Cold Mornings will not crank

[magnet56]

I have a 1997 Explorer 5.0 all wheel drive. On mornings when the temp. is below 38-40 degrees F. the fuel pump will come on and continue to run as long as the key is is the on posistion. The engine will not even attempt to start just spin over. When the temp warms up above about 41 degrees the fuel pump will come on and shut off and the engine will start.

Here is another thing to consider. Anytime you attempt to start the engine ( when the temp is cold or hot )you have to wait for the fuel pump to shut off before it will start. If you attempt to start before it shuts off the engine just spins over like its not even firing. The fuel pump always runs about 20 to 30 seconds which I know is longer than it should. The reason it wont start on a cold day is because the pump will not shut off.

I have dropped the tank, cleaned it out, replaced the fuel pump, strainer, fuel pump relay, and fuel filter. When the engine does start it always runs beautifully. Any help would be appreciated.

 

[magnet56]

Anybody

 

[dogbis]

have you checked the pressure regulator?

 

[Cobraguy]

Interesting. All I have is 96 reference material...but I would guess it's the same thing a a 97 since I believe they are both return style fuel systems IIRC. Of course, you know what assuming does...

The fuel pump is powered by fuse 12 in the Power Distribution Box. This circuit goes from there, to the pump relay, the inertia switch, then the pump. Power to the relay (fuel pump power) is hot at all times. When the relay closes, power is supplied to the fuel pump and it runs. Now, for controlling that relay, power for that circuit comes from the PCM power relay. It comes from pin "30" of that relay. That goes to a splice that supplies power other systems including the evap purge and vapor management. From the splice, it goes to the fuel pump relay. The relay is controlled directly by the PCM by closing the ground side of the switch.

So, if you are experiencing no pump shut off when cold, then it has to be a stuck relay (you have changed that) a bad PCM (I would seriously doubt that) or a damaged circuit. But the real interesting part is the car won't start when the pump stays on. The reason the car won't start is not due to the pump continuously running. It should at least fire...especially cold. And if you go right to crank, it should definitely start. So if it's not starting, something else is dead too. Since the PCM power relay is located in the same box as the pump relay, I'm suspicious of a problem there. Something is getting cold and contracting causing this intermittent problem. For the life of me, I cannot see how the PCM power relay could fail to the point of losing power to the PCM, yet still supply power to the control side of the pump relay. That doesn't appear to be possible. However, I've seen stranger things. You might try a new PCM power relay and see if that fixes it. But what I would really like to know is whether or not the PCM is really dead when it won't fire. The PCM must ground the control circuit of the pump relay, so does it default that way when it doesn't have power? Can you check for spark when it won't fire? Can you check for proper operation of the check engine light when it won't fire? This is a very interesting problem I would love to know the answer to.

 

[fatvdub]

I thought you said cold...

 

[magnet56]

Thanks for the reply guys. Cobraguy I will check the operation of the CEL. I do have access to a 1996 pcm, (I hope it will interchange ) and I will try that this weekend. I have ran this by a couple of really good mechanics, and I am an electronics tech and have looked at the schematics, and it does not make any sense to any of us either. I was hoping that someone here may have ran into this before. I will let you know what I find.

When you key on and the pump starts and then cuts off, can you tell me what cuts the pump off. Is it a pressure that has to be met, or is it a timed cycle?

 

[tripplec]

At best that is cool. -20 to -30C is what were have here this week is cold. You wouldn't even get ice crystals at that temp. Some moisture buildup if there humid air. My beer is colder than that.
How long has it been doing this? Have you tried gas from another gas chain? Is the battery voltage up whey you're cranking at that temperature. I would try a booster pack or another vehicle just to see if you have a bad battery problem (batteries typical respond badly when the temp drops if there is something wrong with a cell).

Good luck.

 

[magnet56]

38 degrees is not cold here either, I am just saying that this is when the problem starts. I have drained and cleaned the tank. This is not a fuel quality issue. There is some reason that the fuel pump must shut off before the engine will start even in warm weather. And when the temp is cooler the pump comes on and stays on. The pump will always run for about 20 to 30 seconds before it shuts off, and I know that this is abnormal also. The engine turns over fine and I have tried using jumper cables to another vehicle. When the fuel pump shuts off the engine cranks as soon as your hit the starter and runs and idles great.

 

[Cobraguy]

When you key on and the pump starts and then cuts off, can you tell me what cuts the pump off. Is it a pressure that has to be met, or is it a timed cycle?

It is a timed cycle. Because it will run appx two seconds and shut off regardless of pressure. Zero or 45 psi...it will run. It has to be in the PCM...that's what is controlling the relay.

I think you're going to find the PCM is losing power (relay?) and defaulting the pump relay to closed. It's the only thing that makes sense unless there is a wiring problem.

 

[tripplec]

It should crank on demand as soon as you turn the key to the start position. If I understand it that is not happening when cold and only after the fuel pump stops. Must be a relay issue or bad contact or the plug itself. Pull the relay and reinsert it, it could be oxidation on the terminals if it will work at the warmer temperatures. Maybe some other interlock in the starting circuit like the neutral switch prevent it from cranking but that should not have anything to do with the fuel pump itself. Schmatic required!!

 

[magnet56]

That is correct, the fuel pump will run continuously on cold mornings and will not shut off. The engine will not crank but will spin over fine. The reason the motor will not start is because the fuel pump will not shut off. Even in warm weather the fuel pump will run for about 25 seconds and shut off, but the engine will only start untill after the fuel pump shuts off. For some reason the engine is being kept from starting while the fuel pump is running by either not firing or not spraying any fuel. As soon as the pump shuts off the engine starts fine and the CEL is not lit. I have looked at the schematic and the transmission switch would keep the starter from engaging and keep the motor from turning over, but my engine turns over fine it just will not start. I have checked the relays and even replaced both the pcm power and fuel pump relays. No corrosion was evident.

 

[Cobraguy]

It should crank on demand as soon as you turn the key to the start position. If I understand it that is not happening when cold and only after the fuel pump stops. Must be a relay issue or bad contact or the plug itself. Pull the relay and reinsert it, it could be oxidation on the terminals if it will work at the warmer temperatures. Maybe some other interlock in the starting circuit like the neutral switch prevent it from cranking but that should not have anything to do with the fuel pump itself. Schmatic required!!

You need to read his problem a bit closer. You didn't understand it correctly. (or I didn't! ) The car cranks just fine. But when the fuel pump won't shut off after a couple of seconds in the "on" position with the key...as it normally should....then the engine won't fire. So it's losing spark during this time. The only thing I can think of is somehow, the PCM is losing power, and when it does, the fuel pump relay circuit in the PCM defaults to ground and closes the relay. That's the only way I see both separate conditions happening. But it could certainly be a bad ground or wiring. Those can cause some very weird issues that are difficult to find and correct.

 

[tripplec]

You need to read his problem a bit closer. You didn't understand it correctly. (or I didn't! ) The car cranks just fine. But when the fuel pump won't shut off after a couple of seconds in the "on" position with the key...as it normally should....then the engine won't fire. So it's losing spark during this time. The only thing I can think of is somehow, the PCM is losing power, and when it does, the fuel pump relay circuit in the PCM defaults to ground and closes the relay. That's the only way I see both separate conditions happening. But it could certainly be a bad ground or wiring. Those can cause some very weird issues that are difficult to find and correct.

IF the PCM is loosing power then there should also be other symptoms. This is not a radical change in temperature for the PCM (designed to operate to at least -50C and more that 45C I am sure) I know people who have been getting those really cold temperatures this year. Anyway, how to eliminate the PCM if in fact the temp it experience is the issue.

I am not certain how accessible it is on that model. I have several vehicles and some are in plan site like the Caravan on the driver side fender. But taking a nozzle shapped hair dryer and pumping some hot air on the casing and see it it starts normally is one tack. Warming other components might also be an option. Years ago we used to be able to buy freeze spray to chill or drop the temp on components. If you can get it testing on a warmer day by hitting the PCM, relays or whatever first then see if it will start.

Without me seeing a schematic at this point I have little more to offer other than the pump relays normally open state will have to be pump off, closed relay state - pump on. The relay is getting power but as you stated maybe some other critical subsystem is not getting sufficient voltage.

 

[Cobraguy]

If the PCM is at fault, it's a defective PCM. Temp will not have an effect on it unless it's defective. It can be something as simple as a defective solder joint that is contracting and separating in the cold...much like the old radio displays did just the opposite. Somehow, you have to tie the no fire condition to the pump continually running. I have the schematics...and I can't see anyway that can happen without it being a defective PCM, defective wiring, or ground, or the strangest set of coincidences I have ever seen...and I don't believe in that.

 

[magnet56]

Here is an update to my problem.

I have already tried heating up different components of the system one at a time to see if I can start the vehicle with no success. I warmed the PCM {which by the way is easily accessible on the firewall behind the engine}, the relay box which holds the pcm power relay and the fuel pump relay, distributor area, and the front of the engine area. Still would not crank. I have also replaced the pcm power relay yesterday, and that also did not help. I also have the schematics and the ability to read and understand them and I cannot for the life of me figure it out. The one thing that I have not tried yet is the power diode that feeds the power to the pcm power relay. I know that electronic components can be affected by temperature change because I also have used the freezing spray to make gate modules come back to life. I will replace this power diode today and try that. If that does not work I have access to a 1996 5.0 AWD PCM module. If it will work in a 1997 I will try that this weekend. I appreciate all the input from you guys.

 

[budwich]

On your "no start" attempts, does your cel light go out????

 

[magnet56]

I found out today that my check engine light does not work. I stopped by Advance auto and had them put the scanner on it to see if there was a code. He didn't tell me the code number but he said that it shows the gas cap is not tight. He said that code could only be the gas cap. That was the only code showing he said. I thought it would give a code for the CEL being burned out.

 

[budwich]

You need to go back to "basics".... just turn your key to "on"...don't try to start. Your cel light should stay on...if it doesn't don't bother going any further until this "symptom" is address.... it may save you a starter replacement.

 

[magnet56]

When I go to key on my CEL does not light. It may be burned out? I have never had a problem with my starter.

 

[Cobraguy]

He said that code could only be the gas cap.

What a load of crap. I can think of a couple of problems that are more likely on an older car. These Autozone guys are scary sometimes...

The 96 PCM should work in your 97. I would certainly give that a try. If you got a code at all, your PCM is alive. But we know that is true because the thing runs normally when it does run. It's just those moments when the pump doesn't cycle and the engine won't fire. That is the only time we are concerned with. Do you have access to a scan tool you can hook up and look at when the problem is actually going on? That way you can see if the PCM is actually processing data.

Oh yea...I would pull the cluster first and check that CEL bulb.

(budwich was talking about burning your starter up by cranking the engine so much)