Trouble accelerating... need help diagnosing

[polizei]

Hello all,

A few weeks ago I noticed that my '87 911 was not accelerating as strongly or as smoothly as it had previously. It's as if the car is being choked when accelerating. I can't remember anything in particular happening from the one day when it was fine to the next when it was not. The problem has gotten worse, and I have noticed that black residue has accumulated on the bumper above the tailpipe. I believe this is an indication that the fuel/air mixture is rich.

I thought it was possible that I had a bad tank of gas, but I put in a fresh tank and the problem has persisted. The only modifications I have made to the car have been a euro pre-muffler, muffler bypass, and a Steve Wong chip. I replaced the DME relay, O2 sensor, and put the original chip back in the car, and none of that has resolved the problem. The fuel filter was replaced about 3 months ago when I got the car from the PO.

I'm at the point where I'm about to bring my car into an air-cooled Porsche mechanic, but I was hoping that someone may have experienced such a problem and have some advice for me. I appreciate any help you can provide. Thanks for your continued help guys.

[Steve@Rennsport]

Andy:

Start the process by VERY carefully checking the Head Temp sensor values and its connectors/wiring for continuity.

[livi]

Sorry to hear about your problem. This is most likely a stupid tech newbie proposition, but is it possible the cause could be as basic as to be found if checking the plugs, wires, rotor and dist cap ?

I know, I should keep my mouth shut when it comes to tech questions, so please enlighten me as why I am utterly wrong. I want to learn!

Hope you resolve it. Good luck!

[stlrj]

My understanding is that the SW chip is designed to enrich the mixture which may have a tendency to foul your plugs more easily that might explain your sudden poor acceleration.

Cheers,

Joe

[CliffBrown]

Do you still have a cat hooked up?

Could it be a clogged cat?

[polizei]

Originally Posted by Steve@Rennsport

Andy:

Start the process by VERY carefully checking the Head Temp sensor values and its connectors/wiring for continuity.

Steve, thank you for your reply. I'm a novice DIY'r and am not sure where to start with your advice. What should I look for in the Bentley manual to follow your advice?

I haven't checked my plugs yet. Hopefully I'll get some time to do that tomorrow as today is "family day". The Cat is no longer on the car. I have a brand new Euro pre-muffler on there from Fabspeed.

[Steve@Rennsport]

Originally Posted by polizei

Steve, thank you for your reply. I'm a novice DIY'r and am not sure where to start with your advice. What should I look for in the Bentley manual to follow your advice?

I haven't checked my plugs yet. Hopefully I'll get some time to do that tomorrow as today is "family day". The Cat is no longer on the car. I have a brand new Euro pre-muffler on there from Fabspeed.

Andy:

Look at page 240-17 & 240-29 in the Bentley manual.

[ZOA NOM]

Check for proper operation of your Throttle Position Switch. You may not be achieving WOT.