Gonna set fire to it

[village idiot]

I wish, but it's not mine any more. Long story short, I sold my 78SC/73RS impostor to an enthusiastic new owner. Two days later I get a call @ 9:30pm that he's experiencing a loss of power/stuttering/shutdown.

I hop in my truck find him and take a quick look and find a vac hose from the throttle body to the bottom of the decel valve has cracked/ is leaking in 2 places. Get the car towed back to my work @ 1:00am. Swap out the hose the next morning and start the car but it's acting like it has a miss and wont idle. Blipping the throttle it has decent response but is blowing black smoke(rich).

I did notice that the tach bounces a bit upon start up for 10secs or so. Car is running very rich 10.2afr verified by a wideband 02 sensor I installed when I put the car on the road last year.

Cant' verify fuel pressure at the moment because I don't have the appropriate fittings. I ohm'd the wur and got this:


Applying vacuum to either ports shows no change in resistance. Neither does warming the unit with a heat gun........

Prior to this the car ran fantastically with the afr's @ 14.6 at idle with no load and between 12.6-13.6 depending on how hard I'm thrashing it.

Any help is appreciated

Oh and for reference is this the correct wur for my car?

[boyt911sc]

Tom,

Find someone who understands how the CIS works. The resistance of the WUR is not controlled by vacuum!!!!! The 25 Ohms reading indicates that it has a good resistance (heater) but that does not mean you have WUR that has the control fuel pressures in spec. A pressure gauge kit is a mandatory tool for fuel injection troubleshooting regardless which system you have. Without one, you are assuming too many things that are critical for a meaningful diagnostic evaluation.

Next, focus on the following:
1). Source of air leak if any.
2). Presence of sparks and correct ignition timing.
3). Have the exhaust gas analyzed (before cat if any).

Since your engine is not lambda controlled, it is a lot easier to troubleshoot. Keep us posted.

Tony

[village idiot]

Thanks Tony, I've checked for any obvious air leaks and cannot detect any. Spark seems ok as the car starts fairly easily. Haven't yet checked timing, but I've never had to touch it before.....

Possible weak spark? will check tomorrow. If that's it I'd be happy

[boyt911sc]

Originally Posted by village idiot

Thanks Tony, I've checked for any obvious air leaks and cannot detect any. Spark seems ok as the car starts fairly easily. Haven't yet checked timing, but I've never had to touch it before.....

Possible weak spark? will check tomorrow. If that's it I'd be happy

Tom,

You need to pressurize the system if you want to locate these hard to find sources of air leaks. Not being able to find one does not mean you don't have any. Test and confirm. Stay away from guess-work and you'll have a fine running CIS engine. Vacuum leak is the Achilles Heel of CIS!!!!!!!! Good luck.

Tony

[rfaust6024]

Tom,
When I buy my next Porsche, I hope it's from someone as "STANDUP" as you! You didn't have to take it back but you did! Your one of a few good men. Great to know there are people like you still out there!
Another fine example of the great people who own these great cars.
Cheers!
Bob

[timmy2]

Running rich now because you had adjusted the mixture to compensate for the bad vacuum line when it was cracked slightly but not failed completely?
Replace all the vacuum lines and tune it to run where it should be, you have the meter so adjusting the mixture is easy.
This is after checking and verifying fuel system control pressures of course!....

[village idiot]

Originally Posted by rfaust6024

Tom,
When I buy my next Porsche, I hope it's from someone as "STANDUP" as you! You didn't have to take it back but you did! Your one of a few good men. Great to know there are people like you still out there!
Another fine example of the great people who own these great cars.
Cheers!
Bob

Thanks Bob, I appreciate it

[village idiot]

What kind of voltage should I be seeing at the wur connector/pigtail?

[rusnak]

Do you have a way to check AFR? Fuel pressure? Timing?

[village idiot]

Originally Posted by rusnak

Do you have a way to check AFR? Fuel pressure? Timing?

I have a wideband O2 sensor installed and it shows very rich. I can't see how timing would change as I haven't touched it and the car starts easily but will not stay lit.

As for fuel pressure, the kit I bought does not have the appropriate fittings, but I'' check my co-workers kit to see if he has what I need.

[village idiot]

Managed to get a fuel pressure gauge hooked up between the wur and fuel dist. Initially I got 20 psi and pressure would rise slowly.

Started the car and the pressure would go no higher than 40 psi with the wur elect. connector plugged or unplugged.

[E Sully]

This link to Jims CIS primer will help if you need information.
Click on the testing link and then fuel pressure, then WUR pressures.
CIS Primer for the Porsche 911

[boyt911sc]

Originally Posted by village idiot

Managed to get a fuel pressure gauge hooked up between the wur and fuel dist. Initially I got 20 psi and pressure would rise slowly.

Started the car and the pressure would go no higher than 40 psi with the wur elect. connector plugged or unplugged.

Tom,

Did you get a chance to check the system fuel pressure too? How long was the car been running/idling when you got the 40 psi. reading? More than 5 mins.? When your engine is fully warmed up, it is desirable to get a 50+psi. WCP.

Definitely, 40 psi. WCP is too low. Try again with the engine warmer and keep us posted.

Tony

[rusnak]

You might change the fuel filter. BTW, only use Mahle fuel filters. I had a Mann filter, brand new, cause lean running because of reduced fuel pressure.

[village idiot]

^ will check/replace that as well.

Check voltage @ wur connector and got 11 volts. But it wasn't consistent. would fluctuate a bit off and on like morse code.

[timmy2]

Noticed your location. Is it ever humid there?
Pull the 14 pin connector at the rear fuse panel and look for corrosion on the pins and sockets. especially on pin #10 Your intermittent voltage could be due to a poor connection.
You should also carefully pop off the cover of the 14 pin connector and check that there is no corrosion in there, and that none of the wires are touching each other. If you accidentally pop all the pins out of the housing I can tell you where they all go.

[village idiot]

Originally Posted by timmy2

Noticed your location. Is it ever humid there?
Pull the 14 pin connector at the rear fuse panel and look for corrosion on the pins and sockets. especially on pin #10 Your intermittent voltage could be due to a poor connection.
You should also carefully pop off the cover of the 14 pin connector and check that there is no corrosion in there, and that none of the wires are touching each other. If you accidentally pop all the pins out of the housing I can tell you where they all go.

Thanks, I did notice the connector looked askew, so I'll look at that as well. I was looking at the wiring diagrams and saw the wur circuit receives it ground via the generator so I'll take a peek at the connections there as well.

[timmy2]

The ground at the alternator also grounds all the other CIS controls. Just check for continuity to ground on the engine block and wiggle the wires you are testing to see if it jumps around. (no need to pull alternator, yet...)

[village idiot]

Did a search on tach bounce and found some info stating that a bad alt/regulator may cause tach bounce. I checked the system and it [i]seems[/s] to be woking correctly though my battery was at 50% health(1 yr old).