Very unusual issue
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Very unusual issue
I thought I had all my ecm wiring straightened out and I may have but I've got a real head scratcher here. I can start the engine and the fan stays off like it should, but if I shut it off & re-start it the fan comes on as soon as the engine fires. I just had a similar problem and tequilaboy & coupeguy2001 both helped me out but now I have this. I believe my car has a normally closed a/c pressure switch but I have an '88 Firebird memcal in the ecm. Could the problem be the memcal or could I have a bad a/c switch? If it is the switch, there are two of them in the high pressure line, do I need the big one or the little one?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Little one. The big one is for the compressor clutch.
Try disconnecting it. That would simulate a N.O. switch. If that doesn't turn off the fan, short the connector to ground, which would simulate a N.C. switch.
Try disconnecting it. That would simulate a N.O. switch. If that doesn't turn off the fan, short the connector to ground, which would simulate a N.C. switch.
Intermediate
Joined: Oct 2007
Posts: 41
Likes: 13
No.
when switch is open = fan on (Logic high)
When switch is closed = no fan (Logic low)
From the helms manual : A.C high Pressure Switch opens at 233psi, Closes at 180psi.
If you want to test if the switch is causing fan to run (always open), disconnect the connector and jumper the two terminals to each other. The fan should stop, if it's the A/C fan request causing it to run.
when switch is open = fan on (Logic high)
When switch is closed = no fan (Logic low)
From the helms manual : A.C high Pressure Switch opens at 233psi, Closes at 180psi.
If you want to test if the switch is causing fan to run (always open), disconnect the connector and jumper the two terminals to each other. The fan should stop, if it's the A/C fan request causing it to run.
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
To sort this out, there are 4 things that need to be determined by the OP:
Until these points are understood we are all working in the dark.
- Does car have an NO or NC A/C high pressure switch? (NO switch is assumed for 85 Corvette).
- Is bin configured for NO or NC switch? (NC setting assumed for 86-89 Corvette based bins).
- Is pin D11 actually connected to the A/C high pressure switch or something else on the car?
- Is pin C1 actually connected to the main fan control relay (pin B) or something else?
Until these points are understood we are all working in the dark.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
I'm beginning to wonder about that.
To sort this out, there are 4 things that need to be determined by the OP:
Until these points are understood we are all working in the dark.
- Does car have an NO or NC A/C high pressure switch? (NO switch is assumed for 85 Corvette). I thought it was NC but I'm not sure.
- Is bin configured for NO or NC switch? (NC setting assumed for 86-89 Corvette based bins). Memcal is stock, '88 Firebird tpi
- Is pin D11 actually connected to the A/C high pressure switch or something else on the car? Yes, checked with cont. tester
- Is pin C1 actually connected to the main fan control relay (pin B) or something else? It almost has to be, it is the only wire I can trigger the fan with.
Until these points are understood we are all working in the dark.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
I just checked the wiring again to be sure, it is as I said. I started the engine with the fan connector on, fan came on as soon as I started engine.
I then disconnected the switch, first start, no fan, second start, fan on.
I then jumpered the terminals of the connector, fan on at start.
I then left it jumpered & grounded the jumper, fan on at start.
Then I grounded just one terminal, fan on second start.
Grounded other terminal fan on at start.
What's with the fan not coming on at first start but coming on at re-start? I think Willie may be on to something.
I then disconnected the switch, first start, no fan, second start, fan on.
I then jumpered the terminals of the connector, fan on at start.
I then left it jumpered & grounded the jumper, fan on at start.
Then I grounded just one terminal, fan on second start.
Grounded other terminal fan on at start.
What's with the fan not coming on at first start but coming on at re-start? I think Willie may be on to something.
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Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
What is the broadcast code on the eprom of the 88 Firebird tpi memcal? Look under the blue cover for a label on the eprom.
Note: F-bodies typically have NO switches, so we may have a match.
If you can determine the broadcast code (bcc), I can check the bin if I can obtain a copy of the file somewhere.
Note: F-bodies typically have NO switches, so we may have a match.
If you can determine the broadcast code (bcc), I can check the bin if I can obtain a copy of the file somewhere.
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
Would be helpful if you can record the datastream during an event. Can you scan the car at 8192 baud and save a log file with TunerPro, Datamaster or equivalent?
Are you getting an SES on the 2nd start, if so any stored codes?
Are you getting an SES on the 2nd start, if so any stored codes?
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
To complicate matters, F-body fan control and wiring detail is a bit different than Corvette fan control and also varies by year and hardware.
http://www.thirdgen.org/techboard/co...ans-arent.html
The info here suggests that the A/C on/off status can also influence the driver's side fan (or main fan in Corvette speak) independently of the A/C high pressure switch.
I think you would be better off using a Corvette based bin that is correctly configured for your car's switch.
We need to know what's really in your bin file to make sense of this behavior.
If you have a programmer, can you read and copy your current bin file?
http://www.thirdgen.org/techboard/co...ans-arent.html
The info here suggests that the A/C on/off status can also influence the driver's side fan (or main fan in Corvette speak) independently of the A/C high pressure switch.
I think you would be better off using a Corvette based bin that is correctly configured for your car's switch.
We need to know what's really in your bin file to make sense of this behavior.
If you have a programmer, can you read and copy your current bin file?
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
What is the broadcast code on the eprom of the 88 Firebird tpi memcal? Look under the blue cover for a label on the eprom.
Note: F-bodies typically have NO switches, so we may have a match.
If you can determine the broadcast code (bcc), I can check the bin if I can obtain a copy of the file somewhere.
Note: F-bodies typically have NO switches, so we may have a match.
If you can determine the broadcast code (bcc), I can check the bin if I can obtain a copy of the file somewhere.
I just got datamaster to work the other day so yes I can scan it. No SES, no codes. I just tried something new, I have a piggyback with a custom tune on it that I put in. The fan is now functioning the way it should but I can't even drive the car with the piggyback in there, it idles rough and backfires out the exhaust. However I believe this tells me the problem is the memcal, am I on the right track? I bought the memcal off fleabay so it is hard to tell what someone has done to it, I'm guessing the memcal and the piggyback are working against each other. ???
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
To complicate matters, F-body fan control and wiring detail is a bit different than Corvette fan control and also varies by year and hardware.
http://www.thirdgen.org/techboard/co...ans-arent.html
The info here suggests that the A/C on/off status can also influence the driver's side fan (or main fan in Corvette speak) independently of the A/C high pressure switch.
I think you would be better off using a Corvette based bin that is correctly configured for your car's switch.
We need to know what's really in your bin file to make sense of this behavior.
If you have a programmer, can you read and copy your current bin file?
http://www.thirdgen.org/techboard/co...ans-arent.html
The info here suggests that the A/C on/off status can also influence the driver's side fan (or main fan in Corvette speak) independently of the A/C high pressure switch.
I think you would be better off using a Corvette based bin that is correctly configured for your car's switch.
We need to know what's really in your bin file to make sense of this behavior.
If you have a programmer, can you read and copy your current bin file?
Edit: Never mind, I was so po'd about the tune being so rotten I threw out the email that had it.
Last edited by Midnight 85; Jun 15, 2013 at 03:51 PM.
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
Didn't find AKFN, but have AKFM. Should be similar.
NO switch setting is set in AKFM bin which indicates bin is meant for NO switch which is typical for f-bodies.
In your datamaster scan, look at the cooling fan duty cycle and A/C bits to determine if the ecm is trying to control the fan:
A/C Status
A/C Request Status
Fan Request Status
Fan Request by ACHP
Get a programmer and some eproms or an Ostrich, use a Corvette bin file and get tuning.
NO switch setting is set in AKFM bin which indicates bin is meant for NO switch which is typical for f-bodies.
In your datamaster scan, look at the cooling fan duty cycle and A/C bits to determine if the ecm is trying to control the fan:
A/C Status
A/C Request Status
Fan Request Status
Fan Request by ACHP
Get a programmer and some eproms or an Ostrich, use a Corvette bin file and get tuning.
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Now that's not likely to happen, look at the mess I made of this project so far. Nope, I'm too old for this technology, I'll leave that to you younger & smarter guys.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
when u start it, is the AC on or off? If my ac is on, the fan comes on right away. If not, it takes a while before the fan will run.
I have a corvette chip you can try, remember?
I have a corvette chip you can try, remember?
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
I've got you & tequilaboy, along with others on this forum who are helping and I have another good friend on the thirdgen forum who is going out of his way to get me straightened out. With a force like that I can't lose.
