Author Topic: Car ECU, replace or repair (Read 44707 times)

Balaur · « **Reply #25 on:** August 04, 2012, 01:29:17 pm »

Hello,

If only you had a Rover or a MG, I would have been able to help you more.

The car ECUs are usually well designed and they requires a good knowledge about the specific engine management unit.

The decision to turn the fan on is usually made by the ECU on sensor inputs (can be the coolant temperature sensor, or an engine bay temperature sensor) or following an algorithm (car speed vs. coolant temperature vs. external temperature). Effective debugging is only possible if you know the algorithm and you can act on a sensor.

Are you sure that there is something wrong with your car? The fan should be on only in specific cases.
In any case, the paramount test is to leave the car running while stationary, for a good 20-30 minutes. At some point, the coolant fan should turn on.
If the fan always stays off and the coolant temperature starts to be higher than usual, then yes, there is something wrong. Otherwise, I would say that everything is OK.

Cheers,
Dan

Simon · « **Reply #26 on:** August 04, 2012, 01:31:51 pm »

well we nearly boiled over while in still traffic. I have got the engine coolant to 100C and the fan won't come on.

SeanB · « **Reply #27 on:** August 04, 2012, 02:02:04 pm »

I used to own a Fordza (Mazda badges but ford internals) and they all have a thermoswitch on the left side of the radiator, about half way down. Might be covered with a cowling and hidden by a battery, but is there. Normally it, or the fuse associated with it, fails. Changed a few on assorted Fords over the years, as they are a common failure. SA is a small market, so the UK fordza mechanicals are often used here in the assembly line ( and are exported to the UK as well)so there is most likely a hidden thermoswitch. ask any motor factor, or get the electronic version of Haynes or Chilterns for your model. Otherwise go to an agent and ask at the spares division to look it up on the microfiche. Then grab that 27mm AF spanner and change it.

Simon · « **Reply #28 on:** August 04, 2012, 02:04:47 pm »

no electrics on the rad at all. there is not much cowling but for what is built into the square fan.

SeanB · « **Reply #29 on:** August 04, 2012, 02:30:42 pm »

Not even on the sides? If it is built into the ECU then disconnect the battery, turn on the headlights and leave the door open for 15 minutes. This will deplete the keep alive memory capacitor in the EMU and the airbag controller ( lights on and door open is so that there is a resistive load across the unswitched battery bus to make sure) so that they will restart with the default values. Will lose the edaption values, though, so you will need to take a long drive again to relearn them.

Simon · « **Reply #30 on:** August 04, 2012, 03:14:27 pm »

nope no electrics at all. putting sensors into radiators is extra expense and complicates things, the radiator tanks are plastic, very cheap design, we'd buy that rad for about £30 at work, easier to just screw it into the engine. The rad thermostat comes in at 88C and the fan should come on around 98C so some leeway. The fan does not even blow on the whole rad, just half including the area covered by the "shroud"

asbokid · « **Reply #31 on:** August 04, 2012, 03:57:01 pm »

It would be a good project to get an ECU 'running' on the bench, with all analog sensor inputs to the ECU generated by a microcontroller. We looked at doing this with a Mazda/Ford ECU but after counting 17 sensors, some 10 actuators, and scant documentation on any of them, the idea was soon abandoned!

In the Ford/Mazda workshop manual, it was ever so vague.. "sensor X should measure between 0.20v and 1.58v" etc.. e.g. no proper explanation of the role of any of the sensors, their transfer functions, nor how the sampled analog data was actually used by the ECU.

The CPU in that particular 1996 Mazda ECU was a 68HC11, an 8-bit microcontroller from Freescale, powered by the Motorola 6800 microprocessor. [1] The firmware was held in a 256Mbit serial EEPROM. In theory, the firmware could be extracted and run in a processor emulation environment on a PC (in QEMU or similar). [2]

ECUs are the quintessential 'black box' device. They have inputs, they have outputs, but what goes on inside remains top-secret!

cheers, a

[1] http://en.wikipedia.org/wiki/Freescale_68HC11
[2] http://wiki.qemu.org/Main_Page

IanB · « **Reply #32 on:** August 04, 2012, 03:58:45 pm »

Just read the whole thread. I would think the ECU is the least likely place to look for a fault. It is solid state electronics with no moving parts. There is nothing to go wrong.

What you have is a control loop. The engine/coolant temperature is measured in one or more places, this measurement is fed into the ECU, the ECU decides when to turn the fan on.

You have verified that the output part of the control loop from the ECU to the fan works OK. But have you verified that the input part from the temperature sensor to the ECU is working correctly? Using the diagnostic computer is there a way to get a readout on the temperature seen by the ECU?

One thing I would do is physically check the temperature sensor circuit. Make sure the sensor is working and that all electrical connections are sound between the sensor and the ECU. You could unplug wires and clean terminals with deoxit and/or fine abrasive. Put a meter on the temperature sensor itself and check that it is sending out the right signal.

asbokid · « **Reply #33 on:** August 04, 2012, 04:01:19 pm »

can you back-probe all the sensors that are used by the ECU to determine fan activation? What is the diagnostic interface like on the Mk.4 Fiesta? Can it diagnose a failed sensor circuit?

cheers, a

EDIT: ianb (with the funny hair) has pretty much said just that

Simon · « **Reply #34 on:** August 04, 2012, 04:52:37 pm »

I don't know if there are more sensors. The haynes manual was written by two faced bastards who specialize in making things as clear as mud but covering the ground. My book covers 5 models all with different engines. I will have to go though all the partial diagrams and see if i can spot any other sensors. As things stand now the break in the loop is the ECU, it knows the coolant temperature because it is telling me it on the diagnostics line, it can make the fan work if it wants to because we made it do it.

I will study the diagrams in detail, see what I can find. Ideally a large printed diagram of the whole car should be included with these books, one per model, the array of partial schematics with details for multiple models is just stupid.

asbokid · « **Reply #35 on:** August 04, 2012, 08:14:33 pm »

Maybe the coolant temp. sensor works to a point, so it passes initial tests but fails once the coolant has got hotter?

Dunno who produced this manual, but there are some wiring diagrams at the back for the various engines used in the Mk.IV. See page 250 onwards.

https://rapidshare.com/#!download|668tl2|362825041|Ford_Fiesta_1995_Service_and_Repair_Manual.pdf

EDIT: Or maybe this one?

http://thepiratebay.se/torrent/4922665/

I'm sure there used to be an official DVD with Ford workshop manuals for most/all Ford models up to 2004, or some such.

cheers, a

Simon · « **Reply #36 on:** August 04, 2012, 10:55:41 pm »

Thanks, will take a look when I'm on a pc. I've gone through the relative schematics in the Haynes manual and can only find 1 coolant temp sensor.

aargee · « **Reply #37 on:** August 04, 2012, 11:17:53 pm »

It wouldn't surprise me if the Haynes manual was wrong, especially covering several different versions of your car. All the Haynes manuals I've ever had to look at have always been a let down in the circuit diagram/description area.
I think they feel that mechanics don't/can't use this information anyway.

Chet T16 · « **Reply #38 on:** August 04, 2012, 11:27:00 pm »

Haynes are hit and miss. One copy I have have diagrams that are largely useless while another for a different model not only has accurate diagrams but in them has illustrations of all the connectors.

One of my cars has three temp sensors, one for the fan, one for the ecu and one for the dash gauge!

Simon · « **Reply #39 on:** August 05, 2012, 01:08:14 am »

I think Haynes should be ashamed of themselves. They have gone from high quality to con merchantry. Non of their texts make sense anymore or are practical. Clearly not written from hands on experience - bunch of wankers !

pickle9000 · « **Reply #40 on:** August 05, 2012, 02:45:23 am »

Hey Simon

I had a quick look at the wiring diagrams and there appears to be 2 temp sensors but that of course depends on the engine.

I'm guessing thermistors but you'd have to meter them to know for sure. In any case I'd disconnect one then the other and see if you get an engine warning light. You should also be able to ID the one that is for the instrument gauge. I know you had it connected up to a diagnostic tool, did it give the temp of the engine?

As for the ecu controlling the fan that is certainly not in the diagram. You could get item 8 in the diagram and wire up the fan in the same way.

Regardless of what you do a switch applying power to the fan will keep the motor from getting damaged. Of course you will have to take the place of the computer. I guess that would be a biologically enhanced car. I unfortunately have had several of them (but only until fixed properly).

...mike

sonicj · « **Reply #41 on:** August 05, 2012, 03:30:07 am »

"The electric cooling fan, mounted behind the radiator, is controlled by a thermostatic switch. At a predetermined coolant temperature, the switch contacts close, thus actuating the fan."

If you don't have wires coming off your radiator, well, you should. The ECU needs control of the fan for AC &/or Turbo. Since you don't have either, you could wire the switch directly to the relay (if it isn't like that already). My bet is on a failed radiator thermal switch.

http://www.ebay.co.uk/sch/i.html?_nkw=ford+fiesta+radiator+switch

-sj

dcel · « **Reply #42 on:** August 05, 2012, 05:58:26 am »

Simon

There are two temperature sending units in your car, find them. One could be labled as a temp switch, fan switch, or whatever the hell they decided to name it. I have seen those sensors on the coolant return from the radiator, down on the bottom of the engine block, it could be anywhere, you gotta hunt for it.
Also look for a BAD GROUNDS, from battery to chassis to engine to dash. After you said that it started running better and then the cooling fan quit, I would really start looking for BAD GROUNDS! Most sensors rely on chassis/engine ground and 5VDC from the ECM to send their signal back to the ECM in a voltage range that it can understand. It is also possible that you have a short to ground or a heavy current draw on that 5VDC line from the ECM. That will create all sorts of strange behavior that is hard to track down. A sensor that is leaky or intermittently shorting to ground or opening up putting 5VDC on the sense line back to the ECU could keep it from knowing when to turn on the engine fan.
Check ALL fuses and links with an ohmmeter to insure that they are not blown. Please don't trust any schematic, manual or diagram, they are likely all wrong. Verify by chasing the harness to the very end connectors and make sure there is no pinches, chafing, burns or missing insulation. Change out the cooling fan relay for a known good one, never trust, verify operation or replace it. Automotive environmental conditions are hell on electronics as you know.

Good luck...

Chris

SeanB · « **Reply #43 on:** August 05, 2012, 06:08:32 am »

Just talked to a mechanic friend of mine, and he reminded me that a lot of those coolant sensors are mounted in plastic blocks inline with the piping for a lot of cars. Look at the plumbing ( you may have to remove a lot of plastic trim covers to see) and look at the water piping for a black object with a connector or two coming from it. Post a photo and WE will be able to ID what the part is.

amyk · « **Reply #44 on:** August 05, 2012, 06:45:12 am »

What's the exact model of car? The 1995 service manual pointed out above does not show any ECU control of the fan.

Simon · « **Reply #45 on:** August 05, 2012, 06:48:16 am »

Fiesta mk4 2000 finesse

Simon · « **Reply #46 on:** August 05, 2012, 07:12:24 am »

Quote from: asbokid on August 04, 2012, 08:14:33 pm

EDIT: Or maybe this one?

http://thepiratebay.se/torrent/4922665/

I'm sure there used to be an official DVD with Ford workshop manuals for most/all Ford models up to 2004, or some such.

cheers, a

Piratebay is blocked in the uk

Simon · « **Reply #47 on:** August 05, 2012, 07:16:44 am »

Quote from: asbokid on August 04, 2012, 08:14:33 pm

Dunno who produced this manual, but there are some wiring diagrams at the back for the various engines used in the Mk.IV. See page 250 onwards.

https://rapidshare.com/#!download|668tl2|362825041|Ford_Fiesta_1995_Service_and_Repair_Manual.pdf

It's a sodding Haynes manual and for the MK3 I think. Has no 1.3L but a 1.4L engine and calls it HCS, this was the predecessor and basis of the endura E I have. Probably the same as my dads old ecscort from 1989

Wilkins · « **Reply #48 on:** August 05, 2012, 07:18:26 am »

I was having all kinds of wierd problems in my bmw with erratic idles and poor fuel economy, i pulled the ecu out on a hunch and cracked it open.

It was heavily water damaged, pins shorted on the IC's, corrosion all over the shop, its a testament to the tolerance of errors in the design that the car ran at all.

I was able to score a second hand one on ebay for about 70 pounds + 10 pounds postage, a lot of the different models of ecu are shared between makes of cars, you just need to transfer the rom that stores the program for your car from your old one to the new one.

So it might just be worth replacing the thing.

Simon · « **Reply #49 on:** August 05, 2012, 07:35:15 am »

the ecu for mine i think does the MK3, 4 and escort MK6. It is I think in the passenger aread behind the facia so should be protected fro water. Where on earth did they put the BMW ecu ?


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Author Topic: Car ECU, replace or repair (Read 44707 times)

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