undetectible Intermittent Starting Problem

Info on the problem.

- 2008 Ford Focus 1.6 Style

- Auto

- 30,000 Miles

Short version of what’s wrong with the car and important notes:

- Mostly heat related starting problem

- The car drives perfectly

- There is no injector pulse when fault is occurring, the most important info here is wiggling the wiring harness WILL get the car to start when the car is NOT hot, however when the engine has warmed to normal operating temp wiggling wires will not have any affect which I’m guessing is due to thermal expansion.

- ECU has been swapped out with another new one and problem persisted.

- Disconnecting the ECT sensor will get the car to start almost 99% reliably.

- ECT sensor has been replaced.

- Crank sensor has been replaced.

- No fault codes ever registered.

I have been trying to trace the problem through the wiring harness but it’s proven to be too difficult.

The current process I’m using to find the problem is to investigate all sensors and their circuits that have anything to do with fuel injection, the only problem is that I do not have a large knowledge base when it comes to cars.

I am wondering if you guys can help me and please be so kind to tell me what sensors you know to affect fuel injection and if you’ve ever heard of such a problem before or know of anything that could help.

I have a scanning tool and have been inspecting how certain sensors work and everything seems to be fine (voltages .etc) to my knowledge which again isn’t vast.

I have had a friend bridge the whole ECT sensor circuit to eliminate it and sure enough the problem is not regarding the ECT circuit.

I’m getting close to having to give up a perfectly good car all because of some stupid wiring problem.

Thank you for any help, it is much appreciated.

Update (03/16/2017)

One other thing I'd like to mention even though it isn't that major is that with the ECT sensor being disconnected the car is still not starting a lot more now, seems like the problem is getting worse which is a good thing in regards to having a chance at finding it!

Update (03/16/2017)

Update:

Throttle position sensor changed to no avail.

further testing revealed that the wires around the fuse box had a significant effect on the problem.

I think from my testing it's safe to say the issue is within the wiring inside the fuse box.

The only wire I can think of that could cut off injectors would be the injector relay circuit.

Is this correct to think this?

Further more I'm having trouble locating the injector relay since the owners manual is useless at defining which fuse/relay is where.

Is there any obvious signs to look for when trying to find injector relay?

thanks for your help!

Answer this question I have this problem too

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dom, could not find much, try the link may help. Sorry you are still having issues.

ftp://ftp.idm.ru/pub/ffclub/2003_5_Focus...

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3 Answers

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After reading through you question Ive come to the conclusion you've done it all save for one thing and you mentioned it in your statement "wiggling the wiring harness WILL get the car to start" I would replace the wiring harness . One of my pet peeves is when a test light is used to find faults in wiring and a mechanic pokes a hole in the wire which then corrodes inside the plastic and you cant see that its gone bad . Then you get weird things like this happening. you can do continuity tests and get fair results but heat the wires up or move them and it can be a different story . I would replace the wiring harness . it may be a bit more than finding the offending wire and replacing it but speaking from experience you can spend a lot of time searching for that wire and if by chance its more than one wire and you think you found it but it was actually two . Just easier and more certain to replace the whole harness. Hope this helps

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Thank you for your comment.

I agree with your opinion on replacing the wiring harness however up until now I've been trying to avoid that as there has already been a large sum of money spent on the car.

Having said that it's come to the point now that I've spent so many hours trying to trace the fault back through the wiring with no success that It is futile to continue searching.

I am currently getting quotes for a new harness and hoping that it will not be too expensive.

Thanks again.

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Hi Jim,

I've replaced the wiring harness and problem still not solved.

The funny thing is that moving the wiring harness still gets the car going!!

I am guessing that this problem is due to some sort of physical problem with a sensor that affects fuel injector pulse as moving the wires must be in turn moving slightly the faulty sensor.

What suggestions would you have to find the faulty sensor.

An obvious one I've thought of is getting the car to not start and then going around and knocking the sensors with a screwdriver etc.

I'm not particularly sure which sensors actually affect fuel injection when starting the engine, if you could advise on this it would be greatly appreciated.

Thank you.

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dom @focusstyle Maybe not it may be the connector to the harness. As for which sensors affect the starting of the car theres the MAP ,the MAF ,The crank position sensor ,the cam position sensor ,the fuel pressure sensor , fuel regulator any one of these can stop a car from starting but I'd be more into finding the reason wiggling the harness makes it go . There has to be something in the wiring

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I've realised today that I have been discounting some important info.

When the car is cold it's prone to hesitation/lack of power when accelerating however when warmed up it operates fine, sometimes when it's about to change up a gear it hesitates as well.

Sometimes the car will start but then stall, if you push the accelerator down when it starts it wont respond.

This hints to me there is an issue with the TPS . I know the only way the TPS should be able to affect injection is if it puts car into flood clear mode and that isn't happening.

Another interesting thing. Once I tried to start it nothing happened, the engine wouldn't crank or anything. So I opened the hood and could hear the TPS was making a continuous electrical beep sound, this happens when the car has first been turned off so the TPS can gauge the position of the throttle plate however always stops after 2 seconds or so. I resolved this by reconnecting the battery and it's never happened again.

Thanks for the help!

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@focusstyle , dom , Disconnecting the ECT sensor will get the car to start almost 99% reliably, possible bad new sensor (iffy), or what this may mean is you should trace that circuit/wire for fault, short/break/corrosion/etc.. Just a thought, maybe try unplugging one injector at a time and try starting to see if a injector is grounding out ECU intermittently. Check the link below, may sound familiar to you. Sorry I could not help more but you have tried so much already. Good luck.

I hope this helped you out, if so let me know by pressing the helpful button.

http://www.focusfanatics.com/forum/gener...

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Thank you for your comment.

The ECT sensor circuit has been bridged and the problem persisted therefore that circuit has been ruled out.

That's a great idea to unplug the injectors one at a time and see if any difference. Is it safe to do so?

Funny you should find that thread. That was one I made a couple of months ago!

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dom, yes you can unplug one injector at a time and try engine, plug back in and go to next inj. and so on, maybe just do not run too long. good luck.

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dom, Was the injector harness changed. Did you try unplug injectors one at a time and note if you do, check wires/wiggle test to see if shorting out computer/shutting down.

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Hi L,

yes i did unplug each injector at a time and there was no reaction from the car when it wasn't firing.

I changed the whole engine wiring harness which includes injectors and everything!

I have a feeling this problem may be related to the TPS for the reasons I have made in my most recent comment to Jim.

What are your thoughts on the TPS being the potential problem.

I'm going to be testing the TPS over the next few days by trying to physically manipulate it any way I can when the car isn't starting and will see if there is any reaction.

Unfortunately all of the readings on live data feeds for voltages etc are as they should be so the only way this problem will be able to be discovered is by moving the faulty sensor and having the engine fire and then testing again as many times as possible.

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dom, shorting/failing TPS, could possibly cause stalling issues.

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Hello. I have a 2008 focus 2.0 with the exact same issue. Was this ever resolved? This car is driving me and the customer crazy. Thanks!

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Hi Ryan,

Unfortunately the car wasn't sorted and after two years of dealing with this issue I decided to get rid of it and get another.

My advice to you if it is the same problem is just get rid of the %#*@ thing. I kept the car for so long because I liked it very much and was worried about buying a second hand car but its really not worth the hassle and money.

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dom will be eternally grateful.
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