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B230FT low boost

leecatd8209

leecatd8209

The Fourfather
Joined
Jul 1, 2015
Location
Reading, PA
1986 760TIC B230FT/AW71 LH2.2
- essentially a +t with a reclocked 15g
- ipd turbo cam
- timing 10* BTDC, but I haven't checked it since setting it

Ever since I got it running my 760 has been plagued with boost issues. Too much, too little, I could never get it just right. The last time I actually drove it I monkeyed with the cheap MBC and from that moment on I haven't been able to make more than 3 pounds of boost, and it runs rough at idle. And it just gets God awful fuel mileage. So bad.

I've never had a turbo car, so I don't really know what I'm doing, but here is what I've checked so far:
- the wastegate actuator rod is tight, but the reclocking bracket has some flex
- replaced CBV diaphragm
- smoke checked the intake system for leaks - found none
- did a compression test, all cylinders are 155#+ dry
- pulled the vacuum line off the wastegate actuator and plugged the leak. This saw a slight gain to ~6#

I'm leaning towards replacing the wastegate actuator, but I'm getting sick of firing the parts cannon. To be fair it's pretty much the only thing that isn't new. Am I overlooking or forgetting to check something simple?
 
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So simple stuff first. Make sure the hose clamps from the turbo to the intake manifold are all tight. If one is loose you’ll bleed boost pressure there and it’ll run way rich.

If you pull the mbc off and just run straight wastegate, what boost do you see? Should be 6-7psi.
 
Marvelous3 said:
So simple stuff first. Make sure the hose clamps from the turbo to the intake manifold are all tight. If one is loose you’ll bleed boost pressure there and it’ll run way rich.
Click to expand...

I did this and smoke checked the whole intake system this afternoon, no leaks thankfully. When I pulled the plugs to do a compression test it looks like it's running lean, if anything. Or really well. The plugs look really fresh with a very light tan color.

If you pull the mbc off and just run straight wastegate, what boost do you see? Should be 6-7psi.
Click to expand...

Straight wastegate I do get 6-7psi, but it's a sluggish and crappy 6-7psi. Edit: Straight wastegate with no MBC is still ~3lbs. If I unhook the wastegate hose and plug it off I get 6-7psi
 
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Can you pull the actuator rod back (wg open) easily by hand? If yes it's probably time to replace. Also try to get rid of the flex in the reclocking bracket, that adds to sluggish boost.
 
If you put a bike pump or something on the wastegate you should be able to test at what psi it opens. Again, should be 6-7psi. If it’s less adjust accordingly.

The flex in the bracket is less than desireable.
 
kyote said:
+1, it's that ****ty 15g actuator.
I'm running this one with a MBC and working like a champ.
https://www.ebay.com/itm/301840261012?hash=item464714df94:g:JREAAOSwZVhWShmR
Click to expand...

It IS this actuator! It's a reclocked 15g, so I needed a T3 wastevate and ordered that one. But I had to run an extension for the rod.

It feels tight, the diaphragm is intact, I suspect it's working. Because:


position emojis

I found a boost leak. Just as I got a leak free spare installed a nasty thunderstorm rolled in.

TBC
 
Even if the actuator is "working" they have a much lower spring pressure and can be pushed open with exhaust pressure in the turbine pretty easily
 
leecatd8209 said:
It IS this actuator! It's a reclocked 15g, so I needed a T3 wastevate and ordered that one. But I had to run an extension for the rod.

It feels tight, the diaphragm is intact, I suspect it's working. Because:


position emojis

I found a boost leak. Just as I got a leak free spare installed a nasty thunderstorm rolled in.

TBC
Click to expand...

Nice! Boost leak found.

Hoping the activity in the gulf fizzles out, we are getting ready up here just in case.
 
cosbySweater said:
Even if the actuator is "working" they have a much lower spring pressure and can be pushed open with exhaust pressure in the turbine pretty easily
Click to expand...

That's my worry with not having a solid bracket. But I don't have fab tools, so that's why I ordered this one off the shelf.

I hoping fixing the boost leak helps.
 
A leak free intercooler made the idle characteristics return to normal, and overall runs significantly better. But still only 3psi
 
ovlov760 said:
Are you sure the turbo is in good enough shape to build that much boost?
Click to expand...

It's feshly rebuilt, lubricated, not passing oil, and seems to blow quite well. I don't suspect it has any issues, and it's made 15+ in the recent past.

I'm on the right track, I just need the right combination of wastegate and MBC that doesn't suck.
 
ZVOLV said:
A cracked/melted turbine housing can cause low boost.
Click to expand...

I don't have any exhaust leaks.

This new eBay wastegate is behaving much better than the old OEM T3 one I had on it at the beginning of this saga. I think the issue is with the rod 3xtension I can't make the rod quite short enough to get a good enough preload on it to get high boost. And I also think the rod extension is rubbing on the oil drain fitting which could be causing some issues as well.

The more I mess with the wastegate the better it is. I also got the kickdown cable routed correctly which really woke the car up. Now I need to figure out why OD quit working... it never ends
 
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