|Heres a few useful 84-89 carrera tidbits that others
sent me while going through my recent diagnosis.
No-start Diagnosis (84-89 Carrera)
1. Remove a spark plug wire and insert a test plug into the wire, place it next to the
engine, have someone crank the engine and look for a spark (or remove one of the plugs and
do the same). I didnt have a second person to crank the ignition, so I clamped vice
grips on my key, ran a wire from the end of the vice grips through the door handle (with
the door open). This allowed me to pull the wire and crank the ignition while standing at
the back of the car looking at the spark. Crude, but it works. You could, of course, get a
remote starting tool to achieve the same, and there are also special long coil wires
available that allow you to see the spark while sitting in the drivers seat (just a
long wire from the coil that has a spark plug socket on the end).
2. Remove the air cleaner cover and air filter, and spray some fuel into the intake.
You will have to hold open the little "door" inside there with something. If it
starts briefy then dies you probably have a fuel problem.
3. You can jumper a hot wire to the fuel pump and listen to it whir to prove that
its working. Run a short wire from the fuel pump fuse (#6) to an adjascent fuse (#5
or 7) at the bottom of the fuse terminal, the pump should whir. BTW my car didnt
have the fuse info on the fuse cover (I think the old one broke), so Jim Bauman gave me
his info from his 86 (#21 is closest to the front of the car):
- 1. window winder, seat heater, sun roof
- 2. booster fan, seat adjusters
- 3. headlamp washers, electric cabriolet top
- 4. clock, radio, interior lights
- 5. locking system
- 6. fuel pump
- 7. brake light, cruise control
- 8. electric mirror, heating control
- 9. fresh air blower, cig lighter, rear window defrost
- 10. wipers
- 11. rear blinkers, back up light
- 12. front left blinker
- 13. front right blinker
- 14. left high beam
- 15. right high beam
- 16. left dim
- 17. right dim
- 18. parking left
- 19. parking right
- 20. fog lamp switch, rear fog lamps
- 21. foglights
4. If the fuel pump whirs (when jumpered), try starting the car this way (this
overrides the DME control of the fuel pump). If it runs, it probably indicates some kind
of DME problem (the DME is not sending power to the fuel pump). If still doesnt run,
its probably not a DME problem. Thanks to Jim Bauman for sharing this tip.
5. If it is a DME problem, replace the DME relay, which sends power to the fuel pump.
This is another one of those parts that is known to be flaky. The relay is under the
drivers seat next to the DME computer. Its highly recommended to carry a spare
DME relay anyways (a $40 part), so go ahead and get an extra just in case.
6. If the relay doesnt fix it, it could be the DME computer itself, faulty
sensors (flysheel speed and position), or faulty grounds. Try disconnecting the DME
computer and cleaning the contacts.
7. Check all ground connections (brown wires) for corrosion. Disconnect them,
clean them, and replace. Check especially the ground points in the engine compartment.
Theres one on the manifold pipes, and another on the left side of the engine
compartment behind the fuel filter. There is another one on the bottom of the car around
8. Check all fuses for corrosion. Remove each fuse and replace. All DME-related
fuses are up front, but there are three fuses under the plastic cover at the left rear
side of the engine compartment.
9. If you have one available, swap in a known working DME computer from a 911 friend.
Be careful that you have the right production year and part number because there are
differences in the pin mappings.
11. If the DME is okay, you can listen to the injectors with a stethoscope, if they
click, then power is getting to the injectors.
12. At this point you probably want to have a shop check the fuel pressure and flow
rate in the system. This requires special tools. In my intermittent problem, this test
unveiled a faulty fuel pressure regulator ($75 part).
13. Finally, Chuck H sent me some detailed info on the DME system. I didnt get
this far (thankfully), but if you want to get down to the nitty gritty, heres the
DME connections. Note that NTC stands for Negative Temp Coefficeint sender (meaning as
temp goes up, resistance goes down).
- 1 coil ground (1)
- 2 micro switch (throttle, idle), closure to ground at idle position
- 3 micro switch (throttle, wot + throttle valve) test connection b,
closure to ground at wot
- 4 t54, starter active, +12 volts while cranking engine
- 5 gnd
- 6 gnd, air flow sensor, ntc I
- 7 air flow sensor +
- 8 speed sensor +
0.6 to 1.6 kohms between pins 8 and 27
- 9 air flow sensor -
- 10 plug for exhaust data (ground)
- 11 t54, speedo
- 12 test connection a
- 13 ntc II
1.4 to 3.6kohms at 70oF
160 to 210ohms at 212oF
- 14 t55, injector control signal
- 15 t55, injector control signal
- 16 gnd
- 17 gnd
- 18 +12v
- 19 gnd
- 20 control signal, dme relay
- 21 t54, goes to speedo
- 22 air flow sensor, ntc I +
- 23 .75ohm connection to pins 5, 25, 26, 8 & 27
- 24 oxygen sensor
- 25 ref mark sensor +
0.6 to 1.6 kohms between pins 25 and 26
- 26 ref mark sensor -
- 27 speed sensor -
- 28 altitude sensor
- 29 a/c compressor clutch on
- 33 idle speed positioner +
- 34 idle speed positioner -
- 35 +12v
pinout, looking at the DME connector, NOT the DME...
| 35 19 |
+--+ - - - - - - - - - - - - - - - - -+--+
| 18 1 |
Doug (87 Carrera Targa)
PS. I sincerely hope you are reading this out of interest (not necessity) and I suggest
that you get in that 911 and DRIVE!