Please help! blm at 160. ECM turning on fans on whenever the engine is running. - Third Generation F-Body Message Boards


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Please help! blm at 160. ECM turning on fans on whenever the engine is running.

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Old 07-16-2018, 08:35 PM   #1  
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Join Date: Jul 2007
Location: Chicago Illinois
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Car: 1987 Pontiac Trans Am GTA
Engine: 5.7L TPI 350
Transmission: 700r4
Axle/Gears: 2:73


Please help! blm at 160. ECM turning on fans on whenever the engine is running.

Hello, I normally read through as many threads as I can. Problem is I can't find an answer so I decided to post. I hope this is the right location.
1987 Pontiac Trans Am GTA 5.7 TPI 700R4 273 axle ratio. Odometer unknown can't read it. The car originally had a 5.0 been swapped twice that I know of once while I owned it. I've had the car 10+ years. This is my dream car. I use ALDL scan app and 1320 electronics bluetooth adapter.
I've tried many injectors over the years. I had Bosch 3 blue 24# with adaptors for a few years. I've been trying to fix my rough idle. The car also smelled rich. Bad mpg 19 20 highway. I used the app and found BLM to be at 160! I've read TPI can't run these injectors properly without a tune. I've had custom chips made no help. Also a new problem started my cooling fan is coming on with the engine cold. I Checked wire C1 on the ECM it is grounding whenever the engine is running but not in run. C1 is the dark green white wire that grounds the fan relay when its requested. The fan does come on as it should when the aldl is grounded. I feared my ECM was failing.
I changed the injectors, to a set of Accel 23# they're the older style chubby 3 hole. I switched back to the stock chip and a remanufactured Ecm. Fan is still turning on as soon as the engine starts. BLM climbs to 160. I looked for vacuum leaks I can't find any. Could the cooling fan issue be causing other problems like high blm? I pulled the fuse no help. I've recently before the injector Ecm swap set my minimum air and checked my timing and TPS. Sorry this is such a long post. I wanted to try and cover my cars information and symptoms as well as explain what I tried to do to fix it. Thanks for reading and for any help.

Last edited by CarlKnight; 07-16-2018 at 08:36 PM. Reason: Typos
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Old 07-16-2018, 08:39 PM   #2  
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Re: Please help! blm at 160. ECM turning on fans on whenever the engine is running.

The fans running while the key is on is a sign of a bad ecm or the fan switch type is incorrect in the tune.
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Old 07-16-2018, 09:20 PM   #3  
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Car: 1987 Pontiac Trans Am GTA
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Axle/Gears: 2:73


Re: Please help! blm at 160. ECM turning on fans on whenever the engine is running.

Thanks for the response. My fans are running only when the engine is running. If you just turn the key to run they're off unless the aldl is grounded. Isn't the primary fan controlled by the ecm based on the coolant temp sensor? The ALDL scan app only shows celcius the cts appears to be working. Ecm is going into closed loop.
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Old 07-16-2018, 09:26 PM   #4  
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Re: Please help! blm at 160. ECM turning on fans on whenever the engine is running.

Your right the fan is controlled bye the ecm and cts. Most programs use 226f as a fan on setting. D11 can cause the fan to turn on . It’s hooked to ac pressure switch.switch

Last edited by Tuned Performance; 07-16-2018 at 09:48 PM.
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Old 07-16-2018, 09:56 PM   #5  
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Car: 1987 Pontiac Trans Am GTA
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Transmission: 700r4
Axle/Gears: 2:73


Re: Please help! blm at 160. ECM turning on fans on whenever the engine is running.

Would disconnecting the ac pressure switches stop the fan from turning on early? I don't have a ac belt currently because the compressor leaks. I want to upgrade to a saden compressor if I ever get that far ahead.
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Old 07-16-2018, 10:22 PM   #6  
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Re: Please help! blm at 160. ECM turning on fans on whenever the engine is running.

I can’t recall if it’s a no or nc circuit. I think in 87 is a nc grounded.
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Old 07-17-2018, 12:07 PM   #7  
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Car: 1987 Pontiac Trans Am GTA
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Axle/Gears: 2:73


Re: Please help! blm at 160. ECM turning on fans on whenever the engine is running.

Good news I disconnected high side AC switch now my fan operates as designed. I found some old burn damage in the harness that runs down the passenger frame rail AC switch and cooling fan are on it along with the charcoal can so I checked it and it was open at idle. I disabled it and the blm drops to the 140s. So I think I'm on the right track. Going to take apart that harness and fix the damage.
when you touch the injectors engine running you can feel them pulsing. Passenger side are strong. Driver side back 2 are strong both front feel weak in comparison. Thanks again.
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