I have a 1987 IROC 305 TPI with dual fans. The problem I'm having is that the fans have started turning on when I turn the key on. at the same time the engine started to have a hard time starting. It will chug-a-lug and sometimes backfire for about two minutes. I turn the key off and re-start and it seems to run fine. GM dealer replaced the ecm and it seemed like the problem stopped for a couple of weeks but now it's started acting up again.

Do the fans turning on prematurely have anything to do with the hard start problem?

Also the car will run fine for about 30 minutes and then it will stumble, lose power, the check engine light comes on and then it stalls when I put in the clutch. When I let the clutch back out while I'm rolling along it fires back up and the problem is gone for awhile.

 

You might want to start there...

Both fan's running at the same time is not something that 'just starts happening' on an '87.

 

I forget if the TPI has the same cooling sensors/senders as the carb motors but you could possibly have a bad cooling fan switch. Also check to see if the relay clicks when you key it on if it does then the switch is closed all the time. If it doesn't the relay could be stuck.

 

start with the coolant temp sensor. the engine will run like **** until it warms up, and depending on where its stuckt, can run the fans from key on

 

could be that the fans are hard wired .... Check to see if anything is wired to your fuse box that could be what it is

 

Not necessarilly - the sending unit (either to the gauge or to the ECU) shouldn't affect fan operation. Only the switch that grounds the fan circuit would cause the fan to come on.

OP, disconnect the fan switch itself and see if they stay on. If it does then the circuit is closing elsewhere.

 

its a TPI car, the fan is ECM controlled.

 

Thanks to everyone for your help with this.

I've ordered a Hypertech stock replacement prom chip. Hopefully this solves all the problems.

I'll let you know how it turns out.

 

Thanks for clearing that up - I just found that out too my friend has an LT1 that is having a similar issue and its PCM controlled as well.

 

Start with the retrieving the code(s). The CEL is coming on, there is an obvious problem... why guess if the ECM is telling you ?

It's an '87, only the primary fan is ECM controlled. The secondary is temp switch only.

The OP stated 'fans' meaning, both. Scanman may be right that they are hardwired, as it wouldn't be normal for the secondary fan to run for anything but temperature over 238° (fan switch temp).

 

The CEL is coming on when the engine stalls but it's not setting a code. The same as when you just turn on the key before the engine starts. I've replaced the coolant temp sensor but the fans still turn on. I replaced the fan relay but the fans still turn on. I disconnected the coolant temp sensor. the fans still run, I disconnected the fan relay and the fans still run.

Does a TPI motor use the additional fan switch that is on the passenger side of the block like the carbed motors?

Everything I've read is telling me that the prom chip controls the fan start up for a TPI engine. It will actually ground the fan circuit to start the fans.

The fans are not hard wired to start when the key is on. They used to work correctly, they just recently started to act up.

 

On TPI cars the fans will turn on when the ECU goes into limp home mode, This would also explain why the engine is running like crap. It's likely your ECU or your prom chip

 

Well the ecm has been replaced recently so now I'm hoping that with installation of the new Hypertech 127051 chip my problem will be solved.

 

I would lke to thank everyone for all the help. the car has been repaired.

I had a new ECM installed, didn't fix the problem, installed a new Hypertech chip, didn't fix the problem $500.00 later and just before I took a sledge hammer to the car I decided to trace the wiring for the coolant fans because when problem began the fans started turning on even when the car was cold.
What I discovered was that this car had two fan relays, one for the primary fan and one for the secondary fan. I also discovered that there was a radiator fan switch on this car just the same as a carbureted engine. When I unplugged the wire to this switch the fans shut off. I removed the switch from the engine block put an ohm meter on it and saw that it was stuck in the closed postion so it was always grounded.

I replaced the switch cleared the codes from the ecm and took the car out for a drive. The fans now work properly and there were no stalling or hestation issues. I drove the car on the freeway and also on back roads for several miles without any problems.

That fact that the fans were always grounded must have effected the ecm in some way.

The good news is that the car seems to be repaired and also the Cleveland Browns beat the the New England Patriots. This was almost a perfect day.

 

Can you give the locations of the relays? It's not a problem for me, but it's something to look at later.

 

Both the cooling fan relays on my car are located on the passenger side of the radiator. One is mounted on the side of the radiator support and the other is located behind the battery.

There is also a radiator fan switch on the passenger side of the block. Close to the dip stick tube.

 

That switch might explain why I had an extra coolant passage hole open after the rebuild lol. Even so, I don't recall having an extra plug that I couldn't get hooked up. The fans have always ran during key on, engine off, never thought anything about it. It is pretty convienient on a hot summer day though lol!!
Just remembered, there is a single black wire without an end that I couldn't figure out what it went to. Maybe this would be it? Probably not the source of the problem since the OP unplugged his to get them to stop, but it would be good to know where it goes so i can get it hooked up

 

The primary fan is ECM controlled and the secondary fan is Fan Switch controlled.

Look at the green wire on both relays and see if there is a jumper wire going between the two. That should be the ECM grounding wire on primary fan relay and the Fan switch grounding wire on secondary relay.

Do both your fans come on at the same time, or the primary first followed by the secondary fans? (when the a/c is off)

 

At key on both fans turn on, engine running or not.

 

It appears that the 87 and 89 wiring diagrams are very similar for the cooling fans.

Courtesy of Autozone: