Interesting Compression Test Results

[andy 0]

I have done a compression test recently on a VR6, one cylinder was low at 155/160, where the rest were 185 ish, this was with the engine hot. However I've done a cold compression test tonight and the dodgy one is up at 185, what could this mean? I've never had one thats better when cold.

 

Any advice appreciated.

[andy 0]

no one? :(

[fla 9]

perhaps a poor seal when the gauge was fitted at higher temp? Just a thought.

[andy 0]

perhaps a poor seal when the gauge was fitted at higher temp? Just a thought.

I'm hoping that's what it was, I did take the guage in and out several times and make sure it looked clean where it seats etc. I will be over the moon if that's all it was. I'm going to redo all the tests tonight cold, hot and wet(if necessary).

[dr_mat 0]

IIRC all your results were within spec anyway, so I wouldn't worry about it either way.

[andy 0]

IIRC all your results were within spec anyway, so I wouldn't worry about it either way.

I think you might be thinking of another thread Dr, there was another one on here recently where all the results were low. Mine are showing 180-200 on most of the cylinders and 155 ish on one. Thats out of spec I would say using the 10% rule of thumb.

[dr_mat 0]

Mine are showing 180-200 on most of the cylinders and 155 ish on one. Thats out of spec I would say using the 10% rule of thumb.

 

Well .. maybe .. but does the car run badly? Why do you think you have a problem worth considering engine work for?

[andy 0]

Mine are showing 180-200 on most of the cylinders and 155 ish on one. Thats out of spec I would say using the 10% rule of thumb.

 

Well .. maybe .. but does the car run badly? Why do you think you have a problem worth considering engine work for?

The engine is running slightly rough. It still performs well but with a roughness/vibration uncharacteristic of VR6s. I do have several fault codes but I thought I'd check the basics with a compression check, whilst I was putting new plugs in.

Its a new car to my fold (we now have 3 VR6s, one of which will be for sale soon) and I thought a general healthcheck was in order anyway. Its only got 69k on the engine from new but its definatley not running 100%, it could be the fault codes but I was very surpised to see a better cylinder compression result on a cold engine than a hot engine.

[dr_mat 0]

The engine is running slightly rough. It still performs well but with a roughness/vibration uncharacteristic of VR6s.

 

Ok, fair enough. I'd expect you to know your VRs then. One thing I would say though, is if it's not been run much (69k means it's been standing unused a lot!) it will benefit from a good thrash. Mine gets rough with lots of short journeys but totally comes alive after a good hundred miles on a motorway.

 

What's the fault codes you're seeing?

 

... surpised to see a better cylinder compression result on a cold engine than a hot engine.

 

This *can* be caused by gasket problems, I'm led to believe - as it only opens up when the temperature increases. But you'd know about this cos you'd be losing oil/water..

[Kevin Bacon 5]

150 is the wear limit I believe. What cylinder is it?

 

Wouldn't the oil be thicker when cold, thus creating a better seal? Just a thought....

[andy 0]

The codes I'm getting are

537 -

561 -

553 -

 

I'm not losing any oil/coolant, its absolutely squeaky clean/tight in that respect.

I have tried a good hard thrash (ye olde italian tune up!) but it just doesn't feel nice doing it.

[andy 0]

150 is the wear limit I believe. What cylinder is it?

 

Wouldn't the oil be thicker when cold, thus creating a better seal? Just a thought....

Its cylinder 5, back right as you look at the engine. Good point about the oil, it just doesn't normally work like that. I've always had lower results when cold, particularly on cars with hydraulic tappets.I really hope it isn't wear, it shouldn't be on an engine of that age. :eek:

[dr_mat 0]

00537

O2S Probe Heater

 

00561

Fuel Pressure Improper

 

00553

Air Volume Meter

 

So you have a bad MAF, bad fuel pressure and a bad lambda. Those would certainly explain rough running.. I'd be surprised if you notice 35 psi compression difference compared to heinously bad fuelling.

[andy 0]

I'm not finding my fault code list right now, but anecdotal internet evidence says that code 537 is blue temp sensor.

That would explain rough running, but I'd also expect poor fuel economy..

Funnily enough It does have bad fuel economy, however code 537 is showing as a lambda type problem on ross-tech.

 

http://wiki.ross-tech.com/index.php/00537

[andy 0]

Also does anyone know what code 553 means, I can't find it anywhere!

[dr_mat 0]

Read above!

[Kevin Bacon 5]

Its cylinder 5, back right as you look at the engine. Good point about the oil, it just doesn't normally work like that. I've always had lower results when cold, particularly on cars with hydraulic tappets.I really hope it isn't wear, it shouldn't be on an engine of that age. :eek:

 

Yeah I realised after I posted that there's no oil on the bores during cranking anyway and you're right, cold, contracted pistons will give a lower cold compression reading.

 

Did you try wet and dry tests? If adding oil to cyl 5 brings it in line with the others, it's definitely bore wear. If it doesn't make any difference, it could be valve sealing or a slight head gasket leak.

 

1, 6 and 5 are the common ones for compression discrepencies but a leak down test would be my next move personally.

 

A bad MAF will make the engine run very badly, that's a fact. As for bad fuel pressure, it's not even monitored so I wouldn't pay any attention to it. The lambda error is probably due to it having to adjust the fuelling more to compensate for the MAF.

[andy 0]

Hmmm cheers. Food for thought. I will redo the tests tonight, cold, hot and wet if necessary. That'll double check if I have a major problem. I have got a brand new MAF fitted, I am wondering, on the other front if that is dodgy, that could explain the fault codes in its own right.

[andy 0]

I remeasured the compressions last night, with a different guage and got good results across all cylinders cold and hot, it must have been a dodgy seal on my original guage I think, its all a bit strange though as I did measure it repeatedly the first time, unless there was some crap on the plug seat thats been removed by me putting the plugs in and out again.

 

So she seems healthy, mechanically at least, phew!

 

I've taken it out for a spin, put some redex in the tank and given it a good hard blast, I've still got the fault codes and the roughness. Its a vibration really at 2k rpm +/-200 rpm. Not sure where to look next. When I fitted the MAF last week, (where previously it never had one, don't ask!) should I have reset the ECU or anything?

[dr_mat 0]

should I have reset the ECU or anything?

 

Yes! It *might* get the point eventually, but it'll adapt a whole lot more quickly if you reset the ECU.

[Kevin Bacon 5]

I remeasured the compressions last night, with a different guage and got good results across all cylinders cold and hot, it must have been a dodgy seal on my original guage I think, its all a bit strange though as I did measure it repeatedly the first time, unless there was some crap on the plug seat thats been removed by me putting the plugs in and out again.

 

So she seems healthy, mechanically at least, phew!

 

I've taken it out for a spin, put some redex in the tank and given it a good hard blast, I've still got the fault codes and the roughness. Its a vibration really at 2k rpm +/-200 rpm. Not sure where to look next. When I fitted the MAF last week, (where previously it never had one, don't ask!) should I have reset the ECU or anything?

 

Good news on the engine block! A nice bit of good news always helps the festive cheer I find :D

 

As for the vibration at 2K, perhaps try a new gearbox mount and a GSF MK2 solid rubber one at that. Of the 3 mounts, the transmission one vibrates the car the most, especially when knackered. You'd be surprised how a bit of roughness from that can fool you into thinking the engine isn't running right.

 

The only other way to get rough running is a from misfire through overly lean burning or ignition problems.

[andy 0]

Good news on the engine block! A nice bit of good news always helps the festive cheer I find :D

 

As for the vibration at 2K, perhaps try a new gearbox mount and a GSF MK2 solid rubber one at that. Of the 3 mounts, the transmission one vibrates the car the most, especially when knackered. You'd be surprised how a bit of roughness from that can fool you into thinking the engine isn't running right.

 

The only other way to get rough running is a from misfire through overly lean burning or ignition problems.

 

Cheers Kev, I have been wondering about the gearbox mount, I have a receipt for a Vibratechnics Gearbox mount, fitted prior to getting the car, do you think that a VT GB mount in isolation might transmit extra vibrations to the rest of the car, i.e. as far as I know the other mounts are standard squidgy oe ones?

 

Failing that I had been considering flywheel inbalance, (unlikely I realise, but you never know) and possibly exhaust (possibly manifold) issues as it does sound a little loud at the rear of the engine.

[andy 0]

Solved the vibration problem, it was the Gearbox mount, its supposed to be a 1yr old VT mount but it was shot when I got it out, flapping arround with moderate hand pressure. Bizarre, now.....must fit that new main water pump but perhaps not in this snow! Cheers Chaps.

[was8v 0]

Solved the vibration problem, it was the Gearbox mount, its supposed to be a 1yr old VT mount but it was shot when I got it out, flapping arround with moderate hand pressure. Bizarre, now.....must fit that new main water pump but perhaps not in this snow! Cheers Chaps.

 

Great news! Don't talk to me about water pumps. Just make sure the one you are putting in is a genuine one. I got the change down to 50 minutes after doing it 3 times within a couple of months due to pattern parts.

[andy 0]

It is a genuine one, I don't muck arround with things as important as water pumps. 50 mins is pretty good, I have done a VR6 one before thankfully, I remember things being pretty tight! Mind you I managed to swap the gearbox mount in under 15 mins!