It Won't Start?!

[rambler323]

For the last couple of weeks (months maybe?) my explorer will randomly decide not to start. When this happens, jumping it doesn't help and it has gas, so that's not the problem. I took it to firestone recently and they can't figure it out either. So now I'm turning to you guys. Does anyone have any ideas about what the problem is? How would I check? Thanks for helping me out!

 

[dman726749]

battery cables may be gone...that seems to be a common problem with the older trucks

 

[rambler323]

thanks. anyway i could test that? with a DMM maybe?

um help a newbie out, i was just reading a thread about cps sensors causing a similar problem and now i can't find it. how do you get to the similar threads list?

 

[dman726749]

at the very bottom of threads is a list of threads that are simmilar....i am not sure how you can test for bad battery cables, i am sure there is a way posted on this thread some how, but i dont know where it is.

 

[MrShorty]

More info needed: When it doesn't start, in what way is it not starting? Is the starter turning the engine over, but the engine won't "start"? Is nothing happening? Is the starter spinning but not turning the engine?

 

[rambler323]

Yeah the starter will go but it just doesn't ignite it seems. Sometimes this will happen after a couple hours of sitting and sometimes its like 5 minutes. But then after a while, again sometimes minutes sometimes hours, it'll turn over and start right up.

I was reading another thread that seemed to have a similar problem that the culprit was the cranks position sensor. I also read one where the battery cables were at fault. Is there anything else that could probably be the problem?

 

[lonestar]

Next time, try tapping the CPS. Crawl under front bumper and look up. It's in front right beside the crankshaft.

try search to find CPS related threads

 

[MrShorty]

If the starter turns the engine, there are only four things required for the engine to start: fuel, spark, air, compression.
1) fuel -- When you say it has gas, do you mean there is gas in the tank, or that you've verified fuel pressure at the rail? fuel injectors "firing?"
2) spark (at the right time) -- put a timing light on a spark plug wire, or pull a wire and see if you have spark. CPS is important in firing the plugs and firing them at the right time. If spark is the problem, then check the CPS, coil, and a host of other things.
3) air -- rarely the problem. About the only interference would be if the IAC valve were suffocating the engine (would show up as "I can start it with my foot on the accelerator, but stalls as soon as I let off the accelerator).
4) compression -- again, not common. If you've verified fuel, spark, and the IAC valve, then check that each cylinder is doing something.
Here's how I'd proceed:
1) run the EEC-IV self-tests on the off chance that the computer can see the problem and point me in the right direction.
2) check fuel pressure at rail. If good (~40 psig), then verify that the injectors are firing
3) check for spark

 

[slag]

another vote for crank position sensor.

super easy to fix and wont break the bank.

Intermittant cps signals are pretty hard to troubleshoot.

 

[BillWms01]

I vote for CPS too. As described in the "Now & Then Won't Start" thread in the similar thread list (pretty slick feature), mine was acting up nearly two years ago. After replacing it, I've had no other starting problems (finding wood to knock on). And, as slag says, it's very difficult to diagnose because it's intermittent.

 

[rambler323]

By "has gas" I meant that the tank isn't empty. I haven't checked for pressure, or spark. Could you tell me how do to both of those things? I don't have a timing light, but I do have a decent set of wrenches, screwdrivers, etc. and a DMM; so hopefully that will be enough to allow me to figure out what wrong.

BTW thanks everyone for your help and suggestions

 

[MrShorty]

Fuel pressure is best checked using a fuel pressure gauge. Can be had at any self-respecting parts store (may even be able to borrow rather than purchase, though they aren't horribly expensive). Hook the gauge up to the Schrader valve on the fuel rail. Turn the key on; fuel pump should run and bring rail pressure to ~40 psig. Any good repair manual (try the vehicle repair guides at www.autozone.com if a print manual is too old fashioned) will have more details.
Timing light is probably least invasive for checking spark. I once bought an "inline spark checker" from Harbor Freight that worked a few times, then died. Otherwise, pull a spark plug wire off of a spark plug, insert a spark plug into this wire, hold the ground electrode of the spark plug to a manifold and see if blue sparks jump the gap while someone turns the engine over.

 

[jfulcrum]

Your problem could be the fuel pump relay. I had a similar problem with my '96. When you turn the key to ON, if you don't hear the electric fuel pump kick in, then turn off the key, open the hood and then the relay box cover. Lightly tap, and /or wiggle the fuel pump relay, and then try the key again, to either listen for the pump and/or to start it this time. If that did the trick, then buy a new relay (~$10). This drove me nuts for a long time, but I found the answer on this site. Thanks a bunch, guys!