power begins loss at 4000 RPMs-help!

Imcoz · Imcoz's Garage

Chasing the issue w/ my 88 911 down for a while now. Replaced O2Sens, Head Temp Sens, full tune-up, tested air flow sens, coil, fuel pres... all passed. When I tested speed and ref sens 1+3 showed good, just showed open circuit when testing the other pin combos???? anyone familiar w/ this?
BTW runs/revs/drives perfectly 'til 4K rpms whether under load or not. Always gets rough at 4K in any gear.

Any all suggetions welcome.

Chris
88 Carrera
99 Boxster

kqw · 09-18-2004, 09:15 PM

Chek the operation of you WOT sensor.

Imcoz · Imcoz's Garage

The Fox,
I'll see where it ties in and see if I actually tested it already, Thanks again!
Chris

Slider79SC · Slider79SC's Garage

Mine was doing this when I had issues with the distributor advance.. just .02

Imcoz · Imcoz's Garage

Thanks for the help... to no avail. Distributor seems right... WOT was good when tested. Others have suggested rust in tank screen, and vacuum lines to fuel pres reg... do somemore looking tomorrow.

Jim Smolka · 09-24-2004, 04:18 PM

Clean and then reset the gap on the flywheel & speed reference sensor.

Also, check the inside the dizzy for rust.

kqw · 09-24-2004, 04:52 PM

Check the gap on your plugs...They should be set set at .28

Imcoz · Imcoz's Garage

Have reset gap on Ref & Speed sensor... if ref was off it wouldn't start and if speed sensor was off it would be missing at low RPMs.. but it could still be off a bit so I'll check it again. Checked plug gap last week.
Thanks for the help all.

pwd72s · 09-24-2004, 05:25 PM

I could be wrong, because I usually am. But I think I'd start checking fuel volume delivery...

kqw · 02:29 PM

Before the swap party begins, check the fuel mixture. Then:

I'd begin with ignition parts: Coil, Dizzy (shaft for sideward movement)cap and rotor.

Keep us informed...

stlrj · 09-25-2004, 02:23 PM

The spring loaded weights inside the distributor may be seized preventing the rotor from rotating as rpms rise to match the advance curve with the distributor cap.

Joe

midlife · 09-25-2004, 03:11 PM

I don't think there are any weights in the distributor on the 3.2.
I think all advance is handled by the DME.

stlrj · 09-25-2004, 08:55 PM

Quote:

I don't think there are any weights in the distributor on the 3.2.

Mine does.

86 3.2

Quicksilver · 09-25-2004, 09:48 PM

The springs/weights in the 3.2 don't control the advance. The DME does all that. The reason they are there is to make sure the rotor is pointed correctly towards the cap's contacts as the advance is increased.

It does sound like it is running out of fuel. Also if the coil is weak it could be having trouble sparking as the cylinder pressure rises.

You said the fuel pressure had been checked. Was it only at idle or was it under load. Also a spark energy problem would show up on the scope.

By tuneup did you mean Plugs, Cap, and Rotor? Also the increased spark resistance at higher cylinder pressure can make plug wires rear their ugly head under higher throttle settings. (but it should be just as bad at 3000 as at 4000.)

Good luck
Wayne

Jim Smolka · 09-26-2004, 03:54 AM

Hopefully, the plugs installed were of the plain NGK or Bosch type. Platinum plugs are not usually recommended for Carreras. Also, there is a tech note from Porsche stating that Anti-Seize on the SP threads is not remmended.

stlrj · 09-26-2004, 06:47 AM

...and if the rotor is not pointed correctly towards the cap's contacts at 4000 rpm as the advance is increased, then what what happens?

Does it keep on running like nothing has happened?

Does it start to miss, sputter, act up, get rough etc?

WydRyd · 09-26-2004, 03:03 PM

Check the simplest and cheapest things first. Check all your vacuum lines to the factory fuel pressure regulator and damper etc...

I had the same problem on my blown 3.2 (well, 3.3 now), and it turned out to be a disconnected vacuum line to the FPR

Good luck!

Imcoz · Imcoz's Garage

Thanks for all the brainstorming on this....

Yes... tuned means cap, plugs, rotor, wires, fuel filter, air.... I did test the fuel pressure at carside not under load. I have not counted out fuel delivery because the car sat for a year, but it was started. I have seen some postes reccomending a fuel pump be replaced especially if it is original. Also replaced the DME relay.
Used NGK when replaced... did put a little antisieze on the threads but only very little... have always done this w/ all my 911s w/out any issues.

When it loses power it feels as though it's out of gas... but returns to running fine as soon as you lift the throttle a bit to under 4K. I will look further into fuel pressure/vacuum issues again as soon as I can get my hands on my buddies Bosch fuel pressure test kit this week.

Thanks again all.