Too much boost... stock?

[paulj31]

I'm pegging 15psi boost stock!
The only problem is the SES comes on and dumps the waste gate ( DTC 78), no reset until I turn key off and restart. All this with no load, just lots of pedal up hill. I get 5psi+ boost just cruising.
I have replaced the waste gate solenoid and it

[patrick m.]

might need to check the boost sensor with a scan tool to make sure it changes readings as the boost guage changes.
some electronic failures dont seem like faults to the computer, so no code is set.
the computer should be self protected from shorted solenoids,,,,,but nothing is impossible.

[whatnot]

It sounds like you have the vacuum lines backwards on the wastegate solenoid.

[Barry Nave]

With JK Big Chip the boost sounds right on.
When SES comes on at a hard pull and lifting foot does the light go out and then you can get back into the pedal?
Vac all seem's normal
My truck will also do this though only at full pedal. By then I'm getting up to 1200* EGT.

[ 11-28-2003, 02:12 AM: Message edited by: Bnave95 ]

[paulj31]

Patrick M: I wish I had a Tech I in my toolbox or I would have checked already. It

[paulj31]

O.K. Here is what I have nailed down so far. First I tapped the vacuum line after the waste gate solenoid and ran with my thumb on the end. When boost was up around 10 psi I bleed some vacuum and bingo, waste gate opened and boost dropped. Can

[gmctd]

Three ways this can happen -
The wastegate actuator on the turbo is hosed directly to vacuum, bypassing the solenoid
Or - no power to the solenoid, applies full vacuum
Or - PCM, or connection to pcm, is faulty, applies full vacuum

PCM bleeds off vacuum by pulsing the solenoid, allowing exhaust pressure to blow open the wastegate, dumping turbine rpm, reducing boost.
Solenoid power is thru the 5 amp Solenoid Fuse.

[paulj31]

GMCTD: I am reading 14+ volts at the 2 contacts to the solenoid. Is this possible? I thought this was a 5 volt system. Where would I find the solenoid fuse?

[Barry Nave]

If the silly node is OK then I would start with all ground's and Elect. connection.
Just a thought :confused:
I was reading the wrong post thinking you had a JK chip

[gmctd]

The EGR and Boost solenoids are 12v powered - as you are reading voltage above 12v, the Solenoid fuse is not open. It should be in the Fuse Panel, probably in the lower dash, left of the steering column.

With engine running, solenoid term A, Lite Blue\black stripe, should have full battery voltage (+13.8 or so); second term B, Yellow, should read less, as it is being constantly pulsed to ground by the PCM. Narrow pulses = max boost, wide pulses = min boost.

Does it dump boost when DTC-78 is set, or just set the code?
If the PCM dumps boost, vacuum to the wastegate will drop.
If the PCM pulls fuel, the vacuum may remain same from some defect, but power will fall off.

I didn't get whether you were original owner or not, but some early "chips" held boost levels while ignoring flags for DTC-78. Which, of course, resulted in DTC-78 during most modes of driving. Your Sub was not 'previously owned', by any chance?

[ 11-28-2003, 05:08 PM: Message edited by: gmctd ]

[whatnot]

If you start the engine then shut it off, if there is still vacuum at the wastegate actuator then the lines are reversed.
From what you said, the lines are reversed and you have a low boost problem, not a high boost problem.
Here is a picture of the correct way the lines go.
http://www.rsixray.com/images/stuff/solenoids.jpg

[jimcreek]

WHEN I HAD A PROBBLEM WITH WASTE GATE NOT WORKING IT TURNED OUT TO BE THE BOST SENSOR.
BUT FIRST I TESTED SOLENOID, BATERY VOLTAGE ON ONE SIDE GROUND THROUGH ECM, (A3 ON CONNECTOR).
FUSE UNDER HOOD IN FUSE BOX I CANT REMEMBER WHICH FUSE

[paulj31]

Gmctd: I am not the original owner. I have had the truck nearly 2 years and prior to the rebuild I don

[gmctd]

DTC-78 dumps boost vacuum indicates the PCM is controlling solenoid.

Whatnot's picture (excellent! thanks) shows vacuum pump source connected to the radiator side of the wastegate solenoid (normally green dot), wastegate line connected to the firewall side. Rest of stuff is EGR solenoids - 2500 series may not have those.

Testing solenoid is easy. Unplug PCM connector.
Connect solenoid term A to battery.
With engine running, vacuum gage connected to wastegate actuator on turbo, ground pin B.
Should dump vacuum, same as DTC-78.

You've probably disconnected the alarm-controlled starter wiring, usually large violet or large orange, or ignition feed, usually large red.
Any of those colors would be cut and spliced into the alarm system.

Don,t know how to tell "chip" origin - GM used blue "carriers" for a long time.
Possibly eprom would be labeled with aftermarket copyright?

IIRC, the PCM bar code label has eprom 4-digit code and 4 letter checksum code on it.

Edited for mis-info redface.gif

[ 11-28-2003, 08:06 PM: Message edited by: gmctd ]

[paulj31]

I guess I will be under the hood and under the dash (I hate that part) the better part of today going bug eyed tracing wires. Any concerns with going the TM route if I can't crack this one?

[gmctd]

If it gets really involved under the inst panel, remove the driver's seat - 4 bolts - for laying- down-on-your-back room. :cool:

[paulj31]

Well, I got it started. Thanks Gmctd, it was the large violet wire they intercepted.

I have jumped the solenoid as you suggested with the vacuum line to the waste gate connected to the front inlet with the metal orifice in the solenoid. When I put power to it the vacuum jumped over 20, stayed at 15 with no power. When I reversed the vacuum connection with power I had 15 and it was dumping with no power. Seems Whatnot may be correct, just something screwy in my system. I could achieve vacuum only when jumping the solenoid, not with the connector attached. I am reading 14 volts at the connector but it doesn

[patrick m.]

PCM unplugged, solenoid unplugged, measure resistance on yellow wire from noid to ECM (as you said connector A, terminal 3).
should get very low resistance---.5 ohms at the most.
Also should get very high resistance to ground.
If wire shows no short to ground, and normal resistance level (end to end). problem may very well be ECM

[paulj31]

O.K., what I have learned so far is that if the waste gate solenoid is good (guessing the 3 of mine are since all react identically) then no vacuum should be present when electrical connector is removed. If the vacuum lines are crossed with good solenoid and the connector is removed then the vacuum reading at actuator will read approx. 15psi. as if normal. Just like tie-wiring actuator when things go wrong but a lot easier if I am interpreting this correct (may also work with bad solenoid but not sure). Seems to be some confusion over correct routing of the vacuum lines, hopes this post helps others. Any thoughts?

So apparently I do not have "too much boost stock", just got my vacuum lines crossed. Way to go Whatnot, if it wasn