Classic no-start with a twist

[MikeStewart]

I would really like to help with pics but I have a 96. However all your tests have shown that the issue is a lack of fuel, for some reason the injectors are not firing but they worked before you pulled the fuse and DME relay.

The pump is running and providing sufficient fuel pressure at the rail so I suspect that if you get a good 12V connection to the common on the injectors - the diagram says red with a black stripe - and turn the key she will fire. Theres lots of things that can go wrong but its usually the last thing you tickled that caused it.

Any problems with the wiring diagram etc. send me an email and I'll do what I can.

Regards,
Mike S.

[John_AZ]

1987 924S-here is a picture of a loose black with red stripe wire;


Not connected...or the solid one as well.

I looked on the internet for a solution and found:

"I went through a similiar problem with an 84 944. It finally came
down to a bad connection on the back of the relay/fuse panel.
You will need to take out the seat and get underneath the dash. Have
someone turn the ignition while you move the wires around until you
find the problem. These aging 944s all have this problem. The
electrical connectors corrode and stop conducting." author ??????

I would put the fuse panel back the way it was when it ran and try the above suggestion.

GL
John_AZ

[MikeStewart]

The DME relay is the one in the middle where the big red and blue wire goes into, from the photo it doesent appear to be fully in the connector. I can see the contacts of the relay and the connector is slightly raised compared to the ones on either side. Take the DME relay out and re-seat so that the contacts are fully home.

[83Zel944]

I've cleaned and lubricated the connections to the DME relay but wont push into the socket any further.

[83Zel944]

*Update*

To eliminate the ignition switch I had someone turn the switch from off to start very slowly as I listened to the DMe relay.

Things I learned:

There is an initial audible click from the relay as it enter the on position then another audible click as you turn the key just into the start position but just before the starter actuates. At that point I can hear the fuel pump humming.

It seems that the switch is in good order. I am just eliminating possible trouble areas.

*BTW:* What should the V+ voltage in the wires at the firewall connector be? I know the smaller connector is for the starter and the big multiwire connector is for injectors.

[MikeStewart]

Ok thats good, it means that the DME relay is working correctly the first click is closing the contact in the DME relay that provides power to the DME controller. Looking at the diagram power is going on across pins 1 & 3 of the DME relay which energises the coil between those pins and closes the contact to the left of the coil. That puts 12V on to the DME controller on pins 18 and 35 through the red/yellow wires, you can see the wires in your pic. It also puts 12V on to the feed to the injectors through the re/blue wire so you should be able to measure the voltage at the injectors with the key in that position.

The second click is controlled by the DME controller, when it detects that the ignition switch is in the start position it then grounds the black/grey wire at pin 20 which energises the second coil thethe DME relay at pin 8/9 which closes the contact to the right and applies power to the fuel pump through fuse 2 on the red/black wire at pin 4.

When cranking the DME controller grounds (a short pulse) the grey and grey/black wires to energise the injectors making them open. So is there a good 12V supply to the injectors and is there a good pulse across them when cranking? You really need an oscilloscope for the second one, however you can take the battery out and measure the resistance from the relevant pins on the DME relay to the top of the injectors and from the DME controller to the bottom of the injectors. In both cases it should be pretty close to zero ohms.

[83Zel944]

There is battery voltage on one pin of the injector. the other pin read zero on my meter. I don't have a scope but i will try and find one quickly.

[MikeStewart]

Ok, do the continuity check just to make sure we dont have a high resistance it might just show up where the problem is. You have been very thorough with the tests and we are close to the cause I'm sure, something is stopping the injectors opening and that can only be insufficient voltage/current.

If you wanted to confirm the injector operation you could pull the connector off the injector and put 12V across it when its in the rail and theres pressure in the rail. There will be a huge rush of fuel out of it, I dont think you need to do this but after all the tests it might be good to demonstrate that this is the source of the problem.

[legoland951]

I bet if I get your car in my yard I can get it running pretty quick... I have spare DMEs, fuel rails/injectors, and just about everything else. I have never seen pulse and no start unless fuel pressure is low. Did you check the pressure at the rail?

[83Zel944]

Yup.. I have 36psi jumpered DME relay. It's got pressure but the injectors are not opening as much as they should i guess. I pulled the rail and the injectors are opening but their volume is low. On crank the injectors left a puddle in blue shop towels the size of a quarter or slightly larger.

[earlr85944]

YOU HAVE THE CORRECT PSI AT THE RAIL, INJECTORS NOT FIRING CORRECTLY POINT TO CLOGGED INJECTORS, VARNISHED FUEL OR MOST LIKELY IN THIS CASE AN ELECTRICAL PROBLEM . MIKE IS POINTING YOU IN THE RIGHT DIRECTION. I RECALL HAVING VOLTAGE AT BOTH SIDES OF THE INJECTOR THOUGH.

Mike, On the previous post, the dme doesnt wait for the ignition start switch, it needs the sensor signal to fire the fule pump.

[83Zel944]

Clogged injectors are a possibility though the car did run and was a DD for the guy I bought it from 3 weeks ago. That's why I don't think varnish is a likely culprit.

BTW: How would a vacuum leak cause a no start. Someone on 944online said it was possible that it could be a massive leak. It was my impression that the AFM plays no immediate role in startup.

[MikeStewart]

You will have 12V on both contacts of the injectors until the DME fires it. This is a short pulse to ground so you wont see it on a multimeter, in the pic it lasts for 2ms, you can only see it with a scope. The pump is running and theres pressure in the rail, it was running before the compression test.

I think its a bad connection from the DME relay to the feed on the injectors so that when the DME pulls the other side to ground the 12V gets pulled down as well so it ends up with insuffieient volage over the injector for it to open. Actually you could prove that by connecting a 12V supply through a heavy guage wire to the feed on the injectors and cranking it.

[Lapponia]

Earl is right here! You should read +12 volt at both sides of injectors when ignition is On and engine not cranking or running (meassured between one wire and ground at a time). If one side reads zero in same condition, either is all injectors grounded permanently or injector coils broken. If grounded permanetly, the DME is at fault, probably the circuit that control the switching of injectors to ground (a shorted transistor perhaps). On the other side.... if all coils are broken what would be the reason? Hmm, the same transistor shorted as mentioned as it carry amps continously through coils to ground which they dont can handle very long I guess.
I take it that you can make meassurement at both sides of the injectors while ignition is ON. It can be a little complicated as you have to slide back the booths and get to the wires.
So, if you get +12 volt across them with engine not cranking, the DME is shot or you have a short to ground somewhere else (between one side of each injector and chassi ground).

In your shoes I would pull DME out of the car and pull all contacts from the injectors thereby have the injector grounding circuit "hanging in the air" so to say. Then take a resistace reading between all injector contacts and ground. Now, if you get a reading of around 0.4-0.5 ohm (from meter wires) you will have a short somewhere. Test all connectors to chassi and make a note here at which cylinder this occured. Remember that injector 1 & 2, 3 & 4 are in pairs so a short can be in 1 or 2, 3 or 4 respectively. If readings show open at all injectors, the wires are OK. Refit DME in car and repeat meassurement between chassi and each wire at the injectors. If 0.4-0.5 ohm (from meter wires) DME is shot (shorted at pin 14 & 15).
And lastly, take resistance readings across each injector before you refit contacts to them. Do you get around 2.5 ohm or are they open? If 2.5 ohm they are elecrically OK but could be jammed to not to open as mentioned by other very knowledgeable Pelicans here.
Dont give up and good luck!
________________________________
Lapponia

[Lapponia]

And use the wiring diagram sent by MikeStewart to follow the circuits when taking resistance readings. Its wery good.
__________________________
Lapponia

[MikeStewart]

If you download vol1 - engine manual from cannels website section 28 has a step by step guide with pics on troubleshooting the DME.

Theres a complete set of workshop manuals for 928, 944, 968, Boxster, 911, 993, 996 also BMW, Subaru, Ferrari 308................... on there which are free to download.

[83Zel944]

I followed the steps listed above and here are my results:

Key in on position - Voltage - each injector contact to ground
Battery Voltage - 12.32v

Injector # Pin 1 Pin 2
Injector 1: 10.43v - 12.27
Injector 2: 10.43v - 12.27
Injector 3: 10.43v - 12.27
Injector 4: 10.43v - 12.27

Resistance - measured across pins on injector - DMM internal resistance .2 ohms
The listed figures are un-corrected

Injector #
Injector 1: 2.40 ohms
Injector 2: 2.45 ohms
Injector 3: 2.51 ohms
Injector 4: 2.50 ohms

Resistance measured in injector clip to ground - DME removed

Injector # Pin 1 Pin 2
Injector 1: open - open
Injector 2: open - open
Injector 3: open - open
Injector 4: open - open

Based on this I can tell that no wire to the injectors are grounding out before the DME. What else do you all see. I still can't find a scope for cheap so that's on hold while I am building a scope interface for my laptop. I am working on the

[MikeStewart]

I take it the 10.43V is on the DME controller side and the 12.27 on the feed from the DME relay?

There are no shorts in the wiring and the injectors are all good.

What is the resistance from the feed on the injector to the DME relay - youll have to pull it to get at the pin.

[TeenerTim]

Listen to John_AZ. The first step in troubleshooting is to determine what changed when the problem started. Put the fuse box back to the way it was when the car ran. It was probably that way for a reason. If it still doesn't start, move the box around while cranking. Something is probably grounding out when the box is secured.

[83Zel944]

I've tried the wiggling the fuse panel while cranking and I had to charge the battery over night because I ran it down cranking. if something is loose it's likely disconnected now.

Mike you mean resistance between the pin on the DME connector under the dash and the injector connector?