1987 911 3.2 no start no spark

[porsche.racer]

Hi guys, I have a track duty 1987 911 3.5L built by TRE.

Driving home from the track the other day the car stalled, and puttered to a stop, I towed it home.

NO START.

I have checked and completed the following:

wiggles and unplug and plug-in of various wires plugs etc.
DME replaced
Fuel Pump checked, fuel flow checked at fuel rail is good.
Coil, new and installed
Reference and speed sensors, new and installed. (swapped and tried just to be sure)
spark plugs new and installed
cap and rotor good

12v at coil with ignition, yes (are there more ways to check this) and what actually triggers the coil to fire?

is there a fail-proof way to see if the coil is sending the spark to the distributer?

Any thoughts??? where to go next. I am trying to source/borrow an ecu, and the relays (driver engine wall) from another car just to try.

As I believe I have checked all the usual suspects, and or replaced old and worn parts I am at a loss and what to do next.

[Jesse16]

Sounds like time to start checking pins at the ECU. Are the signals getting there. Also, remove the big plug and take a look, plug it back in.
Wiggle connectors. Could go through the fuses to confirm.

[porsche.racer]

Originally Posted by Jesse16

Sounds like time to start checking pins at the ECU. Are the signals getting there. Also, remove the big plug and take a look, plug it back in.
Wiggle connectors. Could go through the fuses to confirm.

I suppose I should mention I've done all the wiggles, un plugs and plug-ins etc. Fuses have been checked. I have tried more than one DME relay, as after trying my back-up DME that has been travelling with me for a few years to and from the track, I purchased a new unit just in case, but to no avail.

I had though perhaps the "set-screw" that the reference and speed sensor could have come out and falling out, not sure if that ever happens......

What pins at ECU and how do I check them??

[porsche.racer]

I am happy to pull out the multi-meter again and run tests, Im just not sure what I should test.......

I have searched archives, and found that its usually the normal suspects, DME, Coil< reference & speed senors........ all replaced.

what is CHT sensor and would it cause a no start.

And, the car was running great up until it didn't. There were no indication of any issues or problems.

[Jesse16]

Have you got one, guess its a good time to make that investment and do its trouble shooting. Seems I remember there are tables.

[johnman001]

I had a no start/no spark issue with mine. I started with the troubleshooting section in the Workshop Manual and when I got to the section with the speed/reference sensors I found my issue. I changed out the one that OHM'ed out of spec and all was good with the world.

I have read in previous threads about the set screw in the flywheel (reference marker) coming loose and falling out. Without the reference sensor, I don't believe that the ECU will fire the coil (at least during starting). It's my $0.02 and you got it for free.

I suggest starting from the beginning and checking basics (also check rotor and cap) before getting too deep with checking the ECU plug. If it was running and quit and now won't start, something changed.

Good luck and share what you find.


By the way, I usually use an inductive timing light on the coil wire to verify the existence of spark if I am in question. I also have a very old inductive neon light used to test ignition it flashes in the presence of spark in an ignition wire.
http://www.matcotools.com/ProductImages/spt79.jpg

[DRACO A5OG]

Where you located Racer? I'm in southbay area.

If local, I can help you diagnose, PM me

[ischmitz]

- Confirm power to the DME (not the DME relay) by checking that the ICV is vibrating with key in RUN position
- Confirm you have fuel pulses (NOID light or smell at the exhaust after prolonged cranking) during cranking.

If both check out your DME could be the culprit. You mentioned you replaced the DME but I am assuming you meant to say "DME relay". The DME is the large box with the 35-pin connector.

Ingo

[mysocal911]

Many Pelicans have mentioned this link as helpful for 911 3.2 running problems:
911 3.2 No-Start Troubleshooting

[porsche.racer]

Originally Posted by DRACO A5OG

Where you located Racer? I'm in southbay area.

If local, I can help you diagnose, PM me

I live in Canada now, was in socal for years, but no more.

[porsche.racer]

Originally Posted by mysocal911

Many Pelicans have mentioned this link as helpful for 911 3.2 running problems:
911 3.2 No-Start Troubleshooting

thank you for that link, I will run through all of the suggestions. I did not test for power to the dme.

I have sourced (for test purposes) anything I need from a friends 911, so if its ecm, or an ignition relay or icv, I can now test for those.

Can the ICV cause not start issues?

I keep updates coming.

[DRACO A5OG]

ICV, Maybe, does it vibrate when car turned to ignition?

Canada, Yeah too far for me :-/

Place your DME into your buddy's 3.2 to insure there is no fault in your DME. DO NOT PUT YOUR BUDDY's DME into yours, just in case there is a FAULT in your car. You want to keep a friend :-).

[porsche.racer]

Originally Posted by DRACO A5OG

ICV, Maybe, does it vibrate when car turned to ignition?

Canada, Yeah too far for me :-/

Place your DME into your buddy's 3.2 to insure there is no fault in your DME. DO NOT PUT YOUR BUDDY's DME into yours, just in case there is a FAULT in your car. You want to keep a friend :-).

Yes, good point!! Will do. But he's not that good of a friend!!! Lmao. Jking.

[scarceller]

Get a LED 12vdc test light. You can get this at Walmart for less than $5.00

With the LED test light you can test for coil pulses at the coil. Simply put the light across the '+' and '-' posts. As you crank the light should flicker. The coil always has 12vdc on the '+' and then the DME commands the '-' to ground via a Transistor.

This same test light can be used to test for pulses from the ref and speed sensors by simply unpluging the sensor and placing the light across the pins then crank the starter.

It MUST be a LED light, the LED does not require much current to get it to flash.

And as Ingo already suggested: does the Idle Control Valve hum with key in 'RUN', if it humms and vibrates the DME has power and is alive.

I've also seen a shorted injector cause a no start. Measure each injector to be sure you don't have one shorted at 0hms. They are 3ohm injectors, should read 2 to 3 ohms.

[porsche.racer]

So from what I understand, the dme breakdown is
30 always has power (yes I do)
86,87 have power when key is on (I have power at 86 but no power at 87)
87b power when cranking (I do not)

Anyone explain why I do not have power.......

[ischmitz]

Porsche.racer,

the DME relay has two stages. It is two relays in one housing. Stage 1 is turned on when the key is in RUN or START position (alarm not active). Stage 2 is turned on when the DME sees signals on the reference/speed sensors or while you crank.

Stage 1 is activated by having permanent GND at pin 85 and switched +12V from the ignition switch at pin 86. This turns the 1st relay on. Pin 30 receives permanent +12V from the battery.

Once the first stage turns on pin 87 will have +12V and delivers this +12V to the DME (that is the computer under the seat), the ignition coil and the injectors. It also powers one side of the coil of the 2nd stage of the DME relay. The DME itself will provide GND to pin 85b to turn the 2nd stage of the DME relay on. This energizes pin 87b and provides power to the O2 sensor heater and the fuel pump.

In your case with the DME relay in its socket if you measure +12V at pin 30 and pin 86 with the key in RUN position then you also need to see +12V at pin 87. If not the DME relay is bad.

Out of curiosity, did you ever check whether the ICV on top of the engine vibrates with the key in RUN?

Ingo

[scarceller]

Measure voltage across 85b '-' and 87 '+' with the relay in place and connected to the harness. Then turn key to 'Start' and while cranking do you see 12vdc?

If the above test passes and shows 12vdc then the Relay is bad.

If test fails then the DME pin #20 is not going to ground for some reason while cranking.
Report back on the test result to continue debug.

87b is what feeds the fuel pump 12vdc and without it having 12vdc the pump won't run.

One more cheat test is to simply jumper 12vdc directly to the fuel pump fuse from the adjacent fuse that has 12vdc. You want to force the pump to run by jumpering power to it's fuse. Then once the pump is running (you'll hear it) go ahead and start the engine, does it start now? If so you know everything else is good and you are having issues with the Fuel pump power feed from the DME relay. Do not jumper the pump and call it fixed, that's a safety issue only do this as a test step.

[scarceller]

One more test:

Unplug the DME harness from the DME and measure voltage at pin 4 on the DME harness. This pin MUST have 12vdc while cranking, does it go to 12vdc during cranking?

Pin 4 is tied directly to the ignition switch 'Start' it comes off the same line that feeds the starter.

If it does not then the fuel pump will never be energized.

Do this test and report result.

[porsche.racer]

Tested again:

With dme is working correctly.
With relay installed 30 has power, 86,87 have power with ignition on, 87b power on when cranking, fuel pump works, and icv vibrates.

Still no start.

So the dme relay power is all correct.

Where to next?

[scarceller]

Next: We simply need to know you have coil pulses and fuel pressure.

You need a LED test light to proceed, walmart has these in Auto Section for under $5.00.

Place the LED test light across the coils '-' and '+' it should flicker during cranking if the DME is generating coil pulses.

Also, do you have fuel pressure? You don't even need the key in. Simply jumper the fuel pump on at the FP fuse and measure fuel pressure, needs to be 2.5bar about 36lbs.

BTW - ignore my prior posts we are done with that testing since you know the pump has power via pin 87b, but I'm making the assumption that power is getting to the pump. Have someone turn key to run and listen for the pump under the fuel tank. Or better yet measure voltage at that pump while cranking.