Hey guys, got a hesitation/rpm drop going on here and trying to get a few solid leads on it. My best guess is a vacuum leak. If I go to stop from any speed, instead of coming to a smooth stop the Blazer wants to putt out but jumps back to life. My idle is right around 500, so we're talking a drop to 2-300 RPMs before it kicks back to normal. When I go to take off it does the same sort of hesitation but I can throttle through it. (This makes me nervous in case anyone else drives it and doesn't know what is happening ie; turning left)

I just got back home and messed around with a couple of things to see if there was any specific reason. I put the shifter in Park and put the brake pedal all the way to the floor. I could hear a good compression, this did nothing but raise the RPMs t about 600 and back down to 500.
Releasing the brake it went back up to 600 and dropped to about 350-400. Felt like it wanted to putt out like stopping, but didn't, returned back to 500.

Put the parking brake on, and shifted to DRIVE. This raised o about 600, and then did the same sort of put out to 2-300 and returned to 500.

So, all in all I'm not really sure what I have here. Seems like if it was the fuel related, I would have more noticeable problems at highway speeds, 18-22k RPMS, but I have no hesitation up there. Only the stops & go. I read something about this maybe being the brake booster valve, but it doesn't seem to explain the shift to DRIVE putt.

I know I have to redo the filler tank hose soon. Not sure if it might do anything but there it is.

I can take a video if it helps, too. Thanks!

 

Remove the vacuum hose for the power brake booster from the intake manifold and plug the fitting on the manifold. Start it and see if it changes. With the vacuum line disconnected, you will not have power assist for the brakes so it will take substantial effort to push the brake pedal down.

 

Is the line something I could crimp (or want to crimp, for that matter) with a pair of vice grips? I'm not sure what I could use for a plug.

 

A helpers thumb works really well for a plug. Have also used plastic wrap and a rubber band for a quick seal.

Sounds like the brake booster is leaking.

 

Lanny, that was my initial lead after I read a posting that had near identical symptoms to mine. However it was never resolved. Once is a mistake, twice is a coincidence. Not sure if there's a how-to but I reckon I'll try and put one together... Once this rain stops, I'll be digging in.

 

You can crimp it, but if the hose is brittle, it will crumble. Don't remove it from the booster, the seal or the check valve will probably be destroyed. That's why I suggested pulling it at the engine.

 

Alright, info time. I didn't get to check vacuum, but I don't think it's brake related anymore. I held the throttle for a few seconds at 15-2k RPMs and let her drop back to normal idle. Stuttered and came back to where it should be. No problems idling after that. I did this about 10 times at a few different RPM levels, and it didn't really want to do it unless it was over 1k RPMs.

On a side note, I got my scanner today with Torque (phone) and TouchScan (Windows 8) (free editions, for now). Maybe I'll be able to find something. I checked the fuel trims with my phone but it wasn't reading the hesitation, so I'm going to try with the laptop. Anything else I should be monitoring?

Badco Edit: I got a data log on everything I could. I don't see anything that's out of the ordinary, but I'm not too sure if I'm reading it right anyways lol. I'm throwing a P0147 (02, b1s3 v out of spec)

 

Any DTC referencing B1S3, you can disregard as causing any kind of performance issue. B1S3 is there to monitor the catalytic converter, that's it.

LTFT & STFT should tell if the problem is due to a rich, or a lean condition. It won't tell what the problem is, but it will tell what to look for and what can be eliminated as a possible cause. Fuel trims are a beautiful thing

 

When I did the injector and nut kit on the Jimmy I could not get that vac hose off from the back of the engine, so I left it attached to the plenum and carefully took it off the booster, I did not have a problem.

but.. I was REALLY careful (OCD careful)

 

What should I be reading for regular fuel trims at idle and say, 70 mph at 2100 RPMS? According to THIS they should be single digits...... and what I was reading for F/T 1x1 and 2x1 were definitely not single digits.... more like upper 20s to lower 30s.

So I guess this could boil down to a vacuum leak? lol. I'll try to log my trip to work with torque and see if I can find anything else.