I have an 83 928S that stopped running some 16 yrs back, the vehicle stopped running as I was pulling into the garage , I disconnected the battery and let it sit for 16 yrs , I recently put a battery in it and began
looking for the cause of a the fuel pump failure , the vehicle at that time would not start , however a few drops of gas spread over the air filter and it started instantly , amazingly 16 yrs later , it did the very same
thing , I replaced the fuel pump and fuel filter , cleared out the fuel rails and verified pressure at 2.0 bar , I checked the injectors and found current with ignition on ,however when cranking there was NO pulse
at the injectors (none of them) , I placed fuel into the filter housing and cranked the engine ,it started idled to perfection for about 15 sec. then shut off , I replaced the fuel pump relay , the fuel injector relay , and
rechecked , this made NO difference , I then began the task of checking the wiring which appeared to be in good shape, no excessive corrosion , minor build up at some areas mostly grounds , after cleaning them I retired
and again NO GO, I then pulled the LH Jetronic and verified the pins which were supposed to have 12v did actually have it . I then replaced the LH Jetronic , followed by a second LH Jetronic ( Purchased two units both used)
and BOTH changes yielded any success. the engine will start instantly with fuel manually added , the "Injectors are NOT functional , and I'm fresh out of Idea's , anyone have a Clue or ever have a problem like this ??????
would love to know what is causing failure !! Note :I also changed O2 sensor - black lead was broken , but according to porsche the motor will run with the O2 sensor completely disconnected , it will effect the CO output not the injectors, any replies can be sent to Ptc @optonline.net

 

A minor note on terminology: the 83 US cars are L-Jet. the LH didn't come out till 84 in the Euro and 85 in the US.
I have seen cars that sat for much less than that amount of time have all the injectors stick closed from old fuel. Before I declared the system inoperable, I would test to see if you are getting an injector pulse using a noid light.

 

+928
A noid light will tell you that the electrical circuit is functional, it will not tell you that no fuel is passing from the injector into the engine cylinder.

 

Maybe green wire? I am not sure about the 83 but someone else may chime in on it. but then again you said it started with dumping fuel so that's probably fine.

 

After sitting that long the injectors may be frozen. I would suggest ultrasonic cleaning or sending them out to be cleaned.

Good luck, I know what you are going through.

Stan

 

before you touch the injectors I would suggest that you perform a function test first,
get a 9 volt battery solder two wires to the battery connectors then touch the wires to the injectors ,
OR get a 2 pin AMP connector and solder it to the battery, then plug it into the injector.

NOTE see if the injector clicks,
any injector thats not clicking is stuck, adding PB blaster to an inlet can sometimes free them up
At this point you may need to get a new set or send them off to be cleaned
NOTE use your same 9 volt testing rig to make sure the cleaned injectors are working prior to installing them,
add some PB blaster to each injector this can help to prevent them sticking from the cleaning fluid dryout.

NOTE you can use a 194 bulb plugged into the injector harness connector, to see if its getting power

 

Assuming that you are still battling the very same cause of the car not restarting 16 years ago, it’s probably not stuck fuel injectors that killed the car. A fuel injector can be stuck or clogged - but all eight (8) at the same instance? Unlikely. That being said 16 years is a very long time so clean them.

Do you have any tach bounce while cranking the engine? If not that points to the CPS - crankshaft position sensor.

If any of the wiring in your injection harness is damaged that would cause all of the injectors to not fire.

 

83 doesn't have a CPS it uses the hall sensor inside of the distributor. Hence the importance of a fresh green wire!

 

If the fault was with the ignition system it wouldn't run with the fuel poured into the intake. This is a fuel delivery problem.

I agree the injectors could be an issue now, but all 8 failing 16 years ago causing the car to die is very unlikely.

This car also has 9 fuel injectors, important for diagnosing a no-start situation. If the 9th injector was firing, it would initially fire, then die. Like maybe one or two burbles of combustion.

Let's break down the fueling system of an L-Jet

1. Temp II sensor (first photo) this one sits vertical on top of the coolant bridge.
This sensor controls the pulse width of the injectors. If this sensor is disconnected, broken etc... the car will not run at all. The injectors will NOT fire.

There is a very easy way to test this sensor with a multi-meter. First off see if there is any resistance across the two posts. If not, there's your problem. If there is resistance, do the same check on the ECU side of the harness for those pins. If no resistance there (but there is at the sensor) you have a wiring issue.

As the engine temperature increases, the resistance goes down which dials back the fuel (richer needed for cold starting / running).
12 k-ohms when cool (14-67 F),
3 k-ohms when warm (68-175 F)
400 ohms when hot (176+ F)

Side Note - many L-Jet 928's have a resistor soldered into this circuit to richen the mixture because for some reason these sensors tend to be on the lean side when fully warmed up.

2. Temperature Time Switch (Second Photo)
This switch operates the 9th injector for a set amount of time (few seconds at most) during cranking. Just enough to fire off the engine then the other 8 injectors take over. The fact that your car doesn't fire at all says this injector isn't operating either.
I'm rusty on this part of the formula, but I think if the Temp II switch is faulty or disconnected, the 9th injector doesn't fire either. I would test this on my car right now but I just drove it and it's still warm. The 9th injector is really only needed on a cold engine. In fact, I think it only fires if the engine is below X degrees.
Tomorrow morning I'll test this.

3. AFM or "Barn Door" which is under the air filter box. The engine "should" run with this disconnected but in a limp home kind of a state. Your car has been sitting so long this scenario is tricky. Try disconnecting the AFM and crank it over while giving it some pedal. Another test with the AFM connected is have someone manually work the "barn door" as you crank the engine. There may be a dead spot in the meter. I doubt this is really the issue that caused it to suddenly die years ago, but it's a possibility.

4. L-Jetronic brain. These rarely fail and you've tested more than one. When these do fail typically the engine will run, but you'll notice odd running issues like surging. If memory serves me, the Temperature Time Switch and 9th injector run independently from the L-Jet brain, so again, if that injector were working as designed it would fire but then die as that fuel runs out (just like how it runs when you add gas).

5. The ignition box (what the green wire plugs into). This is located on the inside of the passenger fender. Directly below the 12V battery post.
These boxes rarely fail and when they do it's typically like the L-Jet brains having an issue, random running problems.
I don't think I've ever heard of one of these failing in such a way to prevent the injectors from firing but the ignition system still functions just fine. The L-Jet is only getting a tach pulse from this box (which is also feeding the tach, hence the questions above about the tach bouncing).



Temp II Sensor

 

your right is is an L jetronic , and no your wrong , I puled the rails and confirmed gas is sprayed from injectors , using a 9v battery to energize the injectors one at a time they work perfectly when being manually operated

 

thanks I did use noid light , got a steady 12v light no pluse at all

 

But they don't fire on their own without the 9V battery, correct?

 

tach runs smoothly at 500 rpm engine idles remarkably well considering the length of time it has sat , I will Check CSPS , I am getting power to ea. Injector , minus
any required Pulse , I did pull the rails and injectors , and observe them opening and spraying , and yes I did Spray clean them out just to make sure they were
free of debris and old gas that tends to varnish the surfaces . will check the crankshaft position sensor and get back to you

 

Your car doesn't have a crankshaft position sensor.
The function of the crank sensor is handled by the green wire coming out of the distributor, which also tells the distributor when to fire. If this part of the car wasn't functioning at all, the car wouldn't have any spark and wouldn't run with the fuel you add to the intake.

So it is running and idling at 500rpm? Or is that only with the raw gas you are physically adding to the intake?

 

o did replace the Green Wire from the distributor , to the fender wall just above the ECU for the Ign. The O2 sensor was also replaced
it did have a broken black wire , under the vehicle , it was replaced , the "green Wire " it connects to inside the electrical compartment
under the foot rest passenger side appeared cracked , it looks like a cigarette lighter plug the white wires were good , Question?? this Green Wire inside the Car ,is it the same
Green wire connected to the distributor Green Wire ?? 83 Manual says the O2 sensor can be disconnected completely during service
Procedures for calibrating CO Emissions , the Motor will run ,with elevated CO . , point is the car will still start with the O2 Disconnected
making that another underlying issue ( the Cracked Hall effect Connector) but sill leaves the Main question: what is causing the Fuel injectors
to "ALL" Fail ???