kyporsche87

87 944 n/a it has been sitting for about 8 weeks since I last started it. I have tried another DME not it it either fire or fuel. Give me smoe tips on how to run down the problem. It has about 1/4 of a tank and normally starts great and quick. thanks for all your help.

Travis - sflraver

DME relay?

carlege

so you getting tach bounce? pressure at the rail?

hardtail15

check everything around the maf sensor (j boot and such) and make sure everything is tight and sealed

Pure Bob Saget

fuel pump relay possibly. just go through the motions, pull fuel rail cap off and crank over to see if your even getting fuel, if so then pull a spark plug and crank over while holding spark plug to the valve cover to check for spark.

JohnKoaWood

Not so sure pumping gas out and then applying a spark in the same area is the best idea...

Try cranking the engine and CRACKing loose the fuel damper line... if fuel begins to seep out you are OK fuel wise...re-tighten the line.. I have fuel rail pressure gauge for just this reason, I also carry spare DME relays in both my cars...)

THEN pull a plug and verify spark...

DME relay is a good place to start, there are instructions out there to jumper the relay socket... jumper the socket and try to start..if it starts, buy a new relay...http://www.clarks-garage.com/pdf-manual/fuel-05.pdf

No start is hard to diagnose from a distance (could really be anything from a loose wire to bad sensors to bad fuel pump or a clogged fuel filter..)

verify the fuel supply as detailed above, then the spark... if you have fuel and spark begin looking elsewhere...

Good luck..

Pure Bob Saget

obviously generating a spark by a recent fuel discharge IS a BAD idea, but i thought 944 owners lived dangerously. i probably should have recomended using a fuel pressure gage as well. but hey lets see what happens. worst case scenario we'll see a new thread that states "HELP SMALL ENGINE FIRE"

kyporsche87

Ok it's not the DME relay. I tried another DME thats good so keep the idea's coming. I'll check them later I have a car show at my church that I help take care of. Today is my 35th birthday so as a wish from my Renn buddy's I just want lots of fix it idea's that I can look at when I get home this evening....lol.. thanks guys I love this crew of folks always so ready to help....................

John_AZ

Repeating, Are you getting the tach bounce? The tach needle moves 1/16 of an inch when you turn the key to the start position. The flywheel movement will trigger the reference sensors even at a crank rpm and the tach needle will bounce. If no tach bounce, check the 2 sensor connections at the firewall.

Happy birthday & GL
John_AZ

ballysdad

This should keep you busy..
Hmmmm.... that could be alot! you really have to go step by step and check the ecu harness and voltages to each area as you go. Here is a list of some test you should do one by one and eliminate problems.
Air/fuel/spark/compression
start by making sure we have a battery that is in spec.
all fluids topped off
no obvious broken wires and all vaccum hoses intact on visual inspection.
OK we have 12v at the battery with adequated cranking voltage we get in and turn the key.
12v from battery to ignition switch
12v from pin 50 on switch to pin 4 on dme plug (start signal)
12v on pins 1 (ignition pulse to ign. coil) and 18 (to G5 dme relay power supply)
12v pin 30 at dme relay (fuel pump power supply)
12v to pin 86 at dme relay in the run position (primary coil voltage)
12v to coil + black wire to ground 12v to - (green wire) to ground
12v to one side of the injectors
All ground contacts are clean
Fuel pump will run if dme relay is jumpered 30/87/87b
Fuel pressure at the rail is 29psig +/- 3 (jumpered 36 psig)
20 minute leakdown not under 14.5 psig
Fuel flow rate is 28oz after 30 seconds
Ignition coil primary resistance across + and - is between .4 and .6 ohms
Secondary resistance is between 5000 and 7200 ohms
Ignition wires are good no cracks or splits including coil wire and seated
Plugs are properly gapped
Ignition rotor is seated correctly with the set screw
Timing belt is installed correctly
Firing order is correct
Reference sensors are gapped correctly with .8mm clearance off the flywheel
Reference and speed sensors resistance checks in spec pins 8 and 27 speed 600-1600 ohms and pins 8 and 23 >1m ohm
Reference and speed sensors voltage checks 2.5 and 2v on oscilliscope (good luck)
Reference and speed sensor wiring is not broken at connector to sensor or to dme
Ok Im tired anyone else want to add or be more specific?

John_AZ
Do a compresion test.
Reference sensor tach bounce when attempting to start the engine. The tach bounce is very slight-1/16 of an inch. Clean connections as mentioned above.
Injector "noid" light. Very basic tool but will tell you if the DME is sending a signal to the injector. An oscilloscope is the best.
Clean connections at major parts like AFM, ISV, throttle body.

Travis - sflraver

Um... if you have a bad DME relay and you swap the DME itself, you still have a bad DME relay.

Just saying, no spark or fuel, the DME relay is the absolute first place to look.

kyporsche87

Ok here is what I know I'm getting fire and tach/RBM meter does not move or bounce while cranking or when I turn the key on. and it use to. So now what? How and where do I check the 2 sensor connections at the firewall? thanks

carlege

NO Tach bounce = Speed and reference sensor... is your problem not sending a signal to get fuel to pump to the rail..... check the wiring. replace the 2 sensors

tach bounce is the easiest thing to check... start with the easy stuff then work your way down the list

Now the fun part of removing them.... some people are lucky some are not.

John_AZ

And you can get new BMW or Porsche sensors with a short wire for a lot less than the OEM and they work the same. A great interchange post on Rennlist:
https://rennlist.com/forums/924-931-...reference.html

GL
John_AZ

Multipass

After my car sits for some time and doesn't want to start it is usually lack of juice in the battery. It will turn over, but not fast enough to fire. Try jump starting.