Disco/Volvo
 

Need some help and input regarding engine (like a 760 loaded pulling a trailer scenario.

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.

Using standard turbo with new core. .95 timing, new std nozzles pop tested.
Using Volvo 760 Zf with 4hp 24 front pump and a clutch set. Volvo valve body and gov.

Questions.

Does the Volvo 760 stay on boost continually when flat out?
Is the turbo sequence described above normal?
I never adjusted or disturbed the max speed screw, could I not be reaching max rpm as I had adjusted the throttle lever to throttle shaft after pump rebuild.
As I'm using the euro d2.4tic intake and intercooler I've no overboist control, Is that an issue?

The engine is stock, fitted to 04 discovery.

Tia.
Jerry

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.

Thank you for taking time out to reply.

As I've never run a volvo turbo diesel automatic before, the running characteristics are different. I have an 03 vw tdi automatic, however that trans is electronic and not comparable.

Ive had a few older range rovers and am familiar with their shift patterns.

I will follow your guidance and report back. I will adjust the kick down to raise the shift points, this should keep it in boost longer.

I have a boost gauge t-d into the intake. from a standstill what should the boost be..... foot to floor ( throttle lever against max speed screw) accelerating thru shifts thru converter lockup to max road speed?

What boost number should the engine see flat out foot to floor (should it be 10psi).

TIA

Reread your previous reply and went through in detail. I think pump calibration is the issue. I can do trans kick down adjustment easily enough.

I'm waiting on damper tools to do timing belt.

where could I upload a video of acceleration runs etc. (Im not computer savvy)

Sorry my boost gauge is the Volvo one with no numbers but much like v8volvo reported above, as the engine reaches 2500RPM the gauge heads towards ~75% of max boost, then quickly to max as the RPMs rise and stays there as the auto trans shifts thru the gears, maybe slight blips at each gear change.

As long as the RPMs, load, and accelerator pedal are there the boost will remain pegged, as in climbing a steep hill.

Another IP tuning area that can contribute to your reported boost behavior is the LDA starwheel and preload.

Follow up. After detailed inspection and checking,it looks like the boost pin was in the wrong location . In research I discovered that the mark on the diaphragm plate should coincide with the cut out in the pump body (not the cap) was the best location. I adjusted the max fuel screw up until the rpm hung at the snap throttle test. It was further road testing saw boost thru shifts maintained. I also tweaked the tv cable to raise shift points. Volvo converter has a 2000rpm stall which helps. I still think my fueling is still not enough once I accelerate hard in lock up at 60mph approx. Hoping to do a few flat out throttle runs. Thinking 70mph hopefully. Discovery is a barn door.

Looks like you are on the right track. What are the RPMs at 60?

Yes sounds like progress if it is holding boost through the gears.

Does it make any smoke at full throttle now?

It's turning 2000 rpm at 65mph . That's converter locked. Acceleration is slow . I can watch the boost gauge increase and decrease as I get into it, with no appreciable speed increase. It's probably over geared and doesn't have the torque to accelerate. I'll do flat out runs once I do the timing belt. I'll probably do an in truck rering bearings etc as I'm at it.Ive wired the glow plugs to the start circuit as well as its slow to start, even with a new geared starter and battery. I've got a lot of blowby, at idle thru the pcv puck, with oil in the hose to turbo inlet.

Agreed. Mine turns ~2300 RPM @ 60 MPH, does pretty well. Power really starts at 2500 RPM, shoot for that at or slightly above your cruising speed.

Don't touch the bearings unless you have valid reason. Lower end on these are usually trouble-free.
Hard start w/ good starter and battery which is helped by GPs indicate poor compression. May simply be rings but check the cylinder walls closely.

Follow up. I adjusted the fuel screw again and eliminated the concern I had when the throtttle was snapped idle to high rpm the engine rpm hung before idling back down. Idle speed adjusted after.

Re boost drop off. I removed the boost diaphram and checked the boost pin rod in the pump for freedom which connects to the boost pin. It was ok. I turned the star wheel 1/4 turn in. I set the boost pin to max travel removing the plastic spacer. Refit the boost pin with the ramp on the most agressive side contacting the pin.

Road tested and the boost now holds when the trans shifts and is much more responsive once the turbo kickes in.. At 55 steady Im running 7lbs boost. The truck is heavy so acceleration in top gear converter locked is slow

Sounds like you got a lot of improvement out of it, that is good. The way you describe it working now sounds right, if it is holding boost during gear changes then it's working like it should.

What kind of axle gearing does it truck have? I am not surprised it's pretty slow accelerating at highway speeds, those are tall and square trucks too. The D24T engine does not mind revving 3000 rpm or more so putting shorter gears in it might help it run better on the highway. Pushing that kind of rig I think I would want the converter to lock up no earlier than 60 mph or so. It does sap the punch once that lockup occurs.

Agree with the discovery being a brick. The rpm at 70mph flat out is 2500rpm. Not expecting much better as the weight coupled with 265/70/18 tires and 3.54-1 gear ratio leaves very little when the converter is locked. it locks up about 60mph. Im using the volvo 760 valve body.

You might do even better if you were able to regear the axles (though I know that is a lot of work and expense). That is pretty tall gearing especially with the bigger tires and size/weight of the truck.

To give you an idea, in the Volvo 7 series TD cars with factory automatic, the tire size is 195/60R15 and the rear end is a 3.91. The torque converter lockup occurs at about 45mph and at 70mph I think the revs are over 3000. So, much shorter gearing and smaller tire circumference, plus of course it's a much lighter and smaller vehicle, and only driving one pair of tires. ;) IIRC the Land Rover transfer case runs 4x4 full time with a center diff right? So more driveline friction and inertia too.

Seems like in your setup a set of 4.30 or 4.56 gears in the axles might be about ideal? If such are available?

Or just run it in low range all the time.... :cool:

Would be great to see some pictures or video of your installation sometime, I would like to try one of these builds myself someday.