Caravelle AHU conversion done but still a couple of minor issues.

I have no faults on vag com, timing is spot on and the engine doesn't leak or burn any oil. All is well appart from a couple of minor niggles. When the engine is warm it still seems a little bit noisy and it also seems to have a stutter when you blip the throttle lightly on the wind down which also happens when driving causing a shudder at certain revs. It pulls well but there isn't a lot of torque compared with the old IDI engine it replaced (considerably less) and the economy is no better either.

Anyone got any ideas? Everything pipework wise is new on the N75 and the wiring is fine but they are just minor enough to be annoying. I also find it has occasional lack of power (not limp mode as full boost is allowed) Could this be a problem with the N75 valve which is a bit noisy and worn. I also have very high readings compared with specified on the MAF at idle but it reaches the required levels under load easilly.

I have a list of things to do in the future which might be causing the problems. Worth doing (see list below)?

Decoke head and grind the valve seats.
Replace camshaft and lifters.
Remap.
K&N panel filter.

Anyone got any ideas?

Ok well i have taken the bull by the horns and invested in a small pile of parts which i'm fitting tomorrow based on too many hours of research on here. I will be replacing the fuel temperature sender, coolant temperature sender, camshaft and lifters. Looking at the cam lobes aginst the new one today the tips are rounded off by quite a fair bit so i'm expecting big changes in the drivability.

In my experience, when the N75 become audible, it has not been long before it has become silent, as it seizes and ceases all dithering.

Have you checked the back pressure in the exhaust piping? Unbolt the exhaust before the catalytic converter (for test purposes only, you know) to see if a lack of air throughput could be a contributor?
Is the air passage from MAF to intake manifold totally leak free? Drawing air in after the MAF, but before the turbo would reduce the air through the MAF which would reduce fueling. Blowing air out between the turbo and the intake would make for less in the combustion chamber.

There have been a number of MAF failures attributed to the oil mist from the insect strainer elements getting on the hot wire element. Although these have more often been with the ALH than the 1Z/AHU, you might want to know that Fred's members have tested VW stock air filters against aftermarket, specifically K&N elements, and have reported that the VW filters not only flowed more air but that they also trapped more contaminants.

Lug_Nut said:

In my experience, when the N75 become audible, it has not been long before it has become silent, as it seizes and ceases all dithering.

Have you checked the back pressure in the exhaust piping? Unbolt the exhaust before the catalytic converter (for test purposes only, you know) to see if a lack of air throughput could be a contributor?
Is the air passage from MAF to intake manifold totally leak free? Drawing air in after the MAF, but before the turbo would reduce the air through the MAF which would reduce fueling. Blowing air out between the turbo and the intake would make for less in the combustion chamber.

There have been a number of MAF failures attributed to the oil mist from the insect strainer elements getting on the hot wire element. Although these have more often been with the ALH than the 1Z/AHU, you might want to know that Fred's members have tested VW stock air filters against aftermarket, specifically K&N elements, and have reported that the VW filters not only flowed more air but that they also trapped more contaminants.

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Thanks for the reply and the suggestions, i appreciate it but in fairness i have had these problems forever now and it seems to stoump anyone i mention it to. The parts i am fitting are the only things i can think of left to try. The problem is because its a conversion there are no standard answers.

The exhaust is decat with only one silencer and flows fine but i'm having a custom stainless made for it in a couple of weeks in 2 1/4 inch stainless with a single silencer at the rear which will totally rule it out. N75 has always been noisy but it tried one i "found" at a scrap yard to try and it couldn't stabilise the boost at all, surging constantly so i changed it back. Pipework is all fine with no leaks anywhere and the maf is reading normal figures reaching the maximum airflow easilly on vagcom. I am yet to change the filter and i'm still using a fairly new paper one.

One question for you, the manual says replace the cam cap nuts and i cant get my head around why. I understand stretch bolts and why they need to be replaced but surely nuts are just nuts and nothing special???

Replaced the camshaft and lifters and its a bit quieter but there is still a noticable tapping there. Old cam to new cam there was 1mm worn off each lobe lifters had discolouration but no cracks or signs of other problems. Do the new lifters take a period of time to run in? What else could be causing the noise? Timing is very slightly advanced in vagcom and the Injectors have recently been rebuilt and fitted with new injectors (.216 veg). Turbo spools up a bit easier and lower down the rev range and the exhaust note is much deeper so its a win win for me even though noise isn't massively reduced.

thanks in advance.

More adjustments today on the IQ specificly. I adjusted the IQ when the stumbling was happening after a run before stopping the engine. It was at 2.8mg/s but i adapted it to 3.8mg/s and it idles smoother, runs quieter (less knock) and the stumble on the accellerator pedal has nearly all gone. I think it must have been injecting to much fuel which was causing the stumble. Either way it didn't smoke noticably which is a little odd.

This noise is driving me mad, i can hear how the engine should sound but the tapping engine knock completely overpowers it. Any final ideas as to what could be causing it? For what its worth the clack/knock/tap sounds like its coming from the rear of the engine bay now as apposed to the front before. The other thing that seems strange is that its quiet when warm and noisy when warm which makes no sense at all.

I'm at my wits end here, i just want that stupid noise to go away once and for all!!!

For anyone who cares to have a listen i have recorded a bit for youtube so you can hear the noise in question. You can hear it most at the end of the clip on the right hand side of the vehicle.

LINK HERE!

Thanks for listening, any input would be apprecated.

Sounded normal but then again I can't hear that well...I know because the wife tells me so.

G60ING said:

Sounded normal but then again I can't hear that well...I know because the wife tells me so.

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Thanks for the reply bud. The only way to explain it is like a knock every rotation of the engine which stands out from the normal sound and its only when its warm.