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Cvh Efi Coolant Temperature Sensor/sender.... Location?


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OK so I'm a little stumped as to how the EFi system on the 1.6 CVH senses coolant temperature for the purposes of fuelling. I know the switch on the thermostat housing operates the radiator fan, and the little one by the exhaust manifold operates the temperature gauge on the dash.

 

What I'm wondering is, does one of these also give the ECU a temperature signal or is there a third sensor for this & where's it located?

 

 

We've always suspected the ECU isn't getting the true story regarding temperatures, but just the other day the fan failed to cut in and I've traced that back to the switch having failed.

 

So I'm going to replace the switch (along with thermostat housing, as the threads have utterly welded themselves together to the point I'm scared of ripping a chunk out of the head if I lever any harder on the sensor/switch. But while the cooling system is drained I also want to do some other jobs like replacing the radiator crossmember and refreshing the starter motor so I reckon this would be an ideal opportunity to sort the ECU signalling as well.

 

So if anyone can point me in the direction of the actual ECU coolant sensor, and even better if they could furnish me with a rough set of values to test (say, 10c/20c/50c/80c/100c resistance values) that would be bloody amazing.

 

Here's hoping! lol

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Well, I had a firtle under the manifold earlier and disconnected the sensor. Cold starting seemed improved although it stayed in cold start mode as I expected, so will get a new sensor and give the whole bay a good cleanup soon. Cheers again.

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Disconnecting the sensor will just flag a fault in the ECU.

The sensor has a 5 volt feed from The ECU and The voltage it receives back is what is used to determ nine the engine temperature. It does this by changing resistance with temperature as is is a negative coefficient thermistor. If the sensor is disconnected then the ECU will see zero volts instead of somewhere in between 0.5v and 4.5v. This will tell the ecu there is a fault and a value will be substituted with the same reading as the air intake temperature sensor which is electrically identical. The system is a bit more clever than you think!

Have you scanned for any fault codes?

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Excellent post, and I've learned something in the subbed value from the IAT. I just (made the classic mistake of assumption!) guessed that disconnecting the CTS would default it to cold start mode.

 

EEC-IV seems to get better the more I learn about it, and this makes me wonder even more if the common idling/stalling etc faults associated with EFi on the CVH engine are really "built in" or if the thing can in fact be made to work properly. I'd suspect it really does work well when all it's operating parameters are in spec.

 

If there's any more details on the system as a whole/any personal ideas why a lot of people experience fuelling issues in connection with the CVH lump I'd be interested to hear more if you have the time. Always ready to learn, specially when it comes to something that *should*/did work but doesn't & people seem to have written off as a bad job.

 

I did a flash code read last year and that came back clear from what I could tell, although I've always promised myself I'd buy a proper reader to convert the flashes to numeric codes more reliably as I did find the spacing/length of the flashes quite hard to judge. Perhaps it's time to bite the bullet and do things "properly" even if it would be a bit of a "niche" machine to own. (I'm forever telling folk with modern cr*p to get the codes read before throwing parts at it, I should take my own advice lol)

 

Thanks for the pointers on the sensor "language" of the EEC-IV, I did actually find some details on resistance values at given temperatures so now I have my multimeter back I can actually test the sensors properly too which helps :smile:

 

Thanks again fella, hope to hear back soon. Dan.

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The CVH efi engine was renowned for drivability concerns even when they were new. Don't think Ford ever truly got the bottom of it. You have to remember that, although an excellent engine in its day, it is still an old design. It was dressed up with efi to meet emmission regs etc before the launch of the Zetec.

In the early days the idle speed control valve was a Hitachi unit on top of the air cleaner box. These were dreadfull and was soon modified to have it fitted on the baulkhead so it was closer to the throttle butterfly. Then modified again to have the idle valve bolted to the intake manifold. These were the best ones but still not great. There were modified ECUs as well but were still not perfect.

Think the honest truth is that it is an old design engine which is not designed to run on the lean mixtures required to get through the emission regs and if you run an engine on fresh air it is just not going to run very well.

Leaving the intake air temp sensor disconnected seemed to make them run a bit better but was not considered by most to be acceptable as 'Ford fitted it for a reason'.

Some went for a super chip ECU which I have heard is much better but have no experiance of this.

I remember fannying around with resistors in line with the wiring to fool the ecu and to make them run richer; with some success I might add. (Much cheaper than a super chip anyway)

The only other tip I can offer which is probably the best is make sure it is tuned properly. To do this do the following.

1. Disconnect the battery for 10 mins. This will clear the ecu of any idle values.

2. Run the engine and disconect the idle speed control valve.

3. Adjust idle speed via the air bypass screw until you get an idle speed of 750rpm.

4. Reconnect the valve.

5. Adjust the fuel mixture with an exhaust gas analyser. CO should be on 1%.

6. Put the roof down and drive your car with a big smile on your face, and remember. You are in an Escort cabriolet and not many other people have got one!

Edited by Paul Grainger
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Nicely fella, will sort out the base idle when I get a chance as it just stalls with the ISCV disconnected.

 

It does seem to run more rich than lean though, and can't get use of a gas analyser so can't ascertain CO levels but will have to soon.

 

Thanks for the advice, it's good (for a scatty brain like mine) to have it laid out in a methodical order to go through.

 

We are lucky at least to have the later ISCV setup, although I doubt the ECU is very updated as it's very early Mk5 (I think later 5's and 5b's had a Lambda instead of a CO pot.?)

 

Cheers again.

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Yes that's another thing I've heard of failing, can't seem to locate any new only used though.

 

Fun I certainly will have, I'm determined to have this thing running nicely. I don't really subscribe to the "it's not designed for EFi" theory, based on my experience of the Peugeot/Citroen TU range of 8V OHC engines introduced in '86 with carb/points etc & happily running (very perkily I might add!) on multipoint EFi well into this decade...

 

Obviously I'll share any findings, especially if there does actually turn out to be some kind of panacea that will reconcile the CVH with EFi :biggrin:

 

Thanks again, here's hoping I get the time/weather to play a bit more now.

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