Luis de Prat

Congratulations on fixing your problem. I think we all owe Jimbo some acknowledgement here.

So, is this the level of boost you had before, or lower? Again, you're referring to the stock gauge which is a bit optimistic, so I wonder whether you mean the boost is any lower.

When my car is boosting correctly, the needle often goes all the way to 2 bar, although I know it's just the way the stock gauge operates, but FWIW, the needle sticking at 1.8 isn't my best scenario. Can you elaborate?

In my case, I've never had an LBE or overboost situation on this car. Just a lousy lack of boost. Where should I start?

I'm quite a believer in the "if it ain't broke, don't fix it" philosophy with these cars, since collateral damage is so easy at their age, so I'm not interested in pulling the manifold. Would you say it was necessary the first time around in your case?

I think a lot of the cars we see on Rennlist pulling the manifold to replace vacuum hoses and such have a lot more miles than mine, so it might be overkill and actually do more damage than good, as you've seen for yourself.

At any rate, I welcome your suggestions to fixing my lack of boost.

tommye

Danny,
Quoted from the Factory workshop manual (04/1991):

"Max. boost pressure of 1.75 bar (absolute value) is reached at approx. 3000 rpm. At higher engine speeds (engine type M44.51) the boost pressure drops again and reaches a boost pressure of 1.52 +- 0.03 bar (absolute value) at 5800 rpm. With engine type M44.52, the boost pressure remains constant at 5800 rpm (1.75 bar absolute value) and drops only after this value has been passed."

Also, tolerances for boost pressure is indicated as +-10 %
Since I have a M44.52 (951S), My values are not quite up to specs.

Tommy

tommye

Luis,
My boost pressure is back exactly to where it was before, and the overboost cutouts are gone
This is measured with the stock gauge, which is probably not very good for absolute measurements. However, it seems like it is very consistent, so as far as I'm concerned, I do trust it for relative measurements (detecting changes).

So, for me it was really neccessary to lift the manifold: I fixed several vacuum/pressure leaks, I could do a thorough inspection of all rubber parts, leak test components, do electrical checks, and also, the engine is now perfectly clean even under the manifold! I also expect better gas mileage now, vacuum leaks are bad news for part-throttle mileage....


If you are worried about your meter showing 2.0, just hook up an aftermarket meter temporarly (it's very easy) and you'll know how much to mentally re-scale your factory meter. If it turns out that you really have 2.0 bar, (a) your car might be modified, (b) your boost control circuitry could have a problem, or (c) you could be very lucky (factory states +-10% tolerance on boost pressure......)

For your boost problem, I would start by narrowing down to (a) boost control or (b) boost generation. i.e. clamp the WG-line and see if you can get up to nominal boost.
BTW, I assume you have 1.4 - 1.6 bar now, if you have 1.2 only, the problem could be as simple as a disconnected TPS cable or something like that.

For a pure guess (assuming problem is with boost control) - replace the CV.
Just don't buy it from AMAG.....

And, I do agree with "if it ain't broke, don't fix it". Take your time, do a proper analysis and think before you act.....

Have fun,
Tommy

Luis de Prat

If I do choose to pull the manifold, what items must be replaced before putting it back on, aside from the 4 intake gaskets?

tommye

Luis,
Fuel injector seals is a good idea to replace as well as hose clamps and probably some of the hoses.
My hoses were in quite good condition, but I had to replace all 6 of those little V-shaped rubber connectors.
If you take the throttle body off, replace the O-ring. You could also consider replacing the little O-rings on the throttle shaft (using Bruce's kit).

But, before doing anything, you should really do the clamped WG-line check. It is really quite easy and doesn't require any dismantling. It could save you from lifting the manifold......

Tommy

Luis de Prat

Problem fixed!

My intuition was quite close. I traced the vacuum line from the BOV and found the opposite end was loose, right where it connects to the rubber Y-piece at the Fuel Pressure Damper.

Must have happened when I pulled the airbox cover to check the filter element.

YEAH BABY! BOOST!

tommye

Great news Luis !
Have fun !!!!