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Author Topic: cold start issue and fuel trim error  (Read 879 times)

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dunc52

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cold start issue and fuel trim error
« on: 07 January 2019, 14:28:30 »

Hi...on my 2002 2.6 V6 omega it takes a long crank over to start engine from cold (5sec or more, when it has finally fired up, it is vey lumpy for a further 5 secs untill fuel (i guess) normalises pressure.
Yesterday and this morning when engine caught and settled after 10 sec i turned engine off and re cranked engine immediately.  All ok, no problems started as if all is normal, repeted this a further 5 times, never missed a beat started fine with no lumpyness in the first 10sec or so of being fired up.  What i have changed recently 4 weeks ago, 6 bosch plugs, delphi coil packs, fuel filter, GM fuel pressure regulator and GM temperature sensor all to no avail.  Could it be an issue with the fuel pump or possible air leaks.  The garage i go to did a fuel pressure test and noted when engine was switched off the pressure dropped. The garage is running another check on this today.  Is it normal for pressure to drop after switching engine off??  As for everthing else, all runs very well, after the initial difficult cold engine start the car is perfect for the rest of the day until the next following morning.  Forgot to mention the fuel trim error is present. Any help or suggestions greatly received.  dunc52       
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tunnie

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Re: cold start issue and fuel trim error
« Reply #1 on: 07 January 2019, 14:33:58 »

Plenty of fuel in the tank, is yours an estate?
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dunc52

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Re: cold start issue and fuel trim error
« Reply #2 on: 07 January 2019, 14:40:46 »

Hi....always keep it full or nearly.  Its a saloon, we do about 20k a year in it. Ta
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Doctor Gollum

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Re: cold start issue and fuel trim error
« Reply #3 on: 07 January 2019, 14:57:20 »

Fuel pump on its way out...
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Kevin Wood

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Re: cold start issue and fuel trim error
« Reply #4 on: 07 January 2019, 15:07:10 »

Yep, fuel pump getting tired would do it. Would also be worth checking the fuel filter isn't clogged and possibly that the injectors aren't leaking and dribbling fuel into the intakes when parked up.
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dunc52

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Re: cold start issue and fuel trim error
« Reply #5 on: 07 January 2019, 15:51:22 »

Hi thanks for the ideas and pointers and much appreciated.  I will probably look at the fuel pump as next item, and if that does not resolve issue i will take aim at the injectors.  Re; injectors there is never whiff of petrol.  Fuel filter changed 4weeks ago.  When i have resolved this problem i will post the outcome
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LC0112G

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Re: cold start issue and fuel trim error
« Reply #6 on: 07 January 2019, 16:02:52 »

Hi...on my 2002 2.6 V6 omega it takes a long crank over to start engine from cold (5sec or more, when it has finally fired up, it is vey lumpy for a further 5 secs untill fuel (i guess) normalises pressure.
Yesterday and this morning when engine caught and settled after 10 sec i turned engine off and re cranked engine immediately.  All ok, no problems started as if all is normal, repeted this a further 5 times, never missed a beat started fine with no lumpyness in the first 10sec or so of being fired up.  What i have changed recently 4 weeks ago, 6 bosch plugs, delphi coil packs, fuel filter, GM fuel pressure regulator and GM temperature sensor all to no avail.  Could it be an issue with the fuel pump or possible air leaks.  The garage i go to did a fuel pressure test and noted when engine was switched off the pressure dropped. The garage is running another check on this today.  Is it normal for pressure to drop after switching engine off??  As for everthing else, all runs very well, after the initial difficult cold engine start the car is perfect for the rest of the day until the next following morning.  Forgot to mention the fuel trim error is present. Any help or suggestions greatly received.  dunc52     

In short, no. The fuel pressure regulator is supposed to maintain a constant-ish pressure above manifold (typically 3 bar/45psi) in the fuel rail (at the injectors). That pressure should remain for many minutes (perhaps hours) after you turn the engine off. If the pressure measured in the fuel rail drops quickly then either the pressure regulator (in the return line to the tank) is faulty, or you've got a leaky injector. IMV.
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dunc52

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Re: cold start issue and fuel trim error
« Reply #7 on: 07 January 2019, 17:47:09 »

thank you omega knight, again very helpfull.  I will post a reponse once i have sorted this problem out....
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TheBoy

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Re: cold start issue and fuel trim error
« Reply #8 on: 07 January 2019, 18:11:14 »

I would be initially expecting leaky injectors.

Next time, fully floor (I mean fully floor) then crank.  It shouldn't start, but should clear fuel from cylinder. Then start normally.
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Re: cold start issue and fuel trim error
« Reply #9 on: 07 January 2019, 19:33:08 »

A week pump will also allow fuel to seap back to the tank  ;)
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dunc52

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Re: cold start issue and fuel trim error
« Reply #10 on: 07 January 2019, 19:56:55 »

thanks to all that have replied, at this point i am leaning to the fuel pump as the good doc says "a weak pump will allow fuel to seep back to the tank".  It may be few days to a week to address this as work commiitments begin, but whatever it is i shall tell all from the rooftops lol.
One last query, if the injectors are leaking slightly, i have never smelt petrol in the cabin or around engine!!

Thanks ...
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cam.in.head

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Re: cold start issue and fuel trim error
« Reply #11 on: 07 January 2019, 20:15:15 »

Leaking injector as iní leaking into the cylinderí rather than into the engine bay.
If you can get a pressure gauge on ,see what it does as soon as you turn engine off.if itís losing pressure from the supply side ie from the pump you could clamp off the supply hose and see if pressure maintains or falls. Does the pump incorporate a one way flow valve ?. If it does this should hold pressure .
Thereís probably a better way to check injectors but I suppose taking the plenum off and the top manifold with the injectors on would allow you to see any leakage.
I assume it pressures up a sec or two with ign on .
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dave the builder

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Re: cold start issue and fuel trim error
« Reply #12 on: 07 January 2019, 20:19:41 »


One last query, if the injectors are leaking slightly, i have never smelt petrol in the cabin or around engine!!
leaking fuel will go into the cylinder bores ,wash the oil from rings (borewash) lowering compression when first starting ,
your oil level will increase if bad enough ,and oil will stink of petrol
(because petrol is leaking into the sump )
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dunc52

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Re: cold start issue and fuel trim error
« Reply #13 on: 07 January 2019, 20:41:31 »

Am all confused now lol.  Hey thanks i guess it certainly is poss with regards to leaky petrol and injectors.  In the morning i am going to try the floor test then crank engine, wont start, on 2nd attempt it should, someone advised me in the thread....  see wht happens. Ta for the injector side...
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MonzaGSE

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Re: cold start issue and fuel trim error
« Reply #14 on: 07 January 2019, 21:30:01 »

Hope you figure this out. Because i have a 95 3,0 that behaves pretty much exactly the same can crank from 5-10 secs before firing after sitting for a while. If it just been sitting a few minutes it fires up instantly. Also have the stumbling for a few seconds after firing.
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