'87 Buick Century 2.8 Cooling Fan

[Robert56]

I have replaced sensors, relays, coil pack, and fuses. The second I start the car the cooling fan kicks in. The idle is rough too. I am about out of money and for sure out of patience. What am I missing? Can anyone out there point me in the right direction? Also where can I find a schematic on relay and sensor location?

[bruceallmighty]

my 3.3 on the cutlass was not starting,turning key to on position was causing the fan to go on and injectors to work ,we unplugged the cps and plugged a new one to the harness but not mounted to the block,.key on and fan did not start and injectors not click easy test and after mouting the new sensor all was good ]
]

[GM Line Rat]

You dont happen to have a jumper wire stuck in pins A & B of the ALDL Diagnostic connector under the dash do you? If so, pull it out! If not, I'll bet the ECM Computer in this car is bad. Can you pull any error codes off this car by jumping pins A&B on the ALDL Per instructions? When I got my 91 Buick Century, it ran very rough at idle and the cooling fan allways came on also. Bought a Used ECM Computer from a local junkyard, removed my old one, then opened the top of the old ECM and removed the EEPROM Chip and installed it in the ECM From the junkyard. Hooked it up....car started right up and ran great! Your ECM is under the PS Dash. Disconnect your battery terminals, Remove the glovebox (7mm screws) and look under the dash for a silver box with 2 wire harnesses connected to it. Remove the 2 10mm nuts that hold the ECM in place, lift up and out, push down on the plastic retaining tab on 1 wire harness, then pull on the plastic plug while gently wiggling the plug side to side a little till it comes out...repeat on the other harness plug. AFTER you get a replacement ECM and ready to install it..... on top of the old ECM, you'll see 2 screws and a access plate, your EEPROM Memory chip is under this plate. Squeeze the 2 retaining clips that hold the chip in and gently pull it out and swap your old EEPROM Chip into the replacement ECM, then install it.

NOTE: After removing your old ECM from the car, write down the model and serial #. You'll need this info to match the ECM type at the junkyard. GM used the same ECM models in alot of cars, but used different programmed EEPROM Chips for the specific type of engine, trans and options etc... This is why you swap in your old EEPROM Chip in the replacement ECM.

Here's a link to the wiring for your car (Figure 46)


Autozone - WIRING DIAGRAMS
GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

[Robert56]

Hey there...I'm back. Checked jumper wire, no wires at pins. Just went out and bought NEW ECM. I installed it and no change. What next? I can't take to much more...My head is killing me.

[GM Line Rat]

Is your AC turned off when you start the car? The electric engine cooling fan turns on automatically when the AC is turned on. Also, did the new ECM you bought include a new EEPROM Chip, Specific to your car in it or not? Or did you have to use your old one? Also, have you replaced the "Engine coolant temp sensor" or the Cooling fan relay? Are there ANY "Check engine codes" coming on in this car? Here is a complete breakdown of diagnotics for "Engine Cooling Fan always on". (Note: This diagnostic breakdown is for my 91 Buick Century, the circuts in your car should be similar in design).

CIRCUIT DESCRIPTION :

Power for the coolant fan motor comes through the fusible link to terminal "A" on the relay. The relay is energized when current flows to ground through the quad driver module inside the ECM.

Coolant fan Relay - The coolant fan relay is energized by the ECM. The ECM energizes the relay through terminal "YE8" when the coolant temperature reaches 100°C (212°F). The fan relay is also energized when A/C is requested.

TEST DESCRIPTION : Numbers below refer to circled numbers on the diagnostic chart.



Removing the relay interrupts current flow to the fan motor so the fan should not be "ON."
Test light should be "OFF" with coolant temperature below 100°C (212°F) no code 14 or 15, and A/C "OFF" (no A/C request).
If the test light goes "OFF" when the black C-D connector is disconnected, the ECM is faulty and has to be replaced.

[GM Line Rat]

To make this easier, please list what you have allready replaced on this car (Be specific in part names). Does this car have 1 or 2 electric cooling fans in it? Again, refer to this link to compare the electrical digrams of your car with the diagnosis above. (Figures 46 thru 49).

WIRING DIAGRAMS
GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

[Robert56]

Well once again I'm back. Took the car to the garage, Mechanic put on diagnostic machine. $112.09 later he had to put a pigtail on the fan temp sensor, well the fan is no longer on and it ran good for about 8 miles. Now fuel is running continuosly with key off and on! I have to undo battery cable to stop it. Why is this doing it?? So ready to blow this thing up. I would if I didn't have so many $$$ in it. If it is the fuel pump relay where is that located on my car? It is not by shock tower.

[GM Line Rat]

Originally Posted by Robert56

Well once again I'm back. Took the car to the garage, Mechanic put on diagnostic machine. $112.09 later he had to put a pigtail on the fan temp sensor, well the fan is no longer on and it ran good for about 8 miles. Now fuel is running continuosly with key off and on! I have to undo battery cable to stop it.

Where did he run this pigtail too? did he just repair the wire, or jump it off something else? You fuel pump relay should be located (When looking under the hood) on the PS of the car, mounted on a bracket on the firewall. It has Orange, Black with a white stripe and gray wire going into the socket that holds the FP relay. There will also be Orange with a black stripe wire that will not be connected to anything (It's normal). This is the fuel pump test lead. If you pull the relay out of the socket, hook the battery up, then turn the key forward to the on position (Not started), you should NOT hear the FP Running in the tank. Buy a new FP relay and stick it in the socket. See if the car runs normal when you turn the key forward (FP Should run approx 5 secs, then stop). Did the FP run like this (All the time) before your mech rigged the fan temp sensor? If not,.....FIRE YOUR MECHANIC and find someone who knows how to read a schematic wiring diagram and diagnose a circut!

[Robert56]

With the ignition in the off position and all 3 relays unpluged (fuel realy, fan relay and what ever the 3rd one is). Then putting on the negative cable to the battery you can hear a clicking noise comming from the fuel injectors, and you can hear the fuel pump running all of the time now, it won't shut off. We have replaced the ECM twice. What else could it be? Put in a new fuel pum relay too. Is there a wiring schematic for the fan temp sensor relay available to check out this pig tail thing before I tear it completly up or out?

[GM Line Rat]

Look at where the fuel pump relay was plugged in at. There should be single "Orange wire With a Black Stripe" just hanging down below the relay, not connected to anything. This is the fuel pump prime wire. Is their anything connected to this wire?

[Robert56]

Hey GM Thanks...The orange wire was the problem with the fuel pump running all of the time. Now I have another problem with the car. The engine light stays on and it misses alot. The code it brought up was the ignition module. I have replaced this module 6 times with a brand new one every time and still no change, I had the coils checked out, OHM meter at Auto Zone showed the coils are good. Are They? What else should I do to correct this problem?

[Robert56]

GM Line Rat, When do you usually reply to these forums? Just curious?

[GM Line Rat]

Originally Posted by Robert56

GM Line Rat, When do you usually reply to these forums? Just curious?

In the Early AM and also sometimes later at Night....M-F. What was the error code that came up? Also, were there any more codes besides code 12 (Which is normal).....Post back and I'll reply with more info tommorow.

[Robert56]

I can't drive car up to Auto Zone to Re-check codes because the engine misses bad from fault at ignition module.What the other code was I don't remember, but was told the fault lies from the ignition module area. What I need is an engine ignition electric power & spark diagram on how spark works and what would go bad. Also what to look out for in the ignition module, coils and other components. I will NOT let this beat me. Thanks again for being there.

[GM Line Rat]

Robert, this car is a 1987, which means it's a OBD-1 Computer system. You Dont have to go to Autozone in order to get the error codes off the car, all you need is a 6 inch piece of 18 Gauge wire. Read this link and it will show you how to do it.....It's real easy!

How to get GM fault codes On or before 1995 models:

Insert the short piece of wire in pins A and B of the ALDL Diagnostic connector under the dash with the engine Off, Key out. Put the key in and turn it forward until you see the "Check engine Light" or "Service engine Soon" light in the dash but DONT Start the car. Follow the directions in the link and write down what codes come up besides code 12. Code 12 will flash 1st. When it cycles thru all the present codes, and goes back to Code 12 again. Let it cycle thru again to make sure you got all the present codes in the ECM Computer. When it gets back to code 12, turn the key to off, then remove the jumper wire from the ALDL Connector......Post the codes that come up on here.



86-88 2.8L VIN 9 MFI Trouble Codes

86-88 2.8L VIN 9 MFI Trouble Codes:

13 Oxygen sensor voltage stays between 0.35 and 0.55 volts for 60 seconds during closed loop operation after the engine had been running for 2 minutes and the throttle angle was above 4%.

14 Coolant temperature sensor signal indicates a temperature of over 275° F for 3 seconds.

15 Coolant temperature sensor signal indicates a temperature colder than -47° F for 3 seconds.

21 TPS voltage was above 2.5 volts for 5 seconds when the MAP sensor signal showed manifold vacuum above 15 pounds or TPS signal voltage was over 4.5 volts.

22 TPS voltage was under 0.2 volts for 3 seconds when the engine was running.

23 Manifold air temperature sensor signal showed an air temperature of -31° F for 3 seconds after the engine has been running for 8 minutes.

24 Vehicle Speed Sensor Sensor/Circuit.When engine speed was between 1400 and 3600 RPM and throttle angle was less than 2%, the MAP sensor signal showed low voltage (High manifold vacuum) for at least 3 seconds.

25 Manifold air temperature sensor signal showed an air temperature over 293° F for more than 3 seconds after the engine has been running for 4 minutes and a vehicle speed was present.

32 EGR vacuum switch was closed during start-up or idle, or EGR vacuum switch did not close when EGR solenoid was commanded to close by ECM for 5 seconds.

33 MAF sensor indicated air flow was more than 20 gm/sec for 2 seconds.

34 MAF sensor signal showed air flow to be less than 2 gm/sec, or the MAF circuit was shorted.

41 The number of crank reference pulses did not match the number according to the PROM when engine speed was under 2000 RPM, or the incorrect PROM has been installed.

42 The EST signal did not change when the ECM applied bypass voltage to the ignition module.

44 Oxygen sensor voltage was under 0.2 volts for 60 seconds of closed loop operation.

45 Oxygen sensor voltage was over 0.7 volts for 30 seconds in a closed loop when throttle angle was between 3% and 45% and engine had been running for at least 1 minute.

51 PROM error.

52 CALPAK error.

53 Charging system voltage was greater than 17.1 volts for 2 seconds. Repair charging system.

54 Fuel pump signal voltage was less than 2 volts for 1.5 seconds.

55 ECM error. Replace ECM.