'84 911...after coming out of a rolling start behind a 2000+/- SS Camero, we were both on it hard, I stayed right with him but either at the top of second or the top of third about 6K on the tach or so, my power just let off? Felt like I lost fuel. Never had this happen. What do you think it was? Loss was not extreme and picked back up in the same gear until I shifted. And yes my friend also told me I had no chance of taking an SS which has about 340 hp? But he never pulled away. Love no cats!!!!!

 

Rev limiter?

 

I've heard rev limiters and there was no sound associated with this loss in power.

 

Hi:

6K or so on the tach,..................

Given that rev limiter cuts off fuel around 6600, might you have accidently hit it since these tachs have some degree of overshoot and are not accurate unless redamped?

You will not hear anything, the motor will simply quit pulling and go flat when it hits that.

Does it run OK otherwise? How may miles are on your engine? As these things get older, the valve springs do loose seat pressure and the threshold of valve float creeps lower.

Things to check:

1) Spark plugs

2) Distributor cap, rotor & plug wires/connectors

3) Fuel filter

Hope this helps,

 

Rev limiter...

If you hit it "hard" it will oftentimes feel as if you have just broken the driveshaft, BLAM!

If you simply "nuzzle" up to it, the revs climb reasonably sedately (wrong word for a Porsche, but) to the rev limiter, the engine will suddenly start acting as if 2-4 plugs are fouled.

 

Yes, felt like fouled plugs or loss of fuel. I had always heard a sound associated with a rev limiter at the track and once, before I owned my Porsche, driving besides a Porsche who went high on revs heard same popping sound like he hit the rev limiter, same sound as at the track. That is what I expected. So there is no sound. What is the actual action. Fuel gets cut, or spark?

 

Spark gets cut I beleive. I have yet to experience this myself but the day is still young.

 

Hi Dan:

Porsche rev limiters since 1978 cuts off fuel to prevent cat fires.

Many race cars use a "soft-touch" type ignition rev limiter that interrupts spark every other firing event to help prevent excess stresses on the rods.

 

Steve, Would the rev limiter for my 71 cut the spark or fuel? Maybe thats why I am thinking spark. What about the MSD or Crane setups as I am thinking about one of those soon?
TIA

 

Sound like rev limiter to me, and yes it cuts the fuel supply, not the spark so the car kind of gasps for a second or two.

I make it a point to test it every time I drive to make sure it is working

 

It doesn't sound like a rev limiter incident.

Did the power instantly shut off, kind of like total loss of spark or fuel - then come right back on a second later? My '87 does the same thing, but varies from 5000 - 6500rpm. When it cuts out at 6500 it is definitely a problem - really slams one against the seatbelt. Tonight my car ran fine except for one incident when in 2nd gear, accelerating strongly, it stumbled a couple of times at about 5000 like it was getting no fuel, then ran fine again. This only happened once during an hour of mixed highway and city driving. I have new plugs, cap, rotor, dme relay, fuel filter, and grounds are cleaned up at intake connection.

I will try new plug wires, test fuel pump, new fuel pump relay, internal dme solder connections, all wires going to distributor, coil, and electrical harness, cylinder temp sensor wiring and operation, and O2 sensor functionality. Hopefully I can find my gremlin.

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Dan:
<strong>Steve, Would the rev limiter for my 71 cut the spark or fuel? Maybe thats why I am thinking spark. What about the MSD or Crane setups as I am thinking about one of those soon?
TIA</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Hi Dan:

Pre-cat cars like yours, used a centrifugal rev limiter built into the ignition rotor inside the distributor. These were available in 6500 RPM (T), 7100 RPM (E), and 7300 RPM, (S).
Yes, these did indeed abruptly cut the spark and its none-too-easy on the lower end.

The current crop of CD ignitions such as MSD and Crane use a gentle ignition interrupt that make the engine "flatten out". Its MUCH easier on the bottom end and is easily changed. The MSD's use a rev-assigned, plug-in module and the Crane units have a **** on the end of the case.

BTW, if you do upgrade to one of these CD ignitions, be sure to use the same brand of coil (MSD or Crane) for impedance matching. Its critical.

 

Thanks for all the help guys. Yes it was just a short loss of power. Did not feel the pull against the seat belt or any of the other rough transfers of power mentioned above. I was just expecting a popping sound I had heard before (on other cars on the track), and when I did not hear that assumed I had a problem. I think it is correct I bumped up against the rev limiter from all the descriptions...in the heat of battle I was all consumed.