Compression tests.
Discussion
Just put my 94 chim (pre-serpentine engine)in for a check as it did not seem to be running quite right.
Garage completed a compression test and cylinder 7 was 23% down on other cylinder readings.
My questions are;-
What causes the symptom of reduced compression?
Will the compression continue to deteriorate?
Does this need to be fixed?
If it needs to be fixed what is required to be done?
This may not be related but since I have had my ignition coil changed the rev counter behaves differently.It used to be rock steady at all revs and at tickover but now fluctuates about, even when the revs are steady on the car. It fluctuates approx 3-4mm
What can cause this?
Garage completed a compression test and cylinder 7 was 23% down on other cylinder readings.
My questions are;-
What causes the symptom of reduced compression?
Will the compression continue to deteriorate?
Does this need to be fixed?
If it needs to be fixed what is required to be done?
This may not be related but since I have had my ignition coil changed the rev counter behaves differently.It used to be rock steady at all revs and at tickover but now fluctuates about, even when the revs are steady on the car. It fluctuates approx 3-4mm
What can cause this?
What causes the symptom of reduced compression?
Will the compression continue to deteriorate?
Does this need to be fixed?
If it needs to be fixed what is required to be done?
Worn or scored bores, broken rings, burnt out valve/seat, badly blowing head gasket, nothing good. Basically it means engine apart, find the problem, repair/replace as necessary. Potentially expensive. Sorry!
Just put my 94 chim (pre-serpentine engine)in for a check as it did not seem to be running quite right.
Garage completed a compression test and cylinder 7 was 23% down on other cylinder readings.
My questions are;-
What causes the symptom of reduced compression?
Will the compression continue to deteriorate?
Does this need to be fixed?
If it needs to be fixed what is required to be done?
This may not be related but since I have had my ignition coil changed the rev counter behaves differently.It used to be rock steady at all revs and at tickover but now fluctuates about, even when the revs are steady on the car. It fluctuates approx 3-4mm
What can cause this?
Rex,
I'm not an expert on this but something similar happened to my engine (4.0 Speed Six).
Symptoms - Idle Speed drops down over period of a few months. Idle Speed fluctuates a bit.
Cause - Valve Seats moved, proved by compression tests. In my case 2 of the 6 cylinders were about 40% down. Basically whats happening (in my case anyway) is that the cylinder is getting compressed but some of the gas is escaping resulting in loss of power.
Does it need to be fixed - No, not unless its annoying you or causing you problems.... or the engine is still under warranty.
Don't know if it will progessivly get worse or not.
In my case the only fix was a top end rebuild of engine back in Blackpool.
Disclaimer - my problem might be completely different !
Possibly very bad news and poss just moderatly bad news. Will it help the diagnosis that water level in swirl tank drops slightly but not much. Can't tell if its just finding its level. Needed to top up about an inch after letting engine warm up and taking out on run for 20 mins. Allowed everything to cool down before re checking water level.
Slight concern though was when on motorway run, (prior to concernes about running but only taken for test run since)when changing lanes had white cloud from back of car for approx 2 seconds then nothing. Road was very wet so put it down to excess water sitting on white lines hitting exhaust.
Could this have been headgasket blowing? Surely the temp would have soared and I would have lost a lot of water
Heres hoping nothing big.
Slight concern though was when on motorway run, (prior to concernes about running but only taken for test run since)when changing lanes had white cloud from back of car for approx 2 seconds then nothing. Road was very wet so put it down to excess water sitting on white lines hitting exhaust.
Could this have been headgasket blowing? Surely the temp would have soared and I would have lost a lot of water
Heres hoping nothing big.
Sounds like it could be. Take car to hospital is the best advice. Low compression reading could be caused by gasket failure and that water is no leaking into the exhaust. If slight wouldn't necessarily notice but if left you can have a very big bill instead of a lot smaller one.
Steve
Steve
Cannot see you getting very far with this without taking the head off to be honest, reduced compression can be caused by quite a few things:
Head gasket blown on that bank on that cylinder.
Valve/valves burnt on that cylinder.
Bore/Piston/Piston ring damage on that cylinder.
Cam lobe lifter problem (unlikely).
Whichever of the above is wrong it will only get worse and needs to be sorted sooner rather than later. The missing water could be connected but that is not definite. If a valve is not sealing properly it can damage the head as can the head gasket if that is the case. If a ring is broken and eventually breaks the piston this would not be a nice place to be. In short, the good news is that the damage is confined to one side, the bad news is it ain’t gonna be cheap. You could try one cheap temporary bodge yourself “Holts Piston Seal”, if it sorts out the bad running on that cylinder this would suggest that you have a bore/piston problem.
As far as the rev counter goes, check all the connections first, if that does not help, if you have the oil coil put it back and see if it is ok again, it may be a wrong coil.
Good luck,
Ivan
Head gasket blown on that bank on that cylinder.
Valve/valves burnt on that cylinder.
Bore/Piston/Piston ring damage on that cylinder.
Cam lobe lifter problem (unlikely).
Whichever of the above is wrong it will only get worse and needs to be sorted sooner rather than later. The missing water could be connected but that is not definite. If a valve is not sealing properly it can damage the head as can the head gasket if that is the case. If a ring is broken and eventually breaks the piston this would not be a nice place to be. In short, the good news is that the damage is confined to one side, the bad news is it ain’t gonna be cheap. You could try one cheap temporary bodge yourself “Holts Piston Seal”, if it sorts out the bad running on that cylinder this would suggest that you have a bore/piston problem.
As far as the rev counter goes, check all the connections first, if that does not help, if you have the oil coil put it back and see if it is ok again, it may be a wrong coil.
Good luck,
Ivan
rex said: If it is a headgasket whats the cost of replacement assuming nothing else wrong. Is there any way to be certain that it is a headgasket and not one of the other potential causes of reduced compression (see greenV8S post below)
If the Gasket is blown there will be scorch marks and discolouration,
Tim
Wasn't on mine Tim.... If the break is internal you won't see anything.
Head gasket replacemnt can depend on what else is needed such as skimming the heads as they have warped. Worth getting the cams and rocker gear checked while the engine is in bits. Budget £6-700 and you may get some change. There will be about £150 worth of gaskets and cylinder bolts etc etc.
At least it gave a lot of photo opportunities for the bible. Yes the gaskets and rocker damage was in my engine!
Steve
>> Edited by shpub on Sunday 9th February 15:40
Head gasket replacemnt can depend on what else is needed such as skimming the heads as they have warped. Worth getting the cams and rocker gear checked while the engine is in bits. Budget £6-700 and you may get some change. There will be about £150 worth of gaskets and cylinder bolts etc etc.
At least it gave a lot of photo opportunities for the bible. Yes the gaskets and rocker damage was in my engine!
Steve
>> Edited by shpub on Sunday 9th February 15:40
What causes a headgasket to break? Is it just age or a symptom of something else.
Could lack of use cause a problem?
The journey where it may have blown (although I do not know for sure if this is the cause of loss of compression)was approx 300 miles over 2 runs in a weekend. This was 25% of the total milage covered in the previous year.
Could lack of use cause a problem?
The journey where it may have blown (although I do not know for sure if this is the cause of loss of compression)was approx 300 miles over 2 runs in a weekend. This was 25% of the total milage covered in the previous year.
shpub said: Wasn't on mine Tim.... If the break is internal you won't see anything.
Head gasket replacemnt can depend on what else is needed such as skimming the heads as they have warped. Worth getting the cams and rocker gear checked while the engine is in bits. Budget £6-700 and you may get some change. There will be about £150 worth of gaskets and cylinder bolts etc etc.
At least it gave a lot of photo opportunities for the bible. Yes the gaskets and rocker damage was in my engine!
Steve
>> Edited by shpub on Sunday 9th February 15:40
Yes i suppose it also depends on what the gaskets are made of, i was thinking that if there is a serious drop in compression due to blown head gasket, its likely to show ?
I agree definately check cam & rockers & pre-load if the cam needs changing now is the time to do it, likewise any work to the heads.
Burnt /damaged valves would be also high on the list for causing compression drop.
Tim
joospeed is giving good advice! A leakdown test will identify the source of the leak in almost all cases and it could be just about any of the previously mentioned faults. The coil and rev counter problem suggests;
1) coil is the wrong impedance for the system - use a Lucas Supersport coil for best results.
2) Dodgy wiring.
3) Interferance from a bad earth or broken/damaged leads.
Good luck.
1) coil is the wrong impedance for the system - use a Lucas Supersport coil for best results.
2) Dodgy wiring.
3) Interferance from a bad earth or broken/damaged leads.
Good luck.
Took car to Dave Battys yesterday. Car has been running OK but lumpy upto 2000 rpm. Fitted a new coil DB recommended but still rev counter needle wobbling about the place and running lumpy. Tried Bosch coil off same model year car and car ran perfectly with rock steady needle and no lumpy idle.
Something possibly to do with charge amplifier being on/in dizzy cap which was changed on later model years (writing this from what I can remember as mechanical knowledge and memory as bad as each other.
Have to order part specially from Bosch so will order 2 just in case.
Checked temps of manifold coming off all cylinders and all the same within a degree or 2.
Sounds like a happy ending with no head off needed or cam shaft replacement.
Something possibly to do with charge amplifier being on/in dizzy cap which was changed on later model years (writing this from what I can remember as mechanical knowledge and memory as bad as each other.
Have to order part specially from Bosch so will order 2 just in case.
Checked temps of manifold coming off all cylinders and all the same within a degree or 2.
Sounds like a happy ending with no head off needed or cam shaft replacement.
Very good news that its fixed to your satisfaction, but it's left me a bit confused about No.7 being down on compression 
. Has this been subsequently checked and or resolved .
I only ask as my compressions are down across the board, which I've been told is a clasic sign of (evenly!!) worn cam lobes.
Harry
. Has this been subsequently checked and or resolved . I only ask as my compressions are down across the board, which I've been told is a clasic sign of (evenly!!) worn cam lobes.
Harry
Concerning reason compression being down on cylinder 7 was explained by coil or amplification of ?signal/current? drops the spark in a random manner.
Didn't check this out by taking temp from manifolds after lucas coil (causing lumpy running)was refitted.
I will fit new coil middle of next week and get compression tested again to make sure all OK.
Will let you know once done.
Didn't check this out by taking temp from manifolds after lucas coil (causing lumpy running)was refitted.
I will fit new coil middle of next week and get compression tested again to make sure all OK.
Will let you know once done.
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