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Thought it would be interesting to post just a little of what you can do with some of the modern EFI systems with data logging. I have the Holley Dominator EFI on my car. For reference, it's got a twin turbo 555" big block.
So it hasn't been running great for a while now. When you stuff your foot in it....it's not happy as it builds boost....it will start to pop and lay over.
I thought I knew what was going on since I've seen it act similar when testing on the chassis dyno. It's got two Aeromotive A1000 fuel pumps. One runs when just riding around...but one alone can't handle things when it builds boost and needs a LOT more pressure and volume. So when it's "party time" I throw the toggle switch to turn on the 2nd pump. I "could" have it activated with the Holley EFI...but I never changed it over...I just have them both wired to a two position toggle switch.
Anyway, I also thought I'd heard one of the pumps make some funky noises a couple of times...but of course it never does it when you're checking it.
So I took it out and poked it a few times for a couple of seconds and let the Holley Data Logger keep track of what's going on. When I got home, I downloaded 4 logs and they all show the same thing.
Might be a little hard to read as the colors might not be clear...but where I have the white cross is on the blue line for the TPS reading. As you can see it's reading 100%, which corresponds to the 2nd column of numbers on the left. This shows I had my foot on the floor right there.
The yellow line is the MAP sensor reading...which is boost. It shows 212 KPA which is about 16 PSI. (Gotta remove ambient pressure).
The red line is RPM. which is showing between 5100-5200 RPM or so while I had my foot in it...which is the exact range it shows the issue on each data log.
Now the BIG issue is the green line. That's fuel pressure. On the left side it's running around 43-44 psi which is about right because it's running naturally aspirated there and there's vacuum running to the fuel pressure regulator to reduce pressure. BUT...as it starts to build boost....the vacuum turns to boost and RAISES the fuel pressure about one pound per pound of boost. So, when it's making that 16 PSI of boost it should be putting out AT LEAST 55-60 psi....and keep rising as boost climbs. As you can see...it tries for an instant to increase...but then it starts DROPPING to around 18 psi!! You can see how it immediately starts dropping as boost goes up.
This is how you melt pistons and blow-up engines! In fact I've had it happen once before on this engine when a pump died at the track all of a sudden. BTW--I have safeguards in it now to pull all the timing out if it drops too low (tested that today too).
I'll do some more individual pump and regulator testing to determine if it's just one real bad...or two of them getting weak. Or a messed up fuel line or whatever. Probably time to box 'em up and send off the Aeromotive for rebuilding either way.
Just for fun...even with it running bad...from the time I hit wide open throttle to the time it was making 16 PSI was about .9 tenths of a second. I don't mind telling you....a LOT happens when you double the amount of air going into an engine......555" all of a sudden thinks it's about 1200 cubic inches!! It happens even quicker when it's got slicks on it and the tires don't spin...and when it has fuel pressure and even quicker when I have the timing cranked up for good fuel. Those little turbos don't have any lag to speak of!
Last edited by 427Hotrod; Jul 21, 2025 at 11:33 AM.
I would suspect the fuel pressure regulators as you stated. Do you have data of a good run and compare what's happening now?
I had some...but not anymore. It worked great in the past. But I had one pump start to freeze up once and smoked a piston at the track. Data logs from that showed a similar trace.
Next step is to isolate each pump and see what happens when I put pressure on the regulator. Might even be a restriction feeding a pump which would cause it to make noise also. But of course, if that's the issue...I've learned over the years these pumps get damaged easily if they starve.
Running boosted don't you have to have a sense line to the pressure regulators to increase fuel pressure when boost builds? Is that line pinched or clogged? I'm sure you looked at it by now. Are your pumps in series (fuel flow) and does it shorten the life of the pump that has to "pump" through the other pump or are they in parallel? Not knowing how to plumb a turbo fuel system I do not know. Just spit-balling.
Ya, that piston has seen better days. Back in the day when working on small Cessnas etc. we'd get the occasional burnt piston (mostly on turbo aircraft engines, go figure) and we'd use them as ashtrays. I eventually quit smoking.
Running boosted don't you have to have a sense line to the pressure regulators to increase fuel pressure when boost builds? Is that line pinched or clogged? I'm sure you looked at it by now. Are your pumps in series (fuel flow) and does it shorten the life of the pump that has to "pump" through the other pump or are they in parallel? Not knowing how to plumb a turbo fuel system I do not know. Just spit-balling.
Ya, that piston has seen better days. Back in the day when working on small Cessnas etc. we'd get the occasional burnt piston (mostly on turbo aircraft engines, go figure) and we'd use them as ashtrays. I eventually quit smoking.
Yes....it has a boost line to the top of the regulator. It's sensing vacuum and dropping pressure from mid 60's static for cruising around at 44 psi or so....so it "should" be seeing boost also. But I've seen "flappers" in hoses that sometimes block stuff. All of that is on the ck list. So far just confirmed it's a fuel issue.
The pumps are in parallel with individual -10 lines feeding from the sump on the tank. One is used all the time...the other comes in when it's party time and goes through a ck valve which is necessary because if you didn't have it...you couldn't run on one...it would just blow back through the 2nd pump. They then "Y" into a feed line to the regulator under the hood.
Thanks for sharing the information. Data logging by itself is the single biggest asset to aftermarket EFI systems. I run a data log every time I drive triggered from an increase in fuel pressure. This has allowed me to troubleshoot when needed.
Hey Jim! Totally agree about how awesome data logging is. I have a Haltech Rebel LS on my red '67 and I have totally relied on the data logging for tuning. I'm very interested to see what you come up with.
Thanks for sharing the information. Data logging by itself is the single biggest asset to aftermarket EFI systems. I run a data log every time I drive triggered from an increase in fuel pressure. This has allowed me to troubleshoot when needed.
Except when you're troubleshooting fuel pressure problems.
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
i'm with 2xtrouble. Your AFR should have gone pretty much sky high when the pump or regulator quit running correctly. As you already know, going lean fast usually means boom. I think you will find the issue for sure, GL.
Sorry guys...I left the laptop out in the shop and forgot to pull a new image with AFR...but yes...it went lean. I only let it go for a quick second or so.
For DblTrbl...it's got 160's for injectors. Unless I'm hammering it at the track it's got 93 octane pump gas at all times. I keep the timing low for pump gas. At the track it likes MS109...but ONLY if I crank more timing in it. I don't make enough boost to really need it...but it's safer.
Tonight I tested the regulator and it works fine. Adds pressure with "boost" and subtracts with vacuum. Lines going to it are fine and seal well.
I tested each pump independently (just to watch them react to pressure)...no volume tests but they seem to run fine.
I drained the tank and started checking the inlet lines and prefilters before each pump and all was good. I pulled both pumps and didn't find anything obviously wrong. The one way check valve on the "party pump" works as it should.
Next I moved up to the inline filter. BTW---they are all Aeromotive filters. Guess what? That dude didn't seem to want to let anything through it hardly! I opened it up and it "looked" OK with nothing obviously plugging it up....but it certainly was a son of a gun to blow through. I'm going to let it dry out overnight and see how it is then. Either way it's getting replaced. I'll admit it's been there for a while and I haven't been to the track with it to really hammer it in a long time....so maybe it just doesn't like sitting around as much as it does. I've got an older style Barry Grant filter that's about 3 times as big I might throw on it and test while I'm waiting on new filters to arrive.
If that's all it is....I'll be a happy camper! And a little embarrassed it happened! Guess I'm going to have to step up my maintenance routine. I've got 4 Hot Rod's running, building another, a Harley, tractors and mowers and 4 pickups to keep up with!! LOL
Reinstalled everything last night. Summit is usually one day shipping to me since I live about an hour from their Dallas store.....but even though I paid for shipping...they used USPS which is now looking like Sat delivery for filters. Bummer.
Might go ahead and install the other setup so I can go for a quick run to test and see if it make a difference.
Needless to say, I would put in a safety in your Dominator, to kill boost ( or RPM, etc) if your fuel pressure vs boost drops. Maybe one for AFR vs boost.
That can prevent a big OOOPS even when you're not logging.
Needless to say, I would put in a safety in your Dominator, to kill boost ( or RPM, etc) if your fuel pressure vs boost drops. Maybe one for AFR vs boost.
That can prevent a big OOOPS even when you're not logging.
Yep...need to enhance it some. The boost is manual....so no control there. I've got timing jerked out quickly with fuel pressure but may need to add more for AFR just in case. Lots of ways to do it and add more safety for sure.
Yep...need to enhance it some. The boost is manual....so no control there. I've got timing jerked out quickly with fuel pressure but may need to add more for AFR just in case. Lots of ways to do it and add more safety for sure.
JIM
I'll be honest, I have to update mine too. Since you don't have boost control, you could have the Dominator kill spark. That's better than alarm bells for having the car tell you it's not happy.
I have drive by wire, so I could have my setup reduce the throttle, even though I have the pedal floored to the mat.
Well...guess what? Big block, twin turbo engines really like fuel! Who'da thunk it?
I stuck one of my other fuel filters on it while waiting for the Summit ones to arrive and took it for a quick test drive.
It's back to its old self of wanting to make you drive it as it comes up on boost from a 60 MPH roll in 3rd gear and lights the tires up. Didn't hammer it "too" crazy as the back roads I was on aren't that wide or sticky....but it did pull past 7100 and was still going hard. Time to build boost dropped to like zip.
Fuel pressure did as it should...with 16-17 psi of boost it added 17 psi of fuel pressure just like it's supposed to.
Now I suppose I need to give it a little attention and throw in some new plugs since those have been picked on a few times.
Note to self....pay attention to maintenance on stuff that sits around a lot!
Ok, back to logs and troubleshooting. Since your pumps were trying to send niagra falls through the **** with a little dutch boys finger in it, they were probably drawing a whole bunch of current. Bet you're battery voltage took a hit while your pumps were working up a sweat. Does that show up in the logs? Curious minds want to know.
Edit. That's funny. I wrote a completely innocent statement and the forum changed one of the words to "****" I guess it didn't like the dutch word for a dam spelled: d. Y. k. E
When it had the old filter in it with both pumps running it showed a steady line of 12.7V-12.8V. No real movement whether pressure was running at 43 psi or 18 psi.
It shows a pretty steady 13.0-13.1 with both pumps running with the new filter from 43 PSI to 60 PSI. They liked that.
Fuel pumps like voltage...probably need to look things over there too just to help. They have separate relays within a few inches of them and heavy wire feeding to them.....but I need to check the switch for voltage drops as well as alternator capacity. It's a small Nippondenso unit.
Back to O2 readings....when it was barfed...it would immediately start going lean as pressure went down and boost went up. It spiked 18.4 for an instant at the worst. Started in the 12'ish range and hung around 14'ish for a bit but when it started breaking up it spiked to 16'ish and I'm sure gave all sorts of funky 02 readings at the time. It shows pretty ragged as it banged around a little. The whole timeframe of the test was about 3/4 of a second.
Tonight, the same range stayed in the 12.0 to 12.4 range.
Data logging takes all the guesswork out of things doesn't it?
Fun with Data Logs and Preventing a Big OOPS!
I think you will find the issue for sure, GL. 
