Any special considerations for replacing the DME relay?

monomoy4 · 10-07-2011, 01:32 PM

My 924S cranks and cranks but won't turn over. The fuel pump/filter are new and work. Plugs are new but I'm checking spark this evening regardless. There's no jump or movement of the the TACH on crank - People seem to point to crank position and speed sensor failures here.

However, would there be TACH movement if the DME is bad?? Seeing how removing the sensors seems like a very difficult job b/c there doesn't seem to be any room to work with tools, I figured maybe I'd try the "easier" job of replacing the DME instead and hope the sensors are actually fine.

Sorry for the long lead up, but I'm assuming I need to unscrew the lower fuse holder (1-9) to get to the #2 fuel pump relay? or is there some trick to getting to it without having to unscrew a bunch of stuff. It just seems like such a hassle to remove that relay, given the tight space and awkward position I have to get into to reach the relays.

DME Relais 944.615.227.00

North Coast Cab · North Coast Cab's Garage

The dme relay is in the fuse box under the hood on the drivers side. It is a 10 second swap.
The sensors are very accessible. You need a 10mm with long extension and may need to push some wiring out of the way. Do them one at a time and you may want to unconnected and reconnect them before swapping to make sure they are seated.

Jrboulder · 10-07-2011, 03:05 PM

Quote:

Originally Posted by North Coast Cab

The dme relay is in the fuse box under the hood on the drivers side. It is a 10 second swap.
The sensors are very accessible. You need a 10mm with long extension and may need to push some wiring out of the way. Do them one at a time and you may want to unconnected and reconnect them before swapping to make sure they are seated.

Nope. The relays are under the dash on an early car.

To the OP: I've been able to just pull the DME relay out.

Jackson

SolReaver · 10-07-2011, 06:09 PM

Very simple.

First of all purchase a NEW DME relay. You need a back up anyway.
Second LOCATE your DME relay. Most folks THINK they know where it is. to be absolutely sure ohm out the power wire to the FP back to the DME terminal and for gods sake check the ground and power TO the terminals.

Now, rather than being a parts replacing monkey. Let's get technical. Does your fuel pump get power when you crank the car? Have you tried jumping the DME and what is the result?

When you say the fuel pump is fine...how do you know that?

Check the sensor connector before replacing the sensors. Sensor replacement is a PITA at best. Don't do it before figuring out that they are truly bad and a SIMPLE resistance test is all that is required.

John_AZ · 10-08-2011, 05:10 AM

Quote:

Originally Posted by SolReaver

Very simple.

Now, rather than being a parts replacing monkey , Let's get technical.

Check the sensor connector before replacing the sensors. Sensor replacement is a PITA at best. Don't do it before figuring out that they are truly bad and a SIMPLE resistance test is all that is required.

Sol,

I am getting used to your patient approach in answering members questions.

Or maybe you're working off some frustration after getting home from work.

Your points are correct!!

OP (original poster)

Remove the sensors from the sensor bracket. IF YOU CAN with out damaging the sensors.
Check the sensors, check the connectors for corrosion, check the sensor wires for cracks and bad joints.

BMW Bosch sensors are only $60 or so, half the cost of OEM Bosch Porsche sensors. Use the interchange.

Clean the flywheel studs of grease. Set the sensor gap.

Speed and Reference Sensors - Checking, Replacement, and Adjustment

GL
John

SolReaver · 10-08-2011, 08:14 AM

John: "monkeys" is a term of endearment !! these cute little creatures bring me lots of business.

I actually have great respect for the determined individual who champions on to fix their own car AND I have respect for those who would rather hand it off to a professional. With any luck, the professional will be professional...

There is a problem solving approach that I actually call "parts replacing monkey"

When something doesn't work...just start replacing parts...eventually you will replace everything and have a brand new running car.....

IF you choose the right part...you win! it is kinda like Vegas.

On the day when Alzheimers takes hold and all the hard living catches up to my feeble brain... I will abandon logic and analysis and just start replacing parts willy nilly. As a mechanic I can make a great markup on each part that doesn't need replacing and shrug my shoulders when it still doesn't run. I will begin practicing my mouth breathing and vacant stare in the mirror so that I can make a convincing performance that I really can't figure it out.

But yea, I know I have all the tact of a marine drill Sergeant. Glad to see the folks around here know better than to take me seriously.

Now if the OP can get back to us with a status report, between the bunch of us we MIGHT figure it out. I was thinking we replace the Fuel pump, then the wrong relay, the headlights, the ignition switch, the battery, alternator,

Timmay! · 10-08-2011, 05:30 PM

Momomoy,
The DME/fuel pump relay is quite difficult to remove because there's a relay on either side of it, plus it's up behind the aux fuse block.
BTW, cranking IS turning over. It just won't start.
Have someone put their hand on the fuel pump while you're cranking the engine over. Your 924S has the pump in the open so this is easy. If it vibrates, your DME relay is probably good. The relay is always the first suspect in these cars. Carry a spare.
That relay does two things. It powers up the fuel pump and the DME , or computer. If you suspect it, the first thing you do is bang upward on the relay board with your hand while starting the car. If it fires up, replace the relay.
Do that by:
disconnecting the battery
remove 2 phillips screws holding aux fuse panel and swing it out of the way.
Fan relay is on the top left. DME relay is the tall one next to it. Check orientation of the relay before pulling it. It has 7 pins, several of which are smaller.

Guest765 · 10-08-2011, 05:41 PM

Timmay you have to be trying pretty hard to put it in the wrong way. The pins are set up so that it will only fit one way.

Timmay! · 10-08-2011, 06:06 PM

True, but it's dark and awkward and you have to push pretty hard even when it's oriented correctly.
Kinda like having sex for the first time?

SolReaver · 10-08-2011, 06:53 PM

Quote:

Originally Posted by Timmay!

True, but it's dark and awkward and you have to push pretty hard even when it's oriented correctly.
Kinda like having sex for the first time?

Yea, and just like sex for the first time you are all by yourself and have no idea what you are doing!

SolReaver · 10-08-2011, 07:08 PM

OK folks. Yes the DME relay is suspect in a no start condition, but before we go too far here we should really wait for the OP to get back to us with the facts. We want to know if the FP is getting power when he cranks the car. This can be determined by placing your hand on the pump, located passenger side just forward of the gas tank. When the car is cranked (by an assistant unless you have really long arms) the relay will give power to the pump and the pump will buzz with happiness. you can also check this happiness by putting a test light or VM on the FP and checking that there is 12v or so on cranking. A THIRD way is to crack the fuel line at the rail and put something to catch the gas when it pumps out.

NEXT.... IF the FP is not happy...you would want to "jump" the relay. the forum is resplendent with examples of fancy jumper things. Paper clips work in a pinch as well. IF THAT doesn't work then you try jumping power directly to the FP.

Above all...We are dealing with a 924S here...The DME relay is NOT in the same place as a 944 and extra caution is urged in the identification and confirmation of this unit. SEVERAL apparently intelligent people have mistakenly replaced the wrong relay. See previous post to confirm you indeed have the correct relay. I have a 924S as my daily driver. Trust me in that it is worth the 2 min it takes to be sure. I paint my DME a bright color and have 2 spares.

OK Monomoy4...What is the verdict?

monomoy4 · 10-08-2011, 11:22 PM

Yeah, the relays are unfortunately under the dash here....not the hood.

monomoy4 · 10-08-2011, 11:28 PM

Quote:

Originally Posted by SolReaver

Very simple.

First of all purchase a NEW DME relay. You need a back up anyway.
Second LOCATE your DME relay. Most folks THINK they know where it is. to be absolutely sure ohm out the power wire to the FP back to the DME terminal and for gods sake check the ground and power TO the terminals.

Now, rather than being a parts replacing monkey. Let's get technical. Does your fuel pump get power when you crank the car? Have you tried jumping the DME and what is the result?

When you say the fuel pump is fine...how do you know that?

Check the sensor connector before replacing the sensors. Sensor replacement is a PITA at best. Don't do it before figuring out that they are truly bad and a SIMPLE resistance test is all that is required.

Located the DME relay under the driver dash area. Fuel pump/filter are newly installed this summer, but I did have my wife crank the engine while I felt the fuel pump for vibration/action....it worked. I haven't tried jumping the DME b/c I'm not comfortable, yet, with what I've read so far in Clark's Garage. Figured I'd rather just replace it entirely for now and test later.

Yeah...those sensors do seem to be a PITA which is why I'm going the DME route first. I've got a test for the connectors - but how the heck do I get the connector to separate? I've got limited patience here as I'm fixing issues on my 79 CJ as well...

monomoy4 · 10-08-2011, 11:30 PM

Quote:

Originally Posted by John_AZ

Sol,

BMW Bosch sensors are only $60 or so, half the cost of OEM Bosch Porsche sensors. Use the interchange.

Clean the flywheel studs of grease. Set the sensor gap.

Speed and Reference Sensors - Checking, Replacement, and Adjustment

GL
John

You say use the "interchange" - what's that??

monomoy4 · 10-08-2011, 11:33 PM

Quote:

Originally Posted by SolReaver

John: "monkeys" is a term of endearment !! these cute little creatures bring me lots of business.

Now if the OP can get back to us with a status report, between the bunch of us we MIGHT figure it out. I was thinking we replace the Fuel pump, then the wrong relay, the headlights, the ignition switch, the battery, alternator,

Heh - yeah sorry on the delay on response. Been out working in the yard nonstop - not often we get killer weather here in STL

monomoy4 · 10-08-2011, 11:36 PM

Quote:

Originally Posted by Timmay!

Momomoy,
The DME/fuel pump relay is quite difficult to remove because there's a relay on either side of it, plus it's up behind the aux fuse block.
BTW, cranking IS turning over. It just won't start.
Have someone put their hand on the fuel pump while you're cranking the engine over. Your 924S has the pump in the open so this is easy. If it vibrates, your DME relay is probably good. The relay is always the first suspect in these cars. Carry a spare.
That relay does two things. It powers up the fuel pump and the DME , or computer. If you suspect it, the first thing you do is bang upward on the relay board with your hand while starting the car. If it fires up, replace the relay.
Do that by:
disconnecting the battery
remove 2 phillips screws holding aux fuse panel and swing it out of the way.
Fan relay is on the top left. DME relay is the tall one next to it. Check orientation of the relay before pulling it. It has 7 pins, several of which are smaller.

Thanks Timmay! Yeah, my mechanic mentioned holding the pump while cranking...and thanks on the crank vs turn over = same. So what you're saying is that since the fuel pump works, the DME should be fine??

monomoy4 · 10-08-2011, 11:43 PM

Quote:

Originally Posted by SolReaver

OK Monomoy4...What is the verdict?

Thanks SolReaver - and again sorry to ALL for the delay in response. I have tested the fuel pump...it works. Unfortunately haven't gotten around to testing for spark, yet.

To my earlier question about the TACH jump - does the TACH fail to jump on crank only when the sensors fail? or would it fail to jump on DME failure, too??

SolReaver · 10-09-2011, 12:17 AM

Sorry Monomoy, I never could keep the whole tach thing bouncing stuff straight.

OK, soo...the fuel pump energizes., we don't know if we have signal and we don't know if we have spark...Great.

yea, check for spark. Yaknow an industrious little fellow would have checked spark by now.

If you have a "noid" now would be a good time to use it.

Please don't ask me what a "noid" is...I would just loose faith in you.

With the ignition on check for voltage at the hot side of the coil.

Sensor connectors are taken apart very carefully and yes, they stink. Be aware the plastic that they are made out of has become brittle with age and if you are not uber careful it will all shatter.

When you have the connectors apart measure the resistance of the Sensors as Clarks recommends.

If you have spark...try a shot of starting fluid and see if she kicks.

Getting bored here....

John_AZ · 10-09-2011, 04:50 AM

Quote:

Originally Posted by monomoy4

You say use the "interchange" - what's that??

A sensor from a 1988 BMW 535i will work in place of the OEM Porsche 944 reference sensor--thus interchange and is cheaper.

The wire is longer and Porsche prefers the longer wire to prevent kinking of the wire in a TSB.

Do a search for others that will work on the forums.

I prefer to use sensors with the silver can at the bottom instead of an all plastic sensor. A little more protection for the sensor.

Pelican has both.

GL
John

CatsEyes · 10-09-2011, 05:40 AM

If it does indeed turn out to be the sensors (did you test the connectors yet, by the way?) I'd recommend reading up here before doing the change. It's not so hard, but a bit fussy.

Especially note the advice to cover up the small hole at the top of the clutch bellhousing where you look for engine TDC. Or just stuff a cloth in the opening. I forgot and had my heart in my mouth for a good couple of hours before I finally located the speed sensor bolt, hiding out of sight a few inches away...