Ok, I've got one that I've been wrestling with for a while now. I surrender.

Symptoms:

Off-idle bog AND off-cruising speed bog, which will clear with moderate (past 1/2) throttle application. All at once, as if something is coming unstuck.

Floating idle - will sometimes rest at 800, sometimes at 600 (often from one stoplight to the next)

Attempts so far: fuel pressure was low, so the pump, filter, check valve are all new. Also had a little extra cash, so both FPRs were replaced. Damper has not yet been replaced. Pressure is now fine at idle but I have not checked it at speed.

Idle contact is functioning normally; verified at L-Jet terminal. Throttle cable is new and the TB appears to be opening correctly.

On the ignition side, coil/wires/cap/rotor are new and spark is fine.

It _feels_ like it's starving for fuel. Anyone else run into this? (Oh, and a stupid aside - are the FPRs directional?)

Thx.

 

Those symptoms seem to match those created by my sticky fuel distributor.

 

Maybe I should retrofit a rebuilt one?

 

Absolutely! Proven non-performance you can count on!

 

Hi James,

Just ran through the traps on my '81 with similar symptoms. Starved for fuel, down on power, etc.

There are two areas you can check.
Idle: Floating indicates incorrect info. from the Air Flow Meter or O2 sensor.... or both. Have you checked your mixture setting?

Lean running: Air Flow Meter or plugged injectors

Here's what I would check first:
Air/Fuel mixture: You can do this with a simple voltmeter If it's lean, you can richen it by an adjustment on the top of the AFM (lower left corner as you are looking at the engine)

Reading the mixture is pretty straight forward:
1. Start car and warm
2. unplug O2 wire near fuse panel
3. connect voltmeter to lead coming from O2 sensor
4. If reading is consistently below 0.5VDC, then it is running lean..... consistently above 0.7VDC, then it is rich.... IMHO 0.65 to 0.7 is ideal.
5. Adjust if necessary. Turning mixture screw clockwise enrichens mixture and CCW will lean it out.

If you peg the mixture setting to full-on CCW and cannot get it right, then it's time for a new AFM and probably an O2 sensor.

HTH,
Scott

 

Scott,

Great info! My 81 hunts for a stable idle (+/- 50 rpm, you can't see it on the tach but you can hear it). I have a new O2 sensor and plugs that are going on in the next couple of weeks and I didn't know how to check the C02.

I just did the same as James with new pump, filters, t-belt, coil, wires, cap rotor etc. It pulls good but the idle is still not perfect and I get an occasional bog off the line. This might do the trick..great tip!

 

Agreed; hadn't thought of using the O2 sensor as a test mechanism, but it makes sense.

The sudden onslaught of power feels so mechanical that I never thought to look at an electro-mechanical connection. Bad AFM signal seems more likely the more I think of it...and/or bad temp II signal (sensor is new...sense a theme here?) could be fooling the brain into a lean condition.

Off to join the VAmeter army. Curse you, crunchy old harness.

 

Gentlemen,

Let me know how things go...

Scott

 

Scott, you da man. I'd give you expensive things, but all my money is in my car.

Drove 'er home tonight, detached the O2 sensor. Hmmm...idle sets right on up and stays there. Great! Took 'er around the block; still boggin.

Pulled the AFM, resistance tests are all ok. Pulled the plug...a ha. Under the boot, wires are plenty frayed.

Quick rewire with five separate little plugs (anyone know where I can get a replacement for the original?) and...casually drive to the on-ramp waiting for the bog...let clutch out...drive slowly...mash it...and the tires break free. Squealing like Bo Duke. Thank you, Porsche, for building in that whine that lets you know you're doin' fine.

I probably picked up about, oh, 60 hp with 5 connectors and one disconnect.

BTW, O2 reading was .85. Not anymore!

Thanks, gracias, merci. As you can tell, I'm like a kid in a waaaay over-HP'd candy store.

 

That's a great success story!

 

I'm happy but I do feel a little sheepish about keying in one one set of symptoms while ignoring another.

Hopefully, this is the stuff from which good mechanics are born.

 

I'm guessin' that one covered the cost of your Rennlist membership, eh James.

Kudos to Scott for his insights.

 

Hi James,

Glad to hear you had success!!
I had a similar story and fully understand the resurgance of power. WOW! My neighbors are now fully aware of it as well.... Don't ask me how how the black marks showed up on my street

Now about that torque tube.........

Scott