ArcticSteve

Tried 3 different DME fuel pump relays all working fine in other car. When motor is stumbling bad at idle these relays will get really noisy and vibrate.

Any thoughts?

V2Rocket

i would think the vibration caused by a stumbling engine would be the source of the problem.

ArcticSteve

Let me be more clear. The relay is going bonkers. It's a very fast electrical type of clatering. At the exact same time the Vapour Canister Purge Valve is making a similar racket. The charging volts drop from 13.5 to 13. volts.

bearone

if relays are ok in other car, sounds like voltage going to the relay is a problem, maybe corrosion/bad connection.

87951
95sl320 dd

harrisonrick

Wow Steve, it does sound like a voltage/wiring gremlin. Weird.

Have you cleaned the connections, etc?

TexasBlake

Sounds like the little switches inside the DME relay aren't getting proper voltage or ground.

Each little socket in the DME relay is either goign to be ground or power. You need to pull the relay out, and use a Power Probe or multimeter to check all of the socket. Put a spade connector with a piece of wire coming out to clamp onto the multimeter. You might have to trim a spade connector to fit inside the small terminals.

If you give 87b 12v you should hear the fuel pump come on and get rail pressure. This is why fual rail pressure gauges are good, diagnostic purposes.

86 should give you 12v to the multimeter when the ignition comes on.

85 should give you ground when the ignition switch is on.

30 should give you 12v at all times, ignition switch on or off.

85b gives you ground when the engine is cranking.

If you give 87 12 volts, you should hear the injectors start pulsating. Sounds kind of like vibrating. You need to be in a somewhat quiet spot to hear the pump and injectors come on.

Check and make sure that all these are constant and not jumping around.

John_AZ

Maybe they need a resolder:
http://www.dietersmotorsports.com/te...ay_failure.htm

GL
John_AZ

ArcticSteve

Texas Blake, thanks for that. I'll do those tests.

and John thanks for the link.

bearone

if they all work in the other car i doubt seriously if they all require re-soldering.

87951
95sl320 dd

ArcticSteve

Again tonight I was messing around with it parked and when it begins to stall out I increase the throttle and the more I increase I can get the fuel pressure to drop almost to zero. Hence my original on the read power loss.

At this time the charging voltage was down to about 12.10 volts, enough to run the injectors and the pump. Motor was hot.

Fuel pressure should be constant, more or less. It should not drop to 10 psi regardless of other inputs or lack thereof.

Now I'm just waiting on the fuel pump. Will report the results.

ArcticSteve

Problem resolved. After installing a new fuel pump with no results I eventually noticed a spark coming out of the general area of the reference sensors. Turned out the sheathing on the negative battery cable where it bolts to the bell housing was split. Repaired the cable and reinstalled and operating voltage went up to 13.8 volts and car runs like a top. Essentially a ground issue.

Appreciate the comments.