Dying for no apparent reason?

[lmorgan]

I have a '95 Explorer and it may run great for a week, but then without warning, it will just die. Even going down the Interstate or through traffic. Sometimes it will do it twice in one day, sometimes once a day, sometimes it will go days or weeks without doing it at all. If I'm able, I can pull over to the side of the road and let it set for a few minutes and turn the key back on. When the check engine light comes on, it's ready to start and will fire right up. I've changed the in tank fuel pump, but nothing has helped so far. Other than this very dangerous and annoying habit, the vehicle is in good shape mechanically. Where do I start to trace this problem?

 

[nitro71]

I'd pull codes and see if there's anything there. Sounds like it's dead electricaly until it decides to start? No starter, lights? This sounds like a electrical/computer problem to me. I don't have any experience with those though.

 

[2000StreetRod]

Many possibilities

There are many possible causes for the engine to die. Until you record and post the diagnostic trouble codes we'd all just be guessing. And if you act on our guesses it will cost you time and money.

 

[lmorgan]

I'd pull codes and see if there's anything there. Sounds like it's dead electricaly until it decides to start? No starter, lights? This sounds like a electrical/computer problem to me. I don't have any experience with those though.

Actually, when it dies it just dies. The starter still spins, etc., it just won't start. Let it sit for a few minutes and it will fire right back up. I'll definitely take it in soon and pull codes.

 

[MrShorty]

When the check engine light comes on, it's ready to start and will fire right up.

Does this imply that the CEL is not coming on when it won't start? If so, I'd start with the PCM power supply circuit.

 

[Opera House]

Did it do this BEFORE you changed the fuel pump or was the problem different? I had this problem after putting in a new pump. I changed the pump just to insure no problems on a long trip and that is when it started dying.

 

[lmorgan]

update

To answer the questions... the CEL does not come on until the vehicle is ready to start. Well, actually, very recently, the CEL will come on and the vehicle will still turn over, but not start. I cycle it twice or three times and I can hear the electric fuel pump kick in and then it will fire right up. When the vehicle dies, everything still works... lights, starter, etc. It just won't start.

The Explorer was doing this BEFORE I changed the fuel pump and the relay. There has been no change. I stopped by the local dealership and spoke to the tech there. He said he was unfamiliar with anything like that happening and didn't think he could be of help. He said their computer probably wouldn't read anything that old. Uggghhh. I'm at my wits end, especially when the tech said he couldn't test it.

Any other suggestions? Someone recently said they had a similar problem and it was the ignition switch? Does that sound right?

 

[2000StreetRod]

PCM Power

Does this imply that the CEL is not coming on when it won't start? If so, I'd start with the PCM power supply circuit.

I agree with MrShorty that your PCM may not be getting reliable power. CHECK ENGINE should illuminate when the ignition key is in the ON position to show that the light works and to indicate that the PCM has power. The fuel pump relay is energized by the PCM power relay. No CHECK ENGINE > No PCM power > no fuel pump power.

You may have a faulty PCM power relay located in the battery junction box. You can swap it with the blower motor relay to test it.

 

[lmorgan]

Would it be the relay even though it doesn't do it regularly? I may drive the vehicle for days with no problem at all, and then it just shuts down without warning while I'm driving down the road. I turn off the ignition switch, turn it back on and wait for the CEL to come back on. When it does (and I can hear the fuel pump) it fires right up. I may go three miles or three days before it does it again.

Would a relay be hit and miss like that?

Regardless, thanks for the information. I'll swap out the relay and let you know what happens.

 

[ccarnahan0717]

clean your throttle body thats what was happening to me but that fixed the problem.

 

[MrShorty]

Something intermittent like that is often electrical. I would certainly say a faulty relay could easily be intermittent like that. Of course, so could a loose connection somewhere in the main power/ground circuits or any number of other electrical gremlins.

 

[lmorgan]

With this being very intermittent and the CEL not being on, would it still be possible to pull codes and hopefully narrow the problem down? The guy at the dealer service dept said that the vehicle was probably too old for him to pull codes on (which sounded a little off to me). Would somewhere like Autozone be able to pull codes?

 

[2000StreetRod]

no PCM = no codes

If there is no power to the PCM (as indicated by no CHECK ENGINE when key is On), then obviously the PCM can't detect any errors and set any codes.

 

[lmorgan]

Codes

The CEL does function properly (as does the vehicle), 90% of the time. The CEL does not stay illuminated except during starting, which is what the owner's manual says is supposed to happen. If there is no CEL illuminated all the time, then codes can't be pulled, right?

I'll swap out the PCM relay first and see what happens from there. Thanks for all of the advice. I'll post an update as soon as I have one.

 

[2000StreetRod]

CEL when cranking?

In your original post you said the engine starts when the CEL is illuminated. I assumed that you meant when the ignition key is in ON but does not illuminate when the key is switched to START. That would be normal. Now it sounds like your CEL sometimes stays illuminated when the ignition key is in START. That is not normal. Often that is an indication of a bad crankshaft position (CKP) sensor. When you have an intermittently bad crankshaft position sensor the engine may die while cruising and may not start. Often the PCM does not detect an intermittent failed CKP sensor. It is located next to the crankshaft damper. The electrical contacts may be dirty. I suggest that you disconnect and reconnect the electrical connector a few times to clean the contacts. Also inspect the wiring to verify good condition.

 

[lmorgan]

I apologize if I was unclear. Basically, the CEL works properly all of the time, as per the owner's manual. When the vehicle dies without warning (or sometimes when I kill it to refuel, etc.), the CEL will not illuminate in the ON position as it is supposed to. I let it sit for a few minutes, turn the switch to ON. When the CEL illuminates I can usually hear the fuel pump kick on. If the CEL does not illuminate in the ON position, I don't hear the fuel pump. If I don't hear the fuel pump, I know it's not going to start until I do.

I'm sure this makes it as clear as mud.

Thanks again for all the advice. I'll try the PCM relay and the CKP sensor and see what happens. Someone off forum suggested it may be in the ignition switch or wiring. Does that make sense?

 

[Mirge]

I don't believe it was mentioned, if it was, my apologies.

I'd also check & clean the battery posts, terminals, cable ends... doesn't cost anything, and can't hurt!

 

[lmorgan]

I don't believe it was mentioned, if it was, my apologies.

I'd also check & clean the battery posts, terminals, cable ends... doesn't cost anything, and can't hurt!

Thanks, Mirge. That part I DID do already.

 

[Mirge]

Thanks, Mirge. That part I DID do already.

Oh okay sorry. I'm no help beyond that lol... 2000StreetRod, from what I've seen here, seems like a real electrical guru You're in good hands

 

[2000StreetRod]

ignition switch

If it were a problem in the ignition switch or associated wiring then none of the warning lights would illuminate when the CEL does not illuminate. If the warning lights illuminate in the ignition ON position and the CEL doesn't then that indicates a PCM power problem. Unfortunately, I don't have a wiring diagram for a 1995 model but I do have one for a 1996 which should be similar. If swapping the relays doesn't make a difference I'll be glad to help you troubleshoot the PCM power paths.