Strange Relative Compression VW Transporter

Ask for and share advice on using the PicoScope kit to fix vehicles here.

Re: Strange Relative Compression VW Transporter

Postby RYM6746 » Thu Jul 13, 2017 11:04 pm

The five inconsistent pressure dips in between the injector sync when you zoom in? matching scan data parameters I posted earlier. surely if each injector used the same amount of fuel the dips would be even.

Just noticed the dips are uneven even when the injectors are not being fired what could be the cause of this?
User avatar
RYM6746
TwoWaves
TwoWaves
 
Posts: 98
Joined: Tue Nov 01, 2016 10:58 am

Re: Strange Relative Compression VW Transporter

Postby STC » Thu Jul 13, 2017 11:26 pm

Now I see it - Zoomed in.
It is time to make sure the Injector rockers are adjusted correctly and swap a couple to see if the fault moves between cylinders.

The broken plastic supply tube in the head is a prime suspect here too !

Just noticed the dips are uneven even when the injectors are not being fired what could be the cause of this?

Injector seals, elongated injector ports ... ... .
User avatar
STC
TwoWaves
TwoWaves
 
Posts: 790
Joined: Sun Sep 13, 2015 4:10 am

Re: Strange Relative Compression VW Transporter

Postby Technician » Fri Jul 14, 2017 8:57 am

RYM6746,

A couple of points.

If you remove the injectors for renewal, check their settings before removal. On top of each injector is an adjuster, technical data says the adjustment should be 180 degrees, I had problems with that and contacted both VW and Haynes, who both have the same settings. I experienced injector breakage and a VW tech advised not to set them at 180 degrees, I double checked this with an engine re-conditioner and he said set them at 360 degrees.

The tandem pump is known for giving problems, if you suspect a fuel fault ensure the pump works correctly, the fact the engine runs does not mean the pump is operating efficiently. You are right about the pressure take off point, VW had a good idea there.

To stop fuel supply, simply pull the fuse for the in tank pump.

The injectors, after market seals kits can cause problems, genuine VW ones are more expensive but worth it. After market ones can cause running issues.

The injectors bores wear internally on the thrust side, clean them off for any rough edges before re-inserting the injectors with new seals, otherwise you will damage the new seals after fitment.

VW recommend a injector seal kit tool set to renew them but you can do it without, be careful though.

Injector renewal - If you renew the injectors, ensure the part numbers on them are the same.

Common fault - The injectors wiring harness through the cylinder head can and does give problems, ensure the wiring harness is OK prior to renewing any parts.

Inspect the injector nozzles on removal, they are prone to breakage, also if used injectors are to be used when renewing, ensure they are not worn and damaged on the thrust side face and injectors nozzles.

Have I forgot anything?

Maybe, but if you require any data I have the genuine VW workshop data for what its worth, e.g. accuracy of it!
Technician
TwoWaves
TwoWaves
 
Posts: 229
Joined: Thu Apr 24, 2014 10:32 pm

Re: Strange Relative Compression VW Transporter

Postby RYM6746 » Fri Jul 14, 2017 9:38 am

Thanks for your help much appreciated. What are your thoughts on the pressure dips in the capture?
User avatar
RYM6746
TwoWaves
TwoWaves
 
Posts: 98
Joined: Tue Nov 01, 2016 10:58 am

Re: Strange Relative Compression VW Transporter

Postby STC » Fri Jul 14, 2017 10:00 pm

Rym

With regard to your pressure drops, Indeed we have one that increases in pressure more than the other 4, the pressure drop on that is lower too.

So we have one here that sticks out like a saw thumb and 4 that are "loosely" similar.

So do we have 1 bad - 4 better or 4 bad -1 good ???

I did think that it maybe 1 injector blocked causing that high spike but then your observation that this was also occurring on the overrun shot that down in flames. Plus the fact that the pattern is consistent.

The pump is bolted directly to the head and then the fuel is channelled through a gallery with a plastic sleeve in it. At the injector end we have o rings to keep the fuel where it should be. When the o rings fail diesel will end up in the sump. You could sniff the dipstick for HC's (Has the Oil Level Risen ?)

These are well known for the injectors to move and elongate the hole they sit in, new seals wont fix that, it will be a new head.

The only other option that comes to my mind is that the injectors are faulty internally hence my suggestion to swap them around. If you don't now how then Technician has written a guide for you. :D

Hope that makes some sense and helps.

EDIT
I wonder what we would see if you hooked up the wps to the return line to the tank ??? just be wary of the fuel temperature.
User avatar
STC
TwoWaves
TwoWaves
 
Posts: 790
Joined: Sun Sep 13, 2015 4:10 am

Re: Strange Relative Compression VW Transporter

Postby Steve Smith » Tue Jul 18, 2017 11:39 am

Hello and thank you for what looks to be a great case study unfolding.

I have not reviewed any of the pressure captures but wanted to pass on the following link to a Caddy Case Study here at Pico

https://www.picoauto.com/library/case-s ... cold-start

Here the vehicle suffered from prolonged cranking.

The system pressure reading before and after fix might help bring about a conclusion.

Take care.....Steve
Steve Smith
Pico Staff Member
Pico Staff Member
 
Posts: 476
Joined: Sun Aug 25, 2013 9:22 am

Re: Strange Relative Compression VW Transporter

Postby RYM6746 » Wed Jul 19, 2017 12:25 am

Thanks for all your input. Using the smooth running values on the scan tool as a starting point, the dips in pressure,injector sync and the firing order. I concluded that the scan data was in fact correct. With relative compression being good (in the end). No1 injector was replaced and the vehicle was fixed with no further running faults. My conclusion of the pressure dips still being present even though the injectors were not being fired electronically is that the engine is still going round and the cam lobes are still compressing the injectors effecting the pressure (educated guess).
User avatar
RYM6746
TwoWaves
TwoWaves
 
Posts: 98
Joined: Tue Nov 01, 2016 10:58 am

Previous

Return to Diagnostic discussion

Who is online

Users browsing this forum: No registered users and 1 guest