Another CIS Start then Dies Question (fixed: bad Rev Limiter)
 

(Note: if you come upon this thread as you try to repair YOUR SC, be advised that the repair I first affected proved to be both WRONG and DAMAGED my car's wiring. This occured due to my incomplete understanding of the fuel pump relay circuits operation. Responses on Page 2 from Timmy2 and boyt911sc will explain where I went wrong.)

Good Evening,

This is the first time I've had a CIS issue with my 82 SC. 190K miles, I've had since 2014, bought with engine apart, I rebuilt it. I left the CIS alone and it's been perfection in the 10K miles I've put on it. Was always pro-maintained by original owner. I'm one of those people who enthuse about CIS, but clearly I'm having a hard time grasping the electrical side.

Issue: I started car this morning, moved it out of garage. It did sound odd; I wondered if my a/c belt was noisy (has been before), so at idle I spritzed a tiny diagnostic burst of WD on the belt, didn't change the noise, so I turned off the engine to have a think; this noise may or may not be relevant. Shortly thereafter, I went to restart it and it would crank, catch beautifully, then die within a second. I have since read my Bentley manual, read lots of posts here and generally tried to figure it out.

I believe the main observation is this:
With the air-filter cover off and ignition on, lifting the air-meter arm does NOT cause the fuel pump to come on.
But jumping 87a and 30 DOES switch the pump on, and it sounds fine.
- I switched relays with horn and another spare German red relay; no change.
- I DO have 12V present on the relay socket at 87a and 86 with ignition ON.
- the ground path on 85 seems good.

I also have checked fuse cleanliness, terminal tightness of fuse panel hardware etc. The female connectors in the FP relay socket look good. Car does have fuel in the tank. Wiring at the starter looks good. The pop-off valve is sound and the big boot connecting CIS to the throttle is tight. BTW, I run the car without O2 sensor being plugged-in....When I first set it up after the engine rebuild, it was happier that way. The control unit and relay are still under the right seat and are dry.

I am not a high-level electrical guy but it seems that something in the circuitry for the fuel pump relay is causing a lack of 12V to the fuel pump in what should be the RUN position.

I see that "RPM Limiter" device in the wiring diagram. Could that be interrupting the electrical flow?

Throughout all this, with the FP Relay in, I can try starting the car and it will catch, hit 1200 RPM then die within a second or two. I am not holding the key in the Start position when I do this. The car was perfectly OK until this. Recent work included suspension refresh and installation of SSI's but I've put three hundred perfect miles on since those were completed.

Is this the "RPM Limiter?" I found it near the left hood hinge:

http://forums.pelicanparts.com/uploa...1557613744.jpg

http://forums.pelicanparts.com/uploa...1557613773.jpg

Any thoughts as to what I'm missing or should be doing will be appreciated.

Thanks, John/Connecticut

John, does it stay running when the relay is jump red or bypassed?


Sent from my iPad using Tapatalk

The fact the pump does not run when the intake plunger is lifted makes me think the ground circuit is not being broken and thus the relay does not switch back to connect 87a with 30.

Remove the relay and connect one lead of a test light to a known hot, and the other lead to the socket #85. The light should illuminate indicating that #85 is grounded. Lift the plunger in the intake. Does the light go out? If not, there is a short to ground somewhere along the wire or the switch in the intake is bad. If it does go out, the circuit is good and you have eliminated one possible trouble area.

If it does go out, replace the relay. With ignition ON, slowly lift and let fall the intake plunger. Does the relay click each time it is lifted and again when it comes to rest? If so, normal. If not, and relay is known to be good, you have an issue with the 12v circuit which may be the rev limiter.

Thanks very much Carl and Ossi. I’ll get back on it in the morning and report back. John

Carl....YES.....that makes it run and stay running.
Will proceed as per Ossi next and report back.
Progress! Thanks much

85 circuit tests good

Ok... If after starting the airflow plate returns to the rest position that would tell the relay to shut off power to the fuel pump. As it should. This could be indicative of a large air leak.

http://forums.pelicanparts.com/porsche-911-technical-forum/828834-cis-rebuild-wont-stay-running.html

Did your car recently experienced a back fire?


Sent from my iPad using Tapatalk

One thing you could try, it would require someone to be in the drivers seat and try to start the car while you are in the back and manually raise the airflow sensor plate just a little. If it now stays running I would say that the possibility of an air leak is pretty good. If not... then back to an electrical problem.


Sent from my iPad using Tapatalk

Runs perfect with relay removed and 30 > 87a jumped. No backfire history. Starts (as normal): immediately, proper fast idle etc. I think it’s electrical. (Feeling rather silly for not checking this yesterday.)
Remembered that I’d bought Rob Siegel’s “European Automotive Electrical Systems” book, so just did the complete tests he describes for relays on both my (German) Wherle relays...both test to spec.
Is the cubic black relay I posted above the Rev Limiter? I’ll go do some searching for images of it. I see another one back near the gauges, but oblong (like the size of two square relays joined end to end) but looking at the colors of the wires going to its connector, I’m thinking that’s the seatbelt buzzer.
Thanks all for help thus far.

BTW just found great thread started by HughC and answered by MSalvetti, showing a photo of the Rev Limiter. Will head in there now to hopefully pull the connector and re-test.
In this thread, there was also the reminder from Tony to spread the relay pins with a razor blade. Just did that - had cleaned the posts early on) and it did not fix it.

jj..have you ever tried to unplug the bosh connector behind the sensor plate.It is a safety device ,it will cut the fuel pump off if it is kaput -broken grounded..simulating car is on the roof....
this one
Ivan
http://img.pccreation.net/photos/20190512175413551.JPG

Mark Salvetti and I now share SC’s with unplugged and bypassed Rev Limiter units. That fixed it. Jumped Red and Red/Brown (unit and connector are shown in Bentley). I may look for a replacement or just take the unit out for inspection. Worth noting my car had an electric fire in the OO’s ownership with the main fuse panel and some/all of the frunk wiring harness replaced...there’s still some yellow extinguisher dust/nastiness back in there.... a corrosive, right? Maybe that took its toll on the unit. But for now I have a running SC; yesterday was a glorious Spring day but today it’s pouring. No complaints. Major thanks gentlemen. John

so did you or did you not checked the plug??
Ivan

Ivan....no didn’t check that. Would it make the Rev Limiter look bad, even if it wasn’t? Thanks

for the future if have a problem and do all the checking on relays ..check this plug first;-)

THIS....
I believe the main observation is this:
With the air-filter cover off and ignition on, lifting the air-meter arm does NOT cause the fuel pump to come on."

If you would have disconnect the plug the fuel pump will run with the key on...

Ivan

Please share your test.........
 

John,

How did you perform the test for terminal #85 (FP relay socket) with the ignition switch @ON position? Thanks.

Tony

Hi Tony!
Today I tested that the way Ossi suggested using a test lamp. Yesterday I did the same but using an ohmmeter, as per Bentley, with one lead attached to a ground and the other to socket 85, and lifting the air flow arm opens the circuit. Thanks, John

I'll look at the wiring diagram for how that switch is tied into the circuit, which I now understand (a bit) better. Thanks.

Fuel Pump Relay and socket..........
 

John,

When you get chance, search for DKLever48’s post about FP relay and socket tests. The thread discussed how the 5 terminals are tested and identified for operation. Everything you need to know is well covered in the thread.

BTW, terminal #85 (ground) has several sources for ground contact:

a). AFS (air flow sensor) switch. This is normally closed and opens up once the engine starts to run and produce vacuum/suction causing the ground contact to open wide.

b). Rev limiter. This is normally open and have no ground contact until the tachometer sends signal to the rev limiter to close or make ground contact. Thus causing the FP stop running.

c). Car immobilizer (alarm). If the alarm system is triggered, the brown/red (terminal #85) will be grounded.

Tony

Tony, will do, but it'll be a week or so.

If of interest, here are pics of the Rev Limiter connector and page from Bentley:

http://forums.pelicanparts.com/uploa...1557698337.jpg
http://forums.pelicanparts.com/uploa...1557698433.jpg
http://forums.pelicanparts.com/uploa...1557698460.jpg