problems under boost!

[9dreizig]

Ok here's the problem.. The car ran fine ( been trying to get it ready for the track). Upon finally getting it ready mechanically we thought we'd adjust the valves. After that was done we buttoned it up and thought it would run great.. WRONG it ran rough. So figuring it was some wiring inadvertently messed with, we started checking a few things.. It now runs but VERY rough under boost. LIke a bucking..
Long story short we've:
- put new plug wires in
- new MSD wire to distributor cap ( spark looks good!)
- confirmed fuel flow
- taken the inner cooler off and put back on a few times ( pretty sure there are no leaks there).
- checked to make sure the intake hose doesn't colapse under load

It acts almost like there is an advance or retard that is associated with the boost. Although while watching the boost gauge I'm getting full boost..

Any ideas ??

[mb911]

valves mis adjusted

[9dreizig]

but it runs fine not under boost.. And they were meticulously adjusted.. They were very loose and noisey before..
T

[9dreizig]

bump!!

[pjv911]

Upgraded cams ? Cis injection ? When the valve adjustments are tightened you increase camshaft overlap time. Could exhaust pressure be reversing back into the intake.
Corky Bell says that exhaust header psi is often twice the boost setting. This will then result in exhaust going back into the cylinder and reservrsing up into the intake runner during the short time both valves are similtaniuosly open(overlap).
I believe CIS injection will have adverse affects if this were to happen.
But if your cams are stock or very mild I would not consider this the case.
Most likely not the cause of your problem but its the first thing that came to mind.

Kurt Williams

[stlrj]

put new plug wires in

Never fails. Everytime I do my wires, I always get them crossed no matter how careful I try.

Cheers,

Joe

[dean]

Could it be a weak overboost sw.? How are the plugs?

So it ran good before you did this work?

[9dreizig]

It does have SC cams in it. So adjusting them to spec would be too tight ?

[9dreizig]

Originally posted by dean
Could it be a weak overboost sw.? How are the plugs?

So it ran good before you did this work?

Dean, It ran fine before this. Chris did the valves for me ( and you know how he is LOL). The over boost switch is brand new.
Plugs are good, I haven't changed them yet, but have new ones waiting.
T

[dean]

Did you test the overboost sw.? Sometimes they are weak even new.

[9dreizig]

Oh one more thing. It has an upgraded turbo on it, so i"m seeing the boost kick in around 2200 rpm. Even at 0.2 bar it starts the "bucking".

[9dreizig]

Originally posted by pjv911
Upgraded cams ? Cis injection ? When the valve adjustments are tightened you increase camshaft overlap time. Could exhaust pressure be reversing back into the intake.
Corky Bell says that exhaust header psi is often twice the boost setting. This will then result in exhaust going back into the cylinder and reservrsing up into the intake runner during the short time both valves are similtaniuosly open(overlap).
I believe CIS injection will have adverse affects if this were to happen.
But if your cams are stock or very mild I would not consider this the case.
Most likely not the cause of your problem but its the first thing that came to mind.

Kurt Williams

So would you suggest loosening up both the intake and exhaust valves or just the exhaust ?
T

[quattrorunner]

Overboost switch is my guess.

[dean]

Did you check your fuel pressures under boost? I think there is a spec for that. Are all the hoses on the WUR correctly?

[930turbo]

Be sure to check fuel deliver, not just static pressure. it also sounds a little like it's blowing the spark out under elevated cylinder pressure. Try bypassing the pressure switch (be careful) just to eleminate it from the equation.

[ChrisBennet]

Some data points:
- Valves were very loose before adjustment - like .005-6" I'm guessing (.004" spec)
- Checked system pressures: cold=2.6bar, warm=3.6bar, warm+.7bar simulated boost=2.9bar (all in spec)
- New OEM spark plug wires keep falling off plugs. (!)
- Plugs (assuming they are all the same as the #4 we pulled with great difficulty) are the kind used in the 964 3.3L Turbos. They take a smaller plug wrench. Bosch WR6DPC?
- Power to WUR is not connected (wires were snipped in harness) We supplied power to it in order to get the warm sys. pressure readings.
- Tried to checked large rubber elbow for collapsing and we couldn't catch it "in the act" but it is easy to squeaze with your hands.
- CO mixture not set but A/F ratio set at idle to ~13.5. Under boost it goes to around 12.6.
- Engine originally had a different intake (Carrera?) and intercooler. Engine was delivered to Todd with a stock intake and intercooler. The engine has metal injector blocks. I wonder if they were opened up to match the other intake and I wonder if they make a good seal with the stock intake? The previous owner also replaced the stock lower valve covers with some old magnesium ones before he sold the motor. Nice eh?
- When engine was running fine before, cold start injector was connected. When we couldn't get it started we disconnected it and got it to run.

List of things to do:
- Check fuel pumps for cutting out under boost
- Ground out overboost switch
- Check for vacuum leaks
- Get Todds head checked for putting in the motor without going over it first. It was sooo much fun adjusting the valves on that thing in the car instead of on an engine stand...
- Check fuel delivery - low on the list because that wouldn't have suddenly stopped working when we adjusted the valves and changed the plug wires.

-Chris

[9dreizig]

Ok just checked the overboost switch ( grounded it out), no joy .. so we can eliminate that.
T

[9dreizig]

Ok more info.. just eliminated the overboost relay as well!!..

[9dreizig]

Ok, since my A/F looks good under boost. Is it safe to say I'm getting enough fuel? Here's my latest thinking. I disconnected the vacuum hose from the vacuum unit on the distributor to see if it would make things worse under boost. NO Change! Engine runs exactly the same. So am I correct in thinking that maybe my vacuum retard unit is bad ?? Shouldn't I have seen a difference ?

[ischmitz]

Take the dizzy cap off and check if the advance/retard mechanism is working on the distributor. Maybe the mechanical part is frozen or the diaphragm is ripped.