3.2 No Start Questions

SpyderMike · 01-29-2017, 03:49 PM

Is there a basic flow chart troubleshooting scheme of any kind?

My 1985 has been sitting for a few months on a battery tender. I went to start it and it cranks fine but won't start. I read some threads about checking the Idle Control Valve first and it does not hum; there no hint of activity. I do not hear any fuel pump running either. My understanding is that I need to get a tach signal for the DME relay to work.

After checking ICV, is step 2 the DME Relay jump?

Thanks in advance for any suggestions.

Mike

hayday · hayday's Garage

Yeah..you can jump from the box to get the fuel pump running and try that. No spare DME? Not sure what the temp is where you are, but it could be the cylinder head temp sensor.

Believe it or not, my 84 sat for a few months, would crank and wouldn't start, but it was about 45 degrees in the garage. I put a 500 watt shop light under the engine for an hour right under cylinder 3 and it started right up. Replaced the sensor and that was that.

steely · 01-29-2017, 04:22 PM

The Bentley manual had a troubleshooting chart (below), but it was written for cars when they were 'younger'. For example, it doesn't mention the helpful ICV hum.

Verify the battery and voltage level are ok.
I would look for 12V (furnished by the DME) on the center pin of the ICV and then see if the DME itself is getting +12.
You could try the FP relay jump, but maybe see if it has +12 too first.
Even if you get the FP to run this way, it may be all for naught if the DME is dead.

steely · 01-29-2017, 04:23 PM

here is the chart from Bentley

SpyderMike · 01-29-2017, 04:24 PM

I am in So Cal - it was 77 degrees here today. I will try jumping the DME Relay. I have owned the car since 1989 and have not replaced the DME Relay in that time.

SpyderMike · 01-29-2017, 04:25 PM

Thanks Steely. That is helpful.

steely · 04:32 PM

I may be mistaken, but a bad CHT shouldn't prevent engine start.
If cold (or even broken), the DME discounts the CHT value until the engine warms up and the CHT value starts looking sane.

steely · 04:56 PM

Quote:

Originally Posted by SpyderMike

Thanks Steely. That is helpful.

No problem and good luck.
The lack of ICV hum concerns me b/c the DME furnishes that voltage to the ICV, and if it isn't present, the DME itself may be unpowered, and the DME (FP) relay doesn't have anything to do with that. <<<< WRONG

On EDIT:
I take back what I said, the power to the DME is definitely routed thru the DME FP relay. I apologize for that.
(Hopefully you do not have a burglar alarm)

jlex · jlex's Garage

Is the fuel pump actually working? Give it a quick shot of ether to see if it tries to start, if so, it's a fuel related problem. Don't overdue the ether. If you jumper the socket for the DME relay, you should hear the fuel pump run.

SpyderMike · 01-29-2017, 06:27 PM

I do have a DME disable switch that powers a battery contactor. That is working. I need to check voltage in and out of the DME Relay. I don't hear the fuel pump running...dead silence.

I will keep the ether in mind....thanks.

Joe Bob · Joe Bob's Garage

If you can ID the relay, it's under the seat and there will be an audible click when the ignition is turned on. It' square and longer than wide and plugs into a receptacle attached to the DME box. 1x1x2ish... No click it is either dead or not getting power.

Check fuses, spin them to seat them and knock any crud off the contacts. The ether shot is a good idea to eliminate the fuel pump if the DME is getting power. Do it while cranking the motor. Takes two to do it....

What city in So Cal are you in? I have a spare and in Buena Park CA.

SpyderMike · 01-29-2017, 07:23 PM

I am familiar with the location, I will be checking that first.

I am in Lake Forest, south OC. Thanks for the offer.

Joe Bob · Joe Bob's Garage

Just down the road if you need help....

pmax · pmax's Garage

Antitheft system ?

SpyderMike · 01-30-2017, 10:16 AM

Thanks Joe Bob. I got the cold/flu last night so I am out of action for a while.

pmax, I have a battery contactor that is switched with a hidden switch that energizes the RUN circuitry. It is working as I can hear it engage and I did have voltage through it when checked with a meter. It is from there out that I lose the voltage.

Checking voltage at the DME Relay is next after I shake this illness off.

SpyderMike · 12:49 PM

Okay, back to about 80% after the flu I decided to give it some attention this morning. It was relatively easy to fix. The DME Relay was pulled an opened. I had what looked to be solder issues and reflowed all joints. Still nothing. I pulled it again (real easy) and opened it up and buzzed out continuity through the connections. I found the main coil was open. The relay was dated 1999 and was made in Hungary.

I desoldered the coil and removed it from the board. I then soldered a large jumper wire from pads connected to terminals 30 and 87 to test and confirm this was the issue. It was, this allowed the car to start and run. I have a new DME Relay on order.

Since the DME Relay is easy to reach and replace, I will keep this "modified" one for my limp home solution if/when the next one fails.

steely · 02-05-2017, 07:06 PM

Glad you found it!
Get well soon, am just getting over something myself.

SpyderMike · 02-06-2017, 06:53 AM

Thanks steely.

ClickClickBoom · ClickClickBoom's Garage

I have been using one of these:
Porsche DME Relay SOLID-STATE w/ Pump-Prime 911 944 968 924S

Porsche DME Fuel Pump Relay SOLID-STATE 911 944 968 924S | eBay

SpyderMike · 02-20-2017, 07:14 AM

Okay, to close this off, I got the new German DME Relay, opened it up to see what it looked like inside. I would say that it looks very much the same quality as the Hungarian one I pulled after 18 years. The solder joints look fine.

I popped it in and all is good with my world.