3.2 85 Carrera - Turning the key too quickly

[nagromike911]

Hi Everyone. I imagine this has been discussed before on the forum but thought I would mention it in case others have a similar problem.

I've been trying to troubleshoot a start/stall issue on my 3.2 for a while and started scoping signals in the DME. I kept getting intermittent spark and of course I went straight to suspect the DME. Ref and Speed sensors all checked out. Sometimes I could see the ignition transistor switching and other times I could not.

Long story short, I found I was turning the key from 'ignition on' to 'start' too quickly and sometimes before the CPU could boot (my assumption) properly, resulting in no spark pulse out of the ignition transistor. Other times, for whatever reason, it took me longer to turn key from ignition on to start, and I would get a spark.

I'm not sure how long the boot time is for the DME cpu but if I give it a couple of seconds with ignition on before turning it over, sparks everytime. Now it just starts but stalls right away. The search goes on



Mike

[john walker's workshop]

Why start another post about the same thing? There is no "boot" time.

[ben parrish]

Huh? What are you talking about? How could you "see the ignition transistor switching"?

Start from the basics...tune up to include plugs, rotor, cap. Proper a/f mixture? Correct fuel pressure?

Start and stall sounds like a fuel issue...have ou changed the fuel filter?

[Chuck.H]

If you look at the DME software, it's only a few lines of 8051 code before the loop waiting for ref signal pulses, which starts the injector and coil pulses and the fun that ensues. There is effectively, no boot time required.

If you are not getting coil pulses as you say, I would look again for cracked solder joints on the DME - especially around the coil transistor, which is standing up off the board on a heat sink, and very prone to vibration.

Chuck.H
'89 TurboLookTarga, 438k miles

[jlex]

Sounds like a mechanical problem with the ignition switch...

[nagromike911]

Thanks Everyone for the replies. My mistake I guess, concerning the boot time. I did a search on the forum for cpu boot time but came up empty, and as I said, it was just an assumption. Strange though, that I can 100% turn the key straight to 'start' and get no spark and then 100% turn the key through ignition on, pause then to 'start' and get ignition sparks everytime

Mike

[GH85Carrera]

The "bood" time would be just milliseconds. Unless you are the Bionic man with superhuman wrist action, you are not turning the key that fast. Now there is ONE thing, the fuel pump is not instant. The key to on position sends a signal to the fuel pump to pressurize the system. It is a pump and it has to have a tiny amount of time to send fuel from the pump to the injectors.

The pump only runs for a second or two if you don't get ignition.

Most likely you have a worn electrical portion of your ignition switch. You need a teenage gymnast or contortionist to lay on their back with their head under the dash looking up to get it out. You can do it yourself, but you will want the contortionist to help.