Had a bad lean problem which until I get the A/F ratio readouts next week I'm pretty sure got cured by a new MAF I put in.
-Car had a slight miss to it.
-Replaced plugs gapped at .035
-Installed MSD 8.5 wires tonight
-Replaced Coolant temp sender in manifold and in pass side head(main fan was coming on during first min. of operation)

-Now....Car starts and idles about the same, but main fan no longer comes on like it did. Instead, auxillary fan kicks on at 162 (I have a hypertech fan switch), but main fan???

WTF, is my ECM taking a dump? I've replaced EVERY sensor/tune up/fuel related part in this car.

 

isn't there a A/C switch on the passanger side that could be causing an early fan operation? even though you A/C isn't on it might be getting power somehow

 

I checked that. its plugged in, works the way its supposed to, AC is off.

What confuses me is prior to changing the coolant sensor (in pass. side head)the main fan used to run all the time after a minute of operation. Now it doesn't come on, but the auxillary fan does at around 162.(when the MAIN fan should be coming on)..I could only get the car to 185 idling, so as far as what comes on at 228 who knows.

I'm totally confused, wondering if this thing hasn't been in limp home mode since I've had it.
All I know is I've thrown plenty of money at this car and it still isn't right.

 

Wires switched from one fan relay to the other? The passenger side head device was the IP gauge sending unit. It shouldn't have affected either fan. Have you allowed the engine to get hot enough to satisfy the prom's fan setting? Is the new ECT (manifold) sensor working properly? You can trouble shoot the main fan and relay to make sure everything is working.

RACE ON!!!

 

It can omly be in limp home mode if it has certain codes set. Check, correct and clear all codes. BUT if it WERE in the limp home mode, the main fan WOULD be running.

RACE ON!!!

 

I dont know how to test the sensor in the intake, just replaced it a month ago when I had the intake off as it was the original. Up until tonight, main fan use to runall the time. Only thing i did tonight was put new wires on and change the coolant sensor in the pass side head. Connection was cleaned and made sure it was tight.No codes.
What gets me is the slight miss that is there. Never had it before??

 

"What confuses me is prior to changing the coolant sensor (in pass. side head)"

Bad coolant sensor (even if new)? or wire to it?

 

the fan switch is on the manifold... up front. I would chase the wires and be sure there isn't a chaffed or cut wire up there.

as for the pass head, that is the temp sensor for the IP.

also check the relays and fan wiring... this might simply be a problem that has been there and is manifesting now... if you have the helm manual, I would be checking the schematics...

 

or the previous owner had the 2 fans wired through the aux switch on the drivers side. and now the main fan is dead.

as for the ecm - I had screwy problems last winter - would read 300 on a cold start fan ran - changed sensor went from high to low something like 14*, got code 42 changed the sensor then started setting a 43.

I wasnt going to throw anymore $ at it replacing sensors - found a rebuilt ecm for under 100$ and it has been fine ever since - even with the oem memcal

 

The main fan should be coming on @ 225.95* F, this is programmed in the PROM. The second fan is controlled by the switch that should be in the passenger side head. The gauge temp sender should be in the driver side head and the coolant temp sensor (for the ECM) is in the front of the intake manifold...The air temp sensor is screwed into the bottom of the plenum.
By chance is the heat control set to defrost? The defrost position will also engage the A/C compressor (helps keep the compressor lubed during winter) which may also turn the fan on (non A/C car here so I'm not sure on that one). If you wanted to check the main fan's operation, remove the plug from the sensor, put about a 200 ohm (not 200k) across the harness pins and start the car. The fan should come on. As temp increases the sensor's resistance decreases.

Here is a troubleshooting page you may find helpful http://www.mightyautoparts.com/pdf/articles/tt67.pdf

 

you sure about that? what year did they change it to the pass-side?

 

The fan switch on the drivers side head is from Hypertech, is supposed to turn the main fan on at 160 I believe. Haven't put the chip in (thermomaster) that its supposed to be used with. I think the auxillary fan comeson either with the AC or at 228, no?
\
I have a manual fan switch that I can still turn either fan on or off (havent used it lately) so they shouldn't be wired together.

Its someting simple and driving me bananas!

 

According to a look at the 89 .bin files in tunercat, winbin, etc. the #1 fan comes on at 225*, that should be the "main" fan.
On my car the driver side head has the temp sender for the gauge (I have a single fan) My 90 Formula (L98) has the temp sender in driver side head and the aux fan switch in the passenger head. Maybe the Corvette is opposite, but I couldn't imagine why GM would make them opposite.

 

Pretty sure they are.
89 Drivers side-Fan switch for main fan
Pass side-To gauge?
Manifold-To ECM? ECM kicks aux fan on at 228
Someone correct me if I'm wrong..

 

Dr side is aux fan
pass side is coolant temp gauge

 

WRONG!

There is more false and misinformation flying around this thread, than I've seen in a long time. I have NO clue as to why Morley would cite his Camaro or Firebird as examples for Corvette wiring.

First, The fan switch is not now, nor will it ever be, in or on the intake manifold in a 1984 to 1989 Corvette. In 1984 and 1985 the fan switch was in the right (passenger) side head, between the #6 and the #8 spark plugs. The gauge sending unit was in the corresponding hole of the left (driver's) side cylinder head. Being on the other side of the car, puts that hole, up front, between the #1 and the #3 spark plugs.

In 1986 and through into 1989, the fan switch and the gauge temp sensors swapped sides of the car. Through ALL of this, the ECT sensor for the ECM was in the front of the intake manifold, pointing forward. Including the L83.

Fan motors can be tested by feeding 12 volts to, and grounding them. Relays can be tested in numerous ways, including grounding the circuit at the point that is designed to provide the ground, and watch to see if the (tested good) fan runs.


Man that car is ALL screwed up.

1.) Fan switch for the AXILLARY fan.
2.) Yes.
3.) Yes, BUT, the ECM is supposed to control the MAIN fan.
4.) Done.

Maybe that will help some. IF you can even HOPE for forum help, you need to get that wired like it once was. However, as this thread proves, there are plenty of people ready, willing, and able to provide you with the wrong information, to frustrate your repairs. If you will rewire your fans, according to your FSM schematic, universal help MAY be available. If you prefer your own wiring system, including manual fan switches, you remain somewhat bound to your own design.

RACE ON!!!

 

The switch you put in the drivers side head does control the aux fan. If you put in a hyper switch in the drivers head that is a 160 switch, that's why your aux fan comes on at 162. THE SWITCH IN THE DRIVERS HEAD IS FOR THE AUX FAN.

I am not totally sure what switch (front of manifold or passenger head) controls the dash gauge and which sends its signal to the ecm. What I would do if I were you just to find out is disconnect the switch in the passenger head and see if your dash gauge works.
If your main fan isn't coming on early now after putting the switch in the passenger head I'd guess that that switch was sending a bad signal to the ecm.

You put new plugs in? Did you route the wires decent or are you possibly getting a crossover fire somewhere?
Did you try the spray bottle? If you haven't you could still try it and listen if the car runs worse. It's better to try that while holding the car around 2000 rpms.

 

I put in the best MSD wires I could get my hands on....Being as they are 8.5mm I routed them away from the holders on the valve covers as they were a bit close to the smog rails. Used separators, nothing touching anywhere. CFI, I'm trying to get straightened out on what does what, thus my ?? marks at the end of my previous post.
So if the fanswitch on the drivers side head is kicking the aux fan on at 162, when/what governs the main fan and when is that supposed to come on?
As far as the miss/stumble, I'll check the TPS voltage, timing this morning, and check for vacuum leaks...I dont know what else to look for. It was running pretty lean before...The new Ypipe I have on there is a dark reddish color.
Could I have burned up an 02 sensor from excessive heat?
My other fear is a poss. burned valve


Edit: As far as I can tell, the fans have never been rewired. The fan switch I used was the one sold by Mid America, instructions followed to a T, soldered the joints, all looks good.Its properly done.

 

The main fan is controlled by ECM. ECM takes info from sensor on front of intake, ac compressor and vehicle speed sensor.

 

The ECM prom governs when the main fan comes on and the ECM gets its signal from a switch located either in the passenger head or front of manifold. Since you changed out your passenger side switch and the fan no longer comes on when the motor is cold I SUSPECT that switch was bad and sent a false high heat signal to the ecm thus turning the main fan on early. The main fan comes on in the high 220 degree range.
It now sounds like your fan setup is ok. Like I said just pull the wire to the passenger side sensor and see if your dash gauge works or not. Then you know what controls what.

As far as your lean issue wrecking stuff. Run a compression/leak down test to see how it looks.

LOL