Classic no-start with a twist

[Lapponia]

83Zel944! Highest marks for your measurements...A+++. I forgot to suggest one more resistance measurements between pin 14 & 15 at DME and one pin at the injectors those with grey (gr) insulation and those with grey/black (gr/bk) insulation, following the circuit diagram from MikeStewart. Could they possibly be broken as you never get grounding pulses to the injectors or are pin 14 and/or 15 broken in DME or in the 35 pin plug? I would check them just to be sure.
And I would definately put in a brand new DME relay as the old one probably has bad contacts in it.......in this case the one that supply current to injectors for a change (not the fuel pump). If wires are OK, new DME relay in, and engine will not start, I bet it is the DME not grounding (pulses) your injectors at pin 14 & 15 as supposed to. Try to loan a working one to put in but check those pins in the 35 pin plug before you connect them. All the best wishes
__________________________________-
Lapponia

[MikeStewart]

Yip thats right. From the DME relay to the injector connector.

[83Zel944]

Resistance - measured from pin on injector to pin in DME wiring harness - DMM internal resistance .2 ohms
The listed figures are un-corrected

Injector #
Injector 1: 0.3 ohms
Injector 2: 0.3 ohms
Injector 3: 0.3 ohms
Injector 4: 0.3 ohms

Very low resistance. i tried wiggling the connector on the firewall while checking resistance and there was no change.

What pins on the DME supply 12v and ground

[Lapponia]

DME pin 18 & 35 get +12 volt from DME relay. DME pin 5, 16 & 17 goes to ground. Insulation is brown.

[MikeStewart]

[MikeStewart]

Guys I'm begining to query the results of the tests done right back at the start -

" i did make a jumper and the fuel pump is operating. In fact i used the jumper to test flow at the rail. With the jumper in it wouldn't start. I also tried disconnecting 1 injector to test if the FPR was shot and it still didn't start. "

Everything we are seeing is pointing to the DME relay itself. Theres a procedure in Clarks at - http://www.clarks-garage.com/ - select the Garage Shop Manual tab at the left and when it opens scroll down to -

DME Relay

Technical Information and Testing


Try repeating that test as detailled -

"If you suspect the DME relay is bad and you need to move the car, you may install do so by installing an "emergency" jumper across terminals 30, 87, and 87b on the relay / fuse panel. Some folks will tell you to jumper terminals 86, 87, and 87b instead. This allows you to only run the fuel pump, DME, and injectors when the ignition switch is turned on. Seems like a great idea on the surface. However, realize that the wire supplying power from the ignition switch to terminal 86 on the DME relay is a 1.0 mm wire and is only intended to carry enough current to pickup the primary coil on the relay. The wire connected to terminal 30 is a 4.0 mm wire which is designed to carry full current demanded by the fuel pump, DME, and fuel injectors. I strongly recommend using terminal 30 instead of terminal 86 to supply power via the jumper. "

Note the recommendation to use terminal 30 for power.

[83Zel944]

i reran the test for the relay. The good thing is that i was using terminal 30 already. No start either. I am wondering if it is the DME itself. I did pull the relay and have it in front of me. I will be rechecking its content in a minute.

[Lapponia]

Ignition lock wire to 86 on DME relay is ONLY 0,5 mm in my wiring diagram. It could make a disaster here as other wires from DME relay to injectors, DME itself are 2.5 mm. So Clarks-Garage is absolutely right. The jumper should be like this: 87----30----87b. Pin 30 is the common point wich supply +12 volt power to DME and injectors. With this in mind and jumper connected, the relay contacts (both) are bypassed and cranking the engine is only whats needed to start it (assuming all other items are in working order).
David Boetcher...a Pelican member made some investigations on his DME relay a couple of months ago, so do a search and see how a relay can look like when broken. I recommend you to pull off the relay can and have look. Dont bother to fix them contacts or solderings if they look bad. Buy a new relay.
Do try the the jumper first so see if engine starts while cranking it. Second, test voltage (+12 volt) at number 2 pin in 9 pole contact with the re/bl wire (2.5 mm). Pin 3 (re/ye, 2.5 mm wire) in same 9 pole contact should also read +12 volt assuming you have jumpered DME relay socket. Did you pull this multi contact apart, cleaned and "lubricated" it? Well you can do it now when taking voltage measurements. Note: Ignition key in OFF position.
If nothing of this will work, I´m inclined to agree with you it´s the DME itself, probably circuits behind pin 14 & 15, those who are supposed to make grounding pulses to your injectors.
Try to loan a working DME test it and good luck!
___________________________
Lapponia

[MikeStewart]

We are starting to eliminate almost everything here, so to re-cap again - its beginning to be like Apollo 13 - just tell me whats good on the spacecraft:

We have the fuel pump running and confirmed pressure in the rail at 36psi.
The fuel rail has been pulled and on crank only delivers a tiny ammount of fuel - not enough for it to run.
The tank has had fresh fuel in it.
The tach bounces so we are assuming that the speed sensor is transmitting.
Both the speed and reference sensors have resistance within tolerenace.
It runs on starting fluid so the DME controller must have power and the DME must be getting an input from the speed and reference sensors to provide the spark at the plugs at the correct time.
We have a low resistance connection from the DME relay to the feed on the injectors so the car wiring to the injectors is good.
With the DME controller out there is an open circuit to ground on the DME controller connection to the bottom of the injectors so no short.
The DME relay has been removed and jumpered as per Clarks instructions so is not a factor.

Did I miss anything?

So we have all the conditions at the DME to make the engine run - on starting fluid we have confirmed that the DME ignition timing is good so the sensors are not an issue. All thats left is the "ground" connection from the DME controller to the bottom of the injectors which is supplied by the DME controller. Thats an interesting one as te NOID light flickers suggesting a connection, but the voltage levels can only be confirmed with an oscilloscope.

Its begining to look like the controller but that doesnt make sense given that it was just a compression test. If you can get a scope (hire one?, borrow from local college?) and see what the waveforms are doing across the injectors we might have more of a clue. Or borrow a spare controller and swap it out. If it can fire the plugs at the right time it should be able to spray fuel.


If it comes to it there's schematics for the controller at - http://www.cannell.co.uk/Technical%20Articles/ML31TAU.pdf and http://www.cannell.co.uk/Technical%20Articles/ML31TDU.pdf.

From there both pins 14 and 15 are connected together internally and driven by the same circuit so all injectors are firing together. That makes sense as theres no camshaft sensor on the car.

The faults more likely to be on the car though.

[Lapponia]

83Z! In an earlier post in this issue you have made an interesting discovery in that DME relay (second half of it) cklick at the same time as the starter cranks. If we follow the current flow diagram we can see that pin 4 in DME gets +12 volt together with cranking voltage to the starter from the ignition key in START position. Inside of DME the electronic circuits are activating DME pin 20 instantly to ground thereby activating this part of the DMR relay.... as long as key is in cranking position. This is to make a speedier start of fuel pump to build up pressure to the injectors and make engine start quicker. Now, if engine starts while cranking we usually let key go back to ON position when we realise that engine is running. In this situation the starter AND pin 4 on DME looses +12 volt (current supply). But when engine now is running, electronic circuits inside DME takes over the grounding of DME pin 4 thereby keeping DME relay (fuel pump side) activated. I have not understand this until I got an electronic diagram for the DME computer and searched its functions. So, as a conclusion: you were right hearing the click from DME relay and fuel pump start humming at the same time as key was turned to START position. Of course, one can refuse to accept this, as in a good starting engine, there is such a short time between cranking and engine is firing up.
If this circuit (DME pin 4) is cut off by a broken wire, corroded connectors etc, engine will
nevertheless start but will need longer cranking to start. I assume that cranking speed is enough to make speed and referece sensors to áctivate the DME computer.

[Lapponia]

MikeS! Good to read your analyse! I have only one thing in mind. If that 9 pole connector above brake booster is corroded we can still measure +12 volt at pin 2 & 3 when ignition is ON, with or without LOAD. We can measure same voltage at all injectors as well. Even a noid ligth would flicker, an oscilloscope would get the wanted curve on its screen when cranking. Therefore, one must be absolutely sure that this vital circuit is Low resistance all the way through this multiple pin connector. A year or so ago there was a picture here showing this 9 pin connector melted, caused by high resistance and current trying to pass through it.
I would clean those male and female contacts there, lubricate them before putting them together again, followed by new measurements at the injectors. I would also try to connect a 20 watt bulb between +12 volt live pin at each injector and chassi ground (ignition ON). The bulb should shine brightly at all four places.

[MikeStewart]

The resistance from the DME relay to the injectors was 0.3 ohm with the DMM internal of 0.2 ohm so the would be 0.1 ohm through the circuit so I think that connector is good as we measured through it end to end.

I've looked through the DME controller schematic, please check the resistance between pin 18 of the DME controller to the DME relay, pull the controller and relay. It appears to be the one that supplies power to the injector transistors in the controller. I think it goes through pin 3 of the 9 way that Laponnia mentioned, there should be a 2.5mm red/yellow wire going in and two 1.5mm red/yellow wires coming out.

[Lapponia]

83Z! Do we have resistance readings here between DME multipin connector pin 14 & 15 and
one pin (grounding side) at each injector (multipin connector removed from DME controller)? They should be around 0.3 - 0.4 ohm un-corrected.
1. Pin 14 to pin 15 in DME controller = zero ohm?
2. Multipin connector, pin 14 to injector cyl 1 = 0.3 ohm or open?
3. Multipin connector, pin 15 to injector cyl 1 = 0.3 ohm or open?
Repeat 2 & 3 for cylinder/injector 2, 3 and 4.
If pins and wires are OK we now know that all wires from DME relay to DME controller as well as Injectors to DME controller are OK. Engine should start but I´m leaning towards a faulty DME controller in that area that controls injector ground pulses. Hey, could it be that hotlegged transistor with bad/ageing solder again? If so, open circuits here, no injector function.

[SolReaver]

If you suspect a faulty DME...take the ?? DME and install it in a running car.

If the car doesn't run. It is the DME. If the car runs...it is something else.
I have a perfectly good 87 924S sitting here with it's dash out. It isn't going anywhere for a week. If it is the same DME (dunno) I can be of help. Otherwise find a suitable "test bed" and prove or disprove your hypothesis.


Yes. you really need an O scope to see if the injectors are getting all the juice they need. A noid just tells you it is getting signal, not how much or how long in Milliseconds, and you cant see the pintle shelf either. There is a cheap one that hooks to a PC. I will update this post later.

It is getting a little scruffy here, time for a shave with Ockham's Razor.

[83Zel944]

As soon as the rain lets up I will be checking the resistance. I'll post findings asap.

BTW: I was thinking that perhaps a bad ground to the DME may cause this problems. I'll be checking this asap

[MikeStewart]

Ok,

Lets see what the outcome of that is. If that all checks out then theres not much left but the DME controller. Maybe u could send it to SolReaver to confirm its if its dead, at least you guys are the same side of the pond.

[SolReaver]

First make sure a 1987 924S has the same or compatible ECU.

[TeenerTim]

Originally Posted by SolReaver

First make sure a 1987 924S has the same or compatible ECU.

I would be very hesitant to do this. Since the ECU obviously worked before, there is a possibility that some short in his system caused the ECU failure (if it is in fact bad). If you hook yours up to his system it might burn yours out too.

Hooking his ECU to your system is a much safer bet.

[83Zel944]

Rainy and cold still - I have got to get my beast back on the road - tomorrow for the readings

[MikeStewart]

Ok, just out of interest where is Winter Park?