After a few ideas on this one if possible please, a trader brought me this car a few weeks ago because the MIL light was on due to the above DTC. The car appeared to be running fine except for the hint of a rattle (we all know what that is). I whipped the plugs out, which appeared fine, and did a compression test, all good! I put the no3 coil pack into no2 cylinder and went for a spin; can ran fine and light didn't return so I gave the car back to the customer and explained all.

Since then, the customer has sold the car and sods law the light has come on, the owner took it to VW who diagnosed a faulty timing chain due to the rattle and quoted a fantastic price, the owner then returned to my customer screaming blue murder and after some discussion they agreed to let US change the chain due to obvious cost differences.

The light was on when it came in but no running issues, cleared P0303 and replaced the chain and tensioners etc using proper timing kit. Fired up sweet so I took it for a test drive; after about 1 mile it seemed to hesitate for a second and then MIL came on, no further running issues, at 2 mile marker it lost all power and I nearly got myself killed trying to limp it off a roundabout. It continued to run like a dog in the workshop, not being sure if it was something we'd done I turned it off and read for codes, P0303, cleared it and started it up, runs sweet as a nut again!!!!

It was 5:15pm at this point so I had a look through the live data and everything looked spot-on so I rang the customer and he said he would just leave it with us to sort out, he also noted that he had never had and running issues nor had the new owner reported any, just the light.

Bit stuck for ideas really as it is very intermittent, I suspect something electrical due to DTC clear temporarily solving the issue, also I feel its fuel related due to having already tested the compression and swapping coils round but obviously theres not much I can do without the fault being present. I'm hoping somebody has had this issue before and can point me in the right direction??

Thanks
Craig

If i've got the correct engne code i'm sure these suffer with sticking valves in the guides.

Not sure what the the actual answer is as some say machine the heads and other's say a new modified head is available with an ecu software update.

I'm sure a VW expert will be along soon to give proper advice.

I had one in with a misfire which i'm sure had about 1 bar difference in compression but was enough to flag a misfire code and set the misfire counters running.

I guess you have tried a good wiggle test already??
regards Brad

Hello Craig, these are also prone for burning out exhaust valves. Had one a couple of weeks ago that all three had cracked. Can you swap injectors to see it moves?

Hi Craig,

The ECU monitors the crankspeed for each cylinders contribution.

The ECU control on your vehicle will shut off the injector on any cylinder that is contributing less than the others (incomplete burn) this is to prolong the life of the CAT and reduce emissions.

Im sure somebody will correct me if I am wrong.

Scope the injector current on the offending cylinder or scope them all at the fuse when the code is there and then clear the code.

I have had a few different outcomes with similar symptoms as yours.

A couple with leaking/burnt out exhaust valves.
Ignition issues/weak secondary.
and
1 injector issue.

Can you monitor the misfire counters?

Check the emissions.

Check cylinder leakage, hot and cold.

On this engine I sometimes stick my borescope down the plug hole and with some cotton tied to the end pull the camera is a position so you can inspect the valves.

hope that helps

cheers
James

So it would seem valve issues are common then, am I right in thinking though that valve problems would produce symptoms (excluding todays experience obviously) and be more predictable??

Lee, I think your suggestion regarding swapping injectors is probably the best next step, if the fault stays on cylinder 3 then I'm gunna have to wait for it to misfire again in order to inspect things further!

James, interesting concept for cat saving, makes diagnosing faults difficult though dunt it!!

Thanks everybody
Craig

Craig,

It was Alan's suggestion to swap injectors about not mine but even so its probably a good suggestion.

Ooops think I need to learn how to read! . Sorry Alan!!

Either way I've just swapped them all round this morning so we'll see what happens! Am gunna try and give it a good run this today so hopefully I can report back later with some results!

Thanks
Craig

Ok so heres how my day went.....

Swapped the injectors round and went for a spin, between 3-4k revs under heavy acceleration I experienced a seconds hesitation and MIL illuminates, continue to push it and it drops out and loses all power; read DTCs, P0303, swapped plugs around and went for a spin, same conditions met and MIL comes on, P0303, this time as I now know its not something i'd done wrong with the chain I left it running like a dog and scoped the injectors, sure enough the ECU had switched number 3 injector off; cycle the ignition and it returns to normal. As i've been running around a bit in it I now noticed a tapping noise from the top of the engine; using my top of the range stethoscope (screwdriver), this showed the noise to be originating from around the exhaust valves of cylinder 3. Given my results and the now known fact that these suffer from head/valve issues I decided to leave the electrical things alone and have another look at cylinder conditions.

I removed the oil filler cap with the engine running and a dominant hissing sound could be heard so I smoked the inlet at the throttle body. Despite no visual leaks, the leak indicator on the side of my smoke pro strongly suggested otherwise, I removed the filler cap again and instead of the expected wisp of smoke, I was greeted with a loud hiss of depressurisation and smoke bellowing out of the cam cover.

With a warm (neither hot nor cold) engine I repeated my compression test, although all healthy readings, cyl1-185psi, cyl2-215psi, cyl3-200, the 15% difference between cylinders 1 & 2 was suspicious especially as it wasn't on the mysterious cylinder 3!! I did a cylinder leakage test and number 2 proved to be excellent, number 1 was mediocre and cylinder 3 piss poor!

Having also tested the emissions to reveal very unstable readings at both idle and fast idle, with the exception of hydrocarbons which hovered between 500-600ppm, and also double checked the timing, still ok, I decided to call it a day and recommend stripping the engine for further investigation.

The customer is going to offer the owner his money back and put the vehicle through an auction as it runs spot on with no lights as long as its not driven hard!!!

Its been an interesting experience, and although some of the compression and cylinder leakage tests are the wrong way round I feel that a strip down is the most logical step forward, just a shame he doesn't want to go there, cant blame him though!

Thank you to everybody that helped me on this one it has been greatly appreciated!!

Craig

P.S. So much for the VW dealer and their timing chain diagnosis eh!?!

I have seen skip loads of these Polos with the 3 cylinder kiss-of death 6 or 12 valve engines.They all have the usual misfires codes.Most have had everything bolted on or changed,from coils,injectors,sensors and even a reman Ecu!(how do they do that?).The bottom line is this is a nail of an engine that VW will not admit to being a problem.The only cars that seem to be ok,are those that have had timing chain/kit and a modified cyl head and software update,which realistically now makes these an economic write-off.

Hi Craig

It is a shame you will not see the end of the job.

Have you still got the car?
How long for?

Do you fancy a play with the WPS?

Don't get me wrong I am no expert, but I reckon we will get some good captures and all learn something

The captures we need should only take a few minutes.

Let me know and I'll nip to yours after work tomorrow or you are more than welcome to come to us if you want.

Cheers
James

He's picking it up tomorrow James but I can ask him for an extra day if u like I reckon he'll oblige! Ill text u tomoz to let u know!

Thanks
Craig

andyhyoung wrote: "I have seen skip loads of these Polos with the 3 cylinder kiss-of death 6 or 12 valve engines.They all have the usual misfires codes.Most have had everything bolted on or changed,from coils,injectors,sensors and even a reman Ecu!(how do they do that?).The bottom line is this is a nail of an engine that VW will not admit to being a problem.The only cars that seem to be ok,are those that have had timing chain/kit and a modified cyl head and software update,which realistically now makes these an economic write-off."

Jon Morgan writes: ditto - except in my experience the single cam is more prone to valve trouble - sticking & cracking with sporadic misfires & low compressions. The twin cam is more susceptible to lobbing the chain off, although the valves are also prone to issues. Software update for the single cam alters the fuelling profile & jacks the idle up. Software update for the twin cam unfortunately doesn't stop the chain being slung around the crank sprocket usually after an oil & filter change - leaving the workshop with some awkward discussions with the customer.
As Andy says - both these engines are amazingly crap.
P.S -I can't imagine the dealer got the timing chain diagnosis wrong - it takes 10 minutes to check the valve timing, knowing these lumps intimately it wouldn't surprise me if it managed to lob the valve timing a couple of teeth out tw*t the valves & also have an injector & coil issue thrown in for good measure

Ok so James and I had a good play with this car last night using WPS and completely failed to find any fault at both cranking and idle, both hot and cold. Eventually we noticed we could get the misfires counters to move for cylinder 3 if we held the revs at 4000rpm despite no obvious misfire, we put the WPS into each cylinder again and repeated the test at 4000rpm; cylinder 3 proved to have around 10 psi lower peak compression than the other two. Under heavy acceleration on the road I expect this difference will be even higher. I feel this has confirmed my logic that a strip down would be the next step forward, even though its not going to happen unfortunately!!



Thanks
Craig

No expert by any means, but is there not an issue at the lower section of the graph?

It could just be me, I must find some time to play with this technology.

Mark

It's the first time I've ever played with one mark, I was just following what James was telling me with regards to the WPS readings! If u point out which bit u find suspicious I'm sure somebody could tell us what's happening!

Thanks
Craig

Hi Mark

I too am no expert but I have it on good authoirity that in the finer details of the in cylinder captures are really of no use above 2000rpm.

I took the captures at 4000rpm with loads of time on the screen to see If there was an obvious difference in the peak compressions as it was drawing a block of info across the screen.

I believe there was enough evidence to strip and inspect this car but, after looking at the captures over and over last night I saw no evidence of any of the cylinders not sealing, cold, hot or at 4000rpm.

I would have liked some more play time on this car but me and Craig were both pretty cold, tired and brain dead by the end of the session.

I have got a Rover 214 16v here, that I bought to make some faults and see what effects it had on cylinder pressures.

I have made some faults already like blocked exhaust, introduced an home made EGR system into the inlet manifold and the effects are pretty predictable. I think the WPS is going to be a great tool once I have got my head around it.

I have also noticed that there is a massive difference in peak compression, wether or not the injector is connected or disconnected, but not the way you would think. I will double check my findings on this because it doesn't make logical sense, I will put a post up in technical theories and tips for discussion.

Next week I am going to be altering the Cam timing and causing other unnecessary pain to the rover

I will gladly share my findings with you if you would like

Also if anybody has any ideas on faults I can make on the rover, they would be more than welcomed (no matter how nasty they may be )

Cheers
James

Ps Mark
I will post some of the cranking and idling captures a bit later when I am with my other lap top.

Hi Mark

This is the capture of all three cylinders idling when the engine was warmed up.

All three tests were done one after the other with the engine being roughly the same temperature for each test.

The WPS was in the spark plug hole and the injector was unplugged for the cylinder that was being tested.



Cheers
James

I have had 2 of these polo's with the same fault.and it turned out to be a problem with valve seating when we stripped the head and inspected the seats there was a definite area that was not seating on the inlets we used engineers blue to confirm this.And this would affect hydraulic lifter problems that made problem appear different at various engine loads,both these cars had quite low mileages and there was no real evidence of the cause. we refaced the seats which were off centre by a few thou fitted new vales and reassembled all has been ok with both cars since.Maybe a bad batch of heads that move slightly