911 3.2 No-Start Troubleshooting

[Lorenfb]

Simple tests to localize a 911 3.2 no-start problem:

1. Remove the coil wire from the distributor cap and place the end about 10mm
from the engine case.

2. Remove the #1 injector connector and insert a noid light, buy one at
AutoZone/Reillys or Pep Boys.

3. Have someone crank the engine while you monitor both the coil wire & noid light.

Tests results:

A. Both immediate spark and noid upon cranking then;
Both speed & ref sensors, powers/grounds O.K., and DME ECM O.K. - Check for fuel
pressure and/or spray carb cleaner into air filter and re-do steps 1-3 above.
Check distributor cap next. The temp sensor can be bypassed by jumping the
temp connector (white) with a paper clip, which simulates a warm engine.

B. If neither noid nor spark then; check sensors (1k ohms, speed > 1.0VAC,
ref >.10VAC), DME ECM powers (1/18/35) & grds (5/16/17), or DME relay

C. If noid but no spark then; DME ECM a problem, or power to coil from ignition
switch (if already replaced the coil), also check coil wire for resistance.
Once it starts, remove the ref sensor connector, the engine should keep running
and accel perfectly (If not, then a bad speed sensor). Next, try reversing the
speed & ref sensors on the engine and then the two connectors on top,
i.e. To check for a possible weak sensor.

D. If spark but no noid then; power connection to injectors & ECM (pins 14/15) or
bad DME Relay.

Note: The temp sensor, AFM, and altitude sensor affect the fuel and are essentially
eliminated as problem sources for basic starting by using carb cleaner (A above).

The above is a starting point and NOT an exhaustive/in-detail troubleshooting guide.

[chococrazy]

Is there any way to directly test the dme relay? Without the car.

[LJ851]

Thats a handy basic troubleshooting guide Loren.

Thanks, Lorin

[Lorenfb]

"Is there any way to directly test the dme relay? Without the car."

Yes!

Test setup requirements:
1. 12 volt battery
2. 12 volt test light
3. jumper leads

Test procedure:

1. Connect the 30 & 86 pins to +12 of the battery.
2. Connect one side of the test light to -12 of the
battery and the other side to the 30 & 86 pins.
The test light should light, if not the test light is bad.
Now connect the test light to the 87 pin.
3. Connect the 85 pin to -12 of the battery and
a 'click' will be heard and the test light will light.
This verifies the DME ECM power output.
4. Now remove the test light from pin 87 and
connect it to 87b, leaving the other side connected
to -12 of the battery.
5. While still connecting the 85 to -12 of the battery,
connect the 85b to -12 of the battery and another
'click' will be heard and the test light will light.
The verifies power to the fuel pump.

When in the car, the following must occur:

1. The 30 pin always has power.
2. The 86 & 87 pins have power when the key is "on".
3. The 87b pin has power when the engine is cranking
or running.

[chococrazy]

Alright I just tested the relay I'm hearing a strong click but the test light isn't lighting up on either the ecm or the fuel pump. Here's a pic of my relay board... it looks fine except for a one spot of black on a pin I'm thinking it's gone. Hopefully that's why my 911 isn't getting fuel.


Uploaded with ImageShack.us

[Lorenfb]

"but the test light isn't lighting"

Touch the test light to the common 30 & 86 pins. The test light should
light, if not the test light is bad.

[chococrazy]

Test light is fine tried it on those pins to and it lit up, and checked the light on a battery and worked fine.

Is there a way to force this relay to work so I can see if I can just get the car started?

[Lorenfb]

"Is there a way to force this relay to work so I can see if I can just get the car started?"

Use two paper clips:
#1 - jumper from 30 to 87 - ECM power
#2 - jumper from 30 t0 87b - fuel pump power

Note: Make sure #30 has power.

[chococrazy]

Just removed it from the base and cleaned up the solder points. It's clicking and test light is firing up now. I'm going to force the relay then put it up on my lift to see if the pump will get going.

[porsche.racer]

What do the dme relay pins do?
According this thread,
30 always has power
86 and 87 power with key on
87b power when cranking

I do not have power at 87 and 87b with this test?????? Why?

[PopsRacer]

in case someone lands here with a no-start issue - the relay pin numbering is from the DIN_72552 standard (there is a wikipedia page about it too). Here is your pin-out:
30 - is + from battery directly
85 - relay coil -
86 - relay coil + (important if there is a flyback diode across it)
87 - common contact for switch
87a - normally closed contact
87b - normally open contact

The DME relay does have a diode in it btw. I needed to replace the one in my DME relay. It’s a 1N4003 (200V rated) but you can use any 1N4xxx that is rated the same or higher. It’s just there to suppress flyback from the coil.

If you want to test your diode without opening up the relay you can use the diode testing setting on you DMM easily. Clip the black lead to pin 85 and the red lead to pin 86. You should read the .548V bias. Reversing the leads should give you OL (out of range). If you get OL either way, you need to replace the diode.

[wazzz]

Originally Posted by PopsRacer

in case someone lands here with a no-start issue - the relay pin numbering is from the DIN_72552 standard (there is a wikipedia page about it too). Here is your pin-out:
30 - is + from battery directly
85 - relay coil -
86 - relay coil + (important if there is a flyback diode across it)
87 - common contact for switch
87a - normally closed contact
87b - normally open contact

The DME relay does have a diode in it btw. I needed to replace the one in my DME relay. It’s a 1N4003 (200V rated) but you can use any 1N4xxx that is rated the same or higher. It’s just there to suppress flyback from the coil.

If you want to test your diode without opening up the relay you can use the diode testing setting on you DMM easily. Clip the black lead to pin 85 and the red lead to pin 86. You should read the .548V bias. Reversing the leads should give you OL (out of range). If you get OL either way, you need to replace the diode.

Joe, the pinout you mention above is correct for SPDT standard relays (with the exception that on most automotive relays the 87b pin is actually labelled 87 with no "b").

However the DME relay is different. It has a 85b (not 87b) pin and two SPST switches inside.
I don't understand the purpose of the 680-ohm resistor connected in // with the first coil. Any idea?

[mysocal911]

Originally Posted by wazzz

Joe, the pinout you mention above is correct for SPDT standard relays (with the exception that on most automotive relays the 87b pin is actually labelled 87 with no "b").

However the DME relay is different. It has a 85b (not 87b) pin and two SPST switches inside.
I don't understand the purpose of the 680-ohm resistor connected in // with the first coil. Any idea?

On the 911 618 154 00 relay, the 680 resistor is in parallel with the relay coil.
Pin 86 power is applied thru the diode to relay coil. The 680 resistor is used to dissipate
some of the energy stored in the relay coil, when power is removed from 86.

Info posted in #11 is questionable.