Boost lowers after awhile. Any ideas?

[BuffaloGuy]

I've got a boost master and have it set so I get about 14# boost with a load at 2500rpm, full throttle. Works great.

Lately, after the motor is working for awhile I have less boost. Even not under load, just empty cruising down the road.

I have visually checked my boost gauge supply line but can't see anything wrong. I do have a little more oil the usuall in the intake side of the turbo coming from the CDR. Nothing huge but more than before.

Any ideas?
Ken

[cruzer]

My CDR was letting more oil than normal on the intake side of turbo. I replaced it and it fixed the problem. As for the Turbo master problem I guess I don't understand the problem.
On mine I either have to have a load and have a sustained pull to maintain 14lbs or upon hard accelleration, but when I lift boost goes down.
On the flat empty it runs 3-5 psi. Don't know if this helps.

[DogDiesel]

I tried the turbo master controller and I had a home-made controller, which worked better for 13-14 PSI boost. Same thing, tow and when she got hot, less boost. However, if I ran 10-12 and not higher, it held fine. 14 PSI is OK empty, but there is no where for the heat to go on the spring, and it changes oh hard pulls. Bet, you could let 'er cool down and you had all the boost back.
I now run the Peninsular performance turbo, and my average pull boost is 8-12, with peaks at 13-14 wound tight.
Maybe in retrospect the 14-19 I was running with the GM8 was too much.
Wayne

[BuffaloGuy]

Thanks for the replies guys. Just to clarify, when the motor is just warmed up I have more boost than when it is totally warm/hot. This is true even for cruising empty. I used to get 7 psi at 70 mph warm or hot, it didn't matter. Now I get 7 psi warm and 4-5 psi fully warmed/hot.

I think dogdiesel may have hit it on the head. The spring may loose some of it's strength when it gets beyond a certain temp. This temper weakness may be showing itself even more after time since the spring may be getting retempered every heat cool cycle.

I think I'll call Mr. Heath and see what he says.
Thanks Guys!
Ken

[GMCfourX4]

I may be wrong, but if you're not running an intercooler, the lesser boost is more likely due to the IP backing off on the fuel (it starts lowering the amount of fuel injected after IAT temps get over 220* or so...IIRC. Once you have less fuel, you have lower EGTs (which was the whole purpose of GM doing this, I think) and you will have less volume in the exhaust, hence less air/volume to spin the turbo. If you were able to watch the fuel and IAT values with a TechII you would probably see this.

-Chris

[BuffaloGuy]

GMC4X4, Thanks but I don't think that applies to my rig since it is a mechanical IP. Am I right?

[GARY PAGE]

I must have a good turbo. Mine had to be de-tuned from the boost master instructions. It hits 16 on a romp and setles down to 14 on a strong pull. If I opened up the boost master no telling what she would do. Part of the seceret may be after market down pipe, no cat and a straight 3 1/2 pipe all the way back, no muffler. On a level road at 65 I run 5 to 6 PSI. It's not loud to me; but my hearing is not what it use to be!

[turbovair]

Gotta jump in here...
I recently installed a boost gage(1-15). Its the first time I've actually seen the boost in my truck in 115,000 miles.The system is stock.Im running empty. The only time I see any boost is under demand, such as hard acceleration.Gentle acceleration produces little to no boost.Under hard acceleration it maxes at about 8-9 and begins to fall off as acceleration begins to stabilize. At constant speed..50,60,70 MPH I have basically no boost(needle on peg)Only if I increase throttle do I see a slight increase, and then it returns to zero(peg).Does this seem normal? Should I have a couple pounds @cruise? FYI- EGT @ 225-250 at idle, 400-425 @60 MPH, 2000 RPM, 4:10 ratio, empty.

[kowsoc]

Turbovair,

Yes you should have some boost at cruise. Actually with the truck parked in neutral, revved to 2000 RPM I get about 1 psi.....50MPH cruise about 1psi....65MPH about 4-5 psi empty. I see about 9 psi peak.
At least your boost comes in under load, but if your concerned about fuel economy the more boost during cruise the better your mpg will be.

[moondoggie]

Good Day!

I only show ≈ 1 PSI boost at 65 mph cruise on my 95 pickup. NOT QUESTIONING BUT ASKING: How can more boost increase mpg? If there's no black smoke, I thought that meant complete combustion & max mpg. TIA for your answer.

Blessings!

Brian Johnson, #5044

[turbovair]

Kowsoc,
When you say 1 PSI boost, do you mean one increment above the peg? My gage begins at 1 and thats where the needle rests on the peg.The needle rests on the peg at atmospheric pressure.Should I show 2 PSI? That would be 1 PSI above atmospheric pressure. Hope I'm not making too much out of this.

[kowsoc]

Well internal combustion engines are about 30% efficient. Add a turbo and it is about 40%. The turbo basically uses the heat energy and pressure of the exhaust gases to force fresh air into the intake tract. Without the turbo this energy is just wasted out the exhaust pipe. More oxygen from more air being compressed into the engine gives more power and fuel economy for the same give amount of fuel. If your wastegate is dumping boost then it is also dumping efficiency.

Sorry for rambling...I'm not a scientist.. but when all is well I believe your boost should be between 2-3 psi at 60 mph.