Are you talking about the huge TPS drop right in the middle?

The red line is the RPMs, and there's a huge drop right there too. That's when I took my foot off of the gas to shift to the next gear, and then floored it again.
That wouldn't happen with an auto, I imagine.


As for the TPS ramping up, I've never really been in the habit of just shoving the gas pedal to the floor, but progressively "feeding" it as the engine feels it needs more. So, that's more likely from my driving style, than from anything else.

 

Ok so the TPS & RPM are for the shift and I can see that.
I thought that "capture" and dip was when the issue happens, never thought of shifting of gears. Also ok on the ramp up of the TPS.
See what happens when you don't tell us the full story on the capture picture?

So in the capture where did this issue happen and if not in this one do you have one showing it?
What RPM limit is the cam and what are you using for dist. & IGN. box?
How is it or is it tied into the EFI system?
Dave ----

 

I can see where you were letting the clutch out and then a small dip in rpm just before 48 seconds which is where it stumbled.
Everything makes sense except the extreme variation in A/F ratio.
The O2 sensor has a little time lag behind the injector pulse width change so there will be a small amount of "seeking" but not that much.
Was the system in closed loop or open loop (CL disabled) mode at the time this was taken?

 

Bumping this slightly aging thread - came across it today and curious if you ever sorted out your drivability issue, Abandoned Bronc. My only tuning experience is 4cyl cars on megasquirt and a bit of diesel stuff, but the screen shots look familiar enough. Hope it's running great!

 

Sorry for not getting back to this thread.
No, nothing has been resolved on this, and I haven't gotten any further figuring it out.
However, Holley decided that they're not sure either and have sent me a brand new unit to try. I'm hoping there's just something screwy with it, and it solves the problem! Very generous and appreciated.
I know I have balked a few times about having to twist their arm to get a response, but when they do, they come through in spades.

In the image, the issue takes place when the cylinder pressure (the MAP sensor) kPa gets over 85 - 90 and approaches atmospheric. You can see how, right before it does, the AFR (the pink line) spikes lean, and then drops way down to extremely rich. When it does, the MAP sensor reading starts to spasm and become really spiked.

I initially had my DUI performance ignition on the engine but, wondering if it was an ignition related issue, I swapped the entire system out top to bottom (including down to the spark plugs) for my old DuraSpark II. It didn't resolve the issue.
The EFI system has a [coil -] wire that connects from to - on the coil. Then, there's a wire from the EFI that goes out to the tach. It uses the signal to read the RPMs. During initialization, you tell it how many cylinders the engine has.

The system was in closed loop when this took place, which is any time the system climbs over 160°F. This almost invariably happens when the throttle opens enough to reach full cylinder pressure.
On a few other logs I have though, the AFR spikes up and down more aggressively, but the symptoms are the same. Drop in power, and a spasm/shudder from the engine.



Thanks! Overall, it drives really really well! If I could just get it to stop doing this, I'd be ecstatic with how it drives overall. Very good throttle response, cold weather driving, power, etc. I just can't open up the engine all the way, which is a real bummer with how much I've built the engine up.

 

have you got the new unit installed? hope everything gets resolved quickly for you!

 

I haven't. It won't be here until tomorrow. I might get a chance some evening this week. Otherwise, I'll be out of town over the weekend, so it might not be right away.
Hopefully it does though!

 

 

just a thought but i was reading some of the paperwork i found with my sniper install that it says return line should have no more than 3 PSI of pressure. i don't know what it will do if you have more than that but figured id share. 'murcia! BTW what's a good switched source in run and start i can tap into. all I'm waiting on for my install is for me to do the wiring and the transmission to get done being rebuilt. hope yours gets back to normal!

 

Interesting on the return line PSI. I don't know if there is any control one has over that. It's regulated by the unit itself. But, it's worth checking.

On mine, I used a heavy duty solenoid (like the starter relay) and ran a key-on source to it's on switch.
Then, power from the battery to it, and power from it to the EFI unit. There are two outlets on my solenoid. One's a small gauge and one's a large gauge (like the big post for the starter). The big one goes to the ignition so it has plenty of juice.

 

I would think if the return had to much PSI on it it would back up into the supply side?
Now my thinking like you said it is self regulating but say if the return line was too small or had a kink tis could make the PSI go up.

Talking of returns, where does this fuel dump back into the tank? Could it be dropping close to the supply causing air to get sucked into the supply?
I heard this could be an issue when people add the return to a non-return sending unit and just let the fuel drop from the top.

Just throwing stuff out that may jog something to think / look down a different path.
Dave ----

 

Well, we stayed in town due to the weather, so I swapped out the unit today. It actually seemed to buck a lot more than the previous one. However, it's back at the original setting, without any learning going on, so I'm hoping maybe this one will be able to "self learn" the issue out of itself.
One thing I did notice was that my previous unit always sat right around 5 lb/hr of fuel at idle. This one sits around 3.5 - 4 lb/hr of fuel with the same AFR. That's something I suppose. Who knows?
Maybe after a few days of driving, this one will right itself. We'll see.

As for the return line, this Bronco was originally fuel injected, so the high pressure fuel system, as well as the fuel return line, were already in place. Now... I didn't check the return line to see if it was plugged or anything. I just used it as is. I suppose anything is possible.
However, it's a very direct line with no kinks back to the tank.

 

Ok just didn't want you or others to think "well it is just a return line" how could it have more than xx of psi on it?
To small dia. line, kinks, rubber hose failing on the inside could all add to the psi being too high.

As for the return in the tank if it was to close to the fuel supply pick up could cause aeration and low fuel psi on the supply side.
In your case I don't think that is so being a EFI set up to start with but someone making a return from scratch should think of this.

I hope when it "learns" all will be good and you can enjoy the truck.
Good luck
Dave ----

 

Well, it seems like it's back to the drawing board.

I still can't figure out what is causing this issue, but I'm starting to wonder if it's not the EFI unit.
The new unit has the same issue and even when it actually is getting the AFR correct and holding it at a steady 12.5:1 on hard acceleration, it's still doing the surge/spasm. It generally starts out by being overly rich, but if I keep accelerating, it'l even out and correct itself, get the AFR where it needs to be, etc. but it'll still spasm. I'm just wondering if something else is going on that's making the EFI computer have a hard time getting the fuel mixture correct under those conditions.

It seems to be a lot more prevailant at lower RPMs. I can make it repeat consistently by going 70 on the interstate in overdrive (about 2000 RPMs), dropping to about 60 (1750 RPMs), and then pushing on the gas to speed back up to 70. (Being in overdrive also makes it much easier to drop the engine vacuum to near 0). It'll start to shudder, lose power, but still speed up to 70. Repeat, repeat, and it'll do it every time.

This is really starting to get on my nerves, and I don't know what to do next.


Is it possible that it's something to do with my timing curve?
Does a carbureted application have different timing curve needs than EFI? Maybe something to do with injector pulse widths?


I would think that if something was internally wrong with the engine, like springs/valves/cam, etc. I'd notice it elsewhere. But, as long as I keep the engine vacuum above about 4, it drives like a dream.

 

Just to bring us up to date, what did you try changing on the ignition system?
Have you done a compression check on all cylinders?