85 carrera spark no start!!

84_911SC_Swe · 07-18-2007, 11:23 AM

Have a problem which i think was discussed here before but i can't find the thread.
The DME relay is new
There is plenty of fuel pressure
There is spark, ) if i spray start gas at the air box the engine fires.
The car will not start.

I checked wiring from pins 14 and 15 to the injector banks and found all to be okay.

I have 0,033 ohms on the ground connectors and ground which i would think to be okay.

I measured the voltage at the injectors and found zero volts when the ignition is on and 1,3 volts while cranking the engine. I could probably measure alot more but i thought i would put the collective pelican brain on it,

Any ideas on what to do next.

Des

rusnak · 07-18-2007, 03:09 PM

This may sound like a stupid question, but how long did you try cranking over the motor? Go out and try it again for like 30 seconds with a fresh battery. Sometimes the ground for the cht is sketchy. Also check your ground bolts for the dme, and air leaks in the intake.

TroyGT · TroyGT's Garage

What's the story? Has the car been sitting awhile and now you're attempting to get it running again OR is this a daily driver that just quit on you suddenly? Fuel pump okay... do you smell gas when you're cranking? Faulty alarms/wiring can take out your fuel supply. Stick a cheap noid light on each of your injectors and make sure they're lighting up properly. I had a weird situation where I went through much of the same troubleshooting steps as you and it ended up being a shorted out injector... huge thread on this... search for 'Stranded 911'. More than you'll ever want to know about troubleshooting this stuff. I just went back into the thread again and my tremors, cold sweat, and eye twitching returned.

-Troy

rusnak · 07-19-2007, 09:43 AM

I think you have a fuel delivery problem since the engine fires when you spray starter fluid into the intake. Might check the fuel pump circuit, including fuse. There is a procedure in the Bentley manual for running the fuel pump to check for fuel delivery and operating pressure. You can't check it with the engine or fuel pump not running.

rick-l · 01:16 PM

Just to get subscribed to this...
the previous failure similar to this had one non spec injector that was lower impedance and shut the peak and hold circuit off too soon.

Did you measure the impedance of each injector?

Everyone will tell you to buy a noid light with a Bosch junior timer connector on it.

edit: Here is the thread
TROYGT
Page 14 before he found out the engine would run with one disconnected injector

3.2 CAB · 07-20-2007, 11:24 AM

Maybe it is the fuel pressure regulator, just a thought.

84_911SC_Swe · 07-30-2007, 05:58 AM

Sorry for the disapperance but i had some flooding in the basement of my house and have spent the last 10 days digging!!

I have checked all the grounding and found nothing wrong there, am going to buy a fuel pressure test gauge but i do not think that the problem is there,

I have started to read through troys adventure and will try to use some of the fault finding routines there,

i will let you guys know.

Thanks for the answers so far

Des

rick-l · 07-30-2007, 07:13 AM

Quote:

Originally Posted by 84_911SC_Swe

am going to buy a fuel pressure test gauge but i do not think that the problem is there,

You want to buy a noid light. It lights up if the injectors are being pulsed. I think you could use a tail light bulb also (if you have enough hands to hold all the wires on it).

rick-l · 07-30-2007, 07:17 AM

Quote:

Originally Posted by 84_911SC_Swe

I measured the voltage at the injectors and found zero volts when the ignition is on and 1,3 volts while cranking the engine.

Are you sure you did this right?

The injectors (wht/red wire) should have battery voltage on them with the key in run position. Comes right off the DME relay.

84_911SC_Swe · 07-31-2007, 09:27 PM

Rick your right,

I got my hands on another box! after reading troys experiences i decided to try to rule out as much as possible before digging into the wiring, put the other box in place and presto it started. I have a friend who is an electronics guru, and he is going to take a look to see if he can find the fault in the original box. the voltage with ignition on is way too low.

So thanks for the help, i will try to post my findings when we have checked out the electronics in case it can be of help to others.

Des

rick-l · 07:58 AM

If you put the golden unit in and the voltage appeared on the injectors that means the driver in the DME is shorted. (and something should get quite hot!)

Does your EE guru have the DME schematic?

Edit: Off Steve W's site
http://www.911chips.com/ML31.zip