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McClendon-EspritSE

91 SE cooling fans dont come on

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Dear Esprit fans,

On my 91 SE, the cooling fans do not come on at the 90 degree C point as they did last summer. I have replaced both relay modules and the temperature switch below the intake manifold. The temp gauge shows a slow rise to 80 deg. If the car sits at idle for a while it will eventually climb to 90 and then upwards of plus 100 C. If I turn on the A/C to max then all three fans switch on (as expected). This will eventually bring the gauge temp back down below 80, so I believe that the water pump and cooling system are in good operating order. Is there something besides the relays and the switch that I need to test? If I drive the car at speeds the temp always stays at 80 C, again showing a working cooling system. Any ideas for hidden sensors, relays, switches that I might have overlooked? My research shows that I should have two of the three fans switching on at 90 C.

Cheers from sunny Houston Texas

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Upgrade today to remove Google ads and support TLF.

What happens if you put the air-con on?

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Roger - Read this bit again - If I turn on the A/C to max then all three fans switch on (as expected)

Charlie, plug Freescan into your car and see what temperature readings your ECU is seeing. I'm guessing you've a duff sensor.

In the meantime, leave the aircon on, it will mean that your fans will always be on below 30mph and will keep your water cool. :D

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92C to be precise.

You should have an ECU fault if there is anything wrong with the control side of things.

ECU controls the radiator fan relay in the back of the car's relay board, ECU is fed info from the sensor under the fuel rail - this is NOT the same as the dash board display which is taken from the water pump. If you plug freescan into the car you'll see the reading from the ECU and the true reading....I hate the way they done thisbecuase it causes much confusion.

The dash sensor can fail, go low, go high etc and the car will be fine in most respects - my 1997 GT3 displays about 10c too low all the time for example on the dashboard.

So from the Sensor that feeds the ECU you have an output to a relay in the back (radiator fan control relay), the ECU controls this relay and it is the same relay that clicks in when the AirCon is functioning. This relay then in turn feeds another relay in the font (why I dont know) but there is another relay there which is called the Radiator fan relay, this feeds 3 sets of 10A fuses that fund the fans.

I suggest if you're getting AC control your sensors are shagged....aaand I've just read Bib's post above and typed that all out for bloody nothing... :D

If you have a thermometer (check it at boiling temp 100c) then dunk it in the coolant as the car is heating up, be careful not to let the coolant expand too much or it'll bubble out. Better still a laser thermometer, that way you can zap the engine block to get a true reading.

But with that you should be able to tell what temperature is correct.

In my experience the pump sensor goes more often than the engine block one (under the fuel rail) which is nice.

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Cooling fan update....

I hooked up Freescan last night so I could watch the ECU temps. From a cold start, both Freescan temps and the car dash gauge temps are within 5 deg C of each other (dash gauge being on the higher side, but only by 5 C). I let the car warm up at idle, checking both the Freescan and the dash gauge frequently. Eventually the temp gets up to 80 C, both temps are within 3 Deg C of each other. Continue to let it idle, it evenually rises to 92 C on the Freescan screen, dash reads 95. No fans trip on. After a wee bit it starts to creep to 105, still no fans. I turn the A/C on to max and all three of the fans trip on. Temp drops back down to 80 C within a ten minuted period. Turn the A/C off, and the three fans turn off. I believe that with this test I have confirmed that my temp sensors are both good (and the one under the intake is new Lotus). Keep in mind that I also replaced the two relays (front of car and the one in the boot). Any ideas of what might be going on? Can the ECU be bad?

.

Also, I have a good sized Excel file of the Freescan run from last night if any of the Forum folks would like to take a look at it for me. I ran the car through RPM ranges from idle to 4k and then back down to idle, several loops of RPM ranges to try and capture loads of data.

A couple of concerns I have (may not be valid concerns, as I am learning to understand the program still):

.

a) My Rich/Lean numbers jump from the 70's up to 250, and then fall down into the single digits, then back up again.

b( My Spark Advance seems to jump all over the place, but this might be normal for engine speeds changes, just seems excessive.

c) O2 figures are also a bit random

Let me know if you are willing to review the Freescan files, send me your email address, and I will send you the file to look at.

Many thanks,

Charlie McClendon

91 Esprit SE

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Mine's an 88 so don't quote me but. I made a short lead to short out the conectors to the tempreture sensor, the one in the pipe from the thermostate housing. There is more than one in the pipe and I seam to recall I chose the wrong one first off, but was subsequently able to prove everything worked, as it turned out in my case so did the sensor.

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It's possible, if the AC brings the fans in the wiring should be fine becuase I think the aircon / fans are called by the ECU as well - personally I would double check and test it through by volt checks, continuity and bridging contacts on the relays to force the fans in manually.

I dont know anything about the ECU but it could be that the ECU doesn't realise 92c is time to force the fans on - it's possible there is corruption in the memcal (ie its set way too high ?)

The other alternative is that the ECU thinks it HAS put the fans on but doesn't realise they are not on which is why there is no fault code.

If you have no joy here I would speak to John Welch @ http://www.wcengineering.com who is extremely knowledgeable on this subject and he might be able to help.

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I would check the 'Rad Fan Control Relay' located in the boot and it's associated wiring (as suggested by Jonathan above). This looks like the first thing to check according to the symptoms.

If this reveals no problem then it may be worthwhile running Espritmon to help with this for a couple of reasons;

Espritmon has an indicator to show whether the ecu is commanding the fans on, you can see whether this is being illuminated for both A/C demand and ECT.

You can also enter Mode 4 diagnostics and command the fans to be on and see if they do indeed turn on.

Edited by sailorbob

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You need to check the ecu is giving the rad fan control relay an earth when the fans are supposed to be on. You know the ecu is getting the temp readings fron the sensor so everything from the sensor to the ecu is working properly. If you don't have an earth at the fan control relay trace the wiring back to the ecu and check it there. If there isn't one or it's intermitant suspect the ecu itself is faulty. I had this exact same fault with mine when i bought it which turned out to be the ecu, the only options are to have it repaired or replace it.

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If it is the ECU, depending on the cost of replaceent / repair - you could run a voltage through the sensor (they are resistive, hotter=lower) you can make a little transistor circuit up that can easily mimmik the ECU. Basically the gate of the transistor is connected via the sensor, as the sensor temp increases the restistance drops allowing the gate on the transitor to conduct which then provides power to the relay. Ok it's a bit more complext than that but it will work.

Effectivly you want a low resistance trigger switch, if an ecu is out of the question.

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Friends,

I have downloaded the Espritmon program tonight and will give it a go when I get home from traveling next week. I will check to see if the ECU is giving the Fan On command at 92 C. I also like the ablity to turn the fans on and off from the laptop. After reading the FreeScan Manual on the plane tonight I also learned that the old 91 EPROM/Memcal has some quirks that might have a negative effect on my car at low RPM making it have a rough idle. Might be wise to replace the original EPROM with a modern software update. The ECU seems to be a 90/91 GM unit that is readily available here in the good 'ol USA, so I am not to bothered to replace it with a new one.

I shall keep the Forum updated on my progress....

LOST in Houston Texas,

Charlie McClendon

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