Tacuma 1.8 8v loses compression

[horatiomcblythe]

Strange one this one.When you start from cold it idles fine but if you apply more than 1/4 throttle it will rev then die then lose all compression.If you wait 10 mins it will return and then start again.Once the engine is fully warm you can happily drive at full throttle all day.I have flushed the engine oil and replaced with 10/40 semi synthetic which hasnt made any differance.please help as this one has baffled me.

[Trey05Woo]

Sounds like your problem lies in faulty engine piston compression rings. They are getting stuck in their bores, or are worn. On cold start the engine clearances are greater, but as the engine reaches operating temperature, metals expand... in this case the pistons/rings in their bores and create a better seal. The only true way to diagnos is by performing a cylinder leak down test. You need access to a special adaptor which screws into the spark plug bores, and compressed air.

[horatiomcblythe]

Hi i did wonder that but the compression goes to almost zero but only if you go over 1/3 throttle.I thought it was more to do with oil circulation in the head that was poor and somehow affecting the tappets? No smoke whatsoever either even when cold.Also noticed that the engine management light comes on when you floor it when cold.If you keep the momentum it will regain compression after a few hundred yards of zero throttle? This is doing my head in!! lol.Thankyou for your reply and i hope one day i will have this damn car running nicely.

[daewoomofo]

i wonder if the valve springs arent worn out.

[Trey05Woo]

well if you have a problem with oil circulation the telltale sign is noise. I really doubt it would be valve springs because weak springs cause the valves to float at higher rpms not idle. Your problem lies maintaining idle. the reason the car continues to run when you depress the gas pedal is because engine speed increases and this assists the cylinders in building compression.

A cylinder leak down test will tell you where the compression is escaping to when you lock that cylinder @ tdc on it's compression stroke.

Im betting compression rings though. Daewoos are notorious for excessive blow by and faulty piston rings. Normally they just get jammed in their bores due to carbon build up...

[horatiomcblythe]

I will give the bores a test when i can borrow neccesary equipment.What you say does sound feasible for this fault,the only odd thing is that if you do a compression test when cold it pushes 175 psi but rev it then do another test you get about 20 psi.Also found today that pushing the revs to 3500 when driving it cold makes the engine fault light flash for 20 secs then stay on? No sign of light if i restart car then wait till its fully warm.Hoping its not rings as i dont fancy a full strip down of the engine but be my luck that it is.Cheers all you woo guys for this and lets hope theres a end.

[Trey05Woo]

Hmm the flashing mil is a telltale of valves because sounds like raw fuel is getting into the exhaust and the mil flashes to warn of an overly rich condition which can damage the catalyst. Is the timing correct? Honestly its a shot in the dark until you perform the leak down test, this will isolate the problem.

Whats the history of this car? Has it been in your ownership for some time, or is it a weekend project etc I honestly gave you my opinion asuming you have owned this car for a while and recently started acting up.

[horatiomcblythe]

Hi again the car was a p/ex that came to me when my boss got sick of spending time and money on it!! I have since blasted it to skeggy on the off chance of blasting any potential blockage free but to no avail.I should hopefully be getting a cylinder tester this weekend so will update when i have some readings.It seems to affect cylinders 1 and 2 a lot more than 3 and 4? As when you blip the throttle it will just misfire horrendously and not stall so i quickly checked and 1 and 2 were down.But if you revved gently then it went back to 4 cylinders but if you floor it then it dies completely.damn this car lol.

[Trey05Woo]

Well is it a timing belt ressurector? loool. Make sure to test all cylinders thoroughly because maybe 1 or 2 cylinders display no compression leaks, but the other two do. So I would advise to check all four.

But if this car suffered a t belt failure wouldnt surprise me if valves are not seating right. check out the firing on only 3 cylinders thread... similar to yours...