Car was running and just died!?!?

PorscheLandRovr · 06-21-2002, 01:28 PM

I have and 1981 911SC Targa and was driving to work and it just shut off. When I go to restart it, it will fire and give about half a rev and shut off. I thought it may be the ignition coil because the old one had a little bit of fluid leaking out of it. So I replaced it with no luck. Now I am leaning towards the fuel pump. The fuel pump in my car is very loud, but I can't remember if I ever heard it whining with just the ignition on. With the ignition switch on now, there is no fuel pump whine. I'm not even sure where the fuel pump is located. Has anyone ever had this kind of problem? I don't want to take the car to a Porsche shop unless I have too. I am pretty good with cars and have driven this one for 2 years with little trouble. Any help with this would be greatly apreciated.

Thanks!!

Wes

emcon5 · emcon5's Garage

On an 81, if the wiring is intact, the fuel pump will only come on when either the starter is engaged, or airbox sensor plate is raised, indicating the engine is running.

A quick and dirty test to see if the fuel pump works is to turn the ignition on and briefly raise the sensor plate. You should be able to hear the pump kick on. On an 81 you should also hear the frequency valve buzz.

Just out of curiosity, do your dome lights work? The Lamda system is on the same fuse as the dome lights, and if the fuse blows, it will run poorly, and may be hard to start.

Do you have the stock Bosch CD box? Does it whine when the ignition is on?

Have you checked to see if it is getting spark?

Tom

PorscheLandRovr · 06-21-2002, 01:59 PM

I will give that a try! Thanks. Where is the fuel pump located?

pbs911 · pbs911's Garage

The fuel pump is located under the gas tank. To access the fuel pump you have to remove the cover under the front of the car - 4 bolts.

My car this same thing twice, well three times.
1) The fuel pump relay worked its way loose.
2) The fuel pump went out.
3) The PO had installed a hidden fuel pump cut off switch that went bad. If I had not remembered seeing a funy switch when I R&R'ed the carpet a week before I would have never found it.

Other possibilities are the fuel pump cuts out when it gets too hot or the fuel filter is clogged. My guess is the pump itself or relay.

Early_S_Man · 06-21-2002, 02:14 PM

The #16 fuse, Red fuel pump relay, and alarm control unit (if equipped with the factory alarm) are all suspect!

The following threads have a colored schematic, and relate to a car with identical symptoms. A jumper from pins #30 to #87a of the relay socket will verify that it is a relay problem ... but not necessarily a bad relay ...

Fuel pump electrical problem

'82 SC Won't run

PorscheLandRovr · 06-23-2002, 09:04 AM

Well Guys,

I have jumpered out the fuel pump relay and the car starts and runs great. But the problem is not the fuel pump relay. I swapped it out with the horn relay and it didn't work. I am leaning towards the Factory alarm system. I don't have the key for this system(the one that goes in the door). I was reading a previous post about this same problem(User CMXI-SC) and he jumpered out the alarm module.

Can someone tell me exactly where the alarm module is and how to permanantly jumper it out? I have no Idea where this module is and I can't find any documentation on it. I don't have a factory manual. If I can get to the modual and jumper it out, I would like to just permanantly get rid of the thing. Any thoughts on this idea of scraping the alarm system?

This board is the best thing going for people like myself. Thanks for all the help and hopfully I will be driving again soon!!!

Kevin Stewart · 06-23-2002, 09:08 AM

Im having a simular problem onse in a while the alarm will go off for no reason, please post if you find a way to permenatly dismantle it, Kevin

Early_S_Man · 06-23-2002, 12:41 PM

This is the ONE case I have found so far where the Bentley manual actually has more info than the factory service manual!

The module is beneath the fresh air blower and plenum ... you have to take out the carpet and lay in the trunk to get to it! To bypass the module it needs to be unplugged, and have a permanent jumper with two male 1/4" Faston (spade) connectors and a piece of Blue16 ga wire ... pushed into the socket for the alarm unit. Don't be sloppy or take shortcuts here ... the alternator pre-excitation current from the warning lamp is what was routed through the alarm unit, so if you create a fault that shows up later ... you might replace a Voltage regulator or alternator needlessly!

There is a slight discrepancy in the Bentley manual between the schematic and the module pinout ... but the two #61 wires are what need to be jumpered!

Here is what the module looks like ... module pinout ... schematic ... good luck!

PorscheLandRovr · 06-29-2002, 07:57 AM

Well, It's been a few days since I have had a chance to work on the problem. Today I got to the alarm module and jumpered out terminal 61 to 61a. This had no effect. The car still has the exact same problem. I tried this with just the large Black plug removed from the alarm module and also with the smaller white plug removed. Both ways had no effect. I am not sure where to go now. The only thing that seems to work is jumpering out the fuel pump relay. I guess it would be a bad thing to leave it like that huh? Doe anyone have any ideas what I should check next? Should I just leave the alarm module unhooked and jumpered anyway? If I should leave it unhooked, does that mean both plugs? Thanks for all the help guys!!! And Warren... you are the MAN!!

Wes

Early_S_Man · 06-29-2002, 10:22 AM

Wes,

As the following schematic shows, the only two other possibilities for a device fault causing the fuel pump relay to be operated are the Rev Limiter and a faulty Airflow Sensor.

You may want to disconnect the Rev Limiter and see if that is the source of the problem.

Kevin Stewart · 06-30-2002, 09:02 AM

Did you find the problem, Kevin

PorscheLandRovr · 07-01-2002, 10:06 AM

Well Guys,

I haven't had time to work on the problem since I jumpered the Alarm Module. I took some Pictures the exposed Alarm Module but they are too big to load on here. While I was behind the Fresh Air Blower, I discovered a Black module on the drivers side that had a small white round plug on it that was unpluged. this module is an odd shaped, kinda a square black thing with a Silver tube looking thing on the back side of it. The Small round white plug goes under the silver thing. Did you get that?!?!

Anyway, when I pluged it in, it made no difference. Does anyone have any Idea what it might be?

Do you think I should leave both plugs on the Alarm Module unplugged and the Black Plug jumpered? I will try and find the Rev limiter and the Air Flow Sensor soon. Hopefully they are listed in the Haynes Manual. Thanks again for all the Help.

Wes

Kevin Stewart · 07-01-2002, 10:14 AM

we have the exact same problem as do a couple other people on the board i also unpluged the alarm was ok at first know this craps starting, although i did have some work done at a shop and they were did pretty messy work so i took the blower fan off the motor and was in that general area when it started again i was also bumping around the cd box under the seat so i am convinced its a bad connection, did you try the distributor wire replacement, i havent, my bee worth a shot, hopefully july 4th i can get back to it, this is a year and a half and just recently its not restarting for awhile, either the problems gotta get cured or the cars gotta go, ive been looking at a boxter, would rather keep the 911, but if its just gonna set because i cant trust i would rather get rid of it, keep in touch ill tell you if i find any thing, Kevin

TR89-911 · 07-01-2002, 09:18 PM

Long time reader, first time writer.

I am not sure if this will help, and I have no technical knowledge of my 911, just a large pile of receipts that detail the solutions to my woes.

My 89 developed a nasty habit of dying while driving that made it impossible to drive confidently any distance from home. I could not get the car to repeat the behavior for the fellow who works on my car. However, as it consistently died at the most inconvenient times, with the girlfriend or during rush hour, I was committed to solving the problem. I figured it would probably die on the test drive if I tried to sell it, so I had to fix it.

To make a long story longer, it started to drive very well, and when a problem magically disappears on this car I start setting aside money because I know something is coming. So the car had stopped stalling out until I found myself in a rain storm during which it died 6 times in about a one mile stretch. (It would take about 45 seconds for the car to be willing to fire up again.) I think that the moisture was a large part of the overall problem. With fresh clues to the problem I took the car in to the shop where they tried for three days to replicate the problem. Finally they got it to die for them. The following is the description of the work done to repair the problem.

Repaired the "FUEL INJECTION RELAY, WHICH IS A PART OF THE DME RELAY. RELAY HAD THREE SOLDER JOINTS THAT WERE CRACKED. REMOVED RELAY AND SOLDERED JOINTS AND CHECKED OTHERS." He also replaced the distributor cap, the ignition rotor, and the spark plugs.

He told me that there were two relays(?) and that until he discovered the second and checked both he was missing the problem. He said that the problem would likely have presented itself when there was too much moisture, or when the car was too warm. As I said above, I assume this makes sense as I have no technical knowledge of cars.

Anyway, this might prove useful. I struggled with this problem from February to June this year. It appears that everyting is running correctly, although I have not had the opportunity to drive the car in the rain to be certain.

Early_S_Man · 07-01-2002, 09:54 PM

Wes,

The procedure in Bentley for bypassing the alarm unit is paraphrased from the factory service manual, so there isn't a problem leaving it disconnected.

PorscheLandRovr · 07-02-2002, 04:43 AM

I actually had a little free time on my hands last night. I looked all over for the rev limiter switch but could not find it. Can anyone tell me where the rev limiter is located and what it looks like? And also, where is the air flow sensor? Thanks again!!

Wes

PorscheLandRovr · 07-03-2002, 06:54 AM

HooYah!!!

It looks like the Rev Limiter was the problem in this case. I have it unpluged and the car is running great. I left the alarm jumpered out. I never had the key to it anyway. If anyone has this kind of problem in the future. I would try unplugging the rev limiter first. Only because it is a lot easier than getting to the alarm module. Thanks for all the help guys!!! I know that your help probably saved me a small fortune!

Wes

Kevin Stewart · 07-03-2002, 08:49 AM

Ok so where is the rev limiter ill try anything, Kevin

rhaas · 07-03-2002, 10:00 AM

When my 76 was not starting consistantly, I found that the relay socket was worn out and not getting a good contact. Replaced the socket and was on my way. Havent had a problem with it since.

Early_S_Man · 07-03-2002, 11:21 AM

Wes,

Why don't you carefully take the cover off the rev limiter and take a few closeup shots of the front and back of the circuit board, and send them to me?

It will be interesting to note whether or not Bosch has made any improvements over the original '69 speed relay design, or not???