BHW Tandem pump delete?

[Alberta 7.3]

Looking for some input. I'm planning on a BHW for a RWD diesel conversion project. Is it possible to delete the tandem pump for firewall clearance and use a high pressure supply pump with a regulated return to feed the PD system? I've read that the tandem pump supply pressure varies with engine RPM, would a constant pressure screw up injection quantities at lower engine speeds? I don't need the vacuum pump since the vehicle will have hydroboost brakes, and a small electric vacuum pump supplies the climate actuators and whatever vacuum the engine would need for solenoids/actuators.

I've done a forum search and came up empty handed

 

[devon1996]

No reason it wouldn't work. Youll need the regulator after the head because the ecu uses the fuel temperature exiting the head for fuel table calculations. Just set it to 120 psi and send it. The pump puts out 60-120 psi. The injection quantity maps aren't that sensitive.

 

[Alberta 7.3]

Thanks for the input on this

 

[Straypoet]

I am also in the middle of a swap, and would like to delete the tandem pump.
have you made any progress on this?
I am having trouble finding a diesel capable fuel pump that can pump pressures that high. Did you find any?

Thank you..

 

[oilhammer]

The vacuum pump is an integral part of the crankcase ventilation design, too.

The VAG engines are so short (due to their meager 88mm bore spacing) it seems strange that you'd have any clearance issues, can't you just move the engine forward a bit? You also have the coolant flange exit in the head that sticks out almost as far.

 

[evguy1]

I "think" you would be fine on the lower end of that pressure spec just because I run the stock 45 PSI lift pump on my XJ swap. I had a tandem pump failure last year and the Jeep ran fine just had no power brakes. I didn't drive it far or at full throttle due to no brakes but it ran fine at lower speeds.
Oilhammer, as far as why Swaps need to remove the pump is for the firewall clearance, moving the engine ahead is what is normally done BUT it also moves the gear shift lever ahead so it usually needs modification or you end up smacking the dash when you shift. You also need to lengthen the rear driveshaft and shorten the front one. If the vehicle is a 4X4 then you may also need to modify the transfer case shift linkage. Adapters like what NWF/TDC build are 2" thick and are usually enough to give some tandem pump clearance but not always. On my JKU swap the 2" adapter plate was enough to clear the tandem pump but on my XJ and Ranger swaps I still needed to move the engine 1.5" ahead. The coolant outlet is usually in the lower part of the firewall where it starts to taper back for transmission bellhousing clearance so it usually has no clearance issues as long as you use one that does not have outlets at the back of it or the coolant glow plugs. I think NWF/TDC is going to produce block off plates for a few of the TDI engines once they get their new Billet adapter line completed.

 

[Mozambiquer]

Well, couldn't you also modify the firewall? That would maybe be the way i would prefer personally. You would have to add a fitting on the head for the fuel inlet to the head, and then I would think that it would cause issues with the pcv. But I guess, depends on what you want to modify

 

[evguy1]

On modern vehicles the inside of the firewall is usually crammed full of stuff from wiring and control modules to heater boxes and ducting making it very hard to modify. I stuck a Ford 302 V8 into a 73 Datsun truck when I was young and can remember standing on the rad support with one foot and the top of the firewall with the other and modifying (beating the crap out of) the firewall with a sledgehammer. There just wasn't anything behind the firewalls back then. A machined plate can be made to cover the Tandem pump area with the proper inlet and return ports so that should not really be a problem. I don't think the Tandem pump effects the PCV system??

 

[oilhammer]

You may find there is not much behind the firewall right there, actually. Just depends on where the HVAC case lands, but they are typically not right up against it (heavens knows I've had more Jeep HVAC cases out than I care to remember, LOL). But yeah, I get you on the moving everything else (trans, etc.) forward.

 

[oilhammer]

PDs also get the fuel pretty warm, and as an unintentional but consistent byproduct of the placement of the injectors, tend to weep some engine oil into the fuel system. This is why the lift pumps are always coated in a black film, and why the fuel filters have little tolerance for neglect. Doesn't seem to effect them if maintained properly, but it may be an issue for something cobbled and repurposed from something else. There are high pressure gasoline fuel pumps that'll do 120 psi, but not sure how they'll handle hot soot laden diesel.

 

[PakProtector]

If in the 'real world' the fuel system bits were hard, and fuel incompressible, putting larger nozzles on would never need to happen. As it stands, things flex/bend/expand and larger nozzles deliver more fuel. Common rail excepted; those are constant pressure mode, and for a given duration bigger holes mean more flow. This across a time period comparable to a single injection event; the pressure usually varies to aid fuel delivery across what ever map is chosen.

Can't help thinking that bigger injectors will reduce load on the PD engine's timing belt IFF it happens to be that the pumps are the primary load compared to the cam lobes. Just the ticket to justify bigger nooozles…
cheers,
Douglas