stay6

A couple of days ago my '84 hesitated to start but after about 3 seconds finally did and that was the first indication. The problem did not rise again for a week or so and then it was slightly hesitant again but only once. After being started everything seemed fine. Cold starts seemed to be the new problem area. Yesterday it refused to start at all. Motor turns over at a high rate but no start. Electrical seems good. I'm thinking a fuel pump at 66K miles or a fuel filter. Before I launch of into this does anyone have a suggestion? Any help would be much appreciated.
Thanks, Scott

ron mcatee

The DME relay on the 84-89 Carrera's is prone to failure. I had to replace the one on my 88 Carrera at 73K miles. They are relatively inexpensive. If you know someone with an 84-89 3.2 Carrera, see if they will let you use their relay to verify the problem. Mine was intermittent and I thought all was OK until I started on a trip. Luckily it died within 35 miles of my wrench's shop.

Lorenfb

Use this web page ( www.systemsc.com/diagnostic.htm ) on the "No Start" section.

Don't spend/waste money until you've identified the source of the problem.
Guessing or "throwing darts" at a parts list doesn't get!

hmd

I am having a similar issue, car won't start, spark ok, fuel coming out of pump but no injector pulse.


What should I check? and where are the relays located?

Thanks in advance.

ron mcatee

Please ask Loren, he seems to know it all.

Lorenfb

Since the Porsche Motronic Unit (DME unit) controls both the spark and fuel,
a spark signal but no fuel injection pulse indicates a bad DME unit. This assumes that:

1. the injectors have +12
2. no short exists in the injector wiring
3. the wiring from pins 14 & 15 of the DME are O.K.

MJHanna

http://forums.pelicanparts.com/showt...hlight=bad+DME


more info. you could pick one up at Boardwalk

stay6

Thanks for all the info, it's in the shop now.

hmd

DME swap to another car and worked ok, so must be wiring issues?
The DME relay don't affect injectors?

Lorenfb

The DME relay does affect the injectors, as it supplies the +12 volts to them
as it also supplies power to the DME control unit. It's a simple test to just turn
the key on and check with a test light at an injector connector for +12 volts.
You can also check pins 14 & 15 on the DME control unit connector for +12 volts.

hmd

I think I have resolved the issue. It is traced to the transmission ground strap, I cleaned up the contact areas and now have no issue starting the car (fingers crossed).

The moral of the story is that any thing out of the ordinary in the electrical system (even symptom such as no pulse to injectors) this is the first place you should look.

Lucky for me I had a loan DME unit and quickly determined that my DME is OK. I then ground the engine using a battery jumper lead and the car started immediately.

Thanks to Loren for his pointers in his PM to me.

glenncof

I had a no start situation on a 1985 recently and it sounded like no fuel. My DME relay finally had intermittent failure at 170K miles (Original relay).

I verified this as the problem by first measuring the fuel pump voltage when cranking (must be cranking or engine running) and then putting a jumper from 12V to the fuel pump fuse. On my 1985 it was a jumper from fuse 16 to 17 (you should verify) as suggested in my Haynes manual.