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Another 'strange stall' problem.....

BigBen

BigBen

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Ok, this one's got me stumped and I don't even know where to start:

1995 Yukon with stock engine, etc 281,000 miles.

On the way home yesterday after driving 1.5 hours I stopped at a stop sign. As I lifted my foot off the brake the truck cut out and then surged for a moment before returning to normal operation. (almost felt like when an engine diesels after you shut it down.)

I thought nothing of it because things went back to normal and I kept driving. Everything was fine for another 15 miles.

About 1 mile from home it did it again right as I released the brakes.

Coasting down the next road it cut out for a moment and then came back on.

Once in the driveway it was running very roughly and eventually died.
I put it in park and started it up. As soon as I touched the brake, it died.
Tried it again, it died. Once more, it died.

Let it sit for a while and checked for any error codes, none in the computer.

A half hour later I went out to check on it and the thing started and acted like everything was normal.


The thing may be old, but it's been running great and is well cared for.
Recent repairs that may or may not be significant:

New Brake Booster (diaphram leak) a couple months ago.
New AC distributor (with all internals) and plugs within the last 10,000 miles.
Wires have less than 30,000 miles on them.

Like I mentioned, the thing is in great shape for its age and I cannot, for the life of me, figure out how pushing the brake pedal in can kill an engine like that.

I hope someone's got some ideas here. I'll answer any questions as they come up.

Thanks!

-Ben


One last note: I did notice yesterday that the 'voltage' guage seems a little low. The battery is decent and less than a year old. Any chance the alternator is involved here? (100,000 miles on it)
 
sounds like a situation with the brake booster leaking again.

I know you said its new, but something isnt right...

probably best to put a vacuum gauge on it, and watch the gauge with engine running messing with break like you were and see what it does... if you loose all vacuum pressure you know what your prob is (again)...

New parts arent always good parts (especially now adays!).
 
Had this problem with a customers escalade.Would cut out and die or just sputter like it wanted to die out with no codes.Ended up being the wiring harness was contacting the front drive shaft and rubbed through.Was a simple fix just had to repair some wires and tie the harness back.
 
Well, so far no luck.

There were no vacuum problems while I was messing with the brake pedal the last few times I had the truck started and was messing with it. I can't find my vacuum gage right now, but I'll borrow one tomorrow and see what, if anything, changes when I hit the brakes.

I can tell you that after I shut the truck off the booster holds vacuum and I can cycle the brakes a couple times before the boost is lost. My guess is that if it will hold that vacuum, it isn't bad enough of a leak to make the engine cut out suddenly.

I've traced the wiring harnesses I could find and haven't found a rubbing spot yet.

Still scratching my head on this one.......
 
FWIW: I did also run a multi-meter on the battery while I was testing the truck.

Truck off: about 12.2 volts.
Idle with all accessories off: 13.6
Idle with all accessories on: 12.8 to 13.0 volts.

Is it just me, or do these seem a little low.
The multi meter confirms that what I saw running down the freeway was more like a voltage of 12v and not 14v like I think it's supposed to have.

-Ben
 
Yep, too low. Fast idle and above with medium load and a charged battery, I like 14.5. Some alts are marginal for their use and cannot hold that with everything turned on at idle.
Some won't do it at speed.
But that is just factory cutting corners. Normally its 14.5 all the way.

As for your cutting out problem, take a hard look at your brake pedal arm. Make sure it is not hitting a wire or something under the dash. If you see any wires close enough for it to touch, crank it up and grab and shake them to see if one is loose.
Also look at everything it actuates.
Brake pedals do a lot more than apply brakes these days.
They turn on brake lights, cancel cruise control, release gearshifts, sometimes release emergency brakes.
Any of those functions might require a switch or vacuum switch that might cause problems.

Also, examine your EGR valve. A lot of what you are describing might be caused by it sticking open slightly or opening when it shouldn't.
 
A friend I know had a stoplight switch go bad,and it caused the torque converter clutch to apply when it should have unlocked it,at stop lights!//only did it once in a while,made it hard to diagnose,the other shops who worked on the truck said the tranny was probably going out!....somtimes the truck stalled dead like you forgot to put in the clutch if it were a manual trans,other times it would almost quit,then the converter unlocked just before it stalled and the engine "recovered",and it didn't do it again until you stepped on the brake pedal--but sometimes it wouldn't act up at all for days...
 
Well, that alternator is consistently inconsistent.
Went out today and it gave me:

12.2 volts to start
14.5 with no accessories running at idle.
13.7 with everything on at idle.

I've had it, so I swapped back in the old alternator that I took out several years ago. It was perfectly fine, but I preventively replaced it for a caribou trip to quebec.

Swapped in Alt:
12.1 volts at start.
14.9 at idle / no acc.
14.0 at idle with accessories.

One other thing, the original was a 105 amp, the one in the truck was a 100 amp.
We'll see if that helps.

Along the other suggestions:

I used my little vacuum pump on the brake booster and it held vacuum.

I checked for any rubbing wires. None.
The brake switch moves slightly up at the top when the pedal moves, but I couldn't get anything to cut out.

EGR was replaced a while back and I checked it today. Moving smoothly.

Strangely enough, the damn thing wont repeat the failure now that I'm trying to fix it. AUGH!

I'll take it for a test drive today and see if it acts up for me.
It really did feel like an electrical cut-out when it happened.

-Ben
 
Ben I had a '96 Tahoe many years ago that had an issue similar to yours. No trouble codes. After much aggravation I traced it to a loose ground wire on the front of the engine block, the bolt had backed out and the ground wire end was just hanging there like a shower curtain ring, hence the intermittency of the problem. Worth a look I suppose.

One strange thing I noticed about my issue was that the little orange gear indicator lights would go out from time-to-time as well. But that issue went away once the ground was fixed.
 
BigBen said:
Ok, this one's got me stumped and I don't even know where to start:

1995 Yukon with stock engine, etc 281,000 miles.

On the way home yesterday after driving 1.5 hours I stopped at a stop sign. As I lifted my foot off the brake the truck cut out and then surged for a moment before returning to normal operation. (almost felt like when an engine diesels after you shut it down.)

I thought nothing of it because things went back to normal and I kept driving. Everything was fine for another 15 miles.

About 1 mile from home it did it again right as I released the brakes.

Coasting down the next road it cut out for a moment and then came back on.

Once in the driveway it was running very roughly and eventually died.
I put it in park and started it up. As soon as I touched the brake, it died.
Tried it again, it died. Once more, it died.

Let it sit for a while and checked for any error codes, none in the computer.

A half hour later I went out to check on it and the thing started and acted like everything was normal.


The thing may be old, but it's been running great and is well cared for.
Recent repairs that may or may not be significant:

New Brake Booster (diaphram leak) a couple months ago.
New AC distributor (with all internals) and plugs within the last 10,000 miles.
Wires have less than 30,000 miles on them.

Like I mentioned, the thing is in great shape for its age and I cannot, for the life of me, figure out how pushing the brake pedal in can kill an engine like that.

I hope someone's got some ideas here. I'll answer any questions as they come up.

Thanks!

-Ben


One last note: I did notice yesterday that the 'voltage' guage seems a little low. The battery is decent and less than a year old. Any chance the alternator is involved here? (100,000 miles on it)
Click to expand...


I have this same exact problem. It's amplified when I'm towing my boat from our trailer to the launch ramp through the park at 3-5 mph with speed bumps. Always dies letting off the brake after the speed bump. I have a slight leak on the back of the block, which is not the freeze plug. Looks like an intake manifold leak, so I was thinking that was the root of a vacuum problem possibly. After reading this, it looks like it could be a number of things. Good info.
 
Good thought Craig.

I traced all the grounds I could find and they were tight.

Funny thing, I've got almost 300 miles on it since I swapped the alternator out on Tuesday.... no problems so far.

Knock on wood. It seems far fetched, but I think changing the alternator might have fixed it. I won't claim victory for a while though.

-Ben
 
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