion. Should I do a compression test to verify that it is the head gasket, or is this an obvious case?

V2Rocket

Did you replace the o ring?

konakat

For the dipstick? I haven't, but should intake air have a path to the bottom of the engine in the first place?

MAGK944

No path down there unless your rings are worn or the HG is toast. I would do compression & leak down to confirm.

You still need to change that O-ring though if you can feel the crankcase venting from the dipstick tube.

konakat

Would either a bad head gasket or worn rings explain a rough idle when cold that goes away completely once the engine is warm? I guess that might indicate a head gasket leak that seals itself once the block expands? Thoughts?

mytrplseven

Have you tried replacing the DME temp sensor on the front of the engine? That's the first place I would look.

konakat

I didn't replace it, but I did test it and it seemed fine. Knowing now that I likely have a leaking head gasket that seems like the most logical cause. The only other thing I haven't checked out yet is the afm.

konakat

So it seems odd that I would have a compression leak since the engine pulls strong as long as it isn't idling, even when cold. Is there any place where the intake could leak into the oil passages besides the compression chamber?

Dal Heger

I seriously doubt that it's a head gasket leak. There is a path from the intake to the block via the air/oil separator, part of the PCV system. Depending on where you tested and if you remembered to plug or pinch off the proper vacuum lines. Take a look at the vacuum diagram and do it again.

If you had a bad head gasket you'd know it by a loss of coolant. The open desk design of the engine means that the cylinders are surrounded by coolant, not venting into the crankcase. The rings would cause major oil consumption if they were bad.

You most likely have a vacuum leak, or a bad DME temp sensor that is causing your rough idle when cold. Look for the simple, cheap stuff first.

blown 944

Yeah, I have no idea why anyone would think its a HG.

You should rather pressure test the intake tract. There are a few places that can leak.

Running rough can be a product of many other things as well.

John_AZ

konakat has an early '84 944 (update your signature line pls)

There is no dipstick "O" ring at the bottom on the early 944s (late and 924S use "O" ring # 900 174 044 40 $3)

The vacuum leak could be rotted AOS seals in the same area. (The chamber under the oil fill cap).

If you replace the DME temp sensor, use only OEM Bosch ~$15. Aftermarket sensors may not be built as accurately. Usually just replace it ---cheap insurance.

Per Clarks--"if resistance is too high--car runs rich. If resistance is too low car runs lean"

Item #10
http://www.clarks-garage.com/shop-ma...9.htm#dme-temp

J_AZ

konakat

Do you have a link for the vacuum diagram for an early engine? Which line should I pinch off?

I am testing the intake tract, I have an air line connected in place of the AFM but all the air is leaking out where the dipstick tube goes into the block. I thought it might be head gasket because I don't know **** and that was the only thing I could think of that might separate the intake from the oil passages.

So is it okay for there to be a leak there or should I do something to try and seal it? How can I test for vacuum leaks if the air escapes there?

John_AZ

You can test the entire system for vacuum leaks by pressurizing the intake.

You can do this test with or without bubbles:
http://forums.pelicanparts.com/porsc...oooo-easy.html

To replace the AOS seals (need top and bottom seal/O-ring) you have to remove the intake manifold.
You can check if the AOS seals are bad a second way. Do you have an oil pool on the bottom of the TB throttle body? If yes, usually the AOS seals.

You should also rebuild the TB. The shaft has 2 tiny O rings that rot.
See www.Arnnworx.com

Removing the intake gives you a chance to replace all vacuum lines and hose clamps. Get new hoses under the intake-big and small that cannot be gotten to any other way.

Rebuild the injectors or send them to www.witchhunter.com or similiar.

J_AZ

konakat

I already used that procedure which is how I found the dipstick leak, but how do I test the rest of the vacuum system if I have the aos leak? I also can't find anything about the aos on Clarks garage or in the vacuum system diagram I found, is there a procedure for that somewhere? .

Dal Heger

There is another way to test for vacuum leaks, but it involves using flammable liquids. You can run the engine up to temperature and once you have a stable idle you can spray brake clean on the vacuum hoses and rubber parts. Like I said, this can be very dangerous since you're spraying volitle liquid on a hot engine. Keep a fire extinguisher handy.
You'll know when you've hit a vacuum leak because the idle will change.

Before you do this, take a very close look at the j-boot between the AFM and the intake. This is a common spot for the rubber to split over time and create a big vacuum leak. Anther source of a rough idle would be the AFM itself. I think that there is a test procedure on Clark's-garage for that. Basically the wipers that move with the barn door inside the AFM wear out over time, you may be able to clean and "repair" those with some effort.

I'd also check/replace the rest of the vacuum hoses if you're planning to keep the car, they dry rot over time and oil exposure, expecially under the intake manifold.

Check the cheap stuff first, there is a lot of help out there for someone with at least some mechanical skill.