A leak-down test might reveal more than a normal compression test 

yes true - not sure what i need to spend to get a trustworthy gauge vs a china special

Any chance of listing off all the things youve done and replaced

plugs , leads,cap , arm , dizzy , afm , coil, fuel pump, tb , tps , temp sender , o2 sensor, injectors , rail, fpr , ecu , inj orings , resealed inlet , isv 

 

pretty much every part that makes it run , cept the loom

How far have you driven it rich?

Surely not enough for bore wash.

You ran on carb after the hone and re-ring with new fuel filter, right?

 

https://www.hastingspistonrings.com/tech-tips-faqs/fuel-wash

 

 

Do the compression test from cyl1 to cyl4 cold. 

Do a dry compression test with warm engine. Then wet test.

See if number 4 gets closer to the others.

 

Look for idle flame variation between cylinders with a Colortune?

Swap injectors around?

 

Re-lengthen the inlet tubing to standard? See page 14 of this.

http://www.gunson.co.uk/items/PDF/Products/G4074_Colortune_English.pdf

 

Do a custom fuel injection mapping?

 

dont think its driven enough for bore wash , got a feeling its not so rich above idle as the plugs look fair , yes it did over 1000 miles with a carb and passed the mot with great emissions

 

im gona try another comp test and swap the inj with my mates car 

 

other than that i feel ive done it all with parts swapping /replacing ...theres not a huge amount of parts on these and they all check out , diag machine see's no faults , all the important wires check out doing what they should , common sense has to say its an engine issue

 

tried the paper test again over the tailpipe...no sucking in but such savage pops it tore the paper with one of the pops

 

what about lengthen inlet tubing?

Edited 4 October, 20187 yr by steveo3002

you deleted hot air flap, so there's a shorter length of air that goes past the MAF before it is reflected at the open end, this might be  moving the open loop mapping point.

 

Closed loop should be totally sweet and responsive.  

the flap is still there as such , just removed and blanked the vac hose that operates it - still has the oem airbox and trunking just no vac hose to operate it  

 

theres guys running these with bodged on cone filters and self taping screws blocking off hoses and running fine , i cant see it being my issue

Edited 4 October, 20187 yr by steveo3002

ah, okay. The vacuum closes the flap against a spring when the thermo valve opens. So if the exhaust manifold shield and tubing are intact you've got warmer air coming in than you expect.

PV=RT...

Doubt that makes a difference either. 😕

 

yeah

 

just thinking if i did a bad job of lapping the previously ok valves then they wouldnt fix themselves , maybe good enough at first and getting worse now?   doesnt explain the ok vac readings though

 

im out of ideas

If just number 4 exhaust valve is not always sealing - they turn in their guide - you would still get good vac at inlet, but compression stroke would squish some fuel mixture out to exhaust.

That would catch light sometimes - pop - or not, unburnt fuel  high HC, working at 7/8 to  3/4 power - high C0 if rich or unstable running if lean. Maybe?

 

Or could one or more of the injectors be squirting into wrong cylinder intake?

 

 

 

 

yeah got a whole untouched rail /inj /fpr to try on it ...maybe tomorrow if its dry

 

and will try a a warm comp test and report back 

warm comp test 

 

#1  170

#2   175

#3  175

#4  165

 

used complete fuel rail fitted , put the air/fuel meter on and its much nearer ,got it into the 14.? -1 range with the wideband in the downpipe and still runs , infact would run weaker than that which is progress

 

02 sensor refitted and working on the diag machine

 

one random thing...after id finished i thought id see what the air fuel reading was with the sensor shoved up the tailpipe - shows 19 odd , i'll ignore that for now

 

tailpipe still sounds awefull- no change on that , but progress that it will run at mot'able mixtures so ive gotten a little further 

 

will add some videos later

Edited 5 October, 20187 yr by steveo3002

 

 

Well those comp readings are much nicer.

 

Don't understand why it sometimes needs 22 degrees ignition advance at 875rpm. I know there's some anti-stall advance boosting, but I'd expect maybe 10 degrees max on 5 static.

Is the rotor arm tight in the distributor?

 

Edited 5 October, 20187 yr by dvderlm

yes rotor fits properly

 

i agree, if i had to guess id have thought the reading would sit steady and maybe fluctuate by a couple of degrees , but others dont seem bothered by it

 

this is a vid by forum member gaz of his polo 3f that runs okay

 

just driven mine ...runs okay probably best power ive had so far , but its jumpy at part throttle and idle isnt so stable , exhaust dried out after a run you could see condensation in my vid

 

Gaz shows 0.0 advance until the load is increased then rises to maybe 10.

So any pops? Maybe it was steam expanding in the exhaust.

 

Can you measure idle speed any other way than the ECU or tacho?

Stretchy cam belt?

block 4 , 3rd box along?

 

timing light also does rev counter...all marries up 

 

new skf cam belt..

 

yes still pops and sounds terrible 

Edited 5 October, 20187 yr by steveo3002

also ran a spark tester on each plug lead...all same spark strength

You are running at 83 degrees. ABD thermostat switch point (Febi 18288) is 84 degrees so okay, yet Gaz runs at over 94 degrees. Maybe his fan is about to kick in? 

Are you running stock camshaft?

Stock flywheel not lightened?

Does the camshaft pulley have tight fitting woodruff key? 

Edited 5 October, 20187 yr by dvderlm

7 hours ago, steveo3002 said:

...after id finished i thought id see what the air fuel reading was with the sensor shoved up the tailpipe - shows 19 odd , i'll ignore that for now

Yes, lots of fresh air dilution. If there's no exhaust leaks no worries.

yeah was only warming up...the o2 sensor kicks in at 80 hence me starting to film

 

polo mh flywheel not modded , 3f cam shaft , all aligned to standard marks

Any idea what was up with old fuel rail, pressure regulator, injectors?

nope...they was the injectors i had sent away for cleaning /testing , had previously tried  a spare rail and fpr too