2.7 cuts out at 5200RPM

[Ray 911s]

It feels like a Jake Brake. The car starts and runs perfectly, but cuts out at 5200 every time. It's as if the spark or fuel are removed. I've searched and read extensively - here's why my situation is a little different than previous threads:

I've eliminated everything on the engine. How? It's new. I just installed a fresh 77 2.7 with a new distributor and rotor. No parts were carried over from the old engine including fuel lines, vacuum lines, etc. The situation was the same on the previous engine - at exactly the same revs.

The fuel pump cut-off relay behind the fuel gage has already been removed. Fuel pump relay is new.

What else can I check? Is it time to get rid of the CDI box and switch to the MSD?

[bigchillcar]

wow..i would have guessed a distributor issue, but doing it with a new engine and distributor too? what cdi box do you have..is the oem bosch? permatune (shudder)? have you recently stopped going to church? hit a black cat? may have to think on this one a little while..weird.
ryan

[Ray 911s]

It's the Perma Tune. Shudder?

[klaucke]

Perhaps it's the wrong (or broken) rev limiting rotor? Other than that, the Permatune seems like it could be your problem, especially if the other ignition components were replaced to no avail.

[bigchillcar]

ray,
do a search on 'permatune'..you'll find a wealth of info on the all the warm-running problems other members have had with this unit, but in most cases the car would quit running and not start again until it had cooled..not the same problem as yours, but still could be related. how about the fuel pump itself? when they get old they begin to draw more and more amps..could it have aged to the point that it can't draw fuel to meet the higher combustion demand at higher rpm's? when it cuts out is it abrupt like ignition just cut out or does it struggle and then die, perhaps suggesting being more slowly cut-off from proper fuel flow rate?
ryan

[Ray 911s]

Unfortunately there is nothing gradual about it. When the tach hits about 5200 the engine starves. Literally as if a switch was thrown, or I suddenly removed my foot from the throttle. The car runs perfectly before and after. Also is not temperature or run-time dependant.

[HawgRyder]

How many RPM's were allowed with a "valet" key?
I know it's a far reach but is that the problem?
Bob

[bigchillcar]

i have yet to hear of your symptoms with a permatune box, but i still wouldn't rule out..i would be wanting to borrow someone else's box though to check and see what happens..i know that for sure. like you say, anything else back there that wasn't replaced would be on my priority list to check out. with the bad rep permatunes have gotten on here, it would head my list of items to rule out.
ryan

[Early_S_Man]

Ray,

There is no fuel cut-off relay for a '77 ... that is only for SC engines!

I think you need to provide a bit more detail about the car, and what wasn't replaced with the engine ... does the rpm 'limited' cutoff occur in any gear, or just in 5th gear at cruise? Does it also occur at rest just reving the engine by hand? Is your CD unit OEM Bosch or Permatune, and if Permatune ... is it silver or blue?

You say it feels like fuel starvation, so that would seem to rule out the CD unit. Electrical rev-limiters are instantaneous, not a starvation-inducing phenomenon!

The red fuel pump relay is on the left fender under the hood above the fuses ... check the socket for corrosion.

This sounds like a fuel supply problem ... clogged filter, strainer in the fuel tank, rust in the fuel ines, etc., or a failing fuel pump. Have you tested fuel pump output volume? Its' spec is 750 ml in 30 seconds. Current drain for the fuel pump is not supposed to exceed 8.0 Amps ... so check that to see if wear or rust has caused additional loading of the pump.

[Ray 911s]

The car is a 77. The engine is also a 77. The Perma Tune is blue and has the Porsche Triangle logo on it. The red relay is new, the socket was cleaned with electrical contact cleaner.

The cut out occurs in any gear or in neutral. It is consistant at 5200 RPM by my tach. There is no performance degradation or surging or any other symptom until the cut off. It is not gradual but is perfectly binary - instantly "off." It is running strong and accelerating like a racer right up to 5200. There is no stuttering or low power zones any where else in the rev range. Starting is easy with no WUR idle-hunting.

These things led me to discount any fuel tank/pump/lines as the issue since it seems that they would cause a gradually worsening condition until starvation. It also seems unlikely that a sudden cut-off would occur so drastically and suddenly at the exact same RPM every time. In my case the engine pulls very strongly right up to the cut off point. Nevertheless, I will replace the fuel filter and test the pump pressure. Might as well eliminate any potential cuases one at a time.

The entire engine was replaced - no parts were reused. The fuel lines are new from the CIS to the fuel filter. The CD box was not replaced.

Thanks for your assistance in diagnosing. I'm putting together my shopping list for new parts as we go!

[bigchillcar]

i still say i'd borrow a cd box and see what happens before spending more $$. gotta be a pelican near you in illinois who could assist with loaning one.
ryan

[Early_S_Man]

Ray,

Check your tach against a known good dwell tach to see if an indicated 5200 rpm ... could actually be 6400 - 6600 rpm, and that it could be the proper rev-limit cutoff for your rotor. Spec is 6500 rpm +/- 100 rpm for your engine. The tach is a holdover, so it could be suspect, right?

If you don't have access to a dwell/tach meter ... an alternative would be to build the calibrator in the following diagram. It has been built by several Pelicans for under $20, and used successfully for testing CDI units, Speed Switches, and tach calibration. I have been using the original one I designed ... since around 1969!

[Rex Walter]

Do you still have the rev limiter rotor in the distributor? Or are you using a regular rotor?

Rex