Cannot brake boost

[toomanymodz]

I'm posting this for a friend since he's not on this site.

He's got an 87 GN setup. Mostly stock except for a turbo, cam, downpipe, hotwire and Walbro pump. He's running a TA performance 208/208 cam and a small stock-appearing turbo (he doesn't know the specs).

The car has no throttle response at low speeds and takes quite a few seconds to build boost. Once it builds boost it holds steady at around 13 to 14psi and pulls nice. He let me drive it and I tried to brake boost it. I could floor the gas while holding the brake and it wouldn't build boost. The RPM's would only go up to about 2100. The stall converter is a Pat's 2800.

We did all of the basic checks: fuel pressure, TPS volts, IAC counts. All look good. The idle vacuum is about 15 inches and the needle bounces slightly, maybe an 1/8 inch (that worries me a bit).

Another thing is the engine has never idled smooth. It sounds more like a V8 with a cam. Slight rough idle, almost like he's running a 224/224 or something.

He's had two different turbos on it, and has pulled the front cover to double check the timing chain.

He called a perf shop in Orlando and they want $1500 to degree in his cam, or $3k to throw in a roller cam. My friend doesn't have that kind of cash.

I'm not sure what to tell him at this point. Any ideas???

 

[TurboDave]

Time for a scantool and some readings. Otherwise you're just pi**ing into the wind trying to guess what's wrong.

 

[gn1090ss]

Could be an exaust leak. Been there had that.

 

[toomanymodz]

Agreed. I've recommended to him for months to invest in a Powerlogger. I may just bite the bullet and buy one for him.

 

[toomanymodz]

If there is an exhaust leak, it would have to be a small one that we can't hear. Also, I forgot to mention that several months ago I hooked up TurboLink and captured some readings. It revealed that his MAF was going south so he installed another one. That fixed a lean stumble problem that plagued him for months. But this lazy-no-boost issue is still there. And the mild rough idle is puzzling.

 

[SCOOBY DOO]

Puck completely sealing over the wastgate hole? Actuator set correctly?

 

[toomanymodz]

UPDATE: I just got off the phone with him and he said it suddenly started running worse. It is hard to start (took him 10 minutes to get it started) and the exhaust smells very hot. I'm thinking that the harmonic balancer has slipped somehow and is causing his ignition timing to be retarded. Thoughts?

 

[toomanymodz]

LATEST UPDATE: He just called me back. He discovered a vacuum line that had come loose, so that could explain some things. I told him to check out the puck to make sure it is sealing properly. Thanks for the help guys.

 

[TurboDave]

LATEST UPDATE: He just called me back. He discovered a vacuum line that had come loose, so that could explain some things. I told him to check out the puck to make sure it is sealing properly. Thanks for the help guys.

That would explain a lot of things. Have him double check EVERY vacuum line on the car.

 

[hiboom]

first i think before to much was done other then look for vac leeks.etc. you would want to identify exactly what parts your working with.My first thought was what chip is in the ecm will it work with injectors, turbo what's fuel pressure at the rail right spark plugs .It's kind of hard to fix if you don't know what your working with.It lease that is what works for me.good luck

 

[kevinw25645]

is there a catylatic convertor on it sounds like it could be plugged up how much exhaust flows out the back

 

[toomanymodz]

Yeah, the hard part is that it isn't my car. He knows his car better than I do. But to the best of my knowledge he's running a TT chip matched to his combo. We verified line-off fuel pressure. He's running no cat.

I asked him how he set his cam sensor and he said a buddy did it. Today he turned it slightly clockwise and the car starts much faster now. It used to be very hard to start at times, almost bucking like it was a high compression motor. It starts almost instantly now. So it appears that it was part of the problem.

I asked him if he was running platinum plugs, he said yes. I told him to remove them and go with plain off-the-shelve spark plugs. Platinum plugs aren't the best thing for these engines.

I'm going to order Casper's cam tool so that I can set his cam sensor once and for all. He is going to check his puck this weekend to make sure it's sealing.

His car has been frustrating for him lately. I just don't want to see him throw in the towel. He's put like $20k into it. Built it completely himself. It's not perfect, but it's amazing what all he did.

 

[hiboom]

fix it

Boy it can be tuff with these cars! I've owned several over the years it seems each had it's own problems.that's why every night I come to the forum and read.Unless you have a lot of money or have a good friend that knows these cars your out for a hard time.It seems like they love attention.It looks like you got a good handle on things and will figure it out.I had the same boost problem one time ended up beeing something simple like bad tank of gas.hang in there!

 

[gteatr6]

One of my cars in the past had a similar problem. It would run fine on the road up to speed, but trying to launch, it wouldn't build boost. It turned out the fins in the exhaust side of the turbo were toast.

I also learned back in the day, that you never ever weld the driver's header when it is still on the car! The turbo doesn't like the slag running through it for some reason.

 

[GNregistry]

Not A Guru, But Fixing Problems helps

My problem when I purchased my 87 GN March 2008 - bad/hard brakes and bad turbo, then air in - air out, with quality fuel, NOW 2.5 yrs later - My GN is beast on the street... this past summer - I had problems building boost with brakes on..., turbo building boost, boost over 65 mph, boost over 95 mph, knock, boost, ect, somehow all related to air and/or fuel...

Therefore, Updated spark plugs/wires, coil pack, ensure plug gap using NGK UR5, updated to heated O2 sensor after replacing O2 in May 2010, and updated ls1 3" maf with translator,
the major problem was related to bad fuel driving from Wisconsin to Maine, Maine likes to think fuel is like being in California... and peope in Maine cant or dont buy 91 octane as premium, so it sits loooong time, lucky for me, local airport has non lead 93 octane 4 miles form my house...

Air into engine, exhaust out of the car, I have learned a lot and barely scratched the surface...

I think the first change or attention required is MAF/Translator of type along with SCANMASTER or more for reading engine idle and wot output to see what is right & most importantly what is wrong...
that is how I made changes...

Some updates might be an overkill, such as 3" everything, yet it is ready for future updates or modifications... .

The LS1 3" MAF/Translator was my last change and should have been near the first changes....

May 2010 I experienced low quality fuel that caused all types of problems, bad O2 sensors, knock, low boost, sluggish boost over 12 pounds. I knew bad fuel was a problem becuz I made no changes in 2009 and started 2009 runnigng great on 20 pounds of boost, yet it always ran rich or not running right for one reason or another, YET it was smoking the tires, 13.2 @ 105 mph in the quarter mile on cooper cobra street radials 235/60/15", supposedly running like crap... 2010 I found different gaps in spark plugs, top end was sluggish this past summer due to bad fuel... however, over time this summer... I found the problems asking questions and updating parts... and reading my scanmaster...

Fast forward to October 2010 = Wicked quick and boost up to 20 pounds, no knock! and HRpartsNstuff makes this modified Grand National handle incredible on corners or launching...

lil turbo - big intercooler - open exhaust = abused daily and driven often!

 

[Just a Six??]

There is also some great reading here
Vortex Buicks & Turbo Regal Web Site

 

[GNregistry]

Those links are exactly where I found some great information plus here on turbobuick.com...

 

[toomanymodz]

Thanks for all of the replies. Here is what we found. The problem was two-fold. First, the lines on the vacuum 'Y' coming off of the wastegate actuator were reversed. That explained why his actuater rod had to be shortened so much just to get to 13 psi of boost.

Secondly the puck in the downpipe wasn't completely covering the hole on the turbo. The puck is plenty large enough, but it was way off center of the hole. I'm not sure if this was a defect in the downpipe itself but it sure appeared like it was. We removed the downpipe and had a friend move the puck 1/8 inch and re-weld it. It helped, but the puck still isn't 100% covering the hole, so he still cannot brake boost. He may have to buy another downpipe.

At any rate, his car is pulling much stronger. I set the boost at 14psi, any higher and the O2's would start dropping. It seems like his 38# injectors could be maxxed out.

 

[Just a Six??]

Enlarge the 4 holes on DP for mounting to slide the puck over the hole.

 

[toomanymodz]

That's a good idea. I'll let him know. All he needs is to move the downpipe a little over 1/8 inch towards the front of the car.