weird problem .... what could be wrong

[earthrealm]

in my 05 v6 truck i notice when am stationary with gear in d, but my foot on the brake pedal, i observe a periodic throbbing on the brake pedal, timed it at 6-8 secs interval...and i just installed an ultraguage, so i observed some other things....the ecm voltage drops from about 13.2v to 12.90volts and the engine absolute load % increases from 16.5% to 18%, and these flunctuations are in sync with the throbbing on the brake pedal and lasts about 1sec.

am curious what this means, bought the truck abt 15months ago with 116k miles, now its about 125k.....drives fairly ok...no codes

 

[HokieRunner]

in my 05 v6 truck i notice when am stationary with gear in d, but my foot on the brake pedal, i observe a periodic throbbing on the brake pedal, timed it at 6-8 secs interval...and i just installed an ultraguage, so i observed some other things....the ecm voltage drops from about 13.2v to 12.90volts and the engine absolute load % increases from 16.5% to 18%, and these flunctuations are in sync with the throbbing on the brake pedal and lasts about 1sec.

am curious what this means, bought the truck abt 15months ago with 116k miles, now its about 125k.....drives fairly ok...no codes

Interesting issue. Could be something with the brake booster? Does this occur everytime you are stationary or just intermittently?

 

[cloh09]

Could be the a/c or defrost motor kicking in. Do the rpm's go up slightly? Does it want to go when your foot is on the brake? If that's the case, it's normal.

 

[541joseph]

I'm thinking you have something going on with the abs system. I'd pull the fuse and see if it continues and if it does its not your abs

 

[earthrealm]

Interesting issue. Could be something with the brake booster? Does this occur everytime you are stationary or just intermittently?

it haappens everytime am stationry in drive with my foot on the brake. its not the aa/c, cos it happens with the a/c off or on, the rpm jumps a tad say about 50 to 100 increase.
reaally puzzling...anad u can feel the slight pulse/tremor every 7secs with ur foot on the brake pedal

 

[JB.]

in my 05 v6 truck i notice when am stationary with gear in d, but my foot on the brake pedal, i observe a periodic throbbing on the brake pedal, timed it at 6-8 secs interval...and i just installed an ultraguage, so i observed some other things....the ecm voltage drops from about 13.2v to 12.90volts and the engine absolute load % increases from 16.5% to 18%, and these flunctuations are in sync with the throbbing on the brake pedal and lasts about 1sec.

am curious what this means, bought the truck abt 15months ago with 116k miles, now its about 125k.....drives fairly ok...no codes

Pop your hood and watch and listen to the accumulator on the Hydraboost brake unit. It's a silver canister on the left side of the unit. I'm guessing it vibrates at the same intervals as the feeling in your brake pedal.

If this is the case, then you can decide whether you want to do anything about it. Mine has been doing this at a rate of about 5 cycles a minute for a very long time (years) so it doesn't appear to mean anything like imminent failure.

 

[earthrealm]

thanks...guesss this makes me breathe a lil easier, was thinking the symptoms is related to the infamous master cylinder failure.

noticed on a quiet night that the slight pulsing on the brake pedal is in sync with a whirling/pumping sound i observed from the engine bay.probablly the hydroboost pump actuating, am juist wondering why the slight pulsing feeling is felt on some trucks n absent on others?.........

 

[Kmvreter]

Pop your hood and watch and listen to the accumulator on the Hydraboost brake unit...

... was thinking the symptoms is related to the infamous master cylinder failure...

The brake booster failure is the same thing as infamous master cylinder failure. All parts of the same unit. Rapid cycling means it's on the way out. You just can't predict when.

 

[earthrealm]

am wondering if this problem/issue is any way related to improper bleeding technique after a stuck caliper service...............i have a pal whose master cylinder failed days after a recent caliper service n bleeding,

so my question is _ does the 4runner require a special procedure for bleeding the brakes, i dont know if its just me or something but the pulsing seem to have increased after a recent caliper service

 

[Kmvreter]

am wondering if this problem/issue is any way related to improper bleeding technique after a stuck caliper service...

does the 4runner require a special procedure for bleeding the brakes, i dont know if its just me or something but the pulsing seem to have increased after a recent caliper service

Yes, if air was allowed to get up into the master cylinder. This usually doesn't happen on a caliper service but it might.

Search for threads on "brake bleeding" and "accumulator". [MENTION=66389]BlackWorksInc[/MENTION] has good experience with it as a tech.

I've described something that has worked for me in one of those threads.
See the attached FSM pages. I have learned that at step 2.(a)&(b) I do those 40 pedal cycles (with the ignition off) very slowly, pushing on then holding 10 seconds, then letting off and waiting 10 seconds (3 full cycles per minute at the most.) This takes a bit of time but it works for me. Time how often your pump is cycling now and then again after trying this. You should get to the 30 or 40 second pump cycle as noted in the FSM procedure. Repeat if necessary.

 

[BlackWorksInc]

You can try some of the methods shown to see if you can bleed the master cylinder unit, but it may not go that easy. As I was explaining to some members today on our trip to Hollister; the unit the 4Runners (4th Gen+) use is finicky, you can typically bleed it like you would any car if you don't get air into the unit. Once air gets in it can be tricky to get out, even with the factory scantool it can take multiple tries to do properly as you need to now actuate the entire ABS solenoid pack in an attempt to get the air pocket out of the system.

Bottom line, try the DIY methods and if that still doesn't fix it, try having a friend with a TIS TechStream, or a dealer bleed it.

 

[earthrealm]

wow!.thanks guys....getting hairier by the day!..ignorance is sure bliss
will give it a shot n see.......pheewwww

 

[earthrealm]

update : wanted to confirm if really my truck is abt developing the infamous MC failure

i turned the ignition to ON position, and observed that the pump came on for like 10secs and then shut off....... i then wanted to try out the 40 pumps procedure with the ignition off, @ about the 10th pump, the brake pedal went flat to the floor, i still continued to about 35 pumps, then i turned the ignition to ON, the pump kicked in for about 20secs and then shut off and the pedal returned to normal

also observed that the pumps kick in for about 7secs whenever i step on the brakes in drive or park,........n the pumps keep on actuating every 7 to 10secs if i still keep my foot on the braakes......................

is all this normal or more confirmation that i hv air in my system/ the hydro boost assy is on its way out?

 

[earthrealm]

UPDATE::

SO sadly today @ 130200 miles, my brake system/MC failed......just came back from a 20mile round trip during my luch break, car was ok, parked the car...got back to work, 3 hrs later i enter the truck to drive home, as soon as i start the car and engage gear, i hear a high pitched warning sound and all the lights on my dash light up, brakes rare pretty useless, gotta stomp on them with all my might b4 the truck stops.....

i have had the buzzing/pulsing brake pedal issue for 2 yrs now, so i guess it has finally crapped out, dont have the $$$$$s for a new MC/brake system, so i intend to pick a used unit from ebay, and go from there...........need to figure out how to manually bleed the brakes after swapping out the bad unit [MENTION=66389]BlackWorksInc[/MENTION] i guess anyone with a similar pulsing brake issue, shoud prep for the day it craps out