ENGINE HESITATION ?

[coolchris]

Hi,

My car has started to show some funny symptoms overt the last day or 2.When driving car runs fine and a couple of times all of a sudden the engine has nearly stalled followed by a kangarooing jerking motion this only lasts a little while then the car seems to run fine but it has happened un predictably on me a couple of times could it be fuel pump ? hoping its not ecu related.Just to note car has new plugs/ht leads/coil pack/crank sensor cam sensor and cleaned air filters.Any help or advice would be much appreciated.

Cheers

Chris

[Adrian W]

you seem to have unplugged a lot of connections, I would start by looking there. from memory the standard map only uses the cam sensor for starting so it won't be there.

[coolchris]

You think its a connection issue then Adrian ?.If the car was connected up to a lap top would it show the problem ?

[Adrian W]

coolchris said:

You think its a connection issue then Adrian ?.If the car was connected up to a lap top would it show the problem ?

If it does it every time you press the throttle, otherwise you will need to drive it with the laptop connected.

[macky17]

Probably is the connections but worth checking the condition of your battery in this cold weather. If the voltage drops too far you get similar behaviour as it screws with the throttle position mapping. Trickle charge the battery to full charge then try switching the ignition on and off about 30 times before starting the engine - this allows the software to reset itself in case it's gotten into bad habits. If it still does it then you've eliminated that possibility.

[Blu3R]

Does it only happen on full boost or thereabouts? Or any time you accelerate?

[coolchris]

Well the car had a new battery fitted within the last couple of months so not sure it could be that.Took car out friday night started car drove about 100yards then the engine coughed followed by this jerking symptom for a couple of miles after that it ran fine till I came home then it done it again all be it momentarily.Then went out Saturday afternoon drove 25 miles car ran spot on no tell tale symptoms then as i was stationary the car just died.After this started the car everything appeared fine but 100 yards up the road jerking symptoms again seems to do it at lower speeds if I give the car a bit of beans it clears through and is then fine.Its really puzzling as it does it randomly not sure what I should be checking looking for ? was thinking of running some fuel cleaner through system (thats if its not electrical)certainly wont do any harm

[jdearden]

Uve just hd it mapped. I'm wondering weather the hot and cold stRts are not very good. It took ages to get mine as good as they are.

[Gadgeroonie]

Chris sounds like you have a intermittent fault - my guess is the crank or cam sensor

i know it had a sensor recently - perhaps you have too many volts and the car is killing sensors

check the voltage when the car is running - has the car had a new alternator recently ?

[coolchris]

Hi Mike,

The crank and cam sensors were replaced with intermotor ones from e bay(for a 2.5 mondeo)car has not had a new alternator just battery.Would just be nice to put my finger on it as can be a pain driving fine one min then playing up

[macky17]

Presumably a knackered alternator would produce the same symptoms as a poor battery so it's worth doing the ignition thing just to eliminate voltage drop issues...

[AMG Merc]

coolchris said:

...was thinking of running some fuel cleaner through system (thats if its not electrical)certainly wont do any harm

Chris, I was also thinking fuel when you first posted. A longshot perhaps but consider when you last filled up (do you have the receipt to check the fuel type?), how low was the level before filling?, when was the filter last changed (maybe change it anyway)?

[Gadgeroonie]

i guess your fuel pump may be cutting out but i would expect power to drop away slowly not suddenly

does the problem happen all the time or is it random ?

[coolchris]

I have had an alternator fail on me before and I remember the battery light on the dash was illuminated till I got it replaced.I am thinking along the lines of Rob I am guilty of letting the car run low and the symptoms happen randomly one min driving fine then it jerks and hesitates

[coolchris]

Ok had fuel filter cleaned and car seemed fine then 3 mile down the road same symptoms loss of power(like the cars cutting out and lots of hesitation/jerkiness.Car runs spot on all other times im bloody puzzled to be honest any other ideas guys ?

[sundance002]

Could be faulty ecu, I had a the same symptons, one min fine next min missing and jerking, Dave at jetstream swopped it and end of proplem, I posted it to them.

Edited by sundance002 on Wednesday 17th December 08:11

[tschechone]

Exactly the same problem here.
Mine was suddenly jerking after I drove through a rain. I was driving circa three seconds with power and two seconds without. Following drives (on sunny days) the issue appeared when the engine was warm (with shorter on/off period). Maybe after 10 drives it was getting better and better. After letting the car in the sun for few hours (summer / over 30 degrees ) the problem was gone.
No idea what happened and why...

[V1DL3R]

Electrics to fuel pump, losing current to relays or arcing at the fuses? Arcing would be unlikely as it would normally blew the fuse but the longer i own my car the more it defies the "likely".
Ground to the fuel pump if you are running the mod?
Fuel pipe collapsing, i'm assuming this could happen if on low flow, less fuel to hold it open?

or ECU. Mine cut out a few time, but completely cut out. Was the first signs of the ECU failing. But like I said it would just die, no spluttering which is why i might check the above first.

EDIT: also, just had my alternator changed but have no battery light. However if there was too much voltage it should blow the maxi fuse. Maybe its not enough to blow the fuse but enough to muck with other systems.

Edited by V1DL3R on Thursday 18th December 10:19

[Gadgeroonie]

the 2.5 alternator can overcharge at high revs i have heard

i guess this might affect the ecu

does the problem go away when the lights are on ?

[coolchris]

Okay ran some fuel cleaner through the car and had the fuel filter cleaned drove the car and within 5 miles same symptoms so back to square 1. Pulled out every relay/fuse checked all fine took out new crank and cam and put the old ones in.car ran a little lumpy(thats another post) but took it for 2(prob 10 miles or so) runs and no sign of those symptoms so hopefully the problem has gone but only time will tell ?.