Quote:
Originally Posted by jetfiremuck
From stop to take off. Initial lag turbo builds boos to 5psi, trans shifts 1-2, turbo drops out of boost after shift, accelerates turbo spools as speed increases and very fast 3-4 shift. Pedal near floor to keep accelerating. Slow acceleration to lockup (smooth positive lockup). Foot to floor slow acceleration.
|
In this scenario, do you have the accelerator to the floor the whole time? If you do and you're saying it drops the turbo out of boost after upshifts, then it is definitely not normal.
The automatic cars reach wastegate pressure very quickly and then should never lose it as long as the pedal is held down. Especially with a little bit of brake torque, with the help of the torque converter it will hit 10psi no later than around 2500rpm, in other words, very little lag (the stickshift cars it's much more noticeable, but almost nonexistent paired with the automatic). Then once it has built boost to wastegate pressure (10psi) it should stay there as the transmission snaps through the gears, since RPM and fueling are staying up the whole time.
It sounds like either you're not making enough EGT or RPM, or both, to spool the turbo and keep it spooled during shifts. You've already done well ruling out some of the main possible causes, sounds like timing is good and the turbo is stock size.
Here's my guess, it could be one of these two things:
- something wrong with the calibration of the injection pump on your engine, resulting in insufficient exhaust heat, AND/or
- transmission kickdown cable is adjusted too slack and transmission is upshifting much too early, dropping RPM back out of the turbo's efficiency zone after shifts. This could also be caused by some kind of unexpected interplay between the stock Volvo ZF valve body and the 4HP24 front pump, though I think that is fairly unlikely
I think injection pump mis-calibration is your biggest candidate. Was this the same engine where the A/C compressor was dragging down the idle speed so much that it needed an idle kicker to compensate? That would be another telling sign. It sounds a little to me like this fuel pump is just turned way down in terms of fuel injection quantity.
Are you familiar with what many folks call the "smoke screw" on the injection pump? This is an adjustment on the top of the IP that sets the base curve for fuel injection quantity, then the governor tailors it from there based on engine speed and your right foot. It might be what you're referring to as the max speed screw, but that's not what this is, since there is a separate threaded max speed ("high idle") screw that does that job. The "smoke screw" is not intended to affect the maximum engine speed but rather the amount of fuel injected across the entire RPM range. You don't want to mess with the actual high idle screw since you do not want to overrev the engine, and in any case that high idle screw won't add any more power, just more revs. You DO want to try changing the setting of the smoke screw.
I won't go further describing it and its location on the pump here since you'll be able to figure out what and where it is by reading on other diesel and Cummins boards, or you may already know, but I would start as an experiment by turning that smoke screw inward (clockwise) gradually and seeing what the effects are. One immediate effect will be that it'll increase the base idle speed, so as you do this you will have to also be adjusting the idle stop screw and the throttle spool linkage rod at the same time to keep the idle where you want it. But if your pump is currently turned way down somehow, perhaps as a result of having had it apart earlier and internal parts not going back together exactly the same way, this screw is what will wake everything back up. A little bit goes a long way, so I would start small, probably go only 1/4 turn at a time at most and see what happens. You'll know right away if it's working, since the power and throttle response will increase dramatically. If you start seeing some black smoke at tip-in or sustained full throttle, you can back it off again until the smoke cleans up but it still produces full power and boost pressure.
Let us know what that does if you try it.