Scan tool reading when measuring boost solenoid %
05-26-2004, 03:06 PM
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Scan tool reading when measuring boost solenoid %
I am trying to figure out why my car is melting my spark plugs and I am using up so much gas. I checked out the tps and the IAC and the coolant sensor and those seem fine. The thing I noticed when I was looking at the data from the scan tool is that the boost sol reading is at 100%. Is this supposed to be the correct reading for the car at idle or is the solenoid stuck open or what? I get this reading from my old solenoid and the new one I bought a half year ago. If this is normal, what else do you think could be my problem? I am attempting to replace the fuel filter but the fittings are all rusted on there and I'm about to strip the nut if I go any further. Thanks
05-26-2004, 04:24 PM
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That'* the correct reading for idle. That'* a 100% duty cycle, full bypass at idle. The number will decrease while driving under boost, linear to the change in the boost gauge.
05-26-2004, 08:34 PM
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Ok so what about the IAC? I did check the reading. When its all warmed up it reads about 44 counts at best. I think it should read between 20-30 counts. Does anyone know if 44 is ok? I know it increases as you step on the gas and at wot it is supposed to be 255.
05-26-2004, 09:29 PM
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During idle, the proper position of the iac pintle is calculated by the pcm based on battery voltage, coolant temp, engine load, and rpm'*. If the rpm'* drop below a specified value, and the throttle plate is closed, the PCM senses a near stall condition. the PCM will then calculate a new IAC pintle valve position to prevent stalls.
If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset.
The IAC resets when the engine is started, runs over 800 RPM, and then turns off.
The position of the IAC pintle valve affects the engine start up and the idle characteristics of the vehicle. If it is open fully, too much air will be allowed into the manifold. This results in a high idle speed along with possible hard starting and lean AFRE. If the valve is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed along with possible hard starting and a rich AFR. If it is stuck part way open, the idle may be high or low, and will not respond to changes in engine load.
If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset.
The IAC resets when the engine is started, runs over 800 RPM, and then turns off.
The position of the IAC pintle valve affects the engine start up and the idle characteristics of the vehicle. If it is open fully, too much air will be allowed into the manifold. This results in a high idle speed along with possible hard starting and lean AFRE. If the valve is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed along with possible hard starting and a rich AFR. If it is stuck part way open, the idle may be high or low, and will not respond to changes in engine load.
The scan tool displays the IAC position in counts. Zero counts indicates the PCM is commanding the IAC to be driven all the way into a fully seated position. This is usually caused bya vacuum leak. The higher the number of counts, the more air is being commanded to bypass the IAC pintle.
I have the book open to the IAC diagnostics. What are your EXACT symptoms causing you to suspect he IAC?
05-29-2004, 03:34 PM
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I am not suspecting it specifically. Everything right now is suspect. My car stumles on low rpm when in 4th gear. It feels like im on a bumpy road or something. My spark plugs are getting eaten up. those little metal electrodes were missing on the number 5 and the 4 cylinders. they are regular ac delco plugs. I am getting horrible gas mileage. I did finally replace the fuel filter and had to splice a new line in with the old rusty one. Hopefully the filter helps a bit. Basically its just bad gas mileage and low rpm stumbling. What do you think. The tps seems fine, the coolant sensor is fine, the boost solenoid is fine. The IAC seems fine since my car idles fine. I have yet to specifically check the MAF and the MAP sensors. What else am I missing?! thanks
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