Engine transplant...almost there...need help

porsche_virus · porsche_virus's Garage

I just took the '78 3.0 CIS engine out of my '76 Targa and put it (with tranny) into my '74 coupe. Hence, the '74 CIS 2.7 with tranny went into the '76 Targa. Everything has matched up perfectly so far, with a few misc. unknowns.

First is this green wire that is on the '74 engine wiring harness. It matched up to a similar green/white wire on the '74 car, but the '76 Targa has no such wire that I can find. See pic below.

Second, whether or not that green wire is keeping the engine from starting is a mystery, but I also think there is a fuel issue. I will admit I have no idea how the fuel system works on 911's because it makes no sense to me that there are two fuel lines coming into the engine bay. One line comes from the pump or tank and goes to the fuel accumulator, which has one line coming out of the top of it that goes to the fuel filter, which then feeds the fuel injector distribution block. The OTHER fuel line coming from the pump or tank hooks directly into some rat's nest of fuel lines that go all over the place, starting with the warm up regulator. HOWEVER, there is a THIRD, smaller line coming from the bottom of the fuel accumulator that feeds into a "T" that connects with the line that feeds the WUR, but only on the '76 Targa. No such line exists with the '74. More on this later, as I would like to get my electrical situation under wraps first.

Thanks in advance for any input given.

poorsha · 06-14-2003, 07:52 AM

The green/white wire connects to the body plug at rear on my 74. Need a pic? poorsha@shaw.ca

poorsha · 06-14-2003, 07:58 AM

From reading the wiring diagram (I am no expert) the green/white wire is for the optional oil level indicator. Perhaps this car has the standard guage. This is only a guess.

porsche_virus · porsche_virus's Garage

Well, if that's the case, I doubt it's keeping the engine from starting. I just thought it was something to do with the ignition, despite the lack of a green/white wire at the dizzy. Now I'm thinking it IS a fuel related problem. Thanks for the input.

KC

poorsha · 06-14-2003, 08:12 AM

So I guess it's not for sale any longer?

Is the motor simply not firing? or is it running then dead?

ischmitz · ischmitz's Garage

The reason for two fuel lines is quite simple. One is the input line from the fuel pump to the engine. The other is the return line from the pressure regulator.

The CIS injection uses fuel pressure to regulate the amount of fuel injected. The pumps static pressure is higher than what the engine needs. There is a fuel pressure regulator that directs part of the fuel back to the tank to maintain a constant input pressure.

The green wire is for the oil idiot light. It does not run over the 14-pin connector on a 74. Not hooking it up would simply render the green light in the oil level - oil temp gauge inperational.

Ingo

Wayne 962 · Wayne 962's Garage

Think of the CIS fuel flow like an electrical system. The gas tank is the battery. The fuel flows up to the CIS system in the engine bay at high pressure. Any fuel that is not used, flows back into the tank and is cycled. This helps to maintain pressure and flow (required for the CIS system).

In simple terms, the injectors for the CIS system "tap" into this currently flowing stream through the fuel distributor.

Older style cars with carbs had a single fuel pump that pumped fuel at very low pressures. This enabled the fuel pump to be stopped by the float valves on the carbs.

-Wayne

porsche_virus · porsche_virus's Garage

Okay...got her running! I remembered back when I was messing with the 2.7 after the first rebuild, and it was not producing enough spark. Today I jumped it with another car and it fired right up! I guess the battery was too low to provide the right amount of juice. Thanks for all the input. I am not concerned with the oil dummy light. I'll just tell whoever buys the car to keep an eye on the oil level indicator and engine temp, and to check the oil level while it's running every few days.

I am going to try to sell the car locally for a week or so, and then it'll show up here for sale. After that, it'll go to E-GAY. I don't need two Porsches, and now that my '74 has a 3.0 and good 915 in it, the Targa is just no fun to drive

porsche_virus · porsche_virus's Garage

Okay...car runs good...everything works....except for the TACH! I thought maybe there was a difference in the two so I switched them but still no movement. On the back of the tach there's a black/purple wire labeled "TD", which I figured meant something like "To Distributor", but I can't find a wire like that around the dizzy.

Can anyone give me an idea of what to check/test? I found a black/purple wire in the main wiring harness loom but it disappears under the CIS somewhere.

porsche_virus · porsche_virus's Garage

Nevermind...got it. I was making it harder than it was. I just hooked the black/purple from the wiring compartment to the little plug on the dizzy, which had a black/purple that wasn't really going anywhere. Walla! Tach works! I guess there's just a few little differences between the '76 and '74 that you have to figure out.