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Old 16-08-2006   #1
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compression test

right im going to do a compression test on my car to see if ive got a bent valve, causing the over fueling, but whats the size of the hole that you screw the spark plugs in to?
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Old 16-08-2006   #2
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Re: compression test

1. a bent valve wont cause over fuelling
2. you will find it very hard to bend a valve on a fire engine as the piston and valves dont occupy the same space like most engines
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Old 16-08-2006   #3
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Re: compression test

wont it cause a smell of fuel to come out the exhaust though?


thats what im getting, as the fuel isnt getting burnt.
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Old 16-08-2006   #4
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Re: compression test

Quote Originally Posted by 99sei
wont it cause a smell of fuel to come out the exhaust though?


thats what im getting, as the fuel isnt getting burnt.
How does the car run?

Checked all the plugs are sparking?

Checked HT leads?

Etc...
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Old 16-08-2006   #5
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Re: compression test

If you are doing a compression test, all the kits i have ever used had a selection of threads on the pipes, so it should'nt matter what the plug size is, there should be the correct pipe in the kit.
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Old 16-08-2006   #6
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Re: compression test

ok cheers baildey

jamie - all new plugs and leads, changed the coil pack.

it runs ok then will get a little miss fire another 20 secs later the same
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Old 16-08-2006   #7
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Re: compression test

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Old 16-08-2006   #8
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Re: compression test

cleaned and put back in, will try another this week. cleaned it with a baby wipe, would that have been ok?

think i might have killed the cat with the constant overfueling though
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Old 16-08-2006   #9
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Re: compression test

Cleaning wouldnt have helped if its broken!

Cat may be dead yes.

Bear in mind that the lambda is only switched into the ECU once it starts in closed loop operation (once the engine reaches certain conditions)....so that initial 20 secs of ok running may be open loop (usually overfuelled to heat up the engine), then it may go rough as the lambda is switched in, and found to be dodgy.

Also, the lambda probe failing doesn't cause the ECU warning light to come on....
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Old 18-08-2006   #10
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Re: compression test

got a compression test done today and.....

no compression at all HG has gone

would this have caused the smell of fuel?
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Old 19-08-2006   #11
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Re: compression test

That can't be right, if it has no compression at all it won't run, and head gaskets don't normally cause catastrophic compression loss, that's burnt out valve, broken rings holed piston territory. If one pot has no compression put a bit of oil down the bore. If you then see compression its rings, no change it's valves.
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Old 19-08-2006   #12
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Re: compression test

we tried plugs 1 3 and 4 no compression in any

we took the spark plug out, put the compression thing in and fired it up. is that what you do?

it runs, can get good power out of it when on the road. but emissioins are too high and the smell of petrol from the exhaust.
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Old 19-08-2006   #13
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Re: compression test

you don't fire it up, no. Pull the HT leads off remove the plug of what you're testing, and put the tester in. turn it over on the starter a few times, the tester should record the peak pressure reading.

If you had no compression in 3 out of 4 cylinders, it wouldn't run.
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Old 19-08-2006   #14
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Re: compression test

Quote Originally Posted by 99sei
we tried plugs 1 3 and 4 no compression in any

we took the spark plug out, put the compression thing in and fired it up. is that what you do?

it runs, can get good power out of it when on the road. but emissioins are too high and the smell of petrol from the exhaust.
PMSL, The procedure is to check with the throttle wide open. You remove all the plugs from the engine, pull the connectors off the coil packs so the coils aren't firing. The person turnung the engine open holds the throttle wide open. Then test the compressions one by one. You should get readings within 10% of each other on all 4 cylinders. The compression reading itself isn't that important, within reason, mainly because the gauges tend to be inaccurate. You do want conformity however.

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Old 19-08-2006   #15
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Re: compression test

You don't need to open the throttle if the plugs are all removed. There won't be any significant manifold suction as the air can enter down any of the spark plug holes.

You can leave the throttle wide open if you want, but as it spings closed it can be inconvenient.
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