Roy Patterson

I have read everything I can find, I have tested or replaced every thing I can.
No tach bounce!
I have no spark to the plugs combined with no fire at the injectors (noid light does not flash).
I can make the coil spark by removing the green wire from the coil and grounding the post.
Ordinarily this would mean failed sensor signal, or failed DME response to the signal. I have replaced both sensors (new) checked the adjustment and tested them with a meter both at the plugs to the sensors and from the sensor connector to the DME plug. I have continuity on all three grounds on the computer plug, I have 12 volts on all pins that should have 12 volts, and twelve volts to both sides of the coil.
I have four DME computers which I have switched out one after the other and no spark at the coil and the injectors do not fire regardless.
Thinking about it I need to see if I have 12 volts at the injector connectors, the computer should ground the injectors in sequence to fire them, like I say I have good grounds and 12 volts on the appropriate pins.
The engine should start and run, it has been, I have not had a no start situation it just decided not to start out of the blue and I can not find out why I have no signal to the coil and to the injector connectors unless I have four bad DME computers.
Also the car has the Alarm system in it, I have followed the Clarks Garage method of bypassing the alarm at the control box?
Any suggestions welcome, please don't ask if I checked the fuel pressure.
Thanks

orig944

Grounds for the DME?

931guru

fu

Jfrahm

Did you try bypassing the DME relay via a jumper wire? I do not see that detailed.

You might also check the alarm bypass info, I have read that it's not accurate in some presentations.

Roy Patterson

Yes, all grounds are good.

Roy Patterson

Don't have a scope. I am now going to go after the Alarm, I only have it jumped according to Clark's Garage but I am going to remove the box and jump the wires separately.

T&T Racing

Did you inadvertently switch the speed and reference sensor cable connections from the DME?

Disconnect the DME connector plug. Measure the voltage from pin #4 at the plug to chassis ground or one if the listed grounds on the DME plug when cranking the engine with the starter key. The voltage should be about 10v.
Pin #4 initializes the DME. If the voltage is low or 0, the DME does not initialize, thus no spark, no fuel.
If this is the issue, could be a failed ignition switch or wire from ignition SW to pin #4 has a ground, etc. I believe Clark's Garage has procedure or there are procedures posted on RL.

The voltage at the fuel injector pins (both) with the ignition on and engine off is 12 v.

Roy Patterson

Yes I jumped the relay. I also have have a dozen DME relays which I have switched out the original with.
I am going after the Alarm today, I have read several posts that have alternative ways of bypassing the alarm module.
With no spark to the plugs and no signal to the injectors it's got to be the alarm cutting them out. I never had any issues with the alarm it worked well but I recently had the car painted and the keyed switch was removed, that might have shorted back to the module.

Roy Patterson

I have fuel pressure, sensors are as they should be, repeatedly switched out the ME and DME relay. I now suspect the Alarm bypass method is not working to by pass the Alarm module.

T&T Racing

But with the ignition on, engine off, there is 12v and both terminals of ignition coil. That being said, the thin green security wire spliced to the fat green wire from the coil is not grounded to chassis. The thin green wire spliced to the fat green is at the 9 pin connector located above the brake vacuum booster. It is pin#1, top row, left side if you are holding the 9 pin plug in your hand. It is very easy to isolate the security system by cutting the thin green wire in a place where a wilderness connector with shrink tube can be installed to reconnect.

If go the security isolation test, and there is no start of engine, then refer to my 1st post.
Tom

orig944

Just to be clear, do you have fuel pressure with a dme relay in place, or only with the jumper in place? If you have pressure with the relay in place, it means that the fuel pump portion of the dme relay is energized by the dme module, which implies it is getting the sensor data correctly. It also implies that the alarm jumper is correct (at least the part that energizes the engine electrics, including the dme part of that relay.)

Roy Patterson

Fuel pressure is stable and does not fall off with the DME installed and with the DME relay jumped.
Alarm module removed and jumper wires installed to correct pins on connector.
12v to both sides of the coil, I can make the coil fire by removing the green wire and grounding the post with key on.
I have 12v at the injector connectors, they do not flash the noid light.
Everything is working as it should except that the coil is not being discharged and the injectors are not firing.
I have four DME's that I have switched out repeatedly, with each one I have the same problem the coil does not fire and the injectors do not fire.
I suspected the alarm and bypassed it but no change, I have gone over everything I can think of from grounds to relays, checking continuity and resistance, the results of my efforts have been the same no fire from the coil and no fire from the injectors.
Unless there was a short in the wiring harness somewhere which melted wire insulation I can not figure out why the coil and injectors are at least doing something but the are dead as a horse when cranking.
I know the green wire back to the DME plug pin is good but I have not checked the injector wire back to the DME plug pin which I am going to do now, also I need to trace back the wires I have jumped on the Alarm module pin, see if any of them are not getting to where they are supposed to go.
The thing is I was not having any problem the car was running fine then boom no start, deader than a door nail.

T&T Racing

Hi Roy,
Then this is the test that has not been done.
Disconnect the DME connector plug from the DME .Measure the voltage from pin #4 at the plug to chassis ground or one of the listed grounds on the DME plug when cranking the engine with the starter key. The voltage should be about 10v.
Pin #4 initializes the DME. If the voltage is low or 0, the DME does not initialize, thus no spark, no fuel.
If this is the issue, could be a failed ignition switch or wire from ignition SW to pin #4 has a ground, etc. I believe Clark's Garage has procedure or there are procedures posted on RL.

Based on all your testing, this test has a HIGH PROBABILITY of failing, ie no or too low voltage at pin #4 when cranking the engine with the ignition SW. This test apoears on RL postings for no start condition.
Tom

orig944

I'm going to repeat myself here, perhaps a bit more more clearly: Does fuel pressure come up when cranking with the DME relay installed? In other words, does the fuel pump start working when you crank the engine with the DME relay installed?

Roy Patterson

I have 12 volts at pin 4 on the DME plug and at pin 50 on the ignition switch during cranking..