Intermittant no start back on 85

[dsmyth]

It happened again tonight outside my girlfriends place after sitting for 5 hours. Same place and sitting time as a month ago. It always starts perfect the next day so no time to diagnose it. Happened once last year. Turns over strong but no start or even a try. Tried backup dme so thats not it. Hope it doesn't start tomorrow morning so I can tow it back to my garage and get a chance to check it out. Anyone experience anything like this? Whats the best safest way to check for spark? I presume thats easier than checking for fuel. Virtually every electrical or fuel component is new.(tried to make it bullet proof) Thanks for any suggestions.Doug

[DRACO A5OG]

In your garage, at night, get a Spray Bottle with Water, turn the car on, at idle, lift the engine lid and spray a mist of water in the dark.

If there are errand sparks you will see it.

How old are the Ref and Speed sensors, check the OHMs on both per Bentley.

Next would be is to check the DME for bad solders, splitting the halves is required. If you have a buddy with a DME, swap if the non-start symptoms occur.

Just helped my a pelican this way, his ref & speed sensor were shot. My DME could not start his car either.

Jim

[dsmyth]

Thanks Jim Reference and speed sensors are new as well as wires but the DME was a reman unit from 8 yrs ago. I might be able to borrow one. A definite possibility. Im going to pick the car up now ,hope it wont start. thanks Doug

[Carrera1989]

try fuel pump relay under drivers seat.

[kidrock]

to check fuel, pull the hose from your ICV and spray carb cleaner into the hose. Quickly reattach and attempt to start engine.

to check spark, get a good used plug and pull one wire; put used plug into wire. Use a jumper wire with 2 clamps and clamp one end of jumper to base of used plug, clamp the other to a good ground at engine. Have partner turn engine over while you (safely) observe spark.

[dsmyth]

Darn thing started again when I went over to tow it. How reliably unreliable. Three times now only after a 4-5 hour cool down. Never when hot. Twelve hours later it starts perfect. I need to sneak into the garage in the middle of the night tonight and see if it starts.
Thanks kidrock for the easy check tips. I'm going to arm myself with a can of carb cleaner for the next time it happens. At least I can begin the chase.
Tried the back up fuel pump relay last time and it didn't help.
Starting to sound like something expanding and contracting?
Thanks again all. Doug

[kidrock]

Doug, don't feel bad----I hate to admit it on this public forum in front of God and the Porsche world, but I have a similar problem....just switch the word "cold" to "hot". Whenever the weather gets over 85 degrees, I have an intermittent non-start problem. I've been working on it for the last couple of months whenever I find any free time after work. It's really ticking me off. But I'm still narrowing it down and I haven't given up yet. When I finally figure it out, I'm gonna crack open that really old liquor I've been saving and I'm gonna post it here on this BBS like a proud papa.

Don't ever give up!!!!

[dsmyth]

Thanks for the moral support Kidrock. After it running well today it has cooled down for 5 hours and is refusing to start again. I have a small window to explore the possibilities. So far I know
Its not the dme relay
The Icv is humming when I turn the key
I sprayed lots of carb cleaner in under the ICV and no signs of life so its no spark.
Out I go again

[dsmyth]

Update
Tried backup dme relay and nothing
tried spraying carb cleaner in and no signs of life
Icv is mumming when key is turned
Idle position sensors are new??
jumpered fuel pump and it whirs ..still no start

I would rather rebuild an engine im lousy at this. If anyone draws any conclusions from this let me know.
out again

[dsmyth]

Update
Tried backup dme relay and nothing
tried spraying carb cleaner in and no signs of life
Icv is mumming when key is turned
Idle position sensors are new??
jumpered fuel pump and it whirs ..still no start
DME relay clicks when trying to start
Coil and wires cap ect are new
Socket behind key replaced

I would rather rebuild an engine I'm lousy at this. If anyone draws any conclusions from this let me know.
out again
__________________

[DRACO A5OG]

How about CHTS? Was it replaced as well or at least checked?

[rusnak]

Put your hand ON the dme relay, feel for a second "click" while cranking. You should smell fuel if the first click is present. If not, then check fuel pressure.

Try using a paper clip to jumper the two connectors in the CHT plug harness while cranking.

[dsmyth]

Hi Jim whats CHTS and if my dme relay continues to tick as I try to turn it over does that mean something?

[rusnak]

The dme relay should click twice only. Cht = cylinder head temp sensor.

[dsmyth]

Hey Rusnak My CHTS is new. Im going to go out and recheck my dme relay as it seems to continue to tick as I turn the engine over.

[DRACO A5OG]

Who rebuilt the DME?

[dsmyth]

Just a tick on and one off on the relay however I did release the bleed/test cap for my fuel line(I don't have a pressure guage) and while fuel dribbled out it did not seem to spray at all ie little pressure??
I did try spraying carb cleaner under the icv earlier with no sign of life so I ruled out fuel supply.
I cant check for spark because im on my own here.

[dsmyth]

The PO had the DME rebuilt by Vertex about 8 yrs ago.

[Joe Bob]

If the DME relay continuously clicks, the power to the DME is shorting.

My short was found at the fuse block. I pulled the wire, trimmed it, tinned the end and re-installed. No more problems.

[dsmyth]

Joe Bob After rechecking I think it was only clicking once on and once off.