DME & Fuel Pump

[mcgc0]

Have the C4 which had a completely dead battery while having some minor paintwork done over 5-6 weeks period. Tried jumping but realised first hand that unless the 'donor' battery on the other car is up to it or (almost) the same spec as well it still ain't gonna fire up. It turns over (just) but that was all. However, strangely enough after recalling a couple of previous posts I'd thought I'd give switching DME's a go even though the one I had was fine. Did this and presto - we're in business and she fired up immediately!

After a day or two of driving around I swapped back to the DME out of interest and that works fine too - although a tiny tiny longer on turn over before firing up but fine otherwise. But, for some reason the fuel pump whine up front is permanently on regardless how long any journey is. It never used to do this for some reason. Swapped over the DME again this morning and that has made no difference - loud whine still there. So, a couple of questions...

- What is that loud whine? Maybe getting a new DME might cure this? Or is my pump knackered?

- How or what makes a DME 'degrade' or differ from the next when using my dead battery or slower firing up as examples and can DME performance be measured (test bench or otherwise)?

Thanks in advance chaps...

 

[Dekker]

Hi Marcus

I would double check that it is the fuel pump that is permanently on with a long screw driver as a stethoscope as the DME electrically isn't that complex from the wiring diags.
It has 2 solenoids which control 2 switches so the typical failures are where the contacts of the switches build up carbon over time with the continual arcing from switching or to welding fully closed.
One of the switches controls the Fuel Pump. The other switch activates various sensors and valves. One of them is the Idle Positioning Valve.
I haven't looked at my DME but most of these devices can be opened up with a watchmakers screwdriver and a little gentle persuasion.

 

[vitesse]

Hi Marcus,
I have 2 useful publications-one is the Bosch leaflet on contact reference nos for all devices used on cars-so it it gives you the spade /socket no ie 86 or 52 or whatever for motors,relays,coils etc with little diagrams so helps track wiring in conjunction with the wiring diagram for a car--the other is an American download about all matters relay-with instructions on testing them--basically as David says--carefully remove the metal or plastic can off the relay-normally there are little plip latches moulded in on 2 opposite edges-then make up a power supply by attaching leads to a PP9 battery-that's all that's needed-apply to the appropriate terminal(s) -(Bosch leaflet helps with that)-& you can see what closes ,latches etc.

If contacts are arcing /pips on them etc then subtle cleaning up with a points file/garnish paper can be attempted & the results checked.

I'll see later if I can find them & even PM them to you,if I can cope with all that IT .

 

[ras62]

Low voltage will cause all manner of strange symptoms as the various electronics are very sensetive once 12.5v or thereabouts is reached, so better ensure the battery shows 12.8v+ and that the alternator supplies 13.5v+ on idle.
The DME relays can suffer from dry solder joints and are often of dubious quality. As said previously there are two contacts inside, the first supplies 12v to the DME unit, the second sends power to the fuel pump but only when the DME unit recieves the crank sensor signal when starting.

 

[vitesse]

Found both the Bosch & Relay documents-have also found the Bosch file on my laptop-it was imported from my 1st failed Dell laptop-what a waste of money that was.
I will PM the Bosch file but I can only suggest you search Wikapedia , use google,or visit www.autoshop101.com to find the Relay doc--it's an American publication by Autoshop 101.com called "Understanding Relays written by Kevin R. Sullivan--Professor of Automotive Technology-Skyline College.

Just visited the site myself-the article is almost at the bottom of the Technical Articles section which starts with mainly Toyota features
Realise can't attach a file in a PM so if you PM me your normal e-mail address,I can send it

Cheers,

Colin.

 

[mcgc0]

Nice one gents... really useful advice and suggestions - will go through those docs next Colin, cheers.

Have a new battery turning up (for some reason the current one let me down today at a petrol station this morning and sounded ill - despite being on the CTEK). Hopefully this will be the elusive cure. Whine is located around the filler pipe into the tank and can only assume that, if the pump at the bottom of the tank, then maybe it is resonating up though the tanks an liquid contents - clutching straws maybe with that explanation!?

 

[ras62]

CTEK will not make a dead battery good again but I would think the new battery will solve your problems. Its certainly worth checking the alternator voltage on idle to ensure its ok. Strange noise could be a fan or maybe the amplifier...like I said these cars dont like low voltage and its easy to chase your tail whilst overlooking the simple things. Let us know how it goes!Rob

 

[Dekker]

The 12v feed to the fuel pump is via 15 Amp fuse No.34.

With the ignition on and the whining sound, try pulling the fuse and see if it kills the sound.

 

[mcgc0]

Nice one Rob and valid points indeed. When checking battery purchase date, that I knew wasn't that long ago (Dec '12), the receipt mentioned an Exide. In that car it's a Varta! Buddy Greg reminded me that I put the Varta in the Focus ST when it's battery died. I must have switched then to the battery from the previous C4. So, yup, would like to think the new battery then is the magic wand - we'll see.

David, the whine is only on when the engine is running - not ignition only. A new DME though is on it's way. Will take one apart as you suggest for a learning look...

Marcus

 

[ras62]

Thinking about it Marcus, that whine is very likely coming from the Alternator on full load as it tries to charge the dud battery? Guess all will be revealed soon enough.