Crank Sensor? Need help

Cougarfetish

Registered User
Hello,

For the pas week or so, my 1990 XR7 has had trouble starting only intermittently. Sometimes it starts fine, other times you are cranking it and it seems to have an electronic failure. IT cranks for a few times and then has a harsh stop, the headlights go off, interior lights go off. Shut the key off, crank again, and sometimes it starts sometimes it fails again.

It was starting more times than not so I didn't pay urgent attention to it, but this morning driving down the highway, the car lost power while driving, and this was a first. My tach went to 0, car didn't feel like it had power, but when I put some gas on it, it started chugging. Went to pull over to the side of the road, and before I could come to a complete stop, the car was acting normal again. So I turned around and came straight home.

Now at first I thought failing fuel pump, as it would crank dry for 5 seconds sometimes and not start (And not fail electrically). But I remember reading how if the crank sensor fail, it will cause your car to "Guess" on the timing. Is this the most logical thing to fix at this point?

Can someone give me a bit of insight please? I gotta make it to work tomorrow :)

THank you,
Derek
 
A couple other things I should clarify:

Starter sounds like it's turning fine. When the car is in it's "2 minute not-gonna-start" mood, it will crank for 5 seconds sometimes, other times crank for 2 seconds normally, then crank really slow for 2 seconds (Headlights turn off etc.), then crank normal again. Eventually it will start, but it was the fact that it failed on the highway that has me worried.

Since I have been home, I have checked the ignition switch, there is no indication of wearing wires or anything of the sort. The car has been starting fine everytime I try! I have tried wiggle-testing the ignition cylinder while car is running but it won't die.

I just replaced the battery cable posts yesterday, as I thought it was the problem of the intermittent no-start. It ran fine yesterday, but this morning I found out it didn't seem to help.

Battery is holding charge at +12V, and charging at +14 when running, so it looks normal.

Crank Sensor? Ignition Switch? Battery Connection? Or someone said something about the harmonic balancer in one of the posts.

Any educated guesses are appreciated :)
-Derek
 
Note that intermittent starts typically point to a failing/failed camshaft sensor. As is an intermittent tach.

The normal approach is to check that the wiring hasn't fallen into the SC belt and that the connector isn't corroded - if all that appears servicable, the camshaft sensor itself should then be replaced.

Also note that when a sensor is replaced, the computer should be given an opportunity to relearn the new part - don't be surprised at minor erratic engine running for a short time.

>But I remember reading how if the crank sensor fail, it will cause your car to "Guess" on the timing.


Not correct - this is true if the camshaft sensor has an issue.

If the crank sensor fails, the car simply won't run.
 
Last edited:
Thanks KMT,

The tach only dropped to zero because I believe the power died to the motor completely. Would an intermittent cam failure cause the car to die while driving?

I am beginning to think it's more fuel related, due to the sometimes normal cranking without the motor catching, which would also cause it to practically die on the highway and restart without me turning the key would it not? Early sign of a failing fuel pump maybe?

Thanks for the tip so far.
-Derek
 
>Would an intermittent cam failure cause the car to die while driving?

Yes. It always starts again, eventually, right?

Your symptoms are classic - many others have done thru the same thing, with camshaft sensor replacement being due...at a minimum.

There can be other issues, such as bad grounds, but until you work thru them, including replacing the camshaft sensor, the car will continue to act up.

Do you know how to check fuel pressure? If so, feel free to do that and eliminate that as an issue, but don't go too far without dealing with the camshaft sensor.
 
Last edited:
Thank you KMT,

Thanks for reasserting it, sometimes it's all I need! :)

I will look into the price of a cam sensor. I have a haynes that tells me the fuel pressure check, but I don't have a pressure guage. If necessary I can buy a cheap one I suppose. I just had my car into the shop about 2 months ago due to some electrical gremlins. You acctually helped me out on that post too, I tried DIS Coil pack new wires plugs etc. it ended up being that Lordco sold me some plugs that didn't work with the SC (Single plat, not double plat.).

Anyways, the mechanic at the shop told me they did a fuel pressure check, and it was fine. But a lot can happen in 2 months I suppose, I'll look into getting one of those fuel pressure guages. Probably a useful tool if I'm going to be a XR7 owner :)

Edit>> Ouch, just checked. $75 for a cam sensor. I suppose you would recommend not swapping one in from a junkyard??
 
Last edited:
>Edit>> Ouch, just checked. $75 for a cam sensor. I suppose you would recommend not swapping one in from a junkyard??

BTDT. The logic goes like this:

  • If the second sensor is bad, you'll think that the camshaft sensor isn't the issue and either leave it in, or put the original back (BTW, off the car, a failed sensor ohms out just like a good one). Problem continues...but you start chasing your tail around a tree.
  • If the second sensor works for a short time, you may again think this isn't the issue - either way, you'll be back under the hood and making a run for another...maybe.

Buy a new one, get a warranty and be happy. $50.00 is considered a 'cheap save' when dealing with an SC. Worry when you have to spend $500 on a repair with no promise of any benefit :)
 
You're right again!

Thanks for the advice, I'm going to find a friend with a discount, and see if I can get it a bit cheaper. But I'll make that my first step and keep you posted!

Cheers,
-Derek
 
Replaced Cam sensor. Found a discount for $53. Brand new part of course. Replaced it in about 20 mins due to one of the bolts being a little hard to get at.

Fired it up twice and she was fine, but we will have to wait and see if any gremlins rear their ugly heads in the next day or two.

Thanks again KMT, will keep you posted.

-Derek
 
Thanks for the report, Derek - I'll toss some chicken bones to help ward off the gremlins. Good luck.

Ken
 
I'm gonna have to try this too! My car has been doing basically the same thing minus the loss of power while driving. Would this also cause it to bog almost to point of dying when pushing the gas after cold start at all? It doesn't bog like that after driving after a couple minutes.
 
>I'm gonna have to try this too!

Sorry, I'd have to say your symptoms are not that similar. Pull codes :)
 
Yeah, I wasn't experiencing any bogging, my car literally lost all power for 5-10 seconds, then fired up.

good luck my friend.
-Derek
 
>I'm gonna have to try this too!

Sorry, I'd have to say your symptoms are not that similar. Pull codes :)

No I meant boggin on top of the other things he described.

As far as codes, well I tried and so did David and my car isn't gonna let us in on its problems. It just won't do anything, tried 2 readers and nothing. I'm gonna take it to someone with a more advanced reader soon, any suggestions. Ford, shop, member in the area? anyways since i can't read the codes i'm kinda screwed right this minute without the time to go get it done.
 
>any suggestions

Feel free to do a search with your unique issues, etc. If you still have questions, start a new thread, detailing what you know & have tried so far - try to include the year of the car, miles, mods, recent repairs, etc. so that others can help you get to the bottom of things as quickly as practical. Code reading is highly recommended - the car is complex and was designed with onboard/self-test diagnostics aimed at reducing throwing parts and money at issues that are bound to pop up with vehicles as old as these are.

Good luck w/your car.
 
Last edited:
KMT,

Looks like you found the problem, changed cam sensor and all has been fine for days now.

I can't thank you enough for your quick help!!!

Thanks,
Derek
 
Derek - Make sure to label and/or chuck~destroy the old one so you don't get tempted to keep/use it as a spare :)

Thanks for the wrap up!

Ken
 
i had to do crank sensor before and this sounds alot like that, good to here you got it fixed
 
Last edited:
Back
Top