Kingman Posted November 13, 2008 Share Posted November 13, 2008 (edited) It's always done this since I bought it, but at idle, in park or drive, if I push the brake pedal to the floor, the engine stumbles and sputters for a few seconds or until I release the brake pedal. Sometimes, it will keep stumbling for a few seconds afterwords. It has never done it so badly as to kill the engine, just enough to lower the RPM's and make the engine sound like it's missing. I know the brakes run off vacuum from the engine, but is this normal? Is this a tell-tale sign of something? Edited November 13, 2008 by kingman92010 Link to comment Share on other sites More sharing options...
bitemedoughboy.com Posted November 13, 2008 Share Posted November 13, 2008 It's always done this since I bought it, but at idle, in park or drive, if I push the brake pedal to the floor, the engine stumbles and sputters for a few seconds or until I release the brake pedal. Sometimes, it will keep stumbling for a few seconds afterwords.It has never done it so badly as to kill the engine, just enough to lower the RPM's and make the engine sound like it's missing. I know the brakes run off vacuum from the engine, but is this normal? Is this a tell-tale sign of something? your brake booster has got a leak in it.... Link to comment Share on other sites More sharing options...
Kingman Posted November 13, 2008 Author Share Posted November 13, 2008 your brake booster has got a leak in it.... Wouldn't I be losing brake fluid too though? Link to comment Share on other sites More sharing options...
unccpathfinder Posted November 13, 2008 Share Posted November 13, 2008 Brake booster is pressurized and assists the MC somehow...not really sure how it all works...I had a friend who actually had a bad MC and the weep hole got clogged so over time it filled the BB completely with brake fluid and he became a skeeter fogger. It took me about 30 mins to figure it out b/c i knew it wasnt coolant or oil and i started pulling vaccum lines and pulled the one off the booster and the truck stopped running like ass and stopped smoking like hell If you end up needing/wanting a replacement PM me I've got 1 I can sell you at a good price (really good compared to new) Link to comment Share on other sites More sharing options...
MY1PATH Posted November 13, 2008 Share Posted November 13, 2008 the the oil in the MC and the brake booster are totally independant. brake booster is tapered on the inside wide dowards the firewall and narrow towards the mc. there its a disc inside that rests against the firewall side untill you push the brake as the brake is pressed the disc moves to the smaller side and the gap arrount the disc becomes smaller thus increasing the vaccum and helping you push the peadal farther inward. lastly, all this action comes out the Booster thru a rod that presses into the MC. Link to comment Share on other sites More sharing options...
Indigent Posted November 13, 2008 Share Posted November 13, 2008 Could be the idle air control valve. Disconnect the plug to the iacv solenoid and see if it still happens. You can check the resistance of the solenoid with a multimeter too. It should read about 80 ohms IIRC. hope this helps, indigent. Link to comment Share on other sites More sharing options...
Kingman Posted November 13, 2008 Author Share Posted November 13, 2008 Could be the idle air control valve. Disconnect the plug to the iacv solenoid and see if it still happens. You can check the resistance of the solenoid with a multimeter too. It should read about 80 ohms IIRC. hope this helps, indigent. How is that connected to the brake system? Link to comment Share on other sites More sharing options...
GrimGreg Posted November 13, 2008 Share Posted November 13, 2008 How is that connected to the brake system? The vaccum line. Link to comment Share on other sites More sharing options...
Indigent Posted November 15, 2008 Share Posted November 15, 2008 When you press the brake pedal, the brake boost assist puts an extra load on the engine. The ecu senses the load and adjusts the idle air control valve to compensate the idle for the greater load. The IACV solenoid isn't just for the brake, it is for any circumstance that puts extra load on the engine. For example, when you turn on the AC, it puts extra load on the engine, and the IACV opens up more to adjust for that condition. The brake booster runs off intake manifold pressure, which affects the ammount of air that is moving through the intake plenum. The MAF interprets that airflow change as greater engine load, which gets compensated for by the IACV. hope this helps, indigent. Link to comment Share on other sites More sharing options...
Kingman Posted November 15, 2008 Author Share Posted November 15, 2008 When you press the brake pedal, the brake boost assist puts an extra load on the engine. The ecu senses the load and adjusts the idle air control valve to compensate the idle for the greater load. The IACV solenoid isn't just for the brake, it is for any circumstance that puts extra load on the engine. For example, when you turn on the AC, it puts extra load on the engine, and the IACV opens up more to adjust for that condition.The brake booster runs off intake manifold pressure, which affects the ammount of air that is moving through the intake plenum. The MAF interprets that airflow change as greater engine load, which gets compensated for by the IACV. hope this helps, indigent. Thanks for clearing that up! Could this be ruled out as the problem if the IACV still adjusts for everything else, ie. the rear defrost and air conditioning? Link to comment Share on other sites More sharing options...
Indigent Posted November 16, 2008 Share Posted November 16, 2008 Thanks for clearing that up! Could this be ruled out as the problem if the IACV still adjusts for everything else, ie. the rear defrost and air conditioning? Check out page EF & EC-20. It explains everything that the IACV compensates for. hope this helps, Indigent. Link to comment Share on other sites More sharing options...
Kingman Posted November 16, 2008 Author Share Posted November 16, 2008 Check out page EF & EC-20. It explains everything that the IACV compensates for. hope this helps, Indigent. In the Haynes manual? Link to comment Share on other sites More sharing options...
Precise1 Posted November 17, 2008 Share Posted November 17, 2008 Sounds like the FSM... B Link to comment Share on other sites More sharing options...
bitemedoughboy.com Posted November 17, 2008 Share Posted November 17, 2008 When you press the brake pedal, the brake boost assist puts an extra load on the engine. The ecu senses the load and adjusts the idle air control valve to compensate the idle for the greater load. The IACV solenoid isn't just for the brake, it is for any circumstance that puts extra load on the engine. For example, when you turn on the AC, it puts extra load on the engine, and the IACV opens up more to adjust for that condition.The brake booster runs off intake manifold pressure, which affects the ammount of air that is moving through the intake plenum. The MAF interprets that airflow change as greater engine load, which gets compensated for by the IACV. hope this helps, indigent. correct me if im wrong, but doesnt the iacv compensate for electrical loads? ie heater blower, head lights, and a/c clutch.... its not triggered by vacuum just the electrical signal from those devices. Link to comment Share on other sites More sharing options...
yozsi Posted November 17, 2008 Share Posted November 17, 2008 oh brother... what a wealth of useless info. The brake booster works off of the vaccum in the intake manifold, if the booster has a leak it will cause the engine to miss and run lean because it is sucking air in from the leak in the booster thus bypassing the maf sensor and throttle body. Link to comment Share on other sites More sharing options...
Indigent Posted November 17, 2008 Share Posted November 17, 2008 correct me if im wrong, but doesnt the iacv compensate for electrical loads? ie heater blower, head lights, and a/c clutch.... its not triggered by vacuum just the electrical signal from those devices. We are saying the same thing. Yes it is responding to the electrical signal from various sensors, the MAF included. When the brake pedal is applied, the booster is using air from the intake manifold, which changes the air flow inside the intake. The MAF sees that change in flow as an increased engine load, and the ECU tells the IACV to open a bit more to compensate. hope this helps, indigent. Link to comment Share on other sites More sharing options...
Kingman Posted November 17, 2008 Author Share Posted November 17, 2008 So its suffice to say I need a new brake booster sometime down the road...? Link to comment Share on other sites More sharing options...
GrimGreg Posted November 18, 2008 Share Posted November 18, 2008 So its suffice to say I need a new brake booster sometime down the road...? Not neccisarily, could be a bad hose or connection that is leaking, or the iacv, etc. Gotta poke around and check stuff. Link to comment Share on other sites More sharing options...
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