WR popping at 4000rpm

joss01 · 22-11-18, 04:23 PM

At around 4000rpm my 1985 WR sounds like the engine is popping like it has reached it maximum RPM, checked the throttle body switches all associated connections, earth leads to the inlet manifold but the problem persists has anyone had the same issue.

I have been told it could be the ECU

so I am looking for a ECU B suffix for a 1985 Quattro UR WR please contact me me if you have one.

4v6 · 22-11-18, 06:26 PM

Check all the basics first, like air/vac leaks, plugs and dizzy/rotor arm etc and base timing/mixture.

If it is ecu associated it could be something as easily fixable as a dry joint on the pcb.

jimh · 22-11-18, 06:27 PM

Yes, classic WR fault - possibly the most common of all.

On the top if the inlet manifold, just by the throttle body are 2 wires going into a rubber boot.
Peel back the boot, you will see the wires are (originally) soldered on to solder tags on what is the inlet air temperature sensor.
Those connections must be perfect.

If you are good with a soldering iron, use some decent no-clean flux and lead solder to make good those connections.
With a multimeter, you should measure around 22 Ohms across that sensor with the ignition OFF and engine cold.

If the sensor itself is broken, you can temporarily test / drive it if you solder a 22Ohm resistor across the terminals. That will satisfy the ECU that all is well, but it will not adjust timing for inlet air temp anymore, so be careful if you hear any pinking.

The ECU is going into a very basic and old school "limp mode" where it limits to 4000rpm if it has no signal from the air inlet temp sensor.

By the way, whatever is wrong, it's almost never the ECU itself at fault. I think I've heard of maybe one ECU replacement in 20 years of ownership and participation in all the related forums.

joss01 · 22-11-18, 06:31 PM

Hi all piping has be renewed has a new distributor but not sure if the gears engaging with the distributor are worn or damaged, it has been on a rolling road and all timing and tuning has been check and all fine so will check the wiring going to ECU this has a been a real pig to sought out.

jimh · 22-11-18, 09:02 PM

Also make sure you have the correct rotor arm that has an unusually wide tip
http://www.sealtd.net/quattro/ishamr...otor-arms.html

If the rotor arm tip is too narrow, the ECU could retard timing off the end of it as boost builds.
Otherwise, as timing is ECU controlled (not using the distributor as an input), the distributor either works or it doesn't.
However, 4000rpm is classic inlet air temp sensor.

SorenR · 22-11-18, 11:37 PM

http://www.classic-audi.co.uk/forum/...34&postcount=3

http://www.quattroforum.com/index.ph...6/#post-180693

joss01 · 23-11-18, 08:11 AM

Ok why is the ignition showing 43 degrees advance at 4000rpm instead of 23 degrees advance which it should be 4000rpm can any advise how to correct this mind bender.

slacky · 23-11-18, 09:47 AM

just thought I'd say thanks to all the contributors FOR the O.P

, he seems to have forgot .....

some very useful help and information already provided

SorenR · 23-11-18, 09:52 AM

Quote:

Originally Posted by joss01

Ok why is the ignition showing 43 degrees advance at 4000rpm instead of 23 degrees advance which it should be 4000rpm can any advise how to correct this mind bender.

Static timing is OK?

http://www.sealtd.net/quattro/static_timing.html

joss01 · 23-11-18, 01:16 PM

Thanks for the input all of these issues have been looked into but I cannot get the ignition advance back to 23 degrees as specified and I have a feeling this is what is causing the engine to misfire at 4000rpm

22-11-18, 11:37 PM	#6
SorenR Grown up member Join Date: Oct 2010 Location: Vesterlyng/Föllenslev, Denmark Posts: 563	http://www.classic-audi.co.uk/forum/...34&postcount=3 http://www.quattroforum.com/index.ph...6/#post-180693 Last edited by SorenR; 22-11-18 at 11:40 PM.

23-11-18, 08:11 AM	#7
joss01 Grown up member Join Date: Aug 2015 Posts: 25	43 degrees ignition advance Ok why is the ignition showing 43 degrees advance at 4000rpm instead of 23 degrees advance which it should be 4000rpm can any advise how to correct this mind bender.

23-11-18, 09:47 AM	#8
slacky 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: wirral Posts: 4,452	just thought I'd say thanks to all the contributors *FOR* the O.P , he seems to have forgot ..... some very useful help and information already provided __________________ *90q-Cab.2.3E-Ur-S6-b2-80 Sport* Member 111

22-11-18, 06:26 PM	#2
4v6 Ex Member Classic Audi Club Member Join Date: Dec 2007 Posts: 5,565	Check all the basics first, like air/vac leaks, plugs and dizzy/rotor arm etc and base timing/mixture. If it is ecu associated it could be something as easily fixable as a dry joint on the pcb.

22-11-18, 06:27 PM	#3
jimh Grown up member Classic Audi Club Member Join Date: Dec 2008 Posts: 122	Yes, classic WR fault - possibly the most common of all. On the top if the inlet manifold, just by the throttle body are 2 wires going into a rubber boot. Peel back the boot, you will see the wires are (originally) soldered on to solder tags on what is the inlet air temperature sensor. Those connections must be perfect. If you are good with a soldering iron, use some decent no-clean flux and lead solder to make good those connections. With a multimeter, you should measure around 22 Ohms across that sensor with the ignition OFF and engine cold. If the sensor itself is broken, you can temporarily test / drive it if you solder a 22Ohm resistor across the terminals. That will satisfy the ECU that all is well, but it will not adjust timing for inlet air temp anymore, so be careful if you hear any pinking. The ECU is going into a very basic and old school "limp mode" where it limits to 4000rpm if it has no signal from the air inlet temp sensor. By the way, whatever is wrong, it's almost never the ECU itself at fault. I think I've heard of maybe one ECU replacement in 20 years of ownership and participation in all the related forums.

22-11-18, 06:31 PM	#4
joss01 Grown up member Join Date: Aug 2015 Posts: 25	Hi all piping has be renewed has a new distributor but not sure if the gears engaging with the distributor are worn or damaged, it has been on a rolling road and all timing and tuning has been check and all fine so will check the wiring going to ECU this has a been a real pig to sought out.

22-11-18, 09:02 PM	#5
jimh Grown up member Classic Audi Club Member Join Date: Dec 2008 Posts: 122	Also make sure you have the correct rotor arm that has an unusually wide tip http://www.sealtd.net/quattro/ishamr...otor-arms.html If the rotor arm tip is too narrow, the ECU could retard timing off the end of it as boost builds. Otherwise, as timing is ECU controlled (not using the distributor as an input), the distributor either works or it doesn't. However, 4000rpm is classic inlet air temp sensor.

23-11-18, 01:16 PM	#10
joss01 Grown up member Join Date: Aug 2015 Posts: 25	Thanks for the input all of these issues have been looked into but I cannot get the ignition advance back to 23 degrees as specified and I have a feeling this is what is causing the engine to misfire at 4000rpm