Engine Red-lines on Start-up

[piscator]

Today was a momentous day… sorta…

After spending 8 months on a total refresh of my 1979 SC Targa, today was the day to ‘start her up!’ I put 5 gallons of fresh fuel in the tank, checked the oil (again) and turned the key – it took some cranking to get fuel to fill the new lines, accumulator, filter etc. and when it finally did –

Va – Rroooooooooooooooooooooooooooooooooooooooooooooooo ooooooooooooooom!!!!!!

The engine went right to red-line and wanted to keep going, before I cut it off! And that’s where we are. Every time I turn the key the engine runs away with itself. I’ve had ‘runaway diesel engines,' but I’ve never had this experience with a gasoline motor. I don't even know what to call this in order to do a search on it!

Anyone have a suggestion on what to look for first?

Additional Info:

1) Throttle linkage is disconnected, so is the cruise control.
2) I dismounted the CIS to clean but re-installed it (I believe) exactly as it was. I’ve made no changes or adjustments to the CIS.
3) The engine started and ran perfectly before the refresh and never exhibited anything like this soaring idle.
4) I adjusted the valves while the engine was out, but have made no other changes, except:
5) I installed SSIs and new muffler which I doubt is causing this problem!

As always, Pelican help is greatly appreciated!

[jpnovak]

Well, a giant amount of air is getting into the system. Find the leak.

Throttle stuck wide open? AAV stuck wide open? It will be between throttle valve and metering plate or it would would be so lean it wouldn't run.

[E Sully]

Why is the throttle linkage disconnected? Is the spring attached at the throttle body to keep the plate closed?

[pmax]

Originally Posted by E Sully

Why is the throttle linkage disconnected? Is the spring attached at the throttle body to keep the plate closed?

+1

Without the counter weight, airflow keeps the throttle open.

[piscator]

Good Morning JP, Ed, Pmax,

‘Find the leak,’ O.K. got it! I’ve been reading the online CIS primer and my copy of the shop manual to re-familarize myself with the system. I’ll delve into the auxiliary air valve, throttle valve and metering plate today.

The throttle linkage and return spring was in place and connected when I first started the engine and the red-lining condition manifested itself. After several restarts with no change, I disconnected the throttle linkage, just to see what would happen. I then tried to alter the throttle position with a block of wood. With all the drama and noise of a red-lining engine and the need to shut it off quickly, it was just a dumb experiment that failed.

I’ll reconnect it today, follow through with your suggestions and report back!

Thanks very much!

[gomezoneill]

Look down the throttle housing to confirm the plate isn't stuck open. My bet it is. The only other thing I could think of is a hose is off or connected wrong.

[piscator]

Gomez, will do, thanks!

[pmax]

Pisca,

Another possibility is the cruise control going haywire. I have mine ziptied where it connects to the housing.

[proporsche]

all above or.....if you do have a cruise control..a lot of time the problem is...right here with those 2 Phillips head screws -has to be two washers...one regular and on spring washer.If not the screw will hit the throttle housing and stay open...
Ivan

[piscator]

Good Morning Gentlemen,

Greetings Ivan, Pmax -- No cruise control connected.

JP wrote: “Well, a giant amount of air is getting into the system. Find the leak.”

That was it! I looked around and found this big ol’ aluminum elbow sticking out of the back of the air bonnet with nothing attached to it! And a hose just laying there with it’s other end connected to the oil fill pipe. So, hand me another ‘Moron Award’ for missing that! I’m collecting them these days!

Once I clamped the oil hose the engine fired up and sounded great at high idle, but unfortunately, that didn’t last long. After about 20 seconds, the engine tried to settle down, held steady for a few seconds and then started to stall. Then the RPMs would surge, drop, surge, drop, surge and finally stall. I can keep it going with the throttle lever; but once I release that, ultimately, the engine stalls. I'm thinking this may be a vacuum leak but other than that, I’m not sure what to check next.

Is it common for a Porsche motor to be cantankerous on reinstall? As mentioned, removal of the CIS for cleaning, valve adjustment, and SSIs are the only changes made to the motor. Shouldn’t it be running as smoothly as ever?

And now, please allow me a confession:

This SC refresh has taken eight months and this first restart is making me a bit nervous! Back when the engine was on a stand and I was wrestling exhaust studs, the woodruff key that holds the fan pulley, dropped as I was removing it -- never to be seen again.

At that time, the consensus of Pelicans seemed to be that woodruff keys don’t fall upward toward exhaust ports but downward toward the floor. But after a week’s worth of searching, sweeping, magnets, etc. – I never did find that woodruff key. Now it haunts me!

So this may be paranoia, but yesterday, when I was holding the throttle to keep the engine running, I started hearing a steady, rhythmic, metallic, tapping sound around the right rear of the motor! It scared the bejeezus out of me!

I shut down, checked the oil and restarted. The engine seemed to be running pretty well, but the knocking was still there. There was no smoke or other symptomatic noises. I shut down again.

So now I’ve spent a restless night with visions of woodruff keys in very unusual locations! If you have any thoughts on whether it’s safe to restart this motor, I’d certainly appreciate them!

Thanks for all your help!

[boyt911sc]

Robert,

If I were in your shoes, I will do the following:

1). Drain the crankcase oil and filter it for re-use. Inspect the magnetic drain plug.
2). Remove the sump plate and use a camera probe to inspect the bottom sections of the crankcase. I doubt the woodruff will be there inside. But for peace of mind do a visual inspection.
3). Use a smoke generator to test the integrity of your vacuum.
4). Measure your control fuel pressures from CCP to WCP by running the FP only. Record the initial control pressure until it maxed out. A five (5) minute test run would be sufficient. Save the data.

Prepare for another start up and keep us posted.

Tony

[piscator]

Thanks Tony,

I'll go down and drain the crankcase and measure the control fuel pressure now.

One thing I forgot to mention is I put regular gas in the car. When I went to the gas station to fill a 5 gallon jug, I went into auto-pilot and started filling my truck with regular and then filled up the jug. I'm not that's a big deal, I just thought I'd mention it.

[yelcab1]

Good luck man. You seem to be getting enough help already. These engines are not supposed to be cantankerous, but anytime you mess with the old CIS system by … cleaning it, it will let you know that it does not like that.

[pmax]

Pisca,

Don't start the motor again with the knocking. Turn it by hand to see if it's totally smooth.

About that CIS, if you haven't already seen this, a highly informative introduction to the basic operation.

https://www.youtube.com/watch?v=a4fJAfXYxWk

[piscator]

Tony,

Oil drained. A few strands of metal filings, thickness of a human hair, less than 1/2 millimeter in length. No chunks came out of the crankcase and the oil is clean.

What's the crankcase capacity? I put about 13 liters in the engine, but didn't get much out of the crankcase, maybe 2 or 3 liters. Engine's cold, of course.

Moving on to fuel pressure.

[boyt911sc]

Robert,

Your sump plate should have a screen. Please confirm. If the errant woodruff was lodged between moving parts inside your motor, you won’t be able to do the cam timing after all. The warm crankcase oil is usually be between 3-4 liters. Fill oil tank with oil and this is a trick I use to check cold oil. If you have oil on the tip of the dip stick (motor not running) you have sufficient oil. After you run the motor to operating temperature, check the oil level while the motor is idling on a level ground. The oil mark will be between the two markers. Good luck.

Tony

[piscator]

Pmax, I turned the motor over (quite a lot) and didn’t detect any noise, hesitancy, sticking, etc. Fear of the dreaded woodruff key prompted me to rotate the engine a number of times when it was out of the car and I got the same result. You were smart to suggest I do this after hearing the tapping noise.

Thanks also for the link! I’m trying to learn as much as I can about CIS and that will help. I’ve had a number of cars with K-jetronic and it’s always been very reliable for me.

Yelcab, thanks for your good wishes!

Tony and others,

I did three System Pressure tests -- jumping the fuel pump relay and with my gauge connected between the Control Pressure Regulator and the center fitting on the Fuel Distributor. As per the Bentley diagram, p 240-10. I let the pump run for 5 minutes each time, as Tony recommended.

First Test: 43 psi
Second Test: 42 psi
Third Test: 42 psi

Interestingly, after each test, I switched off the ignition and noted that the pressure dropped to 35 psi over 5 minutes and held there indefinitely. Since the engine wasn’t running, I don’t think that’s a technically valid Residual Pressure test, but it does suggest the fuel lines are not leaking. And, I found no leaks at the fuel pump, in the tunnel, or the engine compartment.

According to Bentley that 42 psi system pressure is way too low and should be 65 – 75 psi. On my computer I found some results from 2009, which show 65 psi at that time. So, I guess a new fuel pump is in order!

Now what to do about the rhythmic tapping noise!?

[piscator]

Tony,

My engine came to me with a sump plate manufactured by a company named “Mainely Custom By Design, which was purchased by “Precision Matters” in Berwick, Maine. They still sell it.

On the version I have, there is a screen I can feel on the inside left of the hole. I can get my finger 1.785 inches into the hole and then it runs into a ceiling. The screen attaches between the bottom of the plate and this ceiling. I probably extends 360 degrees around the inside of the plate, but I can only feel it on one side. I can certainly drop the plate to see what’s there, but I’d need to order a new gasket.

Also, thanks for the oil info and tips. More oil came out after I rotated the engine and pulled the plug to check for the screen. All tolled, I say it is about 3 – 4 liters, including the mess I got on my hands.

[boyt911sc]

Robert,

Do a flow rate test before deciding to replace the FP. If the measured volumetric flow rate is within spec., increase the shims total thickness. Do you remember removing the primary pressure valve of the FD during the rebuild?

Disconnect the fuel delivery line before the fuel accumulator. Test run the FP and collect the fuel for 30 sec. (multiply it by 2 to get volume per min.).

Tony

[mike sampsel]

Robert,

Sorry to hear about your varoom issue. Guess you found a leak.

I’ve lost a few things and was very nervous about that. Managed to find most.

I can furnish a picture of the fan woodruff with a penny next to it if you want.

What is your AC doing if you have one (connected)? My right rear tapping long ago was related to my AC, sadly I don’t remember for certain how I fixed it (tightened up the mount I think). Someone said it was a bearing noise but it was not.