[sp4149]

Went on a 25 mile drive Saturday. On the way back the Cab had no power or acceleration. The car was not missing but would only slowly accelerate to speed and couldn't hold the speed on freeway grades. I limped home and parked the car.



There was no smoke; the car was running a little warm, around 9 o'clock on the water temp; the engine was running smooth, just wouldn't easily accelerate. The Cab is a Tip and the few times I tried to downshift, there was an increase in engine RPM but no accompanying increase in speed. The car was close to empty, I stopped and filled the tank, no change in performance.



Recently I changed the front Hall Sensor (bad connector) and the damper for the Tip. The NGK plugs have about a thousand miles. When the Hall Sensor was disconnected the car was sluggish, but not this bad. Was running great until Saturday, took it to work last week with no problems.



Blink test results,



one long, one short, five short, then repeat. Since there are no 3 number codes, I assume the long indicates the start of the code and that the actual result is 1-5 or no fault.



Vacuum lines appear to be intact and attached, no cracks or breaks seen and no loose connectors. Looked only at top of engine. Are there vacuum lines to the Tip in the back?



No coolant loss, and coolant in reservoir is clean.



There is very little throttle response, could it be a bad throttle position switch? No vacuum advance due to a vacuum leak, or is the vacuum not used by the DME to accelerate.



In a 1986 Pontiac STE I had a similar situation that was due to a plugged catalytic converter. The 968 Has an aftermarket Cat that was on the car when I got it. I have been worried about meeting CAL emissions as this car doesn't smog test as well as those with the stock Cat. The exhaust system had to be dropped ( I saw it on the floor of the shop) to change out the damper for the Tiptronic. I’m thinking that may have been the end of the CAT.



Thoughts? Comments?

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[968rz]

Here are some things I noticed as an Autotech.

Plugged cat conv have a whistling/vacuum sound from tail pipe when they plug up and will get red hot very quick (they can be fine for awhile, like 5-10 miles).

The hall sensor as you noticed does effect perfomance but I don't think it would ever be as bad as you discribed. (any failed sensor should set a code, you had none)

Let the car cool over nite and see what happens on the next test drive (check for a red glow at the cat and vacuum noise from tail pipe

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[sp4149]

[quote name='968rz' post='51989' date='May 6 2008, 01:24 PM']Here are some things I noticed as an Autotech.

Plugged cat conv have a whistling/vacuum sound from tail pipe when they plug up and will get red hot very quick (they can be fine for awhile, like 5-10 miles).

...

Let the car cool over nite and see what happens on the next test drive (check for a red glow at the cat and vacuum noise from tail pipe[/quote]



There was indeed a whistling/vaccum sound coming from under the car (driver's seat) when I started it last night. I didn't let it run long enough to see if it glowed red. I did go back to the tail pipe and there was very little exhaust coming out, it was easy to hold my hand over the tail pipe and shut if off completely. There was no change in the whistling/rushing sound under the car whan I covered the tail pipe, and not much sound at the tail pipe.



Since the exhaust system was dropped to change the TIP damper, it was possible that removal contributed to failure or that foreign objects got inside. It's varmint season, three weeks ago a rat built a nest in the valley of our Bonneville's V-6, ate through the wiring for a couple of injectors, running on only four out of six cylinders the Pontiac was sluggish too. I wonder if a rat made a nest in the exhaust system while the car was on the rack for a couple of days? or if there is a rag now down in the catalytic converter?



Any thoughts that this could be something other than a plugged exhaust system?

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[968rz]

You could drop the exhaust just before the cat and see how the power is. I wouldn't run like that for long as you will be spitting sparks with the pipes that short.

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[sp4149]

[quote name='968rz' post='52389' date='May 12 2008, 02:26 PM']You could drop the exhaust just before the cat and see how the power is. I wouldn't run like that for long as you will be spitting sparks with the pipes that short.[/quote]



Last night I did a quick test at idle of exhaust pressure at the tailpipe, comparing to our '84 944. The 944 had a much stronger exhaust, I couldn't stop the exhaust completely with my hand and there was a lot of whistling of exhaust gas blowing by my hand. With the 968, noticeably less exhaust, little pressure, easy to stop completely and no whistling at tailpipe of escaping exhaust. The Exhaust system is definitely plugged big time. The question is where? seems like it has to be the CAT or the muffler.



-sp4149

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[968rz]

[quote name='sp4149' post='52449' date='May 13 2008, 10:42 AM']The Exhaust system is definitely plugged big time. The question is where? seems like it has to be the CAT or the muffler.[/quote]



My guess would be cat. You can disconnect both before and after the cat (it is flanged so it should be easy to do), disconnect after the cat first (this tests the mufffler(s)) then before (this tests the cat).

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[PorscheDude]

The 968 has alot more pressure at the tail pipe than a 944.

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[sp4149]

[quote name='smokiemon968' post='52453' date='May 13 2008, 09:38 AM']The 968 has alot more pressure at the tail pipe than a 944.[/quote]



Yesterday it didn't. Today it's reborn. Shop installed a German-made OEM replacement, much bigger and heavier than the aftermarket one (made in ??). Local Porsche parts service recommended this Cat over the Porsche one saying the major difference was price. Shop owner said he ran the car up to 125 to make sure the exhaust was free flowing and the car was still pulling when he let up. Good not to be passed by golf carts on the sidewalk.



Old Cat put on by PO had failed big time, chunks were in the muffler. After we bought the car we were told by a local shop, it had an aftermarket Cat, but it passed emissions and things were good back then. Last year it barely passed smog on the dyno test; I had started to expect the Cat was toast and would need to be replaced before next year's smog test. Now that's one less worry.



-sp4149

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[968rz]

Cool! glad you got the issue fixed and can now enjoy your car.

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[sp4149]

[quote name='968rz' post='52825' date='May 19 2008, 08:37 AM']Cool! glad you got the issue fixed and can now enjoy your car.[/quote]



Took the Cab to Palm Springs last weekend. Great drive, problem definitely cured.

On the way back the outside temp got up to 119 F, temp gauge hit the ten o'clock mark.

Stayed there until started the climb up to Beaumont on I-10, outside temp dropped down to

105 F and temp gauge dropped to nine o'clock. Taking a backroad cutoff around Hemet the

outside temp dropped to 95 F and the temp gauge was down to eight o'clock.



Glad I didn't take the scenic route over the mountains, given how hot it was and high the

temp gauge reached on relatively level ground; those 6% + grades might have been too much;

or I would have had to slow down which would be no fun.



-sp4149

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[968rz]

The temps don't sound to high, if you think it is or that it moves to much replace the t-stat and bleed the system good.

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[sp4149]

[quote name='968rz' post='53212' date='May 24 2008, 08:21 AM']The temps don't sound to high, if you think it is or that it moves to much replace the t-stat and bleed the system good.[/quote]



I agree, in and around San Diego, no problem. I just wish it had a little more cooling capacity so that I could attack those stiff grades and curves on the super hot days. I've done the route when it was only around a 100 F and after 7-8 miles the temp gauge was at ten o'clock. As soon as I crested the summit it dropped back to eight o'clock. With temperatures nearly 20 degrees hotter, at the hottest time of the day, it was just sensible not to push my luck and take the easier path home. So far the new German OEM Cat works fine, the real test will be the next smog test in a year.



-sp4149

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