fuel injection question 81 SC
 

What are the typical problems with a CIS system when the car stumbles when you gas it? It will pick RPMs but not quickly. Not even close to the throttle response of my 914-6 with carbs. It starts perfect but never runs real smooth. Is it in the lambda brain? or something like warm up regulater,throttle position sensor, etc. Any guesses are welcome realy just shooting in the dark.

Ben
77 911 3.0
75 914-6 2.7

Hmmm, check your timing advance, fuel mixture, and see if you can test or swap out your CD box. If it's just a general lagging, you can advance the timing and richen the mixture. A general tried and true recomemndation is to;

1. Disconenct O2 sensor
2. Richen mixture to 3.5% CO
3. Set max advance to 35 degrees BTDC at 6K RPMS, vacuum hoses connected.

This WILL give the car some go. Proir to this my 80SC would get a kick of power at about 4K, now is constant thru the range.

As for the CD box, my former SC developed a *stutter* between 3-5K RPM's when the unit was failing.

I also need to add;

Run a bottle of Techron thru the system

Change out your fuel filter if you are not sure it has been.....if ever!
I recently did this and was amazed at the difference. My records seemed to indicate it had never been changed. Afterwards I had a smooth idle and a stronger pull to redline.

Good luck!

Hey Ben

You got to tell us a little more info about your transplanted engine. what year is it. 3.0 engine from 78-79 used an air pump so there is no lambda system or 02 sensor. 80-83 used a lambda system so you have an 02 sensor, but you also have a frequency valve. Since your car is a 77 when you converted to the 3.0 did you get everything with the engine? IE the brain?

Lots of things to check:WUR, Ignition Wires, Plugs, Cap, Rotor, Distributor Advance, Timing, Injectors, Fuel Lines...

Brad, I set my timing a few weeks ago and did it per Bently's. It said to disconnect all vacuum lines and set it at idle. Is the 35 degrees BTDC@6k rpm a more reliable method? On my old VW with a Bosch 009, you were supposed to set it for the max advance also, but I thought that was more for a centrifigul advance distributor.

Hi Matt...

Well, there are a whole lot of us SC folks who have followed this recommendation.

I believe it's more reliable because you are actually using the vacuum advance to set it, thus, this ensures it is actually working. Since the timing is advanced so much, there is a slight chance of detotation, or pinging under load. If so, just back it off a few degrees. I do not experience any and run 91 Octane. BTW, the 35 degreed max advance dictates to about 10-12 degrees at idle on my car.

Be sure to disconnect the O2 sensor as part of this process and you'll probably need to richen your fuel mixture as well.

Do a search on *timing* and *35* and you should get quite a few hits.

As Kemo mentioned, though, there are quite a few things that could be into play here.... :)

fuel filter is where to start. if thats not it it was a good maintenance ttask

Ok to answer all questions I think in order

1. I had a perma tune on it first and decided I wanted something more relible as my wife will be the primary driver so I just installed an MSD 6al on it. It runs the same before and after.

2. ruf-porsche It is an 81 engine with a lambda brain in unknown condition. The fuel injection did come with the car but somethings were not hooked Ie the warm up regulator and cold start injector. also the vacum line that goes to the 4" inch diameter vacum diaphram thinges was plugged off. The wiring harness on the engine(to brain) versus the brain end has one extra wire that just doesn't jive? I mine as well just have you come up and look at it first hand as always ruf-porsche you are a big help.

3. I have not changed fuel filter but will do that ASAP I just can't imagine that one could be that pluged to cause this problem. It almost seems like a vacum leak or the vacum retard and advance are not working. Please keep the ideas flowing.

Ben

the lambda system must work. it needs to activate the frequency valve in order to have any decent power. with the frequency valve inoperable, it feels like you're dragging an anchor. the relay next to the lambda computer may be dead, or not getting 12V. pull it out and see if the engine idle gets rough, which would mean it works, or if nothing changes.

Are you talking the small inch by inch or should I say 24.5mm by 24.5mm relay? or the small box the the round plug connects to?

thanks
Ben

The 911SC with Lambda control should have an
enrichment circuit. Pin 11 of the control unit comes
from the enrichment relay unit mounted next to it.

During hard accel, the relay cause the Lambda unit
to enrich the mixture almost to the same extent as
it does during warmup. You can test this function
by grounding Pin 11 and the mixture should become
richer. Pin 7 of the Lambda unit is the warmup input
from the oil temp switch, which provides maximum
enrichment for warmup.

Check this out. It may be your problem.

Good luck
Lorenfb@aol.com

JW is right as usual, you need to have the Lambda system working if the injections system has the lambda fuel dist.. The lambda computer is located under the front pasenger seat in my car, but since your car is a transplant, hopefully whoever did the conversion would have copy the Porsche design.

An alternate would be to replace the fuel dist. with an early non lambda distributor.

You were able to start the car with all these system not hookup?

but somethings were not hooked Ie the warm up regulator and cold start injector. also the vacum line that goes to the 4" inch diameter vacum diaphram thinges was plugged off. The wiring harness on the engine(to brain) versus the brain end has one extra wire that just doesn't jive? I mine as well just have you come up and look at it first hand as always ruf-porsche you are a big help.

Amazing!!!!!!!!!!!!!!

As far as who did the transplant I do all my own work if possible. The car starts perfect without any of that stuff hooked up. It is a porsche and all they want do is run right? I tested the relay next to the brain and found out it is no good so off to the local shop to get one. I will keep you posted.
Ben

Looks like another bullseye for John.

Ok replaced relay and that fixed most of the problems. It runs perfect but seems to idle at about 2000 rpm no matter what you do. It has very good throttle response but I can't seem to get that idle down. What should I be looking at? I plan I taking it for a spin tommorow to see how it runs warmed up but could use some help.

Ben

Anybody mention fuel pressure?

Hey Ben

You may have to reconnect the WUR. Contrary to some people belief, the WUR regulates the fuel system at all time and not just at initial startup.

It is already hooked up but do you mean it is possible it is not working properly? I also read that the aux air regultor could case this? If these are the cases does any one have any extras that they would want to get rid of so I could use them as diagnostics?

Ben

Ok I have determined the AUX air unit is not working properly. If I pinch of the lines to it The car runs great. Can I just simply remove this unit? I see that they are NLA . Or can they be repaired? One other thing the line going from the boot on the fuel mixture device leading to the oil tank. If this line is opened the car stops running and if pinched off it is fine. What is the deal with that?

Ben