Boost = Hesitation

[BNaylor]

Originally Posted by dhoeschen

Bnaylor, the spark plugs are OEM style Autolite #606 I don't know the heat range. The e3 plugs I pulled out looked normal in color. The DIC boost gauge will peg instantly. The problem happens at any speed or RPM when I push the throttle a little more which would require some boost. My scanner does not show KR or live data.

Do you have any mods especially like supercharger related? Using AL spark plugs is fine and 606 is equivalent to the OE stock from the factory AC Delco 41-921 or NGK PTR4B-15 double platinum spark plugs.

Head scratcher on this one. Maybe the KR is too high or kicking in due to the abnormal boost condition causing the reduction in power and the sputtering effect or in other words the PCM module is retarding ignition timing.

[dhoeschen]

It's just a winter-beater grocery-getter...

It's got to be related to KR, I've tried everything else? I'm going to try resetting the ECM and see what happens...what the hell, I've tried/tested everything else!

Probally got a load of bad fuel; I remember filling my Tahoe with "premium" once and it was pinging like crazy. I went back to the gas station (why did I bother) and complained about paying for premium and getting something less, didn't help that the owner had no idea what the difference in octane was!!! He thought it was how "clean" the fuel was!

I believe I disconnect the battery for 30 minutes to reset the ECM?

[olopezm]

Originally Posted by dhoeschen

I believe I disconnect the battery for 30 minutes to reset the ECM?

Sorry I can't help any further.

Yes, 30 minutes should be enough.

Best regards,

Oscar.

[BNaylor]

Just to be sure on the boost control solenoid and valve does your scan tool have MAP readout capability? If you do there is an easy test. MAP (Manifold Absolute Pressure) value decreases while the boost solenoid is on. MAP value increases while boost solenoid is off. Or you can use a vacuum gauge at the boost signal hose.

The PCM module commands the boost control solenoid to operate at a 100% duty cycle (ON) for full boost pressure on demand. When there is rapid deceleration or the engine load is extremely high then the PCM will reduce boost pressure. Then the PCM commands the boost control solenoid to operate at a 0% duty cycle (OFF) which opens the bypass valve. When the bypass valve is open boost pressure is reduced.

[dhoeschen]

Thanks BNaylor, my scan tool does not tell me anything other than errors. I normally work on non-computerized "muscle cars" and this car is just my winter-beater. Perhaps in the future (warmer...) I'll troubleshoot into this further - here is my solution for now...

From what I can figure out, it seems like "premium" fuel around here is not what it used to be, octane may be a little low so I added a bottle of 104 octane boost to the tank. Did it help...??? Who knows...

Next, I may have made things worse on myself by changing out the e3 plugs in place of the Autolite 606 - even though this is what the guy behind the counter said works for my car - they don't. I checked the owners manual and found out what plugs I should be using and went a little "colder" with an Autolite XP104.

After taking a short test drive, I was able to get a little boost but still must have had some pinging (from what I've researched, the hesitation is from the computer sensing knock and retarding the timing) so I decided I'd rather have the car "drive" than slowly destroy its self so... I disabled the boost bypass valve and locked it in the open position.

The second test drive provided that my theory worked, although I don't have any boost I really don't care at this point - if someone offered me a reasonable price for the car I would take it and run away, far, far away... it's been that aggravating!

My only hope is that perhaps the quality of fuel will increase and/or the ECU will figure out how much advance it should be adding - then maybe the car will drive like it used too... I'm out of ideas and have spent way too much time on this car - I still can't believe that one day it was fine and the next day sucked!

I'd like to thank everyone for offering their help, support and suggestions you all have really helped me through this and I'm grateful Thank you!

[tblake]

What is a decent offer on the car, and do you have any pictures?

Its a bummer because I was just in cloud yesterday. I could have swung up with my powertuner and pulled up every engine sensor's data to see what exactly is happening.

Good call to go with the AL104's, although aren't the xp104's pricy? I'm just using the copper 104's in mine, but I replace them often.

[tblake]

I will see if I can shoot a short video of my Boost bypass valve inoperation so you can compare. I still think your problem may lie with the bbv for some reason.

[dhoeschen]

It's just a green 4-door not worth much in my opinion, I'll probably end up keeping it for a while... I don't want to think about making payments again! Don't get me wrong, It looks good from the outside but it has some hidden rust holes in the rocker panels under the plastic body panels. I'm concerned with the unibody integrity, the driver rear door has rubbed a spot inside the door - there is clearance at rest but obviously it's hitting/rubbing under driving conditions.

I'm just frustrated with it and probably won't give up quite yet - but I do need to step away from it for now. I have access to a big-ol' Snap-On diagnostic, perhaps I'll bring it over there one of these days.

Yes the XP104's cost me about $7 each, about the same I paid for the e3's.

I'm not sure about the BBV actuator. It seems to work, but I still have unanswered questions about the bottom vacuum hose connection... and that little electrical thingy afterwards. I drove it with that electrical thing unplugged - no change. I can hold vacuum on the top hose connection but nothing on the bottom.

[tblake]

That sensor with the foam at the end of it is normal.

I think the BBV requires a large vacuum source, so I dont know if you used a manual hand pump to apply vacuum or how.

Like you say, when you start your car, the bbv will suck the valve open. Then if you feather the throttle, it will allow spring pressure to overcome vacuum and the rod will move down in correlation to how much throttle you give it.

[ktrap]

OP any luck on the problem yet? I'm having some what if not the same thing, I have a 97 GTP with @ 180,000 miles on her. The instant the boost kicks in, boom hesitation...!! let of the gas for a second and let the boost drop back off and it's fine. I've had the sc belt of and it ran just fine?? So I feel your frustration..!!

[dhoeschen]

I've been driving the car around for months with the boost valve tied open so there is no boost - and no problems. Stupid me took the tie off today to see if it may have fixed itself NOT!

Could this be a problem with the high-speed mode of the fuel pump? Like the high-speed mode is not "kicking-in" as it should? What can I do to force the pump into high-speed mode?

[old_master]

This thread shows how to bypass the resistor: http://www.automotiveforums.com/vbul...d.php?t=658282

[BNaylor]

Originally Posted by old_master

This thread shows how to bypass the resistor: http://www.automotiveforums.com/vbul...d.php?t=658282

To the OP if pump high speed mode is out it will start and then stall within seconds or minutes but doesn't hurt to try the bypass procedure. In a worse case scenario based on your symptom the supercharger internal seals may be bad.