No Start Voltage Question
 

Hello All;

Continuing to work on my NO Start Problem. At my last repair attempt session I noticed that with the key in the "On" position, my voltage at position 30 of the fuel injection relay drops to 11.89v. With the ignition in the "OFF" position I have a reading of 12.19v at position 30. Could this be the reason the fuel injectors will not fire? Do they need the full 12v to operate in the "On" position. I also noticed that with the key in the "On" position the headlight switch lights up. Is this normal, I can't remember since its been so long since the car has been running. Could this possibly cause the voltage drop that prevents the injectors from activating? (BTW all of the light work just fine and the ignition switch is new).

I also have 12.19v at one side of each of the fuel injector connectors and 10.41v on the opposite pin of each connector (both check to ground). Is this correct?

My car is a 1983S.

Thank for the input!

Battery voltage is good.
The voltage across the injectors with key on but not running is normal, one side of all injectors is wired to the 12v line via the relay XVI. The other side goes to the control unit, and the circuits in that are holding the injectors off from firing, which is correct when not running.
Give us a list of what you have done so far and we can suggest what next.
BTW, headlight switch on when key on is NOT normal.

http://forums.pelicanparts.com/uploa...1309367140.jpg

Thanks Neil;

I knew that the light should not be on so I will definitely check into this.

A littile back ground on my problem, Last June I took the car on a 350+ mile trip to Michigan with no problems. Ran fine. About a week before it shut down it became a little hard to start but was not a big problem. On my next trip it was hard to start but I decided to drive it on a 180 mile trip anyway. About 90 miles in it just shut off like some one turned off the key. Put in new relays on the road but to go. Has not started since except for puffs of the cold start valve. Fuel pressure is 35+ at the fuel rail and I have spark and what seem like a rotational signal though I have not checked with an ocilliscope. I have done a bunch of things to get this problem resloved:

Parts Replaced;
New Ignition switch
New Green Wire
Temp sensor II
Temp Time Sensor
New Coil
New relays, both fuel injection and fuel pump
L-Jet
TSZ Box
Plugs
AFC
Battery ground strap

I have Checked:
Cleaned all gounds
All relays and fuses
Cleaned 14pin connector
Checked for vaccum leaks
All ignition test in the WSM
All pin and ohm test on L-jet connector
Removed and checked the central electrical panel
Disrtibutor
Timing belt

Battery was replaced about 1.5 yrs ago and reads 12.39v without a charge on it and was reading 13+ volts when car was running at the jump post. Cap and rotor about the same age.

I have scanned the electrical layout but nothing has worked so far so I thought fresh input may help!

Thanks

TonyD.

Tony, few more questions.....
Will it fire and run briefly if :
1)You give it as shot of starter fluid?
2)Unplug the air flow sensor - does it try to start then?
3)Unplug the throttle valve no load switch?

What do you mean by rotational signal?

Good Questions Neil
I thought right away of the Fuel Pressure Regulators for some reason. Electrical is always high on the list with Porsche
Had a Pressure Regulator go on the Hi Way on a 944 and it just stopped cold like the Key was turned off.

Thanks Guys;

Neil - Rotational signal is the signal from the distributor thru the green wire to the TSZ to the L-jet. Checked at the CEP with an analog voltmeter.

Good info aluminum, I'm gonna order a new pressure regulator and try that since I have checked and rechecked the electrics. Can't hurt! At least that will be new too!

Tony D.

Sorry Neil;

I try your suggestions today and report back! I did check these out with the meter and they check OK but won't hurt to try!

Tony, did you find both of the computer/sensor ground points on the pass. cam cover?
One is hidden by the emissions valve on USA cars.

Yea, cleaned both of these and checked for ground on the L-jet plug. Grounds are good.

Thanks Landseer!

Tony, I don't think its a fuel pressure problem.

Rotational signal from pin 16 on the ECU up front goes off to the rev counter ( does it bounce when you try to start?) AND to the fuel pump relay ( XVII pin 31b) AND to the L Jet controller via W6 to pin 1 on the L controller to provide ignition timing. If it is missing at pin 1 it won't trigger the injectors. Do you hear them ticking when you try to start? Power during starting comes in on pin 4. Is it present?

Thanks Neil, I will check this again.