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boost solenoid

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rerrico

New Member
Joined
Feb 5, 2003
Messages
7
Car overboosting. Seems that the boost solenoid it not doing its job. Traced problem to the gound wire. Not grounding. checked everything. it seems that the ecm is not gradually grounding the boost soleoind like it should. My question is what makes the ECM do this? Thier must be a sensor or something that tells the computer to react to the boost.
 
if your car is overboosting...sometimes the orifices in the vacuum lines going to the turbo wastegate and turbo are not according to correct specs...it might be too small of a hole...check that...also what the wastegate (boost) solenoid does is it sends pulses to the ECM letting the computer know how much the solenoid is bleeding boost to control it...the ECM and chip can only control very little of your boosting conditions...most of it has to do with the wastegate rod setting, wastegate puck hole, etc....
 
The ECM does NOT react to boost, since it has no boost sensor. It will react to knock, but that is not the same as boost. The chip has a boost program built in. At WOT, it opens the solenoid to bleed pressure off of the wastegate actuator. If the solenoid is stuck open, then it would overboost. If there is a bad ground, the solenoid won't open, and you will only have the boost that the initial setting of the wastegate actuator will allow, usually about 12 lbs. So, if you have a SHORT to ground, then you might have overboost from an electrical problem. But a bad ground will lower the boost. You can get overboost from leaks in the rubber lines connected to the boost solenoid, or as mentioned, it the orifice in the lines is sized wrong or oriente wrong.
 
Thanks for the replies. The hoses and Y are new from GM and checked where each goes. The pink to the solenoid is hot once the key is on and loops through the purple all the way back to the ECM. No short any where. Lowered the boost considerably. The performance and spool up where horrible and the car still overboosted once it got there. Only thing I did not do is measure the ground as the car spools up to see if the ECM is reacting. But seems as if solenoid stays open all the time. Again, the car was running perfect for a while at the same setteings with no overboost until I raced a car. With one hard downshift, this all started. I set up tuner and it was fine, although I thought the car felt better before at the same settings. This is GNX 509
 
How exactly does the chip control the solenoid if it doesnt know how much to pulse? (Based on the amount of boost)
 
Originally posted by GrndNatnl
How exactly does the chip control the solenoid if it doesnt know how much to pulse? (Based on the amount of boost)

It is called a WAG (Wild Assed Guess) with a knock sensor to tell it when it guessed wrong. I believe it is actually a factor of LV8(load) and RPM's and 3rd/4th gear switch with it being backed off when knock is sensed. I am sure the chip guru's can be more exact but that is close enough unless you plan to try to trick it somehow to attempt higher boost at a certain point.
 
The ECM "knows" what the baseline boost is, then adds additional boost when appropriate, according the chip maker. On a Thrasher, for example, the chip puts in more boost in first and second gears, where the engine load is lower, and detonation less likely, then backs off in third and fourth. There are a lot of tuners who bypass the solenoid, and just use the wastegate, but that gives up some options, like the first/second gear increase. The wastegate, by itself, reacts only to the amount of boost. The wastegate solenoid allows the ECM to add to the boost, when load, temperature, MAF readings, etc, allow more.
 
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