Issue with engine not liking boost

[TexasBlownV8]

On my KB 2.6, 18 psi, GT500 pumps, I have an issue that recently developed.

Driving around part throttle, staying out of boost, car runs fine, at all rpms and speeds. When I go into boost, whether part-throttle or wot, the car spits and sputters and acts like it is missing out or not getting fuel. This happens at any RPM where I get into it, typically in the 2000-3500 range.

I drained the fuel and changed the filter a while back to resolve this, no help, as initially i thought it might be some bad gas that I bought. That was 2 half-tanks ago that I did this.

The BPV is working properly, opening and closing as expected.

The issue seems to manifest itself when the GT500 pumps kick into boost-mode (dual BAP power increases to them; I monitor that via a couple of LEDs), and the fuel pressure jumps up into the mid to upper 40 psi range on my gauge. Boost tries to get up only gets to about 3-6 psi while this is going on.

When I get into less boost, just barely below the threshold where the GT500 BAP kicks on, the issue does not occur. I can build a little boost and hold it just fine (but what's the fun in that!).

Strange thing, this will sometimes not happen at all, and the car will go into boost and run like a bat out of hell, but I think only when not fully warmed up. Although, most times when trying to get into it, it happens.

Coolant temps and IATs are normally.

AFR appears to stay what it was before going into boost (although I dont stay into it long to see it change). I would expect it to go rich if there was any misfiring, but it isn't.

I checked the air intake and it looks normal and correct.

The COPs have upgraded wires running to them (no boost-a-spark). Have had no previous issues with spark blowout.

The car ran flawlessly last October while being dyno tuned by Lito and for a couple months after that. I tried an older (not one I'd use any more) tune, and it does the same thing. I'm confident this is not a tuning issue, but something else is going on.


No DTCs get thrown.

Next I'm thinking of checking the spark plugs, see what they look like; they are not that old, were replaced maybe 1000 miles ago, last year. Maybe try a previous set, see if it is a spark plug issue.

And if still occurring after that, I'll do some datalogging.

Maybe a fuel injector issue, since the AFR is not radically changing? Although, I can't really go full WOT, it'll just sputter and barely stay running.

Any useful suggestions?

 

[BruceH]

Bypass valve.

 

[TexasBlownV8]

Bypass valve.

I checked the mechanical lever and vacuum control, and the BPV appears to be working properly, at least at idle (opens under vacuum, closes with no vacuum). This is on a KB intake, so to see the butterfly inside, I removed the vacuum fitting right above the BPV and looked inside, and verified the butterfly is moving (opening and closing) as the external lever is moved. Nothing appears to be out of place there. The spring is very stout.

 

[CPRsm]

Bypass valve.

What's you thought there?
Bypass wouldn't hold boost if malfunctioning. But the maf would still read correctly if it was bypassing under a heavier load and fuel correctly either way.

I'd look into the pumps. Did you change the prefilter on the pumps? As they warm up they're probably not putting out as much. Maybe from age, or heat if a prefilter is clogged. (I know you said you changed the filter. Hoping you meant between pump and injectors.)

 

[TexasBlownV8]

I think there's a way to datalog fuel flow; I did that the first time this problem showed up, and Manuel (aka Lito) said the pumps were flowing fine (but, how can the pcm know for sure what is flowing? The fuel pressure does go up, but is it right?)
I should do some datalogging again of course, if that will help.

By filter, yes I meant the inline fuel filter between the pump and fuel rail.
I have not messed with the pumps nor prefilter since they were installed a few years ago.

It is acting like either it is being starved for fuel or the bpv is not closing. But the fuel pressure does jump up.
Puzzling.

 

[CPRsm]

My guess is fuel flow is inferred, not a real measurement.

Does base pressure drop over time at cruising or idle? That's what we'd see. All round pressure drops.
I completely missed a paragraph. Now that I read it Brice's post makes sense. Boost jumping might feel like a miss. Can you shim the valve shit or apply constant pressure to it to keep it shut for testing?

 

[TexasBlownV8]

I was thinking of doing that to test the BPV (make it stay shut), and run it just hard enough to get past that point where I observe the issues. That would verify or rule out the BPV. If the spring has for some reason weakened, the BPV wouldn't stay shut.

But, with things going on as the BAP kicks up pump voltage (using the 20 volt race version dual BAP here), it would seem that would not matter.

I was just looking at a datalog I took awhile back, with the same issue. The fuel pressure actually goes up when the BAPs kick in, naturally. The pressure before then hangs steady around 38/39, then jumps to 57, and briefly to 67, back down to 63, 55, and settling in around 47-50 under those conditions, until the BAPs go off. (that's pid "inj_press_drophir"). The flow rate pid is FPUMP_FLOW_RATE, and it is around .19 at idle, and gets to around 2.6 under 'boost', during the same conditions when pressure goes up. During cruising, pressure stays steady (38/39).

Can't be many possible things here, just a matter of figuring it out

 

[Jeffk]

Really sounds like the pumps are struggling once they get hot to me but I'm not an expert.

 

[Fullboogie]

Just curious why you don't have the BAP wired to run all the time? It's real common to set it up that way rather than using the pressure switch to activate it. I can't help but wonder if that has something to do with it misbehaving.

 

[Dubstep Shep]

Just curious why you don't have the BAP wired to run all the time? It's real common to set it up that way rather than using the pressure switch to activate it. I can't help but wonder if that has something to do with it misbehaving.

I'm with this. I don't know why you wouldn't run the BAP all the time.

The BAP is designed to reduce the overall duty cycle of the pumps. They actually are more efficient with it on.

 

[Fullboogie]

I'm with this. I don't know why you wouldn't run the BAP all the time.

The BAP is designed to reduce the overall duty cycle of the pumps. They actually are more efficient with it on.

I will add that according to Lund when he did my tune, having the BAP run all the time must be tuned for. Keep that in mind.

 

[TexasBlownV8]

The dual bap is the 20v racing version. Running it all the time is not something I'd want to do. The fuel pressure definitely jumps up when the pumps get that voltage boost.

Based on fuel pressure readings alone, it does not seem to be a fuel issue.

But it is something:

- if there is not enough fuel, wouldn't the AFR go lean and fuel pressure drop?
- if the BPV is not closing, how would that show up? (leaner AFR? changes in maf counts?)
- if there was a spark issue, wouldn't AFR show rich due to unburnt fuel?

 

[BruceH]

What's you thought there?
Bypass wouldn't hold boost if malfunctioning. But the maf would still read correctly if it was bypassing under a heavier load and fuel correctly either way.

I'd look into the pumps. Did you change the prefilter on the pumps? As they warm up they're probably not putting out as much. Maybe from age, or heat if a prefilter is clogged. (I know you said you changed the filter. Hoping you meant between pump and injectors.)

I'm sure it will make me a hater but kb are known for having bypass issues and it sounds to me like it's fluttering but it's just a guess.

OP, why do you have the dual bap? At your power level on gasoline you should be fine with gt500 pumps unless you have small injectors.

Something to keep in mind about baps and gt500 pumps is that one 40a bap will suffice. Notice that the one power wire goes into the relay and two come out from the same terminal. You could probably sell the "Race" dual bap and replace it with a normal 40amp so it could stay on all the time or even use the dial to lower the voltage.

 

[TexasBlownV8]

A fluttering or opening BPV is what I'm thinking at this point. I didn't know about any reliability issues.

I am going to do a little testing and figure this out. Fuel or BPV, I'll narrow it down today. Going to run w/o the bap (removing the switch from vacuum) to see what that does, and/or hold-open the bpv. One of those should do it.

If this does turn out to be a fuel issue, I'll change things at that point.

 

[Dubstep Shep]

I will add that according to Lund when he did my tune, having the BAP run all the time must be tuned for. Keep that in mind.

Oh absolutely. I'm not experienced at all tuning this stuff, but I would think it wouldn't be more difficult with it on all the time.

Could be different with the race BAP. I'm not familiar with those.

 

[TexasBlownV8]

The race BAP spits out 20 volts vs. 17 on the street version (according to product details).

Well, using the Hobbs switch and turning the BAP boosted-voltage on only when under boost is not working out very well and appears to be the cause of my problem.

When I blocked off the switch and just ran the GT500 pumps naturally, I could get into boost at levels and hold it where I could not before (2-6 psi under part throttle), with no issues other than running very lean, which is where the BAP would normally bump up the pumps. Fuel pressure was holding steady around 40 psi during this, too.

Looks like I will need to change my fuel setup here a little, and some re-tuning to match it. Might just go ahead and upgrade to an ethanol-capable system, since I've been thinking about it, remove the dual bap and pump.
Oh well, that's how it goes. Learn and move on... make it better, stronger, faster...

Odd that it was working OK for quite some time (about a year) with no apparent issues.
I tend to agree with everyone, though, do away with the Hobbs switch and just run things at a steady voltage, whether stock or increased voltage.

 

[Dubstep Shep]

Yea, usually you can pulse wave modulate whatever you need to with the BAP all the time rather than turning it on and off.

I would say that any less than 600hp is perfectly fine on the GT500 pumps on pump gas. I'm sure there are plenty of people running them a lot harder than that though.

If you're considering getting rid of the BAP, I've been mulling the idea of getting one over so I can run e85 myself. PM me if you're interested.

 

[TexasBlownV8]

We dyno'd right under 600 rwhp on 93 octane with this fuel setup, through an automatic, with room to spare. We're 'a bit beyond' 600 engine hp.

It this point I am considering doing something different and take out the dual bap, but nothing is set in motion yet (Dubie, you'll get a pm if I do that; thanks).

 

[JoshK]

I too have a GT500 dual pump kit and a competition dual bap kit. I have my BAP on all the time though. If have the BAP wired in before the FPDMs you are not going to be sending the full 20volts to the pumps all the time. The FPDMs will still regulate the voltage, the BAP just allows them to go up to 20volts instead of only up to say 13volts. You are not running full volts all the time and overworking the pumps. I have run this setup as high as 21lbs of boost on E85 and it works well. I do have a -8 fuel line from the tank to the fuel rails also though. I am at 86% pump duty cycle with this fuel system at 21lbs and E85

 

[Dubstep Shep]

We dyno'd right under 600 rwhp on 93 octane with this fuel setup, through an automatic, with room to spare. We're 'a bit beyond' 600 engine hp.

It this point I am considering doing something different and take out the dual bap, but nothing is set in motion yet (Dubie, you'll get a pm if I do that; thanks).

Damn, those are some nice numbers.

Eventually I'm going to go with the Aeromotive Cobra Jet system. It'll run as much power as I'll ever want to make and it's a complete kit tested, tuned, and used by Ford which is always nice. Pretty pricey though. Even without the fuel cell it's over two grand.