^^^ I'm interested in how you run an inline pump and don't have it running all the time. If they are plumbed in series, you'd be pushing fuel through the inline pump when it's not running. Is that what you're doing? If so, I think I've figured out why your pumps are burning out...

 

Yes, it pushes fuel through the pump when it is not running. The pumps that burnt out were running all the time before I used the AEM Low Side switch to toggle a relay based on boost pressure. I haven't had any problems since I changed the design to only switch on at 5psi, in fact, that might have saved my previous pumps from failure. If anything, running them all the time was why they burnt out.... too much back pressure on them while they were running probably because they were overrunning my return system.

 

Oh boy.

Pumps in series need to be run full time.

Also, headpressure shouldn't kill a pump.

 

I bet there's a lot more pressure trying to push fuel through a non-running pump closer to the working pump than trying to push excess fuel through an small return.

 

I can only tell you what my experience is with them, not theorectical study. 2 walbro inlines running all the time = 2 burnt out walbros. A bosche inline running all the time and now only above 5psi = still working bosche. Dunno what else to tell you. There were no other variables, both pumps were run in the same location on the same circuit I built directly wired to the battery with a 2 relay setup (1 to ignition 1 to the AEM boost signal). I will, however do a bit more research on the problems with running a series setup that isn't on all the time and weigh the risks. So far so good though.

The one benefit I did notice when switching is that it seems to be able to hold fuel pressure a little better on the top end.

 

That's fine, but dual inline Walbro pumps running full time are present on thousands of cars. As to why you had a problem with pump failure is because you were trying to do something that is not recommended.

The biggest issue here what CO_VR4 described. You presently have a in-tank pump that has to struggle to push fuel through a 'dead' pump (a situation for which neither is designed). The dead pump is like an engine trying to dump exhaust gas into a system with a clogged cat converter. The in-tank pump will struggle until it can manage to achieve the set rail pressure with that big potato in the fuel line.

It's a great way to stress the pump(s), and offers no advantages in return. Sequential pumps need to be run full time.

Just FYI.

 

I would be curious as to how much more stress the pump sees compared to normal. Not sure if anyone has actually done the study or not. The pump only has to maintain the base pressure (43ish psi) when the inline pump is dead, so is that equivalent to 60psi with nothing in the way?, because once the boost goes up (fuel pressure too), both pumps activate anyway.

If I read up on it and find it is really really bad on the in tank pump, then I might change it back to run all the time. Should be an easy switch since I just have to make a quick change in the software parameters that drive the aem switch.

However, if it is not that bad on it, then I would rather have the benefits of added fuel pressure on the top end.

 

i got an inline walbro and intank walbro, no problem at all. making 462 whp, 450 tg. 30psi, e85 fuel, fp red 80mm, 1200cc pte. works great. can go to 550whp with this fuel setup. tuned at batlground.com in atlanta georgia.

 

we also used the hobbs swith . the inline walbro turn on when boost reach 4psi. Used to have single intank walbro, not good enough for e85. After adding an inline walbro, fuel problem solved.

 

The only bad thing is not running the series pumps full time. There is absolutely no need to stage them. It doesn't solve problems, it only creates them. Apparently, it creates enough stress to kill at least the in-tank pump, not to mention the possible detrimental effect of applying high pressure differential across an inactive pump.

Hobbs switches are needed for twin parallel pumps. Understand that two pumps in series directly increase the pressure potential of the system, but do not directly increase the volume of the system. Conversely, twin parallel pumps directly increase the flow volume potential of the system, but not pressure. Series setups are more advantageous for high pressure applications, and do not use/need Hobbs switches.

Remove the AEM trigger and run the pumps full time. You'll almost certainly not suffer any more problems. If the series pump is noisy, get it away from the firewall and near the back of the car, which is the way it is almost always done, for that reason.

 

One interesting thing I noticed, was while at idle, light throttle, the inline pump would be quite loud (like it was seeing a lot of backpressure) and once I got on the throttle a little more I couldn't even hear it anymore (like it was using enough of the fuel to relieve the back pressure).

Anyhow, I will read up on it and see what I find. There are quite a few people doing their setups the way I do it as well without issues, so I don't think the cons are that bad. I guess time could tell me the same thing. I have had the same in tank walbro since I pretty much bought the car back in may 04. If it suddenly fails in a year, I guess the extra stress was too much, if it lasts another 3 years, then the cons certainly are not bad enough to justify having to A) put up with the extra noise. B) relocate the pump with a LOT of extra fuel line being needed.

 

Ok, but what I am trying to make clear to all who read this discussion is simple:

A Hobbs switch is not something that is desirable. It contributes nothing to power or reliability. It's just another dongle that can fail. In the case of parallel pumps, it is used to solve a problem inherent to parallel pumps. With series pumps, that problem does not exist, and therefore there is no reason or advantage to staging the pumps. Doing that only creates problems, and solves none.

Finally, as for trying to push fuel past the seals of a dead pump, it's unwise and I doubt that anyone will find either Walbro or Bosch to consider that an example of good design.

That's all folks.

 

I don't use a hobbs switch, I use a low side output from the aem which I drive through software from the aem, using the MAP input signal. Your statement that says it solves no problems is incorrect. I don't have to listen to the noisey pump or relocate it to a place that is a pain in the *** to install it at, so it does solve that problem. It also does seem to give me more room on the top end as far as max fuel supply goes (.3-.4 richer on my A/F readings).

As far as cons go, I have not seen any yet, so I will do more research and go off my own experience. Whether it is an "ideal" setup or not is not a concern to me. Often real world designs are not ideal. I did plenty of ideal studies in college (Computer Science Engineer) and now having 3 years experience in the real world I understand the compromises you have to make.

What I really am worried about: Do the pros outweigh the cons.

 

Had the pump been installed toward the rear of the car, the noise wouldn't be an issue. I'm not saying it's necessarily fun or easy (?), but that is how to solve the problem without resorting to a design that creates a bigger problem than it solves. If it were me, that's what I would do. In fact, I would install that pump such that the mount was insulated in order to minimize the transmission of vibrations to the chassis. FWIW, you aren't the only one to run series pumps on an EVO.


The cons are burned out pumps, and you have seen that.

The only pro is reducing the noise of the second pump due to its present placement.

 

Same concept. No difference in operation. You just have an expensive Hobbs switch

Compared to what? When both pumps are running, the system works the same...

There's no benefit to having a fuel system below 5 PSI that is choked up by a non-running pump in the feed line. There is a substantial con to that idea, because you are forcing the in-tank Walbro to work much harder to push fuel past the non-working second pump. Lots of people have killed in-tank pumps in this situation when the in-line accidently failed. You're doing the same thing, but on purpose...