'83 944 no spark, no start

Nitromike54 · 08-03-2021, 01:44 PM

This car was brought to us after being in storage for about 20 years. First I pulled the DME relay and jumped the 30 socket, the fuel pump and the fuel injection power supply sockets, numbers 2,4 and 8 at the relay socket. I have power at the fuel pump and the injector positive wire. With the key on I have 12v on either side of the coil. No coil triggering or spark, no injector pulse.
Checking the reference and speed sensors at the computer plug I get 930 ohms resistance on both. On cranking the reference sensor shows 1.3-1.5volts. Checking the speed sensor the same way I get 1.5-1.7 volts. Both sensors are new.
Coil and fuel pump are both new.
The computer- pins 18 and 35 are hot from the dme relay
pins 16, 17 and 19 are grounds, all good
pins 25 and 26 for the ref sensor show continuity when jumped and 930 ohms with the sensor. Same for the speed sensor at pins 8 and 27.
I have an original looking computer and a recently (2020) rebuilt computer. Neither seems to work.
Is there anything else this computer needs to work? My understanding is/was that 12v and ground and the crank sensor inputs was what the computer needed to operate. Any and all help greatly appreciated.

drew1 · 07:21 PM

Heat at computer pins may come from loose connection or bad ground.Check grounds real good. Clean connections with contact cleaner and make sure they are in good shape.

Undo speed and reference sensor bracket and clean any trash shavings, etc off of sensing face. Do not remove sensors individually from bracket. This will require resetting the gaps.
(Look at this real good to make sure this old man is not confused. before taking bracket loose. There should be not adjustment for it and adjustment should be in sensors threaded body. )

From memory it should crank with airflow meter unplugged, but cut off imediately, but I would check this connection, too.

Did you use a noid light or a meter to see if injectors are pulsing?

Is the other coil terminal not hot side, but the one to 1 on the computer pulse when cranking?

Seems like I was fooling with one years ago that had an alarm that kept it from cranking.

OK-944 · 08-05-2021, 01:35 PM

If the car has been sitting for 20 years there is a good chance that the alarm was never disabled/jumpered, but simply re-set after battery changes.

I solved my own recent no-start by following the alarm jump procedure outlined by Clarks Garage. Very easy and only takes a few minutes. Will need to fabricate jumper wires (I used 16 gauge with spade connectors). Easy!

drew1 · 08-11-2021, 02:52 PM

From a buddy that works on German cars I learned I was wrong on sensor bracket it is slotted and the whole thing moves.

Chalt · 08-11-2021, 04:57 PM

To disable the alarm:

Go to: Clark's Garage Home Page
Click Garage Shop Manual > Click Alarm System Bypassing (under Electrical)

Here are the Jumpers you need to do:

Chalt · 08-11-2021, 05:05 PM

If the speed and reference sensors work and your DME works, you should get spark. There is no way I am aware of to test the DME (ECU) other than swapping it for a known working one.

Are the new speed and reference sensors Bosch brand or OEM Porsche? I have heard others on the forums had problems with some other brands, mainlly with FAE.

drew1 · 08-16-2021, 06:36 AM

I reread your opening post and notice the car has been sitting for 20 years. The strainer on the line going to the gas tank might be gummed up. Spray some ether starting fluid into the intake manifold through the open throttle body and try to crank it. If it starts and dies, fuel is not getting to the injectors. I also noticed no new fuel filter.

Spring44 · Spring44's Garage

I think that Drew is correct. I revived my '84 after a 7 year storage and tried to start it by only adding gas. The sump on the bottom of the tank was completely filled with gasoline varnish , large amounts of iron oxide sediments and about a quart of a heavy, viscous tar-like substance that would barely flow at all. The fuel pump was locked up on this trash too, as was the fuel filter from my initial attempt to start it.

I tried to clean and flush the tank with solvents via the filter screen hole, but was unsuccessful. Ended up sending the tank out to be professionally cleaned, blasted, coated inside and out and pressure tested by Gas Tank ReNU. Replaced the fuel pump, filter and had the injectors cleaned and flow tested. No problems in 3 years now. FI systems love clean fuel!

Yeah, I know that this requires that you drop the transaxle, but no one ever said life was fair. Sometimes the longer path is the shorter path.