wobbiest

76 911 with a 77 911S engine.

Here is what is going on:
- Car has been sitting for a long time, used good engine replaced the old one. Used engine appears in all counts to be a great, clean and well taken care of engine.

- After installed, car took a little cranking and started and once warm ran pretty good. Shake down drive was good and 4000rpm+ the power was all there.

- Car was parked and cooled to bit more than ambient. No start, but cranks. Has spark, has fuel.

- If I were to hold the air flow plate up and "prime" the system, it would catch for basically a revolution and die. With an injector pulled under cranking the fuel kind of just dribble out of the injector. With the flow plate up there is a strong spray. Tried 20-30 times, no start. Pulled an injector, pushed the flow plate all the way up, but the injector back in and the car started. Huh??? But was done on power and running really rough.

- Ran the car to running temp, no difference. Let the car sit overnight and next day, same symptoms - no start. Came back to it a couple days later. Now with the air flow pushed up there was no pump coming on nor any back pressure on the plate. 12V getting to the pump, cleaned the terminals and still nothing. Pulled the pump and bench tested and pump worked great. Big siphon on the gas lead line when the pump was pulled. Put it back in and guess what? Pump worked great and air flow sensor cued it up. Huh???

- Tried to start - same symptoms as before. One revolution then dies. Checked system fuel pressure - 4.6 bar. Has brand new WUR too. Has spark, not crazy strong, but good enough. Pulled each injector and all have flow. Tried to start it and it stumbled to life after holding in the starter for a while but was running awful so I shut it down after less than a minute.

-Pulled injector #4 and left the fuel line on. Put a spare injector in the engine to keep compression in. Started again to see how the injector was behaving. Dribblely at crank, once running had a nice spray. Engine seemed to be running good despite it being down a cylinder. Put the injector back in, and started right up and sounded really good. Huh???? I didnt run it more than a 1 minute though.

So:
The dribble at start concerns me
The erratic start issue needs to be addressed and so does the random horrible run condition

Before I jump into this rabbit hole, anyone have any advice?

Thanks.

psychoideas

Thermal time switch? Cold start enrichment valve? I'd start with fuel pressure test right at the pump first and then at each point down the line that requires a test.
You need a CIS manual and troubleshoot with that.

http://vwts.ru/injector/k-jetronic/g...tronic_eng.pdf

I've been there, good luck.

Or this closer to home,

http://members.rennlist.org/vilhuer/...p%20Manual.pdf

wobbiest

Thanks for the response. the second link is great. Never had a 911 give me such weird symptoms before.

Just wanted to add some new symptoms.

-After sitting a overnight, the air flow sensor when pressed has no pressure and does not kick on the fuel pump until it is pressed ALL the way to the top. Then the pump comes on, pressure builds and it will stumble to life.

-Car does not want to stay lit and when it does it runs rough like its missing badly. I hear what could be some denotation.

-What is odd is that is ran good and hard earlier after its first start, now its crap.

theiceman

no if its s starting and not staying running ..i dont think its the thermal time switch , sounds like the CSI is doing its job ,

the key here is the pump not running as soon as you lift the throttle plate.
makes me wonder .. what year did they start the emergency cut off plate on the air plate ..
as soon as that plate lifts the fuel pump has to run and take over , the CSi has done its job and started the car , as far as i know , that initial start lifts the throtle plate lifts immediately kicks to life the fuel pump once off the safety switch. Im not sure how it works if there is no safety switch but this is defiinitely the area to be troubleshooting.

TroyN

Maybe it's the CDI unit? Especially if it's a Permatune vs Bosch could be the problem. Or "a" problem, your cold start issue could be a bad fuel pump check valve or something like that.

wobbiest

The odd thing is the issue keeps changing its face. Engine ran strong on its first start up and several shake down drives. Plate made pressure over and over with only a tiny lift. That is only recent that it has needed to lifted all the way to the top.

I would imagine if it was purely a CSV issue or similar it wouldn't run like junk cold or warm like it is now.

It is making the right fuel pressure, but I don't want to run it too long since its making some what sounds like detonation. I don't like the injector spray at crank, its a dribble. But if I pull the injectors and lift the plate (after the first initial raise to get it going) the spray is really good.

Could the fuel dizzy be thinking the air plate is in a much lower place and letting in much less air? I havent touched the mix yet. Im just hesitant to start tweaking mix when it ran so good first.

theiceman

"Plate made pressure over and over with only a tiny lift. That is only recent that it has needed to lifted all the way to the top."

this is where i would start ...

MUSSBERGER

Dont rule out the fuel accumulator. I had a simular issue with my cis equipped benz.

arborist83

Check or replace inexpensive fuel pump relay, you can jump the relay pins too.

theiceman

Or swap it for any other just for testing

psychoideas

You can only use the red relay for the fuel pump as it is fitted with a diode that is tied in with the cut off switch in the sensor plate.

Ask me how I know

theiceman

Good info Frank. I always thought the red was just a higher current relay.

wobbiest

See here is the funny thing:

Went to go start it yesterday.
Key on, lift the plate...nothing. Up and down 20 times... nothing. And zero pushback. If tried to crank, I would get a quadrillionth of pushback from the plate about mid lift.

Pulled the fuel pump relay, which mind you is a black relay, but I have known many 911 to run just fine with a black relay if at least even on the temp. But let's even assume the relay is the problem...here is where it gets interesting.

I tried to jump pin 30 to 87. Nothing. Tried to jump 30 to 87a. Nothing. Now for all purposes and reason, one will turn the starter and one will run the fuel pump. I have done this many times. Nothing on each. Tried 20 times. Then tried jumping 87 or 87a (I dont remember which is the starter at the moment) to the fuse panel right below. Car cranks! Well ok, sounds like an issue with pin 30 then! Tried jumping the fuse panel to the fuel pump pin. Nothing. Huh? Tried this a bunch of times and same result. So even if it was the relay, I don't see why it wouldn't jump the starter or the pump. (that said, I have a red relay on its way)

Meanwhile, I plugged the relay back in and lifted the air sensor and no pushback and no pump, but I hear a faint click noise from somewhere forward on the car. So I lift the air sensor 5+ times quickly to try to track down the click. I get click, click, click, (etc) then the lines pressurize and fuel pump is on. Huh??

Turn it over and it starts (poorly) and with foot planted fully down on the gas revs don't move over idle. Struggling to stay lit the whole time. This time instead of having ok fuel pressure while running the needle is bouncing 1 bar down and back to good pressure.

Everytime I feel like I have a set of symptoms to work with its presentation changes. I have had some challenges, but this has been a chameleon!

Thanks fellas.

theiceman

Fuel pump


As a test just put a meter on the pump Lift the plate slightly. If you see 12v at the pump. I'd suspect the pump

wobbiest

Pulled the pump and bench tested ok.

And....

got a red relay. Plugged it in. Car cranks over the second I turn to the "on" position not the "crank" position. So crank is under consistent power. Huh???

What a bizarre presentation.