Suspected vaccum leak?
Discussion
I'll qualify this by making it clear what I know about engines is almost nothing other than rebuilding a 1969 vw Beetle when I was 17 (a long time ago).
Just looked at a VW Polo which when started showed a spanner on the display, no other lights. Started ok but the engine was "hunting" or lightly surging so the idle was up and down slightly. I under the fuel filler and the revs went up and evened out, cap back on and it was varying again.
Am I right in thinking this sounds like a vacuum hose needs replacing or could it be any number of expensive things?
On top of that, starting it three times killed the battery(!) but that could just be a flat battery I guess (or a new battery and knackered alternator).
Any thoughts?
Just looked at a VW Polo which when started showed a spanner on the display, no other lights. Started ok but the engine was "hunting" or lightly surging so the idle was up and down slightly. I under the fuel filler and the revs went up and evened out, cap back on and it was varying again.
Am I right in thinking this sounds like a vacuum hose needs replacing or could it be any number of expensive things?
On top of that, starting it three times killed the battery(!) but that could just be a flat battery I guess (or a new battery and knackered alternator).
Any thoughts?
If it's a recent petrol engine vehicle then there will probably be a fuel tank vent via a carbon canister, and a mechanism to purge the canister by opening a connection to the engine intake under the right conditions. If the engine runs differently with the filler cap off, I'd suspect a problem in that area.
Since you have a warning light, there ought to be a fault code in the ECU and you should be able to read this with a suitable reader. OBDII readers are commonly available for a few quid and may be all you need. You will need to look up what the fault code means, and Google is your friend there. You may well find the fault code tells you exactly what is wrong - if not, it should at least tell you which area to investigate.
Since you have a warning light, there ought to be a fault code in the ECU and you should be able to read this with a suitable reader. OBDII readers are commonly available for a few quid and may be all you need. You will need to look up what the fault code means, and Google is your friend there. You may well find the fault code tells you exactly what is wrong - if not, it should at least tell you which area to investigate.
GreenV8S said:
If it's a recent petrol engine vehicle then there will probably be a fuel tank vent via a carbon canister, and a mechanism to purge the canister by opening a connection to the engine intake under the right conditions. If the engine runs differently with the filler cap off, I'd suspect a problem in that area.
Since you have a warning light, there ought to be a fault code in the ECU and you should be able to read this with a suitable reader. OBDII readers are commonly available for a few quid and may be all you need. You will need to look up what the fault code means, and Google is your friend there. You may well find the fault code tells you exactly what is wrong - if not, it should at least tell you which area to investigate.
Thanks for the reply. God knows why but I meant OIL filler, not fuel Since you have a warning light, there ought to be a fault code in the ECU and you should be able to read this with a suitable reader. OBDII readers are commonly available for a few quid and may be all you need. You will need to look up what the fault code means, and Google is your friend there. You may well find the fault code tells you exactly what is wrong - if not, it should at least tell you which area to investigate.
Squishey said:
Where abouts are you? If you're in the South East then I can lend you a OBD reader and a multimeter.
OBD to read the fault codes which might give you a clue about the idling problem, the multimeter to check the battery voltage with the engine off and again with the engine running.
Cheers, appreciate that but I'm in South Devon. I'm half minded that its voltage related.OBD to read the fault codes which might give you a clue about the idling problem, the multimeter to check the battery voltage with the engine off and again with the engine running.
Will keep thinking.
If you undo the oil filler cap then you are introducing an intake air leak via the PCV system. If that clears up a lumpy idle then it may be the idle was previously too low and/or too rich. There are various potential causes for that, and the fault code that triggered the warning light should guide you to the fault.
Sounds like an OBD diag needed. TBH not going to bother as its a first car for my son so "on to the next" unless he can pick up an '05 polo cheap, I can teach him how to "fix it" and sell on after six months use and not lose anything.
He doesn't know it yet but hes an engineer and this sort of thing (it a sample fix) would get him interested.
Ta all
He doesn't know it yet but hes an engineer and this sort of thing (it a sample fix) would get him interested.
Ta all
Gassing Station | Home Mechanics | Top of Page | What's New | My Stuff