Omega Owners Forum
Chat Area => General Car Chat => Topic started by: al brown on 26 February 2017, 15:50:01
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Hi everyone, sorry but I've not been on here much lately, the estate is say on the drive waiting for sunny weather so I can weld the sills up for the mot.
Anyway, the wife's corsa c 1.4 twinport has suddenly decided to be a bugger to start when is cold. It tries to fire but doesn't catch fire the first 8 or so tries, when it does start it takes a few seconds to fire on all counts bit then runs spot on and can be stopped and restarted fine until it's been sat for an hour or so. There is pressure in the fuel rail, coolant is showing as 8*, coil has been temporarily swapped with a known good one, plugs are new, compression in all cylinders is good and no fault codes are showing.
Anyone have any ideas? It's frustrating as its not all the time so it's hard to track down and I don't want to go buying parts just cause.
Cheers, Al
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Got a scope? Check CPS signal.
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No, don't have a scope, computer reads rpm when I crank it, it's the fact that after it finally fires up it can then be stopped and started fine, or is this how the crank sensor on these fails, I'm used to the mig where it fails when warned up.
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Also worth checking Cam Sensor but that normally through a fault Code.
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I'll see if I can find a scope to check both the crank and can sensor.
Why would either of these sometimes cause poor cold starting, but then as soon as its started the first time it will start first go with the next hour or so?
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I'll see if I can find a scope to check both the crank and can sensor.
Why would either of these sometimes cause poor cold starting, but then as soon as its started the first time it will start first go with the next hour or so?
Because it could be a high resistance connection that gets better when warm. I'm not saying it definitely is this... just that without an accurate RPM signal you're goin nowhere and seemingly they don't set fault codes readily. Had a renault trafic van that liked playing the same game when the CPS was on the way out the door.
Check for an injection pulse with a DMM? If the ECU doesn't get a comprehesible CPS signal it most likely won't pulse the injectors. / can you smell fuel when it's cranking / does it splutter as if it might want to start?
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When was the fuel filter last changed ?
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I'll see if I can find a scope to check both the crank and can sensor.
Why would either of these sometimes cause poor cold starting, but then as soon as its started the first time it will start first go with the next hour or so?
Because it could be a high resistance connection that gets better when warm. I'm not saying it definitely is this... just that without an accurate RPM signal you're goin nowhere and seemingly they don't set fault codes readily. Had a renault trafic van that liked playing the same game when the CPS was on the way out the door.
Check for an injection pulse with a DMM? If the ECU doesn't get a comprehesible CPS signal it most likely won't pulse the injectors. / can you smell fuel when it's cranking / does it splutter as if it might want to start?
Not checked the injection pulse, but there is fuel when I cranked it with the plugs removed, but then again it doesn't always fail to start so maybe I checked it on a good start, it started fine this morning but then failed again 3 hours later. It coughs like it wants to start and after 4 or 5 goes it does start, then it feels like its adding cylinders one at a time for the next couple of seconds, then it idles and runs fine. If I turn it off as soon as it starts it will start straight away again fine every time unless I leave it for an hour or so.
I don't like swapatronics but maybe I should try a crank sensor.
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When was the fuel filter last changed ?
Not sure, we've not had it long but once it starts it runs fine.
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Check resistance from engine block to batt neg. Might not be sparking properly? *
(and if you're going to check for spark by removing plugs and grounding them be careful not to electrocute yourself and remove injector conn. for that cylinder so you don't blow yourself sky high ;) )
If you've got fuel coming through you've most likely got some form of CPS signal.
Edited to add : * although one would assume this would record a fault code :-\
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I'll see if I can find a scope to check both the crank and can sensor.
Why would either of these sometimes cause poor cold starting, but then as soon as its started the first time it will start first go with the next hour or so?
Because it could be a high resistance connection that gets better when warm. I'm not saying it definitely is this... just that without an accurate RPM signal you're goin nowhere and seemingly they don't set fault codes readily. Had a renault trafic van that liked playing the same game when the CPS was on the way out the door.
Check for an injection pulse with a DMM? If the ECU doesn't get a comprehesible CPS signal it most likely won't pulse the injectors. / can you smell fuel when it's cranking / does it splutter as if it might want to start?
Not checked the injection pulse, but there is fuel when I cranked it with the plugs removed, but then again it doesn't always fail to start so maybe I checked it on a good start, it started fine this morning but then failed again 3 hours later. It coughs like it wants to start and after 4 or 5 goes it does start, then it feels like its adding cylinders one at a time for the next couple of seconds, then it idles and runs fine. If I turn it off as soon as it starts it will start straight away again fine every time unless I leave it for an hour or so.
I don't like swapatronics but maybe I should try a crank sensor.
^ possibly as much to do with fact it's flooded with fuel by that point as anything else.
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In addition to the above, I'd be checking the coolant temperature sensor. :y
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In addition to the above, I'd be checking the coolant temperature sensor. :y
My code reader showed it at 8 degrees, that was my first thought. I know there is more than one sender, and I'm assuming the reader is showing the one the ecu sees.
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In addition to the above, I'd be checking the coolant temperature sensor. :y
My code reader showed it at 8 degrees, that was my first thought. I know there is more than one sender, and I'm assuming the reader is showing the one the ecu sees.
Sorry. I'd missed that. :-[
I have an oscilloscope (or two :-[ ) by the way, but if the ECU is reporting stable RPM while cranking I think it knows all it needs to. I wonder if the fuel pump is taking a while to prime. You say there's pressure at the rail, but maybe not enough?
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In addition to the above, I'd be checking the coolant temperature sensor. :y
My code reader showed it at 8 degrees, that was my first thought. I know there is more than one sender, and I'm assuming the reader is showing the one the ecu sees.
Does your code reader show you the air inlet temperature?
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In addition to the above, I'd be checking the coolant temperature sensor. :y
My code reader showed it at 8 degrees, that was my first thought. I know there is more than one sender, and I'm assuming the reader is showing the one the ecu sees.
Sorry. I'd missed that. :-[
I have an oscilloscope (or two :-[ ) by the way, but if the ECU is reporting stable RPM while cranking I think it knows all it needs to. I wonder if the fuel pump is taking a while to prime. You say there's pressure at the rail, but maybe not enough?
It's not exactly a stable rpm figure as the car tries to fire, it feels like no fuel to me but equally it could be a poor spark and then wet plugs as mentioned above. I've tried running the pump for 20 seconds first and it makes no difference so maybe fuel isn't the problem. I've ordered a fuel pressure tester (good excuse to buy one) so I'll check when it arrives as there is no pressure reading I can see on my computer.
As for air temp, it's it does although I don't remember what it was reading, I didn't think that would have to much of an impact on the fuel delivery unless it was way off, there is certainly no code though
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Inlet air and coolant both were reading 8 degrees.
With ignition on there is 3 bar fuel pressure and the pump can be heard running.
MAF reads 0 with ignition on.
Crank sensor has been swapped with one from a working car.
Coil pack swapped with one from a working car.
Car still struggles to start but as before runs perfectly once started and can be restarted within an hour or so without problem, occasionally starts from dead cold also still and smells of fuel during cracking when it fails to start.
Only thing I haven't changed that I can think of is the cam sensor (different on the donor car I have), I am assuming the cam sensor is involved in the ignition timing.
Any ideas before I buy a cam sensor?
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Inlet air and coolant both were reading 8 degrees.
With ignition on there is 3 bar fuel pressure and the pump can be heard running.
MAF reads 0 with ignition on.
Crank sensor has been swapped with one from a working car.
Coil pack swapped with one from a working car.
Car still struggles to start but as before runs perfectly once started and can be restarted within an hour or so without problem, occasionally starts from dead cold also still and smells of fuel during cracking when it fails to start.
Only thing I haven't changed that I can think of is the cam sensor (different on the donor car I have), I am assuming the cam sensor is involved in the ignition timing.
Any ideas before I buy a cam sensor?
From the Car or the Engine bay, or unburnt fuel perhaps, go back to basics, is each plug sparking?, pull them out one by one or if its an inline one piece pack pull them all out and test each plug spark by earthing using a jump lead or something. Even if its only firing on 2 it should still catch and fire up, so either all or nothing on the sparks
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After a minute or so of cranking it smells of fuel from the exhaust.
Was struggling to find a way to check the actual spark as its a one piece pack which doesn't lock onto the plugs, the contacts are sprung loaded. It does try to fire, just doesn't catch. Will try and check the actual spark.
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After a minute or so of cranking it smells of fuel from the exhaust.
Was struggling to find a way to check the actual spark as its a one piece pack which doesn't lock onto the plugs, the contacts are sprung loaded. It does try to fire, just doesn't catch. Will try and check the actual spark.
Yea its tricky, but pull the whole pack off then check each spring output by touching with a earthed spark plug, your probably throw more fault codes doing this be the way
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Will give it a try when I can get a second pair of hands. If it's not sparking, or not sparking well at least what is the likely culprit? I've already tried a working coil pack.
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Would it not give a code of the was no spark, or is a poor spark enough to stop a code registering while still not letting it start.
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Just be very careful with the coil. It produces quite enough voltage & current to be lethal.
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Have you checked the integrity of the engine block earth?
Try unplugging MAF, Coolant temp sensor, air temp sensor and see if that makes a difference. In the absence of a signal the ECU should substitute a "safe" guess-timate value.
Does this engine have idle air control or an electronic throttle body?
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Would it not give a code of the was no spark, or is a poor spark enough to stop a code registering while still not letting it start.
It should throw a Miss fire Code, Multi or Cyl blah Blah, assuming the ECU is not telling it not to spark or inject fuel for what ever reason.
I always start with the sparking on any missfires, plugs, plug holes, leads, Pack etc, its normally the easiest and cheapest fix, if Im convinced thats doing what it should be doing then move on the something else. In your case you just want to prove its sparking correctly on cranking.
Yes, obviously watch out for the high Volts when messing around.
Also, as said, dont rule out Cam Sensor or Temp Sensor
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Well after some clever clamping of plugs etc it seems to me there is a good spark, but then again when I put the plugs back in it started straight away so I think I'll check again when it won't start.
I was thinking cam sensor as its about the only bit that hasn't been swapped for a known working part, or at least been checked, coolant temp and air temp both read fine add does the maf. Would be nice to work it out before I buy parts, but I'm running out of ideas.
Cheers for all the help.
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I would expect a fault code if the cam sensor is dodgy, and it should still have a strategy to start with that sensor failed.
You have a coil pack for each cylinder and individual coil drivers in the ECU, so checking for a spark doesn't really tell you much other than that the ECU is seeing the engine crank over. Any ignition fault would only affect a single cylinder. :-\
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Had this on a Corsa 1.2 Twinport it was the crank sensor and it does not throw up a fault code a lot of the time, I changed both the crank and the cam sensors as they were cheap anyway and were 10 years old, ours was a 2005 Corsa with about 70k on the clock at the time. Easy fix.
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Well, it seems the car is running now. I had it where it was not starting and then straight away swapped the crank sensor, which didn't seem to help as it was still coughing and not starting. Later that night I pulled all the plugs and checked the spark, without trying to start it first. When I put the plus back in it started straight away and now has done several times over the last couple of days.
My thoughts are it was the crank sensor, as many have suggested, and the train it didn't start straight away after I changed it was because I had flooded the plugs trying to start it before I swapped the sensor.
Thanks everyone for the help and advice, if it turns out to not be fixed I'll be back for more help, but it seems like it was a faulty crank sensor that didn't throw a code.
Cheers again, Al
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Sounds like a plausible explanation. :y
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Well, after 4 days of starting straight away, it's back to how it was and has struggled to start twice today.
After reading horror stories on Google about the chain going slack and throwing the timing out I've had the cam cover off. The chain seems tight, there are no marks on the cover from the chain hitting it, the top guide seems fairly new with very little wear on it, so it seems the chain is fine and as it is only a recent thing that is struggling to start I have to assume the timing is correct, plus the compression is good.
It's currently starting fine, so my plan is that next time it feels to start I'm going to try it with the cam sensor unplugged, thinking that if the sensor is dodgy but not too the point of putting up a code it could be putting the timing out a bit so the car struggles to fire. With it unplugged (as Kevin suggested)it should use a default setting to start.
Any other ideas greatly appreciated, it's driving me mad as its so intermittent.
Cheers, Al
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Bear in mind also that if the cable to the sensor is damaged it doesn't matter how good the sensor is...
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Bear in mind also that if the cable to the sensor is damaged it doesn't matter how good the sensor is...
Yep, that's true. It's the fact it never misses a beat once it's started and the fact it sometimes starts fine that's got me stumped.
I will get there in the end, just the fact it's intermittent it's hard to know if it's fixed or not or if anything I've done had made a difference.
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Hmm.
Some more generic ideas:
Dodgy fuel pump relay?
Immobilser circuit? (a lot of cars will still crank even if they're immobilised)
If you can get hold of a wiring schematic it might help understand how the ECU/electronics are colluding to get the thing to run and thus highlight potential weak points.
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There is fuel in it?
::)
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There is fuel in it?
::)
Yep, filled it full of diesel as it gives a better mileage :y
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Hmm.
Some more generic ideas:
Dodgy fuel pump relay?
Immobilser circuit? (a lot of cars will still crank even if they're immobilised)
If you can get hold of a wiring schematic it might help understand how the ECU/electronics are colluding to get the thing to run and thus highlight potential weak points.
Fuel pump runs on my computer and it didn't start after activating the pump for 10 seconds before cranking.
No immobiliser light flashing on startup and it's the same with either of the 2 keys.
Seems like the timing is occasionally out, fuel or spark I'm not sure but as it has good compression and when I've checked ur seems to have fuel and a spark I can only think that at times the 2 aren't having at the right time.
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No problems with your dashboard?
http://www.vauxhallownersnetwork.co.uk/index.php?threads/how-to-fix-intermittent-starting-dashboard-lights-problem.310180/
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There is fuel in it?
::)
Yep, filled it full of diesel as it gives a better mileage :y
There'll be your problem :D