Hello.

I've had my 86.5 automatic for about a year and it's been running fine, but I have 2 symptoms that I believe are related to a vacuum problem and needed some advice. I think the car is definitely pinging at heavy acceleration...I hear a "gurgle" when the windows are open and I accelerate hard. As I easy on the pedal it goes away. I suspect the vacuum to the ECU may not be working correctly, since it's not telling it to retard when it should. Is there a way to test it?

Second, if I accelerate and I'm on the 3rd gear (it's an automatic) and then I keep the foot down, it shifts fine to the 4th. But if I take the foot off the pedal in 3rd, it lags when shifting to 4th, like it lost the vacuum to the modulator. The shifting always felt kind of hard on this car, which may point to the vacuum.

So, I took the airbox, MAF and found out that the "spider" (or underpressure distributor) is hiding underneath that thick cable so I couldn't really see it or inspect it, and it's sitting on a puddle of oil and I can tell that all vacuum lines are there.

My questions:

1) can the "spider" go bad? I guess I should replace it anyway.

2) Could the rubber intake boot be bad and leaky? I don't want to remove that large intake pipe unless I have to.

3) Does the placement of the vacuum lines on the spider makes a difference?

Any help or suggestions are appreciated. Thanks.
Elias

 

If your car has not had a top end refresh then yes, there is a great chance you have a number of vacuum leaks.

 

Check for vacuum at the EZ computer when the engine is idling. Pull off the hose and see if your finger is pulled tightly against it. Normal readings are around 18-20" hg.

Pinging with stock chips is usually a sign of an old MAF. If it is original, it likely needs rebuilding.

There may be vacuum leaks, but a slow 3-4 shift can also be a (minor) trans problem. My '86.5 auto does this. (There will also be a little delay into reverse if it has this issue.)

 

'spider' is usually the term for the early intake manifolds here on RL (early like, pre-'85 US). I think the vacuum connection you're looking at is generally referred to as the '7-way' connector for obvious reasons.

It's just a plastic connector with all of the internal channels connected. The order or direction of the hoses doesn't matter as long as they're all connected to something and not leaking. Vacuum should be constant throughout the system when the car is running so as Porken suggested, testing it at the EZ computer is the easiest way to tell if the system is leaking or not.

Those rubber intake boots leak all the time and if you've had the car a year and haven't had them off, it's time!
They get old and dried and when the car heats up you can be getting unmetered air in there. Removing them and replacing them isn't hard at all.
See above+928- Sean would know

When I saw the thread title I was just going to respond with 'yes'.

There are a million places for unmetered air to get into the system and if your car hasn't been through the 'top end refresh' it's long overdue.

In addition to the vacuum leak issue you could have some safety concerns (especially in an automatic) that should be addressed like the fuel lines (they get cracked and brittle just like the intake boots, but when the fuel lines leak you could have a FIRE.) You should also check your PS lines and in your car, check the trans fluid lines from front to back. There is a failure mode of the trans cooler lines where they can leak onto the catalytic converter and cause a fire there. I've personally only seen it happen on an '87, but I think the S3 autos have the same line in the same place.

I'm not trying to freak you out, I'm just guessing based on what you said in your post that you haven't done much if any work on the car and if the rubber and lines weren't checked and refreshed by the PO, it's due.

 

Mike, PorKen

Thanks for the comments. I did check the vacuum at the EZ computer and it's fine and strong. I bought the car from a guy who kept it in great condition with regular service and all maintenance done by a pro. I also took to my mechanic (who worked with 928s for years) when I got it and did a trans fluid change, TB and timing. Car runs great and the only annoying problem is the noise on acceleration. Maybe is not pinging, but valve noise? I do plan to do a top engine R&R and update all vacuum lines and have the organ pipes painted...eventually.

Thanks again for the help.
Elias