Lizard928

I had installed a set of camshafts into a members car on the east coast recently.
After driving the car for awhile the car started to have some issues.
The car had needed an intake refresh, so that was done, and numerous other checks were performed to try to find the source of the problem.
The problem is that the engine would surge when idling in D/R.

A compression check showed correctly. Everything to do with the camshafts was double checked and checked out proper.

I ended up having to return on a whirlwind tour to try to find the problem as it was seemingly being very elusive.

Thankfully the car had an X-pipe installed with the WBO2 being in the drivers bank, and a factory NBO2 in the passenger bank. When the car was cold the WBO2 was reading the correct AFR rich when really cold and shortly settling to 14.7:1. However once everything was 100% heat soaked, the WBO2 sensor went from rearing correctly to 22.4 which is what it reads as if the car is off.
I know that the WBO2 was just recalibrated with a new sensor etc. And it was working when cold. Even as it heated up it was working, but once 100% heatsoaked, it read lean. Yet through the Sharktuner the NBO2 sensor rear the normal up/down of the NB sensor.

From this information I determined that there was a problem happening with the 5-8 bank of cylinders.

Now there had been 2 different set of fuel injectors in the car. And the chances of them creating an issue which stayed with that bank was unlikely, they also were clicking along nicely, and all evenly when listened to. So on to the other half of the equation. The car had had a couple of compression tests run, so we knew the chances of it being caused by something internal was nearly impossible. So I pulled the ignition leads 1 at a time on the 5-8 bank, as it was running and the WBO2 reading 22.4.
Cyl 5 major change to how it was running,
Cyl 6, no change,
Cyl 7, no change,
Cyl 8, major change to how it was running.

So for sh*ts and giggles, I swapped the 5 and 6 plugs, and the 7 and 8 plugs to ensure that the problem wasn't a fluke plug failure. Same results from pulling the plugs while the engine was running.....

From this information I was able to quickly determine as to what the failure was. Can anyone else guess as to what it was?

(those of you that know, don't reveal the secret yet!)

While I was there, and the intake had been refreshed, I retuned the car and made it run a smidgen smoother. Car pulls much much nicer now......

GlenL

Mis-routed FI connectors or plug wires.

davek9

I recently seen an S4 do an idle "surge" just sitting in the parking lot, it almost seemed like someone was in the car and hitting the throttle, sometimes holding it.
The car had sat over the winter and we just installed one of GB's brand new Autos, so thinking it was a vacuum leak.

Nope, it was dirty connections on the Temp II, cleaned them and Surging went away and car runs great now.

Dave

SeanR

I'm guessing this is the same car I've been talking with Stan about? I gave him some suggestions but never heard back but from what you are saying, i'm guessing I was correct.

Lizard928

So far no correct guesses..... ��

hwyengr

6/7 plug wires damaged where they cross over the front of the engine from the distributor?

killav

What year car?

If 85/86, cracked boots that tie the outside manifold lugs to the main manifold.

Otherwise, ignition rotor cap issue?

davek9

6 and 7 as they are fed via right side distributer cap were reversed at the cap?

GlenL

String or nothing.

mark kibort

distributor cap crack?
bad plug wires on 6-7?

Kevin in Atlanta

Wrong coil wires?

Lizard928

All ignition leads were new and good.
Coil wires were brand new.

Distributor did not have and 'visible' signs of damage.

Everyone who has linked and guessed that the 6/7 are related are on the correct track to the failure.

However Killav (Mike) was the first one to guess correctly.

The passenger side distributor cap had an internal fault on the two long traces inside of it. When hot those two traces would open up or have enough resistance to stop the spark.
When cold, the connections touched and worked correctly.......

KenRudd

BWahhaha!

ROG100

Never miss an opportunity - - -
Distributor caps Bosch $64.95 each
Rotors Bosch $44 each

terry gt

So now we have to share Colin with the east coast ?
most guesses were pretty close ,just shows how good this list is .