Refuses to idle 83 sc

[Walt Fricke]

1) The alternator light should only be on with the key in run but the engine not running. When you start the engine, the alternator light should go out. If it doesn't, that typically means the alternator or VR or both are bad, or the fan belt has come off.

2) If the AFM/(air flow sensor per the parts manual - it isn't measuring air flow, just an on/off switch indicating the sensor plate is down on its stop - no air flow and switch on, or up a very little bit off its stop, there is thus some air flow, and the switch is open) is unplugged (the safety feature), the engine should start and run just as always. You don't have the safety feature - get in a crash, stall the engine, and without that feature your fuel pump will still be pumping away unless you can turn the key off. But the cars were that way for some years without the feature - your choice.

3) It isn't an idle problem. Your correction made it clear that it was a wouldn't run problem - you can't drive the car. If it won't run, it won't idle. It is easy enough to have the engine run OK, but not idle well, or die at low RPM. Different issues, not the one you report.

4) If the AFS wire which connects to the FP relay is accidently grounded somewhere, the car will start (the starter circuit works on the normally closed circuit of the relay), but once the key goes back to run, the relay won't move the contacts to the N0 side. The pump won't run, so neither will the car. That wire is (per the schematic) brown black from the AFS plug to T2a (somewhere in the engine compartment, I don't have a list for the 2 circuit plugs in an SC, but a 1977 2.7 has a T1a near the regulator panel over by the CD side), br/bk again to T2e (which is shown as also below the regulator panel, though that doesn't make sense to me), then brown/red to terminal 85 of the fuel pump relay socket, and it must come out of the large main multi wire bundle up front and go directly to the fuse socket.

This or these wires are wires you disconnected when removing the engine, and are not part of the big 14 pin connector, nor the smaller 12 pin CIS connector. Maybe that one didn't get reconnected?

However, inadvertent grounding of this wire doesn't seem common. Seems it would nicely fit the symptoms. Being inadvertently open would not fit.

[timmy2]

T2a is at the 2 pole CDI power plug on the SC’s Walt.
It is the Tach and CDI plug for 77 and earlier.

[marty911sc]

I dont know how all the above leads to runs except idle. As far a fuel pump goes….There is a fuel cut off switch that controls the fuel pump relay. in the Fuel Distributer. It is a green connector on top rear of the FD under the air box. There tab in the Venturi that moves up when air movement from the rotating engine. It is a safety device. You can reach in and lift it with igntion on and fuel pump will come on. If my car sits it may not start because of this switch. If the battery is even slightly weak or no full charge there is not enough air movement to either move the tap up or hard press the switch closed past possible Contact issues. Once I’m driving once week its ok. I installed a momentarysun roof switch and wiring to bybass the fuel relay. This is the big reason CIS does not roar to life when you bump the igntion if it sits. The tab has to move….fuel pressure slowly builds up (relatively) in th FD ..accumulator… fuel line .. poppet fuel injectors.. Just bump the momentary switch next to the sunroof sw and hear the pump go on and change pitch with fuel pressure. Bump igntionand go
no matter battery condition how long it sits. Fuel pump relay contacts safety switch contacts. Dependable……

[boyt911sc]

Originally Posted by Walt Fricke

4) If the AFS wire which connects to the FP relay is accidently grounded somewhere, the car will start (the starter circuit works on the normally closed circuit of the relay), but once the key goes back to run, the relay won't move the contacts to the N0 side. The pump won't run, so neither will the car. That wire is (per the schematic) brown black from the AFS plug to T2a (somewhere in the engine compartment, I don't have a list for the 2 circuit plugs in an SC, but a 1977 2.7 has a T1a near the regulator panel over by the CD side), br/bk again to T2e (which is shown as also below the regulator panel, though that doesn't make sense to me), then brown/red to terminal 85 of the fuel pump relay socket, and it must come out of the large main multi wire bundle up front and go directly to the fuse socket.

This or these wires are wires you disconnected when removing the engine, and are not part of the big 14 pin connector, nor the smaller 12 pin CIS connector. Maybe that one didn't get reconnected?

However, inadvertent grounding of this wire doesn't seem common. Seems it would nicely fit the symptoms. Being inadvertently open would not fit.

Walt,

Terminal #85 @ fuel pump relay socket (brown wire) is connected to one side of the air flow sensor switch plug. The other side of the AFS switch plug goes to D- @ alternator as ground. Refer to PSM wiring diagram. This is by design. If there is no ground (@ #85) the FP would run as soon as you turn the ignition switch @ON. This is analogous to pulling the green AFS plug from the air flow meter switch.

87a - 30 ............NC (normally closed).
87 - 30 ..............NO (normally open).
86 - 85 ..............terminals of the coil switch.

Ignition @ OFF:
No power supplied to any of the above terminals.

Ignition @ RUN (not START):
Power is supplied to terminals 86 & 87a. The normally closed 87a - 30 would instantly open and become 87 - 30 if terminal #85 is grounded. If terminal #85 is not grounded, the FP would start to run as soon as you turn the ignition switch to ON position.

If the sensor plate is at rest, it means the motor is not running and terminal #85 is grounded. This is the principle behind the SAFETY SWITCH & rev limiter. Presence of ground @ terminal #85 (fuel pump relay socket) terminates the operation of the FP.

Tony

[Walt Fricke]

Tony - right, this is what I was saying (or trying to). If your car starts, but won't run, a continuing ground on the safety circuit between the switch and the FP relay would cause this behavior. Since the circuit diagrams show two plug type connections between switch and relay, somehow grounding one of them - such as one separated when pulling the engine out of the car - would be something worth checking.

The circuit diagram does not show a purely brown wire here. Brown black, brown black, then brown red.

Dennis - my puzzlement has to do first off with the apparent change from '77 to the SCs - the '77 has a T1 connections in the sensor circuit. The SC diagram calls out T2s. Assuming the "regulator panel" is the fuse and relay panel in the engine bay, the letter designations, regardless of the T1 vs T2 part, show both of the plug connections as being by the regulator panel. Anyway, it might help troubleshooting of the problem to know what to look for and where.

I've had my SC engine (in a 2.7 tub, and hence basic wiring system) out many times. Perhaps by luck I've never gotten this wrong despite it not being on my radar (unlike, say, rewiring T14 for the conversion). The only wiring not included in T14 or T12 that is in my mental inventory is the wiring to the CD box (and that to the starter/back up light switch). I probably just added an additional single plug pair and wire, or converted somehow to a two pole plug.

You know this circuitry better than I do, but the US SC circuit diagrams show T2a and T2e as the two plugs involved in this safety circuit. T2a shows the other wire for the SC as in the power supply to the CD box and to the engine mounted heater fan circuits, with a fuse in the fan circuit. These T2 plugs are polarized, so you can't get things mixed up reconnecting them, and even if you could I don't think it would lead to a ground for the safety switch.

It would make sense for T2e to be up by the front trunk fuse panel, as it also connects to the optional alarm circuitry. The factory manual says that is "below the regulator panel" same as for T2a, so maybe both front and rear fuse panels are called regulator panels? That would make more sense, as having two connections for the same circuit in the rear doesn't make sense.

Marty - I can understand how a low battery might prevent the starter's cranking from moving enough air to move the air flow plate up enough. However, when you crank the engine with the key in "start," the FP relay uses a different circuit, which in effect bypasses the effects of the safety switch and the fuel pump runs. As soon as you release the key from Start, the relay switches to its other mode, which requires an "open" at the 85 terminal for the pump to get power. Having the battery at full strength is certainly always good, but it doesn't seem to be the cause of the problem here (and I think he reported it as being good).

Leaving aside identifying the two plugs back hidden behind the engine by their color or the color of the wires to them, perhaps there is another simple way of checking if they are plugged in backward: Make sure nothing is plugged into the CSV, but leave what you have plugged into the safety circuit plug. Turn the key to run. If the fuel pump doesn't run, unplug it (by now you have gotten good at getting your hand way back and over and know which fixed plug is which). If the pump then runs, you have it right and can cross getting the plugs reversed off the list.

If "starts but doesn't idle" isn't the same as "starts, but won't run at any RPM" or "starts but won't keep running no matter where the throttle is," please clarify this.

[boyt911sc]

Hugh,

Let’s go back to square one and begin our discussion on the same page. Search DKLever’s thread about testing the FPR socket terminals:

87
87a
86
85
30

There are several test conditions we have to do before we could discuss further. Otherwise, we would be chasing our tails to eternity. Thanks.

Tony

[hughc]

Hi guys, thanks for all the information.
As I mentioned in my last post I tried plugging in the two connectors in question today and the engine fired up and kept running. As near as I could tell the connectors ended exactly where they were when I started this ordeal. I call it an ordeal because it was the first (and hopefully last) that I had to troubleshoot electrical connectors behind the engine. Those of you that have done it will agree that it is very uncomfortable trying to reach back there and find what you are looking for.
Anyway, I didn't find anything wrong so I can only assume one or both connectors were not in tight enough, which ended up being a blessing.
Unfortunately a lot of you guys had to put your thinking caps on to try and explain to me how it all worked and I'm very thankful for that.
I did get out for a short drive and other than the A/F gauge reading higher than normal (16.5), the car seem to run quite nicely.
I expect to put more miles on the car this w/e so we'll see how it all works out.
Thanks again for your time.

[proporsche]

good job ..it actually ended up as you mentioned in your post # 2

Ivan

[hughc]

Originally Posted by proporsche

good job ..it actually ended up as you mentioned in your post # 2

Ivan

Yes, it is good that it finally started and kept idling, but......., I'm not out of the woods yet.

I previously mentioned that on my first drive the fuel/air ratio was higher than normal, staying at 16.5/17.0 whereas last summer I was satisfied when it was at 14.4/15.3.
So that concerns me.
So today when I tried starting the car it was very reluctant but after a few tries it started and kept running , roughly, and at an elevated A/F ratio (around 18.0 to 18.5)

My previous experience (last summer) on a cold start the A/F ratio was at ~13.5 until the engine warmed up then the A/F ratio settled at ~14.7. So something is amiss.
I also noticed today that when I would give more throttle the A/F would climb to ~18.5 when I expected it to drop to the 13.5 range.
So the A/F readings are opposite to what I would normally expect.

I don't want to keep running the engine at what appears to be a somewhat lean situation but I'm not sure what direction to go in to try and correct the problem.

I can't see that anything that I did over the winter would cause this problem so like my previous problem, the solution is probably a no- brainer but I'd still like to hear from those of you that have experience with A/F system.
Thanks

[Schulisco]

Bad mixture. Either too much air - or too less fuel...when reading AF of 18 after pushing the throttle and nothing changed on the FD or WUR I would expect there's either a vacuum leak in the CIS or a hose of the vacuum system is wrong connected...checkout the diagram in post #7 and make sure that all hoses are connected as described. Did you separated the vacuum hoses of the (ignition) distributor? Check the ignition timing on idle.

Thomas

[T77911S]

check fuse 18
make sure the FV is vibrating

[hughc]

Well now I am getting more and more frustrated. The engine won't start at all this am. It turns over very strongly but will not fire.
I tried it with the jumper wire (to replace relay). I tried swapping the FV and AS plugs to no avail. I pulled an injector to verify fuel flow and I did get flow although I put a socket under the air sensor plate. So this no start problem is new and will undoubtedly prevent me from further trouble shooting.

Originally Posted by Schulisco

Bad mixture. Either too much air - or too less fuel...when reading AF of 18 after pushing the throttle and nothing changed on the FD or WUR I would expect there's either a vacuum leak in the CIS or a hose of the vacuum system is wrong connected...checkout the diagram in post #7 and make sure that all hoses are connected as described. Did you separated the vacuum hoses of the (ignition) distributor? Check the ignition timing on idle.

Thomas

I tend to agree with you Thomas with respect to your comment about bad mixture. I did a bit of reading on the purpose of the FV and it seems it controls the amount of fuel in the lower bowls of the FD and consequently controls to some extent the amount of fuel to the injectors thereby causing the mixture to be either lean or rich. If that is the case then a faulty FV (or not getting a good signal) could be the reason for the air/fuel ratio to be staying on the high side.

But, having said all of that, I recall the engine would only run with the FV disconnected so that might explain the higher than normal fuel/air ratio.

So the priority now is to get the engine started so that I can do more testing by swapping the various plugs and the back of the engine.

At this point I can't imagine why the engine refuses to start and I don't know what I might have disturbed that would cause the problem.

I hate to think I might have to drop the engine again so that I can have a better look at what there is to see at the back of the engine.

And yes, T77911S, fuse 18 was blown (can't explain that) and no. the FV is not vibrating.
Thanks

[Schulisco]

Troubleshooting a CIS car can be frustrating, indeed. But you need to be patient and go step ny step logically...the satisfaction after sorting the problems out by yoourself afterwards is priceless...

You're right - the frequency valve is to control the "control pressure" of the fuel distributor. It either leans or richens the mixture in the fuel distributor. It has to vibrate while the sensor plate is lifted by the vacuum of the motor. The FV pulses around 70hz and the "ECU" under the passenger seat controls the pulse width of the FV to open and lowers or rises the control pressure given by the WUR (by the ECU prolonging or shorten the pulse width which is nothing more than opening the FV longer or shorter). The WUR richens the mixture for cold start and afterwards it gives a more or less constant warm control pressure which is varied by the FV. The o2 sensor gives the ECU a signal for either too rich or too lean signal. For a proper troubleshoot you need to have a CIS pressure test unit. Without that a serious and logical troubleshoot is almost impossible on a CIS engine.
If the engine ran good before dropping it I guess everything should have worked properly. But unfortunately you cannot be sure that this is still the case when putting it back in. Therefore you have to check alomst everything by hand...probably you created a vacuum leak or one of the parts of the CIS system decided to drive you crazy...

Do you know Kurt from Klassik Automotive Training School and his superb CIS videos on a 911? It's most important to understand the whole CIS system for a successful troubleshoot. His videos are the very best starting point ...
https://www.youtube.com/channel/UCbo48hJkHDikGut5DoL6-sQ/search?query=CIS%20porsche

Especially the "rebuild CIS" one is very handy because he describes all the steps necessary for a real good founded initial setup after some works on it and he shows all steps in right order! And this might be also the right way for you to check all relevant points on your car.

Also have a look on his website https://www.klassikats.com/ - he also has tons of informative and documentary material about Porsches and other cars on his page.

Thomas

[Walt Fricke]

Having the FV system working properly is a good thing, especially for fuel mileage and emissions.

However, the FV system is not controlled by the O2 sensor under two conditions: Idle and a bit above, and at wide open throttle. There is a pair of switches on the right side (as you look at it from behind) of the throttle body. They tell the "ecu" which of three conditions the throttle is in: idle, part, full open. At idle and WOT the ECU sets the FV at a 50% rate, which should result in a richer than "perfect" AF ratio. The FV adjusts things at part throttle (i.e., cruising), for best fuel mileage and least emissions. So I'd forget about the sensor as the cause of hard or no starting.

When removing an engine for top end etc work, there is no reason to disconnect directly this switch. Its wires run over to the 12 pin plug through which most of the CIS control wires pass. That you do have to disconnect, though that ought not to cause problems. Like the 14 pin connector farther to the rear, it is keyed - only attaches one way.

With your ability to measure the AF ratio you have a leg up on diagnosis, but you really do need to be able to check the standard parameters of the CIS: system pressure, cold control pressure, and warm control pressure, along with how fast pressure disappears after the engine is turned off, Knowing which of these is out of spec is a large step forward toward diagnosis. You can expect to hear that from about every guy who has worked on the CIS, from us home brew guys to someone like Tony, who makes some sideline retirement income from working on CIS stuff (for instance, he has bins full of used component parts, which he tests before selling).

My pure guesswork at this point about hard starting points to checking out the cold start system. With an ohmmeter you can check most of the operation of the cold start thermostat in the left chain cover. If that isn't letting 12V get to the cold start valve, it can't work. Checking if it is working if it gets 12V, however, is trickier.

As to the lean running, you have seen people point to air leaks. For sure those will lean things out a lot, and there are a whole lot of places for air to leak. The best way to check for those is the smoke test, where you blow smoke into the intake (with all normal exits blocked) and watch for smoke coming out of some place it shouldn't. An alternative is, with the engine running, to spray carb cleaner or brake cleaner fluid at likely places for leaks, to see if the engine picks up a beat.

The WUR affects the starting mixture. However, if the internal heating coil is kaput (or somehow disconnected), that won't lead to a lean condition. Just the opposite. A cold WUR has a bimetal spring which pushes in such a way as to decrease the control pressure, enriching the mixture. Heat from the heater, or eventually just from the whole engine heating up, causes the spring to bend in such a way as to increase the control pressure, and eventually its working end completely disengages from the pressure control system - it doesn't touch it. So it is out of the equation. At that point the mixture is controlled by the amount of air flowing, the adjustment of the little screw down in the FD area, what the ECU/FV are up to (remember, at idle the FV should be at 50%, and you can measure that indirectly by a dwell meter - look up dwell meter and and the basic setting of things inside the WUR. These are the things you need to measure.

To some extent the distributor advance can affect the AFR, so confirming that is set correctly is important. Though obviously requires an engine with at least a half way decent idle.

Good luck on all of this. The normal troubleshooting after work on something starts with what was worked on/changed, and assumes everything else stayed OK. However, if some component independently gives up the ghost, that makes figuring things out much harder. And the old mechanic's approach has been to concentrate on electrical stuff (which used to mean ignition) before look into the fuel/intake system.

Here, the jostling involved in an R&R of the engine could easily cause a crack in an old rubber line somewhere, leading to an air leak. One place this can happen is the big boot which connects the two sides of the intake system. I had one crack, and the symptoms were intermittent. I finally found it in a service bay of a friendly gas station at night while on a trip with a girl friend, and duct tape solved things just fine until I could order a new boot. Sometimes the crack was closed enough that the engine would run, other times it opened enough to cause misfires and off and on again running. Also, if the boot was removed for some reason, it is easy enough when putting it back on for one or the other round seat parts to not be seated in a full circle.

If your fuel pressure numbers are within a normal range, you will know to look elsewhere for the starting issues.

[boyt911sc]

Walt,

How many times did the OP declared VICTORY. Problem solved and within hours came back with the same problem. An AFR is a good tool to have but if you have unmetered air going into the system, it won’t be effective. You have to test and confirm for the absence of unmetered air source/s. At this point, I don’t believe the OP has demonstrated it. Wrapping the air box with plastic bag while installed on the engine is a big joke.

Tony

[hughc]

Well, it's been a month since we last discussed my woes so I think it's time for an update.
I took the vehicle to my favorite shop and they assured me there were no air leaks.
The connection was made to the FV but not to the AF sensor as that would immediately cause the engine to quit. So now the FP comes on when I turn the key on but from what I can figure, that really isn't much of a concern. I can deal with that when I next drop the engine. Immediately after leaving the garage I took off on a 500 mi trip, and the car ran quite nicely. We did run into heavy rain, to the point where all traffic pulled aside for 15 min or so, then we carried on. I arrived at my destination at parked the vehicle and didn't attempt to start it until next morning when I was ready to leave.
Well it refused to start but it was turning over quite nicely. Looking under the engine bonnet but not knowing what I was looking for, I changed the CDI unit ( I carry a good spare) and I replaced the distributor cap and rotor, still wouldn't start. There was a lot of moisture around the coil cap (from the previous day) so I dried that as much as possible, still no luck.
Finally after about three hrs it sputtered to a start and I was on my way. It ran great all the way home.
Even though the car ran great i was concerned that the A/F ratio was running somewhat richer than what I was accustomed to seeing, suspecting that maybe it was running a little richer than usual, but I'll have to drive more highway miles to get get a better indication that my mileage has in fact dropped.
So at this point I'd like to mention a few concerns that I have which make me think everything isn't at 100% yet
1- Most mornings it takes several attempts before the engine will start, but it does eventually start, roughly, and idles at 1200 to 1400 rpm. It never behaved that way previously.
2- After a long ride, with engine well warmed, the car idles well (maybe a little low) but if I pay close attention I notice the A/F ratio dropping to as low as 12 and at the same time the rpm goes uo a couple of hundred rpm.
Maybe #2 is related to #1 and in my inexperienced opinion there might be a problem with fuel mixture even though the fuel distributor has neve been tampered with.
Do the experienced minds suspect that the engine is running a little rich. This is really not something I want to tamper with but I will if necessary.
I should mention I've checked the fuel pressures and they are within specs and I also checked the AAV and it seems to be doing what it's supposed to.
I think I've covered everything.

So, what next?

Thomas, thank you for the heads up on those links. Very informative.
hughc

[boyt911sc]

Hugh,

The package you sent to me arrived to my house while I was in Europe vacationing with my family. I told you that the package must not arrived before August 1 because there was nobody to receive it and you agreed. The package arrived several days before August 1. Glad my neighbor noticed the package and took it for safekeeping. The package contained the following:

WUR-090
CSV
TTS
6 fuel injectors (new)
6 fuel injectors (old)

First Test:
WUR-090 #145..........failed the test. The CCP is too low (11 psi.) @ room temp. and the bi-metallic spring is not deflecting. Did you try to tinker the WUR before you sent it to me? This could be the culprit causing your problem. There is a clear indication that the WUR was tampered by someone.

Tony

[AndrewCologne]

Originally Posted by Walt Fricke

Having the FV system working properly is a good thing, especially for fuel mileage and emissions.

However, the FV system is not controlled by the O2 sensor under two conditions: Idle and a bit above, and at wide open throttle. There is a pair of switches on the right side (as you look at it from behind) of the throttle body. They tell the "ecu" which of three conditions the throttle is in: idle, part, full open. At idle and WOT the ECU sets the FV at a 50% rate,

No señor, at idle and engine operating temps the lambda control works as it should, if initial CO is set up correctly the duty cycle swings at idle at approx. 55% +/-5%.
The only states where the control is off at all loads/modes ist at engine oil temps < 15°C and at acceleration with throttle open > 35° and there the duty cycle is not at 50% but at 65% for enrichment. The only state where 50% duty cycle is give is when the sensor plug is disconnected like in case of CO measuring.

[hughc]

Originally Posted by boyt911sc

Hugh,

The package you sent to me arrived to my house while I was in Europe vacationing with my family. I told you that the package must not arrived before August 1 because there was nobody to receive it and you agreed. The package arrived several days before August 1. Glad my neighbor noticed the package and took it for safekeeping. The package contained the following:

WUR-090
CSV
TTS
6 fuel injectors (new)
6 fuel injectors (old)

First Test:
WUR-090 #145..........failed the test. The CCP is too low (11 psi.) @ room temp. and the bi-metallic spring is not deflecting. Did you try to tinker the WUR before you sent it to me? This could be the culprit causing your problem. There is a clear indication that the WUR was tampered by someone.

Tony

Tony, I think I replied to your queries by email and I only just now realized you had posted here on the forum.
I was told by the delivery Co that the parcel should arrive by Aug 1 so I apologize if it arrived earlier At least you were wise to make arrangements with your neighbor to pick up all parcels delivered before your arrival.
As I explained in my email I did try to make an adjustment to the WUR by messing with the adjustment screw. I no doubt was a little heavy handed and ended up screwing thing up worst than they were.
But now I am confident the WUR is in capable hands and if for some reason you are unable to save it then I'll pay for a good replacement.
Thank you.

[ahh911]

hughc,

That sucks, it's hard to break a bi-metal strip of that thickness, I don't think the adjustment screw even touches it.

Did you re-install in upside down? Maybe someone before you?

Tony, how do you break such a thing?

Phil