Run 1000cc injectors

 

What would that do, it only happens at idle, when off idle its fine, I think the IAC needs some fine tuning to get it to idle correctly.

 

I must have misread something, sorry.

 

Set your base idle screw until IAC reads about 3 to 5% duty cycle. Also, play with target AF ratio for idle. Surges are usually from too rich of an idle or timing table irregualrities around the idle position on the spark table.

 

I was under the impression that too lean causes a surging idle. Not questioning just that’s what I thought as I went through the same issue with my truck and when I added more base fuel to idle it went away but my idle went up. Actually I still have a slight surge when it first goes into closed loop while warming up, then it goes away after a minute or so. Just trying to learn.

 

NX, the Sniper is only controlling the fuel as of now, no timing yet. I'll play with the base idle a bit and see what happens, I was told to take the IAC duty cycle down to zero, it was at like 38% out of the box, so i tried taking it to 0 and it made it a little better but its still doing it enough that i'm worried about pushing through the brakes.

 

Lean or rich won't make a surge. You want lean idle 15.2 to 15.5:1 for plug maintenance and economical use of fuel and keep the smell down. The surge coming from anywhere oscillations, such as fuel map and overcompensation of the iacv and timing map and even pcv flow regulated changes. To smooth the surging you will
1. smooth idle regions where the fuel and timing map sits '4 corners' of cells all make similar numbers
2. pressure test the intake system for leaking and update pcv hardware, consider fixed orifice pcv flow
3. slow down iacv compensation stepwise so smaller adjustments take place over time to the airflow
4. reduce idle timing if needed
5. Make use of timing compensation tables if available to help stabilize idle

 

Is the timing stable in the idle range? If it's moving around it may make it hard to get it to settle down.

 

Ive dealt with efi cars that surged cuz of lean. And only because it was lean enough that the iac was trying to control it from stalling. So it would go into a constant surge. Added fuel to the happy point of the motor and it idled smooth.

 

As Tbird says above, lean can cause it if it is way too lean, but the O2 sensor should be telling you where you are and go from there. With the base tune files, holley usually has target af at idle in the 13 to 1 range or richer, which if the car has a larger than stock cam, it will be letting unburnt air and fuel into the exhaust, which the O2 can't see the fuel, it only sees the air, so it sees lean and adds fuel. That can cause a surge. If target AF is around 15 to 15.5 as F4 said, then it could be a tad lean causing the surge but doubtful. Mine usually idle rock solid when the target is set to that but you must ensure that the cells around the idle cell are all the same target and fuel values. Don't try tuning with VE if tgis is your first time, use lb of fuel as it makes more sense. Jmho.

 

I haven't had a chance to look at it yet, my sons hockey team has had away games for the past couple weeks and then a tournament that was also out of town, so my time has been spent with him doing his thing, as soon as I have a day I'll check into the AFR readings and see whats going on with that, thanks for the suggestions.

 

I had a chance to look things over, noticed right away my volt gauge and my snipers display were reading 2 different voltages, I decided to look into the electric problem first, got everything reading 14.5 volts except the snipers screen reading 13.5 volts, I've checked everything and narrowed it down to the snipers main power wires, I need to check those out to see why its losing voltage, then I can figure out the surge issue, my hope is the surge is connected to the electrical issue.

 

Generally, ECU report less than input voltage because of dropout from diodes and similar.

It could display the input voltage if there were some comparator, analog reference, and added code. But I don't think they care that much to show input voltage when you could just measure it yourself. I think if you measure the input volts to the ECU it will be higher than the ECU is reporting. Usually by only 0.3 to 0.5v though I would think.

 

measured the wire at the harness, it tested 13.5 and the battery is at 14.5 so there is an issue somewhere in the wiring to the battery from the snipers harness. I'm hoping to get it sorted out this weekend.

 

A battery can't really charge to 14.anything volts. That is a surface charge phenomenon.

https://www.corvetteforum.com/forum...mechman-170-amp-alernator.html#post1607413802

Automotive electrical system should be able to run at 12.0v. At wide open throttle I always command 12.85 to 13.3v near battery capacitance for smooth signals within electronics and to prevent engine failure due to alternator failure (the engine is tuned at 11.8 to 12.8v ranges with adequate fuel flow).

 

Sam you dont by chance have a battery charger connected while your doing this test?

 

no charger hooked up to the battery, I looked over my afr gauge and its all over the place when the surge happens so is the vacuum gauge, so its hard to tell what exactly is going on, ran the car for about 30 minutes this morning and no surge at all, but just idled it in park, I don't want to take it into traffic an risk getting into an accident since it can push through the brakes. I don't know if it makes a difference but I have the battery mounted in the trunk and I need roughly 22 feet of wire to get there, and the wires are 14 ga on the sniper main wires, so I was thinking about swapping those out to 10 ga for that long of a run, the 14 has a giant amount of voltage drop compared to the 10 ga at that distance.

 

Im not trying to be mean but you have no idea what you are doing, and there is nothing wrong with that. But you need to decide if you want to learn properly or if you just want somebody else to do it for you.

If you want help to learn properly OR want somebody to do it for you both of these I recommend you start here
https://forums.holley.com/forum/holley-efi/sniper-efi


Engines are simple devices, meter the air and fuel properly with followthrough diagnostics and they always do the same thing. Before tuning any engine you should always
1. Timing test
2. Compression test
3. Pressure test intake
4. Pressure test crankcase & Setup factory PCV

Then you can tune the engine by comparing what you know about how engines should run e.g. the mass of air and fuel at some diameter iacv/injector opening for some periods of time result with How much kilowatt or units of power the engine derives and how much is lost to friction and waste energy. Simple, yeah if you know down to every last atom how it works. Which you can learn with enough time and obsession.

 

What does the fuel map look like in the idle area ? Try making cells in the idle and surrounding area the same. A surge can be caused by it moving from one cell that's say too rich to one that is too lean or vice versa. One causes the engine to speed up the other to slow down causing oscillation or surge, timing can do the same thing. If you flatten everything out in the area and it helps then you can work from there.

Different engines like different AFR at Idle, Mine will idle fine from 13:1 up to over 15.5:1 but 14.7 is the sweet spot on my car.

 

Something else, I don't know if Sniper has closed loop learning with a AFR target map. If it does set the fuel table break points so that the engine idles at the intersection of four cells. I then set the AFR target map so that the break points are between the cells in the fuel map. In other words in the target map it would idle in the center of a single cell and the fuel map it would be between the cells. This makes for a map with smoother transitions and smoothes the idle area. The four idle area cells will most likely require slightly different values to achieve a steady AFR.