Starting issues

450knotOffice · 450knotOffice's Garage

Guys, I'm sorry but I just don't have time for an involved search so maybe you can just give some ideas here. I've noticed that the last couple of times I've tried to start the car ('84 Carrera with 3.2 Motronic, of course) it has taken forever to light off. I mean like 8 to 10 seconds of fast spinning before if finally lights.

This just started happening. Battery is good. Starter motor spins fast. Runs great once it's started.

Ideas?

slodave · slodave's Garage

On a whim... Have you tried a new/diff DME relay?

Dave

ruf-porsche · ruf-porsche's Garage

speed sensor or reference sensor.

DW SD · 10-02-2006, 01:42 PM

I'm thinking there is a possibility that the fuel pump check valve may be bleeding pressure. Though eight seconds would be a long time for the pump to build pressure. I don't run a check valve in my setup and a long start for me is 3 seconds. If I prime the system by running the fuel pump before cranking (jumping the pump) I start instantly.

Maybe a combination of somewhat old pump, clogged filter and broken check valve.

Personally, I would think a reference sensor would work or not, but not sure why it would take 8 to 10 seconds to begin working?

Doug

johnsjmc · 10-02-2006, 01:55 PM

I suspect the DME relay.Does it start normally sometimes and sometimes not?

450knotOffice · 450knotOffice's Garage

Sorry for the late response guys. I was out most of the afternoon. In fact, when I typed the message the engine was running in the driveway which was why I was in a rush.

The car has started great all day since this morning's looooong start attempt. On the first attempt this morning it spun and spun with not even the slightest hint of a light off (and no gas smell either) and then it just fired right up and ran smoothly. It seemed as if the injectors weren't spraying at all so it seems quite possible that the fuel pressure may in fact be bleeding off after some down time.

The engine did this to me last week after sitting for a few hours at Paul's shop (Pkaaso) while I installed a factory short shift kit. When I attempted to start it that time, the same thing happened.

I will say this: the car has the remnants of an old alarm system still installed. All that seems to be left is the touch pad wired into the wiring bundle under the dash. It's been there since I bought the car and has never caused me any problems. I would have removed it eons ago but I wasn't sure what it was tied into and I didn't want to just snip it out for fear of disabling the car. So I just tie wrapped it up out of the way and forgot about it. Last week at Paul's shop I moved it out of the way without a second thought. The starting issue happened right after that. I wonder if I might have disturbed a wire up there which is now causing an occasional hard start issue (other than the first start this morning it has started instantly every time today).

Paul seems to think it could be my ignition switch. Does a failure of the switch manifest itself this way sometimes?

To answer the DME relay question, it was replaced 1 1/2 years ago. I suppose I might have bumped it or the bundle leading to the DME itself when I slid the driver's seat all the way back last week to gain more room for the shifter R & R.

(edited for clarity)

DW SD · 10-02-2006, 03:55 PM

HMMMM, ignition light off process works like this:
1. turn ignition on, which turns on stage 1 of the DME, which gives power to the computer.

2. crank, speed sensor sees engine cranking.

3. DME then provides power to stage II of the DME relay which is the fuel pump relay (Remember, DME relay is two relays in one). the fuel pump runs to build pressure.

4. DME Computer controls spark timing, fuel delivery and amount, etc.

The starter relay is totally independent of the DME relay, so the ignition switch could be beginning to fail. You'd have to check for power at the DME relay (stage 1), when you have the no start condition.

I'd be surprised if the alarm bundle is affecting your ability to start. Seems like it could kill the engine when it is running just as randomly if that were the case.

Doug

johnsjmc · 10-02-2006, 04:02 PM

The DME relay sits beside the DME it is a 2 stage relay which is responsible for switching on the fuel pump when it gets a command from the DME. They are known to fail causing an intermitant no start .Borrow a known good one or buy a new one You can keep the old as a spare You will need to replace it eventually in any Motronic car.

450knotOffice · 450knotOffice's Garage

Thanks Doug and John. I suppose it very well could be the DME relay but, dam* if I didn't replace it 1 1/2 years ago. Do these things fail that often? I still have my old one, btw.

DW SD · 10-02-2006, 04:12 PM

You should be able to test with a test light, if it is the relay.

Test for power at the fuel pump during cranking.

My experience is that power should come on as soon as cranking begins to the fuel pump.

Doug

johnsjmc · 10-02-2006, 04:20 PM

Do you remember why you replaced the DME relay last time? Try the spare relay.

450knotOffice · 450knotOffice's Garage

Slodave said:

Quote:

On a whim... Have you tried a new/diff DME relay?

and I answered:

Quote:

To answer the DME relay question, it was replaced 1 1/2 years ago.

OK, I'm a moron. The car wouldn't start again today so I decided to pull the DME relay. Guess what? Dummy me found one from 1989 in there. It all became very clear suddenly. I in fact did buy one 1 1/2 years ago but simply threw it into the glove box for future use. I never actually replaced it. Duh! I swapped it out with the new one and it fired right up.

It sucks getting old (42). Your mind is the first thing to go.

DW SD · 10-04-2006, 04:45 PM

All's well that ends well.

Glad the problem is solved.

JP911 · JP911's Garage

I was thinking maybe the problem was a protest against the new addition to the garage.

450knotOffice · 450knotOffice's Garage

I like to see what's going on (if possible) so I pulled the relay assembly out of its box. I quickly found the area where the solder had come off. It looked like it was making only occasional partial contact, so that was the problem right there. As Steve Wong has pointed out, someone who is good with a soldering iron could fix this right up good as new.

The arrow points to the area missing the solder and I also circled the date on the relay's box. That thing was fairly old.

The actual relays on the back side of the circuit board. There are two of them there. I circled the contacts (sorry for the blur) just so you guys would have some idea what it looks like in there (under your seat).