engine sputters on WOT @ 3500rpm

Daveymaclad · 22-08-12, 11:27 AM

This is a new problem that's just manifested itself in the last few days.

The car in question is my 87 URQ.

The symptoms are the car feels spritely enough but when I put my foot to the floor on WOT the engine hesitates and sticks around the rpm it was doing but with a sound like you're driving on the rumble strip coming from under the car (guessing near the back), but on anything other than WOT rpm progression is fine.

The only thing that's changed between it working and how it is now is I tried to temporarily bandage the back box as it's near death. A few bits of the box fell off as I was putting my temporary fix on. Would something like part of the back box falling inside cause it to stutter as described above? oh and when I got home from the 30 odd mile trip the exhaust back box was very hot, hotter than I was expecting!

The only other ailment with the car is (was) the oil warning light coming on occasionally at 1.500rpm + but that's not happened at all since changing the tank last week.

I'm hoping to get exhaust changed this week so can eliminate that from my suspect list but would be good to gauge opinion in the mean time.

Thanks

Dave

msh · 22-08-12, 04:21 PM

Sounds like insufficient fuelling. Experienced something similar with my NG when fuel flow was restricted by some rubbish, only difference was that I got something like rev limiter.

Isn't the 3,5k rpm the spot where turbo starts blowing at full?

kerker21 · 22-08-12, 04:35 PM

just clean the air temp censor on top of the inlet manifold it will clear, spray it with carb cleaner

it useualy manifests as a splutter at about three and a half tho rpm or just above .

WOT · 22-08-12, 04:36 PM

Good old fashioned boost leak IMO

Daveymaclad · 22-08-12, 04:40 PM

Quote:

Originally Posted by msh

Sounds like insufficient fuelling. Experienced something similar with my NG when fuel flow was restricted by some rubbish, only difference was that I got something like rev limiter.

Isn't the 3,5k rpm the spot where turbo starts blowing at full?

Yup 3.5k is spool up time! Hoping it's not a fuelling problem as the tank is fresh in and flow was checked prior to install, all hoses to the accumulator are to spec and brand new too. I do have a new fuel pump to fit when I'm finally brave enough to give it a go!

Quote:

Originally Posted by kerker21

just clean the air temp censor on top of the inlet manifold it will clear, spray it with carb cleaner

it useualy manifests as a splutter at about three and a half tho rpm or just above .

Sounds like something I can check so I'll give that a go!

Quote:

Originally Posted by WOT

Good old fashioned boost leak IMO

Doesn't sound like something I've got the spanner skills to check, what would be the best way to eliminate? Would a boost leak still allow normal acceleration at anything but full throttle?

WOT · 22-08-12, 04:43 PM

In the 1st instance check every rubber hose between the turbo and the inlet manifold and make sure they are all clamped properly. Also check the hoses to see if any of them are cracked or damaged. You'll find boost leak testing equipment on ebay or your local garage will have a smoke tester which is very effective.

Hanuman · 22-08-12, 05:54 PM

I know your car has had a few issues.

Fuel pump.
Is there a decent 12v supply? If the fuel pump is not getting a good supply, then delivery can become so erratic. Even the connection in the fuse box can result in this, along with the old wiring, and exposed connections.

The fuel pump relay drives the supply to the pump via quite a long line. There is a simple mod which has a second relay under the rear seat driven by the fuel pump relay in the fuse box. It switches a 12v straight from the battery with a fuse inline.

WOT switch and solenoid.
Is your car WR and associated fuel injection? I cannot recall. Do the micro switches on the throttle body work as they should.

Fuel delivery
Worth doing the test to see if equal and sufficient fuel flow is available. 900ml/30 seconds.

Air leak. And infact the setup. Is it idling well. Does it behave as it should when you take the oil filler cap off? Ie stall?
Or does it stay running?

Earths.
Again. Fuel pump earth. Also engine earth.

Among a few things worth checking

Audi Derek · 22-08-12, 07:52 PM

Dave if its like you hit the wall ie car won't go any more like its on the rev limiter then that will be the air temp sensor.

As kerker21 (John) has said..

..

kerker21 · 22-08-12, 10:24 PM

air temp defo if its a wr its like hitting the rev limiter splutter splutter no boost no power wall , its the simpelest thing to check and clean costs you nothing to sort just above the throtle body on top of manifold black thing two 10mm bolts hold it in and two wires facing the back of the car dont be tempted to solder them on always use correct size insulated spade clips as soldering changes the resistance if you get stuck pm me and ill give you my number
john...

john johnson · 22-08-12, 10:38 PM

As briggers says like , ive found a wr with an air leak wont tick over properly ... Rephrase that a healthy wr

22-08-12, 04:35 PM	#3
kerker21 Senior Member Classic Audi Club Member Join Date: Jul 2007 Posts: 1,412	just clean the air temp censor on top of the inlet manifold it will clear, spray it with carb cleaner it useualy manifests as a splutter at about three and a half tho rpm or just above . __________________ chairman of the quattro owners club 85 UR WR Quattro 52 ford transit faf specialised big hit mtb ex Z1000R owner ex KTM Duke owner

22-08-12, 05:54 PM	#7
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,025	I know your car has had a few issues. Fuel pump. Is there a decent 12v supply? If the fuel pump is not getting a good supply, then delivery can become so erratic. Even the connection in the fuse box can result in this, along with the old wiring, and exposed connections. The fuel pump relay drives the supply to the pump via quite a long line. There is a simple mod which has a second relay under the rear seat driven by the fuel pump relay in the fuse box. It switches a 12v straight from the battery with a fuse inline. WOT switch and solenoid. Is your car WR and associated fuel injection? I cannot recall. Do the micro switches on the throttle body work as they should. Fuel delivery Worth doing the test to see if equal and sufficient fuel flow is available. 900ml/30 seconds. Air leak. And infact the setup. Is it idling well. Does it behave as it should when you take the oil filler cap off? Ie stall? Or does it stay running? Earths. Again. Fuel pump earth. Also engine earth. Among a few things worth checking __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

22-08-12, 07:52 PM	#8
Audi Derek “Been raced and rallied” Classic Audi Club Member Join Date: May 2008 Location: Bridgwater Somerset Posts: 1,431	Dave if its like you hit the wall ie car won't go any more like its on the rev limiter then that will be the air temp sensor. As kerker21 (John) has said.. .. __________________ Vorspurng durch Technik (see it does work)

22-08-12, 10:24 PM	#9
kerker21 Senior Member Classic Audi Club Member Join Date: Jul 2007 Posts: 1,412	air temp defo if its a wr its like hitting the rev limiter splutter splutter no boost no power wall , its the simpelest thing to check and clean costs you nothing to sort just above the throtle body on top of manifold black thing two 10mm bolts hold it in and two wires facing the back of the car dont be tempted to solder them on always use correct size insulated spade clips as soldering changes the resistance if you get stuck pm me and ill give you my number john... __________________ chairman of the quattro owners club 85 UR WR Quattro 52 ford transit faf specialised big hit mtb ex Z1000R owner ex KTM Duke owner

22-08-12, 10:38 PM	#10
john johnson Moderator of sausages Classic Audi Club Member Join Date: Sep 2008 Location: sheffield Posts: 13,331	As briggers says like , ive found a wr with an air leak wont tick over properly ... Rephrase that a healthy wr __________________ Mr OCD http://s159.photobucket.com/albums/t144/jsquatts/ Daily rs4 b7 with buckets that play havoc with my piles And if you are reading this as James may would say ' you're a cock '

22-08-12, 04:21 PM	#2
msh 4 ring whore! Join Date: Jun 2008 Location: Rucava, Latvija Posts: 3,816	Sounds like insufficient fuelling. Experienced something similar with my NG when fuel flow was restricted by some rubbish, only difference was that I got something like rev limiter. Isn't the 3,5k rpm the spot where turbo starts blowing at full?

22-08-12, 04:36 PM	#4
WOT Grown up member Classic Audi Club Member Join Date: Mar 2012 Posts: 119	Good old fashioned boost leak IMO

22-08-12, 04:43 PM	#6
WOT Grown up member Classic Audi Club Member Join Date: Mar 2012 Posts: 119	In the 1st instance check every rubber hose between the turbo and the inlet manifold and make sure they are all clamped properly. Also check the hoses to see if any of them are cracked or damaged. You'll find boost leak testing equipment on ebay or your local garage will have a smoke tester which is very effective.