95 LaSabre - Fan runs and eng.won't start!

[regal5575]

I have a 1995 Buick LaSabre, it is in pretty good condition with a good, one year old battery. My problem is the car will intermittently refuse to start. When this occurs the electric fans on the radiator run. The engine will crank over vigorously but the engine will not fire up. Then, after 5 or 15 minutes of leaving the ignition switch in the on position the fans will quit running and the engine will fire up immediately and run normally. I have wiggled all the wires and connectors I can find and can neither make this happen or unhappen. What gives? Any ideas out there?
Jerry
PS: I tested the spark with a powered Timing Light. I tested two or three spark plug wires while I was cranking the engine and the timing light flashed on and off, but the engine still wouldn't start.

[imidazol97]

Originally Posted by regal5575

I have a 1995 Buick LaSabre, it is in pretty good condition with a good, one year old battery. My problem is the car will intermittently refuse to start. When this occurs the electric fans on the radiator run. The engine will crank over vigorously but the engine will not fire up. Then, after 5 or 15 minutes of leaving the ignition switch in the on position the fans will quit running and the engine will fire up immediately and run normally. I have wiggled all the wires and connectors I can find and can neither make this happen or unhappen. What gives? Any ideas out there?
Jerry
PS: I tested the spark with a powered Timing Light. I tested two or three spark plug wires while I was cranking the engine and the timing light flashed on and off, but the engine still wouldn't start.

Check battery cables at battery for corrosion. Check between the positives if it has multiple cables clamped together and down into the copper part.

Could be contacts in connector at the spark control unit underneath the coils.

It could be the contacts in the ignition switch itself at the foot of the steering column. There are multiple contacts when the key is turned ON and RUN that can corrode and pit with use. This is not the key cylinder which is at the top of the steering column; that connects with a link to the actual electrical switch down lower on the column near the brake pedal.

BUT I'd suspect the PCM, computer, because of the odd reaction that the FANS run. It sounds like the computer thinks it's in a different mode. I base that only on that there seem to be more problems with computers in 1994 and 1995 models H-bodies than in other years.

You can look for a rebuilt computer or a recycling yard computer.

[regal5575]

All the contacts seem clean and solid.
What happens is when I get in the car and turn the key to the on position the dashboard lights do their normal thing and the fuel pump runs until it builds up pressure and stops. After it stops the radiator fans will either run or not run. It they don't run the engine will start normally and run normally. On the other hand if the fans do start running after the fuel pump stop then the engine will crank normally but the engine will NOT start. When the engine is cranking there is spark to the spark plugs, but engine will not start. After sitting for 5 to 15 minutes with the ignition in the on position and the fans running the fans will quit running and I will be able to start the engine on the first try and it will continue to run normally.
My first guess is it is a bad engine coolant temperature sensor but I can't find the *%^& sensor. I know, it should be easy, but . . . . believe me I have looked. I'm looking on the drivers side, rear half of the engine for a sensor with a black and orange wire and I don't see it. Does anyone have a picture? Should I be looking from the top or the bottom? Do I have to remove something to see it?
Any help would be appreciated.
Jerry

[HotZ28]

Originally Posted by regal5575

My first guess is it is a bad engine coolant temperature sensor but I can't find the *%^& sensor. I know, it should be easy, but . . . . believe me I have looked. I'm looking on the drivers side, rear half of the engine for a sensor with a black and orange wire and I don't see it. Does anyone have a picture? Should I be looking from the top or the bottom? Do I have to remove something to see it?
Any help would be appreciated.
Jerry

You may have a problem with the coolant fan relays, anyway here is a pic of where the coolant sensors are located. The 2-wire is used to send info to the PCM. Good Luck!

[regal5575]

OK, now we're rolling, I finally found the ECTS aka.CTS and it's no wonder that I couldn't find on my own. It is really buried in there under and behind the throttle body. Now I have to try and get it out of there without having to remove too much of the stuff that's in the way. Before I do that, I've got to ask: is there any way to test that sensor with out removing it? If that isn't the problem then it looks like the next candidate is the PCM. Hmmmm. Now where is that located? Oh well, one thing at a time, I'll check out the cheapest part first, and then the PCM.
Thanks for help so far, I've still got a ways to go to answer the question - - - Why? with the key in the on position the cooling fans run on a cold engine and the ignition will fire but the engine won't start. But after 5 - 20 minutes the fans will quit running and then you can start the engine and it will run normally.
Jerry

[HotZ28]

Originally Posted by regal5575

is there any way to test that sensor with out removing it? If that isn't the problem then it looks like the next candidate is the PCM. Hmmmm. Now where is that located? Oh well, one thing at a time, I'll check out the cheapest part first, and then the PCM.
Jerry

The sensor is a thermosistor, as the coolant temp gets higher the resistance drops. The ECM supplies the sensor +5V and measures the voltage drop through the thermosistor to determine temperature. Some resistance vs temperature values follow:

*F--------Ohms
210----------177
158----------467
104----------1459
68------------3520
32------------9420
-4-------------28680
-40-----------100,700

The sensor is used for open/closed loop operation and is used in the calculation for fuel and ignition.

[jd-autotech]

fan rely switch with another identical

[HotZ28]

I think what he was trying to say, is to change the coolant fan relays with another one from the same fuse/relay panel located on the firewall. See pic below for location. Caution, do not use the ones from the ABS!

[regal5575]

OK, it's time to step back and analyze the facts and assumptions.
Scenario One:
Put the key in, turn it and the engine starts. Fine everything is OK.
Scenario Two:
Put the key in turn it the engine cranks but doesn't start, the fans are running with the key in the on position.
Why are the fans running? The ECM is tell the fan relay to close. Why? Because it is broken or a defective ECT is telling the ECM the engine it too hot. OK the ECM tells the fan relay to close. NOW the BIG question, even with the fans running the engine should still start shouldn't it? Why won't the engine start? I tested and know it has spark so it should start unless the ECM isn't telling the injectors to fire.
With the key in the on position, after 5 - 20 minutes the fans quit running (WHY?) and the engine starts normally.
Why do fans running prevent the engine from starting.

More info - I unplugged the ECTS aka.CTS and took an Ohm meter reading across the terminals. The meter read 5600 ohms and it was a cold engine in a 60 - 65 degree garage. So according to my way of thinking the sensor functioning like it should. ? ? ? Right ? ? ? and if that's true then it isn't tell the ECM that the engine is hot! So why are the fans running (sometimes) at start-up?

[Jrs3800]

There is a good chance the PCM has gone Belly up... But I would like to get a scan Tool on it to see what info the PCM is seeing and what its actuating for what its seeing..

[regal5575]

Yes, I didn't want to say those words but I too think it may be a defective ECM that's causing all the problems. I understand Rielly's in our area loans out scan tools so I'm going to stop by there today.
The next thing to do is to find out where the ECM is located in a 95 LeSabre so I can take a look at the part number on it. I hope it isn't as hard to find as the coolant sensor. Or as hard to get to! I'm searching the internet now for a remove and replace procedure, hopefully with pictures.
Jerry

[HotZ28]

The PCM uses quad drivers to ground the relay for the fans to turn on. Look for "Quad-driver" DTC's when scanning. The PCM is located under the passanger side dash, behind the glove compartment. It's not too hard of a job, but not as easy as removing the ones located under the hood.

[regal5575]

Originally Posted by HotZ28

The PCM uses quad drivers to ground the relay for the fans to turn on. Look for "Quad-driver" DTC's when scanning. The PCM is located under the passanger side dash, behind the glove compartment. It's not too hard of a job, but not as easy as removing the ones located under the hood.

I have read in different postings where the computer in the 1995 LaSabre is an ECM, it is described as OBD 1.5., it isn't a true PCM. It has an OBD2 style terminal block but it is my understanding that it isn't wired like a true OBD2 terminal block would be wired. Is there a way to read it without a scan tool?
.

[Jrs3800]

Not sure what you have been reading... But there is a lot of misconception out there...

ECM is Engine Control Module... For GM this means that the Computer( ECM ) only controlled the engine with he Exception of the TCC Apply.. The trans would be hydraulic..

The PCM is Powertrain Control Module... For GM this means that the Computer( PCM ) controls both the Engine and the Transmissions( Electronic Trans )

Every GM car with a 4T60-E uses a PCM, this started in 1991 in some models..


The 1995 Lesabre is OBD1 Compliant, but it uses the OBD2 connector and Codes.. This was GM's step towards getting ready for OBD2.. This PCM doe not have the diagnostic flash feature... You have to use a scan tool to pull codes from the PCM..

The system is wired like an OBD2 system... But it does not speak the language... The car has a data line has all of the Modules plumbed into it, this way a tool such as a Tech 2 can talk to the modules on the same data line..

an example would be that its much easier to wire a 94-95 GM 3800 for an OBD2 PCM than it is a 91-93 PCM...

I hope I have made a little bit of sense...

[HotZ28]

Originally Posted by regal5575

Is there a way to read it without a scan tool?