Low boast

[victor50]

98 6.5 3500 HD. Have replaced boast solinoid on valve cover. Vacuum pump and turbo. Max boast under load is 4 Lbs. I give up does anyone make a mechanical control that fits this truck? Thanks for help!

[Robyn]

HI
Welcome to TDP :):)

There are several things that can cause low boost pressure.
You have eliminated some key ones, but one big issue that comes to mind is the exhaust system.

How many miles on the rig ???

Has the CAT/soot trap ever been changed or removed entirely ???

A plugged CAT will choke things up to the point that turbo can't spin fast enough to do much.

YES
There are things that can be done to get the boost up.

A mechanical waste gate controller is available (Called a turbo master)

In order for these to work properly you will need to get the ECM reflashed with the proper software.

First off, make sure the exhaust system is free flowing.

A good 3-1/2 to 4 inch system from the downpipe back is needed.
The original CAT can be removed if you are not having to deal with emissions testing.

Once the exhaust is free flowing the rest is a snap.

Adding performance goodies to a plugged stock system will do no good at all.


Let us know what the truck has had done to it.

Robyn

[victor50]

Truck has 286k miles,186K on present motor. 3 1/2 straight thru exhaust. Runs great uses no oil. Truck is heavy with service body and tools. Pulls balers regular at 4 to 6 K Lbs.

[Robyn]

Great.

With the 3-1/2 pipe there is little issue with restriction.


Make sure you are getting about 22"of vacuum at the waste gate actuator.

Make sure the waste gate move freely with the engine off.

You should see 26" vacuum at the vacuum pump itself.

If all you are seeing is 4-5 psi boost then you are actually not too far off of stock settings.

Get the ECM FLASHED to use a mechanic waste gate control and push the fuel up a bit.

Without the ECM flash the thing will scream and defuel when the boost hits about 8 or so.

Set the mechanical gate control so under a hard pull the thing yields 10 psi no more.

Be sure you have an exhaust gas temp meter in the beast as well..
No more than 1000F at the outlet of the LH manifold under a hard pull.

Do not install the EGT probe after the turbo as it is way too cool by then.

1000F at the ports is max temp.

Going up into the land beyond will melt things in these engines if allowed to run more than a few seconds at high temps.


A good reprogrammed ECM and 10 psi boost will get about all the 6.5 can live with.


Good luck

Robyn

[JohnC]

Make sure the hoses on the vacuum valve aren't reversed. It's been a while, but I think the vacuum pump connects to the port with the restrictor in it and the wastegate actuator connects to the unrestricted port.