Boost Stopping

[sceric]

Alright please forgive me if i cover something in this that has been asked a million times but i used the search function the past three hours and couldnt come up with an answer.

i have a car that will not boost past about 7 lbs. it does fine with spool and everything right up until seven pounds or so then stops. everything appears to be tight and went over it for good measure. thought it was a wastegate problem so i undid the pushrod and wired the flapper shut and still the same thing. no over boost or anything. the impellar is free spinning with almost no shaft play. it also does break up around seven pounds like the knock sensor is snatching all the timing out of it like its sensing detonation. theres no bov on this car. any suggestions? the car is setup with 36lb injectors a ta44 turbo (i think) art carr converter alky injection manual boost controller exhaust cut out bigger throttle body and a few other things including a chip to go with the setup. before it sat for 5 years it was running low 12s on 15 lbs of boost. while it was sitting someone put a water pump on it but the setup was left unchanged.

[turbofrank]

If car sat for 5yrs its not practical to expect a good outcome . I suggest a spring cleaning. Coil/mod,fuelpump/filter, injs are some of theitems you need to check.

[Keller]

it also does break up around seven pounds like the knock sensor is snatching all the timing out of it like its sensing detonation.
Possible. But I doubt it would pull it down to 7.

Actually, the stock wastegate is set to 10 PSI. So if it has a stock wastegate, and the rod is the stock length, your really should not be able to see less than 10 PSI.

My suspicion is that you have other issues. You may even have a leak to the boost gauge. (Stock boost gauge or aftermarket one?) You may have a leak in the hoses to the wastegate. The odd thing is that it is low, not high. If you do not have adequate pressure going to the wastegate, your boost would be too high.

You may have an exhaust leak or intake tract leak. Perhaps even a headgasket leak. The suggestion of a "Spring Cleaning" is a good one. I'd suggest a compression test as well, and some leak checks, too.

[sceric]

heck i was just thrilled it cranked right up and idled. i mean it didnt hesitate or anything it fired right up. it even does fine getting to the 5lbs of boost. it has the stock guage which claims its making a ton of boost and then it has a vdo boost gauge that says between five and seven pounds. i went over everything again last night tightened and re tightened checked the fuel pressure it was a little low so i adj it with no significant change. it doesnt smoke at all until it starts breaking up and then its black smoke from unburnt fuel. i checked as much as i could with a multimeter and such and im to the point where im thinking its a fuel issue or a sensor issue. all of the hardparts seem to be just fine and everything is nice and tight.

[kenmosher]

The fact that the factory boost gauge and the VDO don't match would indicate that more investigation in the VDO hookup would be in order.

Either something is hooked up wrong (is it in a vacuum line with a check valve or something? Like for the charcoal canister?), the VDO or indash gauge are defective, etc ...

Check the plastic tube that is usually used for aftermarket boost gauges ... it's not uncommon at all for it to get pinched or creased in a sharp bend when routing the tube through the firewall and around the engine compartment. If that happens, it'll restrict the reading to the gauge.

[sceric]

ok i went over the plumbing for the boost gauge and just went ahead and replace it all from the t to the gauge. it still has the same deal as before. i wasnt really concerned about what the stock one said because it says at idle it has like three pounds of boost. lots of little things wrong with the car because it did sit for five years. i pulled the plugs and it has autolites in it and they were gapped to like .042 so i know thats wrong. im hoping maybe it was getting spark blowout. im going to grab a set of ngk or some other brand of nicer plug and gap them correctly and see if that helps. im in the process of trying to find a scantool i can use this weekend so hopefully ill have some more data soon.

[Keller]

AC Delco R43TS gapped at .035 are fine. Don't go for gimmick plugs.

If you show boost at idle, you have problems...

[sceric]

The factory boost gauge doesn't work as it should. The tach doesn't either its lit up all the way across no matter what. The vdo boost gauge doesn't show anything at idle and that's how it should be. I put a set of ngk plugs in it this weekend checked fuel pressure and all fuses. I'm still having the same issue. Only now it starts missing almost at the hit of the throttle. Wtf? When its sitting still it will free rev just fine no hesitation or anything. Going down the road it spits and sputters and won't do anything now. Now what the hell do I do? I've went over it and did spring cleaning its got good gas in it and there's no check engine lights. I'm completely lost.

[Keller]

Which NGK plugs were used?

How old are the coil and ignition module? Are they both AC Delco pieces?

[sceric]

i used the ngk iridium plugs. the coil pack and all appears to be ac delco so it could very well be as old as the car is.

[sceric]

Ok so I put a new mass air meter on the car today and it smoothed out all the spitting and sputtering and nonsense but......................................its still won't make higher boost.

[Keller]

I'd suggest a compression test.

[sceric]

ok pulled a compression test and realized after that i didnt open the throttle body during the compression test so my numbers are low but i got in the 120's across the board.

[kenmosher]

It's probably something in the wastegate system such as:

* Leaking flapper ... crude around the flapper hole or frozen/sticky flapper arm that allows it to remain open

* Oil soaked actuator diaphragm (although I'd expect that to cause run away boost)

* Exhaust leak pre-turbo (you'd hear that though)

* Turbo bearings/bent impeller/turbine melted

If you disconnect the actuator vacuum line and do a quick test ... CAREFULLY get into the throttle with it that way while driving and the boost should shoot up VERY quickly (because you basically are holding the flapper shut with the actuator spring and no signal to open the wastegate).

If that happens, it narrows it down to actuator/plumbing problems. If that doesn't happen, then it becomes more likely to be flapper/actuator problems and/or turbo.

[sceric]

i did something similar to this in disconnecting the waste gate rod and wiring the flapper valve shut. it still wouldnt make more that about 7 pounds of boost. when i had the plugs out last night. all of them looked very white to me and im wondering if its not running out of gas which i suppose would prevent it from boosting anyhigher if the motor wont spin any faster. i set the fuel pressure at around 38lbs with the line off of the regulator. if the in tank filter on the fuel pump is stopped up that would prevent it from getting all the gas it needs. i know i grasping at straws. the impeller on the turbo spins really freely and i checked both sides of it and all the fins look to be in good shape. it seems like all of the hard parts are fine. what is the sensor on the passenger side of the motor on the valve cover with the two connections for vacuum lines?

[kenmosher]

That's scary ... you need to get a fuel pressure gauge on it and tape it to the windshield and see if it rises properly with boost. Should go up 1 psi for each psi from the base reading.

i.e. if base pressure is 43 psi (no vacuum), then at 10 psi of boost, it should be 53 psi.

[sceric]

ok ill do that today in just a few minutes. what do you recommend as a base fuel pressure setting? any ideas on what that sensor is?

[kenmosher]

43-45 psi (WITH NO VACUUM) ... i.e. disconnect the regulator vacuum line so the manifold vacuum isn't in play. Once it's set, reconnect the line and do your test.

The "sensor" is an actuator ... it's the solenoid that opens (to atmosphere) to bleed off boost to the wastegate canister. It's what controls how much boost the wastegate "sees" and how far it opens.

It's a "blind" or "open" algorithm ... i.e. the ECM commands a duty cycle with no idea if it actually does what is intended or not ... there's no feedback.

So, it the solenoid is lazy or plugged or whatever, the ECM has no clue and is fat dumb and happy.

That's one thing to check, now that I think about it ... there's a little "nipple" on the solenoid ... it SHOULD BE OPEN TO AIR (or have a little foam filter on it). It should NOT be plugged or hooked up to any hoses ....

If it is, that's very likely your problem...

[sceric]

ok no the sensor or actuator as it is on the valve cover about halfway back is open and plugged up. im gonna leave in a few mins to head to the house to get the car and put the fuel pressure gauge on it. hopefully i can get some good news be cause this car that was a great deal is turning into a headache but with anything that has sat as long as it has i suppose its to be expected to have some problems with it.

[sceric]

ok so it makes fuel pressure just like its supposed to one pound per psi and its dead on the money. in a delightful new twist its blowing off vacuum hoses now. mostly the ones to the egr valve and also now the one to the fpr as well. what the heck?

[Keller]

Maybe something in the air pathway (leave a rag in it?) or exhaust (clogged catalytic? someone do a potato trick on you?) is blocking things.

[sceric]

it has an exhaust cutout and ive been running thru the exhaust as well as without it doesnt have the converters on it. i went back thru all of the hard piping and didnt find anything. maybe when they put the water pump on it they bumped the cam position sensor around. is there anything i need to unplug before i set the timing?

[kenmosher]

Cam sensor has nothing to do with ignition timing ... it's usually a pretty on/off kind of thing and affects injector timing more than anything else.

Move your boost gauge over onto another line from the top of the plenum. If it's blowing hoses off, good chance there's boost there (more than you think).

[Keller]

Make sure it is not plumbed in behind a check valve.

Helped a guy once who kept blowing head gaskets, but "only could get 10-12 PSI". Looked at the car, and found he had plumbed his boost gauge in wrong, behind one of the inline check valves in the vacuum line plumbing. After I corrected that, we went out for a run with my Turbolink connected. As he slammed the throttle down on the highway, the boost rose...and rose....and rose...it was going over 23 and I was screaming for him to let off. The O2 numbers on Turbolink were sinking like a lead balloon. Deep into the low 700s and below. He was headed into blowing another set.

After I took 8 or 10 cranks out of his wastegate rod, it was much better. He was disappointed it didn't have quite the initial punch, but at least it kept pulling hard, and didn't sound like the Rockettes doing a tap number at full boost. Plus he got to use the same head gaskets for more than a week.

[sceric]

alright guys ive tried everything i know and everything that everyone has suggested. idk. im lost. i know its gonna be something as dumb as the day is long and its prob smacking me in the face i just cant see it. since theres no one in my area that really knows anything about these cars ill just let it sit till i figure something out.