944 turbo trouble

I'm trying to figure out if I did something or if this is an unhappy coincidence. I spent some time 2 nights ago trying to clean up the grounds on the beater '86 951, including the one on the bellhousing by the reference sensors. I also fed it a quart of Marvel Mystery Oil because it was a quart low and had a nasty lifter tick. I drove it yesterday so I could get it teched for my upcoming track day. The good is the valve tick is gone and the idle is now steady. The really bad is there's a new raspy, tinny rattle noise from 2-3k, it no longer makes full boost (the gauge shows 1.4 bar, full boost is 1.7 and leaving the cycling valve disconnected gives 1.2) and is makes a sound like a giant vacuum leak with some fluttering when I'm hard on it. I don't think I disturbed anything while cleaning the grounds, and the amount of boost and the fluttering being on power, not on overrun, tells me it's probably not an issue with the wategate. While it was getting teched on the lift I banged around the exhaust and there's a high-pitched rattle noise at the front of the cat. A number of experienced 944 owners there concurred that it's not an exhaust shield. Does this sound like clogged cat to you guys, or something else?

I'm not too experienced with turbo-specific troubleshooting, but the other items you mentioned led me to think "clogged cat" before I read your last sentence.

Maybe a cat with the internals broken loose....

if the ceramic in the cat has come loose and turned to block airflow, it could cause the symptoms you described. i would think that if the MMO broke something loose and stopped up the oil supply to the turbo it would take a bit longer to break something than half a day, but i've seen bad oil kill a turbo in under an hour of driving

Do you have a compressor? If so, pressurize the intake tract with the throttle closed, check for leaks, repair. Next get a spark plug line fitting, turn motor so exhaust valve is open on one cylinder, blow through exhaust, see what you find...

Turbo car vacuum diagnosis almost always requires a compressor (safe, fast, easy) because if nothing else you can 'hear' the leak with the motor off. Can't tell you how many times I've found leaks on the XR4 this way...

Did you replace all the vacuum hoses on the car? If not, do it now. Cut them off the connectors, as the connectors are very brittle by now and will break if you pull the hoses off.

Check the hoses to and from the intercooler, hose from the turbo to intercooler and the idle stabilizer hose.

These cats do "explode" I recently had mine go to bits. I actually had a clogged muffler as most of the bits ended up in there. I had to remove the entire exaust and remove all the chunks,bits etc. I would start by dropping the cat back and taking a look in the cat.

dj06482 wrote: I'm not too experienced with turbo-specific troubleshooting, but the other items you mentioned led me to think "clogged cat" before I read your last sentence.

This.

I guess I get to figure out how to unbolt the cat - I'm hoping it's not a total nightmare. Good thing I finally broke down and bought a small propane torch last weekend for use in cleaning the corrosion from under one of the caliper stainless sliders (of course I didn't wind up needing it then). If it's bad I may just gut it, or have a shop cut it out and weld in a "test pipe" - this is my track only car and I don't have to deal with emissions testing so I don't feel too bad about doing that, and I don't want to spend $350+ for a bolt-in test pipe.

Just remove the innards and bolt it back in. Cheaper and OE look and having the open chamber of the cat acts as a resonator. Ever hear one of these with an open exhaust? Yeepers is it an awful sounding thing.

A common problem on those cars is an internally collapsing downpipe. It happened on my 87. Basically you'll start losing power until eventually it's almost fully collapsed and you have very little power.

Raze wrote: Do you have a compressor? If so, pressurize the intake tract with the throttle closed, check for leaks, repair.

This is a great idea! How do you usually pressurize the intake tract? And how much pressure?

I have another cat pipe if you need it.

You could've just titled this thread "944 turbo" and the "trouble" would've been implied.

Well, after dropping the rear muffler section it appears that the cat is already gutted since my cheater pipe, a 3 foot section of 2" black iron pipe, went right in with no resistence. There was some obstruction in the exhaust at the front end of the cat that I punched out and vacuumed clear. Still no change. I'm guessing that somehow I created a boost leak screwing around at the rear of the motor trying to clean that ground on the bellhousing, so I'll have to go back there and check all the vacuum lines to make sure everything's connected. I don't have a compressor but my neighbor has a little pancake one that will be perfect to pressurize the system to 20# and find the leaks. I did figure out one reason it runs on the pig rich side - the O2 sensor is not connected to anything! The wires are ripped right at the sensor, so I'll have to order a universal sensor and splice it in.

So I thinking found the problem:

JB weld to reattach that 1/2 vac nipple back onto the intake manifold is curing.

To pressurize your intake go to Home Depot with your intake hose that attaches to the airflow meter. Buy a rubber or plastic cap that will fit the hose. For rubber hoses I use a screw in type PVC or ABS cap so it won't pop out. For metal pipes buy a rubber cap to put over the pipe. Either way you'll need to secure it with a Hose clamp. Next stop off at a tire store to buy a valve stem. Drill a hole in the cap, install the valve stem, and pressurize to 25psi or so depending on your setup. It'll be easy to find leaks.

Just back from a test drive and full boost is restored! Booooooooost is good!

Boost is Sooooooooooooooooooooo Adictive. I am going to get another one of those cars some day. The only thing that will stop that plan is if I could get my hands on a 928s4 that I have been eyeing.

I have a set of autothority chips waiting for after my HPDE next weekend, for a bit more boost