4.5k rpm issue running problem

[28hodge 22]

I have been searching the forum a lot to try and diagnose this issue,

 

Car has previously been off the road for 25odd years - see thread here 

I have rebuilt and have the 205 on the road now and have put a few miles on it to see what now needs sorting. It seems to run well, ive initially been gentle on it and it runs a pulls really nicely ticks over nicely, however this last week ive started to open it up a little more and it isnt keen on running well in the higher RPM range, checking the plugs it would appear to be running lean. it also pops on the over occasionally run when you press the clutch to change gear which having read some posts this could be a symptom of lean running.

 

 

When driving it feels strangled at 4500rpm but not all the time, if you go WOT through 1-2nd it seems to run fine through the rev range, but entering 3rd and foot down and the revs wont progress, come off the throttle and back on it will sort itself out but not always. It drives nicely anywhere below that range and will go above 4500, but if you tried to redline it through 2nd to 5th its hitting this soft limiter almost at 4500ish. I was think its fueling and maybe fuel pressure being low causing it to go lean on extended high throttle inputs. this was also linked to the plugs which to me look a little lean - plugs were brand new and have done less than 200miles - 

 

Cylinder 1

 

Cylinder 2

 

Cylinder 3

 

I think they look lean but appreciate the color will be mostly from idle as these pics weren't following a plug chop.

 

I have read and and spoken via pm regarding the AFM cog and richening up the mixture, have marked the orig position and moved it 4 teeth in total anti clockwise, its had a small effect and the pop on overrun is a lot less, but i don't want to do anymore without having a way of analysing it, I have got it booked on a rolling road for next week, but i don't want to go and find I have an elec issue that stops being able to do anything further and set it up.

 

Its got a fresh fuel filter fresh 98ron fuel spark plugs were new, however I haven't changed the HT leads dizzy rotor arm or cap. I need to check the valve clearances but it isn't tappety, however the injectors are pretty noisy. I have used the screwdriver in the ear method to figure out that it is them making the noise.

 

As the issue is revving beyond 4500ish could it be a failing AMP? I have a couple others I could try on it I have taken the existing one off cleaned it up and the heat sink plate and then re-attached with transfer paste but this has had no effect.

 

The Injectors were sent away and cleaned so they should be fine, I do not have a fuel pressure regulator so can't check that. I have got it booked to go on a rolling road with a guy that has built plenty of hillclimb 205's etc. But he can't do that till back end of next week so just looking for a fix that sees the engine safe till then. I don't need to use the car as it is not my daily but I'd like to get some miles on it to see what else is in need of sorting out, it just needs some test miles putting on it.

 

Happy its not the head gasket, not using water and the oil appears A OK, but have only done maybe 1-200 miles in it  the MOT CO reading was 0.39 which seems very low with Hydrocarbons at 160ppm, the tick over is quite high though at around 1600rpm, I have no real history as to what's been changed and played with previously, but the AFM does look like it may have been opened in the past, but inside the track looks perfect, the car only shows 30,000 miles so the components shouldnt be mechanically worn out.

 

Really just looking for a little advice on the plugs color (I know its not ideal as it'll mainly show idle running) but also the pops I get when I come off the throttle and the stunted acceleration around 4500 and above rpm I think are lean running symptoms?

 

Thanks

[Tom Fenton 1,542]

Need to check the fuel pressure while driving it under load.

[28hodge 22]

I have another 205 i can nick the FPR off and see if it makes any difference, if not I'll see if I can rig up a test.

[Anthony 1,003]

It does sound more fuelling related, but if you've got another ignition amp, it would be worth quickly trying it to rule it out - feeling like it's hitting a rev-limiter around 4000-4500rpm is certainly a common failure mode.

[28hodge 22]

I'll swap it out, i have 2 used but unknown bosch mtr01 ones and a new one but thats a "Powertrain" amp so may be utter turd.

 

Do the plugs look lean to you, l know its not an exact thing reading plugs anymore with more modern fuels. I put a new Grp N exhaust on it from special tuning (like for like replacement for the one that came off and they are only 20mins away so i could go grab it) I put that on maybe 80miles ago and the end is a little sooty but nothing excessive. 

[28hodge 22]

Just nipped out and changed to one of the other ign amp, initially it then wouldn't start so suspected it was duff, turns out I'm the duff one as I had pulled a connection off the coil whilst I was doing it! anyway re-attached that and it fired straight up.

 

Once small people have gone to bed I'll wang it down the road and see if we have any difference, I may drive to the other 205 which is kept elsewhere and pull the fuel reg off it if there is no change.

[petert 588]

Also similar symptoms to having the valve clearances too tight. Fine when cold but then turns bad when it warms up.

[28hodge 22]

47 minutes ago, petert said:

Also similar symptoms to having the valve clearances too tight. Fine when cold but then turns bad when it warms up.

Would that effect the engine across all Rev ranges once warmed up or just higher up the Rev range?

 

ign amp swap hasn’t changed anything. I came back and moved the afm another 2 teeth, making 6 teeth in total from its original position and again, feel like this has seen and I can feel a small improvement and will Rev through to 5k. The plugs still look quite lean to me, the temps never get to high but I am nervous of causing piston damage with excessive heat build up on the crowns.

 

I will take the rocker cover off tomorrow and check the valve clearances.

 

0.15-0.25 inlet 

0.35-0.45 exh? Have read to set the exhaust to 0.30 as the std spec is to slack?

Edited January 12, 2022 by 28hodge

[petert 588]

0.30 is absolute minimum.

 

Also check fuel delivery. Disconnect return hose from the fuel rail and place into a container. Start engine. You should get >500mL in 15 sec., ie 2L/min. If not, you have fuel pump issues.

[28hodge 22]

8 hours ago, petert said:

0.30 is absolute minimum.

 

Also check fuel delivery. Disconnect return hose from the fuel rail and place into a container. Start engine. You should get >500mL in 15 sec., ie 2L/min. If not, you have fuel pump issues.

 

I'll go and check the fuel rail this morning, its a new Bosch fuel pump that i put in it so it should be fine, but I'll check all the same.

[28hodge 22]

9 hours ago, petert said:

0.30 is absolute minimum.

 

Also check fuel delivery. Disconnect return hose from the fuel rail and place into a container. Start engine. You should get >500mL in 15 sec., ie 2L/min. If not, you have fuel pump issues.

Started and ran for 15secs and got approx 700ml, so the pump is working fine, however could that suggest a leaky pressure reg? and the rail not being held at 3.0bar

[petert 588]

The only way to test the pressure is with a gauge, plumbed in between the filter and the rail.

[28hodge 22]

Ordered a fuel pressure gauge tester used dirty amazon so that it lands tomorrow, try to avoid using Amazon if I am honest but needs must.

 

Checked the valve clearances, all inlets are within spec between 0,178 to 0.203

 

Exhausts are all at 0.305 bar one which is 0.356 so possibly tight. though I think lots run them at 0.30 so although its not ideal I cant see that being the reason.

 

I have some fresh HT leads inbound as I've just found one is a little damaged where it runs underneath the AFM on the stock induction setup. I had them ordered anyway but see if these help at all. I really just want to make sure there isn't anything other than the fueling that's a problem so that when it goes on the rolling road it can be setup and its not a wasted day.

[28hodge 22]

As I have read a lot of threads that never give the final solution I am 99% sure I have solved this - 

 

I had tested the timing and fuel pressure and changed the HT leads plus all the above checks that i had already done. Nothing was showing up as a problem, and I wasn't really getting very far.

 

When I collected the car it came to me having been sat for 20+ years, and was semi incomplete in some minor areas. One was the induction pipework, it was complete bar the snorkel on the slam panel, there was another slam panel in the boot which was in far better condition (not rusted) and had a snorkel on it so when I rebuilt the car I used this snorkel and slam panel.

 

Big mistake!!

 

Turns out that this isn't a GTI snorkel, its made from soft plastic with like a corrugated air tube that connects to the long induction pipe from the slam panel up to the airbox, you can grab and squish this snorkel completely flat with your hands like you would with a plastic disposable cup. From looking online the GTI snorkel is made from hard plastic.

 

I had gone about 12 teeth on the AFM cog and decided I was chasing the problem in the wrong place so disconnected the snorkel and let the induction pipe be the main feed, instantly it revs right through no problem, I need to go and return the AFM cog to its original position and see if all is well still but I am sure it will be.

 

I am assuming that in the higher rpm and at higher wind speeds the vacuum effect and wind pressure of the intake and wind was flattening the snorkel and starving the engine of air. which also makes sense that if I babied the car through that rev range it would manage and that below those rpm ranges the car ran perfect.

 

I'll get a snorkel sorted, if I cant find 2nd hand I'll get one via BBM and come back if its not sorted but hopefully that's it.