whitefox

Hypothetically, if an 87 S4 automatic was to start hesitating at around 100 MPH and the driver has to play with the gas pedal to get it over 100 and it continues to hesitate what would cause this? Also I beleive the car passed that mark with no hesitation a few days ago. I have no records of the fuel filter ever being changed would that cause the above problems?


Note: For anyone that has anything to say about speed limits and safety send me a PM.

jpitman2

My guess would be fuel delivery or an ignition device breaking down under load. Cant hurt to change the filter.
jp

Charley B

Ross - Is this happening in 3rd or 4th gear? Should we assume that traversing the same rpm range in all other gears delivers normal smooth operation?

SharkSkin

Check for arc tracks in the distributor caps. Fuel filter could be changed to help troubleshoot. Also, could be a horked in-tank pump or screen.

whitefox

4th gear only at 100 mph, the engine is as smooth and powerful as can be until then.

Cameron

I had a hesitation issue and had to replace the in tank fuel pump.

Jim R.

Ross,

I don't know if the '87s had the in tank fuel pump, but if so that is a suspect here. You may want to pull a spark plug or two immediately after a hard run to check the color. If dark and wet looking, you should look to ignition issues. If very light or white, check fuel deliver (lean)-filter, pump (in tank/external), or filter. Fuel needs under load at 100mph are much different than at cruise around town.

There are many other possibilities, but those are easy to check .

BTW, be carefull. Things happen real fast at those speeds.

Jim

Darien

Clogged CATS!!

whitefox

The only solution must be an X-pipe then huh?

Darien

Or a test-pipe When I installed mine, it made a huge difference.

Fabio421

Lets see.
1. "Mystery" illegal substance in the glovebox
2. 10 days out of school suspension for having a knife in school
3. Extremely excessive speeds in a flashy red Porsche

The chances of you being able to go the the Daytona PCA race and Shark gathering are getting slimmer by the day.

whitefox

I never said there was anything illegal in my glovebox, I just asked in the case if I ever did have something illegal in my glovebox if I could lock it and be relatively safe.

I also never exceed the speed limit and the officer planted the knife on me when she searched me.


I will be at Daytona.

dr bob

For those reading at home, this is perhaps one of the easiest things to check. A vacuum gauge attached directly to manifold vacuum will go to atmospheric pressure and the car will no longer accellerate. In Whitefox's case, that would be at 100 MPH, but it obviously changes depending on how plugged the cats really are.

Keep in mind that a really worn engine will show the same thing on the vacuum gauge, as will wrong ignition or cam timing. If it pulls hard then flattens out quickly at speed, and it isn't missing, suspect the cats.

whitefox

When you say test-pipe, do you mean an H-pipe, or just replacing the cats with a straight pipe?

Imo000

Just for diagnostic purposes, you can completely remove the cats and run the car with only the exhaust manifolds. If you can get passed 100mph without a problem then you know it’s the cats, if not then its something else. This a cheap and easy way to test for clogged cats. Just don’t drive around too much or I’m sure you’ll get pulled over in no time.