I had some rough running, power loss on my way back from Billing.

I did hit the rev limiter 7000rpm soft cut a little before this.

 

Could not find any carb blockage at a service station.

Looked at AFR logs and nothing obvious, just that I drove at lower power after that stop.

 

At home found cylinder 3 spark plug had one apparently melted (or maybe bent) electrode.

 

Now fitted brand new WR5DS plugs. Old Beru Ux56 were actually tan at the tip, white below. Damaged plug was darker.

 

But... I think cylinder 1 is now not firing from the sound and exhaust manifold temp using a laser thermometer.

70, 180, 190, 185 degrees C.

AFR says 14.3 at 2000rpm no choke, will idle only very slowly, not got to full operating temp though.

 

It was number 3 that had the melted electrode, so that's odd.

Checked new number 1 plug was oily wet so pulling in fuel.

 

I'll check for spark when it's darker. Annoyingly it's the one with longest lead so I can't swap leads.

 

I'll compression test too.

report back when you comp test it ...got one here if you need it ?

 

can try a spare plug on that lead and hold it against the head /metal part and see if its sparking ...be aware it will shock you so be careful

sparked with a spare plug held in a jump lead...

The oily fuel on plug might have come from the choke circuit and there could still be a blockage in idle circuit. Dellorto effectively have a mini carb just for starting.

 

Lifted the progression hole cover but seemed clear under it.

Need to blast it out with compressed air.

 

Thanks for comp tester offer. You are always kind to me.

 

I've got one in storage about 14 miles away and car will still drive, (I think,) but want to avoid driving it until I know the cause. And just in case another cylinder stops while underway.

 

I could see back of head of inlet valve from spark plug hole. Never noticed that before.

It has double springs. Need to look how it moves  when I crank by hand, and check valve clearances.

Maybe a valve spring broke at high revs?

 

Though I'm now thinking burnt exhaust valve. Comp tester should reveal.

 

I can try vac gauge on just cyl 1, to see if it sucks.

I'll use the RAC patrolman trick number 1 to clear carb passage ways too as it will idle, just.

 

Inlet valve is moving fine as I turn crank by hand.

 

Cleaned the sparkplug hole and refitted plug.

Found cyl number 1's idle jet not fully tight in its hole.

 

Still inconclusive.

Need my comp tester.

Edited 10 July, 20215 yr by dvderlm

Comp test (new tester £17 delivered)

 

Dry..... 1...  2...  3..  4...

 bar     16.4 16.2 13 16.2

Wet

 bar   ...................16.0 ....

 

Added tiny amount of 5w30 oil to number 3, refitted test adaptor and it reached 16 after 5 cranks.

 

Cleaned up the plug hole face where plug gasket touches.

Will try again after waiting for the oil to drain past the rings, in case it was tester not fitted tightly enough first dry attempt on number 3.

 

 

 

be interesting to test it hot if youre prepared to run it

Indeed, was cold, all plugs out, fuel pump and Hall sender disconnected, throttle fully open.

Readings are slightly over last year's (hot) with my Draper tester.

 

That's probably next after retest compression.  Running I can use vac gauge on each cylinder's inlet.

 

There was pressure so not holed or cracked. Pressure went up with oil, so not a valve. But maybe rings? Or not fitted tester well tight?

Did number 3 again (cold, dry), tester properly screwed in hand tight.

13.5 bar.

 

15% or 2.5bar below others, so kind of okay, and also way above the wear limit of 8 bar. Must try it at operating temp.

 

Oh interesting. New expected pressure is 11 to 15 bar according to So Wird's Gemacht page 30.

 

So, either the gauge is over-reading compared to the Draper, or cold test is quite inaccurate.

 

I'm sure the head work for bigger valves did not increase the compression ratio more than sensible. It was just refaced not skimmed.

 

3 years ago warm dry readings were

Dry..... 1...  2...  3..  4...

 bar     14.0 15.2 15.0 14.0

 

Hot

Dry..... 1...  2...  3...  4...

 bar    15.5 16.5 14.5 ---

 

Could not be bothered with number 4. Have to  take the brake servo hose off to get access.

Just loosened that plug.

 

 

not bad enough to make it misfire then

Nope. 

Checked the Amethyst settings.

I was sure I had set max 30 for Unleaded 95 not Momentum99.

 

But in fact I had max 32.

 

Made up of 30 centrifugal at full throttle (low vac),  or 30 plus 2 at high vac high revs due to sufficient vacuum, plus 5 static. 

 

That makes 37 which is bowl in piston limit (with sufficient high octane fuel I guess).

 

Reduced it to 30 max and checked the value sticks when put the ignition key back in. You need to press the Save Map button not the Load Map button in the Amethyst app. 

 

VW wanted super 98 leaded when it was made. It will run on 95 with the Dignition and twin choke Weber and shared inlet manifold.

 

Back to Momentum and Optimax. 

and 

One step colder plugs.

 

Looking really closely at the AFR logs, I think I've found evidence that it leans out at high revs, though I'm not recording RPM, so I have to go by manifold pressure changing from way below atmospheric.

 

With throttle plate only a little open there's high manifold vacuum. Wide open throttle is low vacuum or atmospheric.

BUT 

I can see positive pressure peak of +0.428 PSI at 15.2 AFR which must be due to my new short 3D printed trumpets inside the Dergo and Ramair foam filters giving better induction ram effect, because I've not seen over +0.34 before.  Had 40mm trumpets which looked nice (parked with foam socks taken off for show) but were too loud as they faced the bulkhead.

 

This peak inlet pressure is occurring in a sloped bump sample of 2.7 seconds (hard acceleration I imagine) of AFR rising from 12.4 (accel pump?) and climbing to 15.2 then inlet pressure decreasing again to +0.27 as gets leaner still, maybe 16.4?

 

At low loads, lean is not harmful but exhaust temp rises.

At high loads more air (oxygen) needs more fuel.

 

I'm going to increase mains by 5% cross section. So from 119 to 122.

Then vary air corrector if required.

 

The 122s will take a while to arrive.

 

Found some 155 air correctors in my DHLA jets collection.

I had already gone down from 120/200 (light tuned 1.3 Polo on 30mm choke recommendation by shensiek)  to very near 120/180.

 

I'll swap those in the meantime.

 

 

nice mpi conversion would solve all this 

On a dyno for 4 hours it'd be easy.

 

 

 

It was about 0.8 seconds spent between 15.2 and 15.5 at high load.

 

so is it running ok with new plugs?

Not driven anywhere yet!

 

Idle is back to normal. AFR says 14.7 and 10.6inHg at about at 950rpm.

 

I have managed 12inHg before - though at maybe 14.3:1 AFR.

Perhaps not quite as refined on the WR5DS single electrodes as with the 4 pronged electrode Beru UX56 plugs, but I had twiddled the mixture screws while trying to work out why cylinder #1 was on strike, so perhaps not reached exact stoich in each cylinder.

 

Might put the UX56 back just to test that once warmed.

I'd also like to see whether the colder W4CS will foul.

 

Gentle progression (no load) to 3000rpm is smooth.

 

at least there wasnt any melt down then ...nothing permanent

Yeah, not even lost any metal from the electrode which melted and bent inwards, downwards.

I suppose it nearly fused or had too small gap to ignite at that point and stopped sparking.

 

If plug or valve had burnt it would surely have scored cylinder wall.

Lucky escape.

 

 

Found the cause. 

 

About 1.5 miles from home.

 

The Hall sender connector.

 

Heatshrink sleeve is damaged and crimp solder connection is really poor. 

 

you can get  new crimps for those

Vehicle Wiring Products part 192175 female terminal.  

 

cable seal 0.5 to 1mm 192177

 

Junior power timer 192148

 

From the paper catalog

 

Is vehicleproducts.co.uk up?

 

 

 

 

cheaper on ebay with the postage