Dueling fuel pumps causing a pulse?

[billschroeder5842]

I noticed a "faint pulsing" this morning when I firsted headed out.

I started my 91 and without warm up drove easy for a few miles. I noticed upon light acceleration I felt a faint "pulse" every 1/2 second or so. On steady cruise the pulse was gone so I'm suspecting fuel pressure.

The car has 82k, new FIC injectors, headers and a tune (Thanks Steve Schroeder!) in February this year. The fuel pumps are original.

After my stop, and with the car fully warmed, I drove home with no pulsing or performance degradation. I popped a fuel pressure gauge on the engine and it showed 40 at idle. I taped the gauge to my windshield and took it out for a quick ride. I got on it and showed (after a quick blip down after punch)40 at cruise and 48 with WOT.

So, I know that upon cold start both fuel pumps run til the engine get to 172-ish or so when the secondary shuts off and the car operates on main. Could that pulsing I felt be "Dueling fuel pumps?"

I'm not super worried just more curious than anything. Thanks!

[Paul Workman]

More info (data) needed. But, that said, and you can check w/ Marc, but those readings are low compared to data from my Z and others: more in the 43-45 in normal cruise and 53-54(ish) at WOT.

And, you could be experiencing a misfire - which would explain the pulsing sensation (more likely, I'd guess).

Ignition switch ON but motor not running, you can test you fuel pumps current draw by measuring current between the battery and the pump diagnostic connector. Normal current draw is between 8 and 10 amperes combined (4-5 amperes for each pump).

And, let's not forget that an injector or two could also cause a pulsing sensation. (Maybe not as likely if they are new - But! Never assume...)

I replaced a bad coil with under 50k miles. I replaced the ALL at that time. But, first I detected and open circuit between the output terminals of (what I assume was) the bad coil.

"Pulsing" is one of those things that has many brothers (causes). Gonna need to dig a little further to narrow which it could be. Do you also have an FSM??

And, BTW, ALL ZR-1s have dual fuel pumps. Pulsing wouldn't be the result of having two pumps. But, if there is fluctuation 'BLIPS' in fuel pressure, then that might cause it - and make me think about possible fuel regulator issues, maybe? More info pleaze!

[billschroeder5842]

Thanks Paul.

I drove the car yesterday about 40 miles and did not notice anything out of the ordinary although I did let it warm about 10 minutes before I took off. On Sunday it was turn the key and go. I did use a looooong Texas on-ramp as personal drag strip and the car pulled every bit as hard as before.

I'll check the amps pull when I get home tonight.

With more clarity, in February the engine got 16 new FIC injectors, new plugs, new plug wires, new coils and SW headers mated to a full Corsa. The car was put on the dyno and tuned. New fuel filter about 2500 miles ago. The FPR is original (what ARE guys doing for new ones??) Sure, something could have gotten wonky.

This does not feel like a "miss" but more like the old fashion "feathering" of carburetor--very faint and "soft" not a sharp feel.

Yes, I consulted my FSM but could not find anything about my experience. Again it is faint and maybe out of scope for the FSM?

Now with all this, I do admit to having a full overactive imagination and could be imagining things where none exist. When I turn off the engine the DM flywheel still makes me think I broke something- logic be damned!

[jss06c6]

Bill,

What was the temp that morning?

Steve

Sent from my SM-G950U using ZR-1 Net Registry mobile app

[Hib Halverson]

Fuel pumps don't "duel", but if they could, you'd see it in your pressure testing.

[XfireZ51]

As Hib points out, fuel pumps aren’t “dueling”. Sounds like it occurs in Open Loop.
What exactly do u mean by “pulsing”? Is the motor bucking? And is it occurring at all throttle positions or just very slight? Etc etc.

[billschroeder5842]

The pulse was very faint and it was a cold morning (30's) and the engine was stone cold. I usually let the car warm for a few minutes before taking it out, but not that time.

The pulse was very muted, the car ran fine with no performance degradation and the pulsing went away when I gave the engine some gas, hence me thinking that this is fuel pressure sensitive?

Now, I had the car out yesterday (70's) and it started and ran just as always. No pulsing and felt like it always does.

I think I had an one off anomaly or was imagining things.

[LGAFF]

Most cars as they transition during warm up can have some odd behavior, my SLKL55/E550 both do this, as does my ZR-1...not unusual.

[billschroeder5842]

Originally Posted by LGAFF

Most cars as they transition during warm up can have some odd behavior, my SLKL55/E550 both do this, as does my ZR-1...not unusual.

Thanks- I'll just chalk this up to my cars "personality"

[rkreigh]

check the plugs As the gaps get wider you can get some mis fire under load in upper gears that "goes away"


get some monitoring software tracking the aldl data traces so you have some info to work with


EASE or Diacom or many of the modern software products are pretty easy to use and will provide you a world of info to help diagnose the problem