ChatGPT Troubleshooting

 

Why your A/F ratio spikes lean and it wants to die

Two main culprits (usually both):

1. Decel Fuel / Dashpot not set up correctly

When you push the clutch:

• Fuel may be reduced too aggressively

• RPM drops faster than the IAC can react

• The engine briefly goes lean → stumble or stall

If AFR goes high right when the clutch goes in, that’s a dashpot/decel issue, not VE learning.

---

2. Idle Air Control (IAC) can’t catch the RPM drop

If:

• IAC Position is already near 0%

• Idle target is too low

• Dashpot decay is too fast

Then the engine simply doesn’t get enough air to stay alive during the transition.

This is extremely common on:

• Light flywheels

• Small engines (like your MGB-based setup)

• Manual transmissions

• Aggressive cams

---

Will Sniper eventually “learn” this?

Short answer: No — not automatically.

Long answer:

• Sniper will not learn during clutch-in decel events

• These events are outside the learning window

• You must tune idle, dashpot, and decel fuel manually

However — once you fix those areas, the rest of the tune will learn just fine.

---

What actually fixes it (in order of importance)

1. Raise idle target slightly

Especially with a manual transmission.

Try:

• If idle target = 850 → try 900–950

• This gives the IAC more authority when RPM drops

---

2. Increase Dashpot airflow

This keeps the engine from nose-diving when you push the clutch.

In Idle > Dashpot:

• Increase Dashpot Position

• Slow down Dashpot Decay Rate

You want RPM to float down, not crash.

---

3. Check IAC position at hot idle

At fully warmed idle, in gear or neutral:

• Ideal: 2–8%

• If it’s 0% → not enough base airflow

• Open the throttle blades slightly and re-set TPS

This is huge for clutch-in stability.

---

4. Reduce aggressive decel fuel cut

If Decel Fuel is pulling too much fuel:

• The AFR spike gets worse

• The engine stumbles before idle control kicks in

Try:

• Raising decel fuel slightly

• Or delaying fuel cut until lower RPM

---

5. Verify TPS and MAP behavior

When clutch goes in:

• TPS should return smoothly to ~0%

• MAP should rise but not spike erratically

A jumpy TPS will absolutely kick it into OpenCL harder and longer.

---

What “good” behavior looks like

When properly tuned:

• Clutch in → RPM drops smoothly

• AFR may go slightly lean but recovers quickly

• No stall, no dip below idle target

• Sniper re-enters Closed Loop within a second or two

---

TL;DR

• Sniper goes Open Loop on clutch-in by design

• It will not learn during that event

• The stall/lean spike is an idle + dashpot tuning issue

• Fix it with idle speed, dashpot airflow, and proper IAC setup

• Once fixed, learning resumes normally everywhere else

If you want, tell me:

• Hot idle RPM target

• IAC % at hot idle

• AFR when clutch goes in

• Engine + cam specs

…and I can give you specific numbers to plug in rather than generic advice.

Holley Sniper Stealth EFI - Part 14 (Start-Up)

This morning, I performed the start-up process as defined in the Sniper manual.  The steps primarily consist of using the Wizard to define some variables, confirming your throttle position sensor is reading properly (0 to 102% in my case), and checking for leaks.  When that is complete, you cycle power and then are ready to start the engine.

This is the point where you always hesitate just a little and start to think over everything that you just checked to make sure you feel good before turning the key.  I turned the key and it took between two and three seconds and the engine started.  It ran rather smooth and with the outside temp so low the coolant temp was at an initial 69 degrees.  The engine would not start to learn until it reached operating temperature of 180.

When the engine first started the idle was close to 1,200 RPM (set to decrease to 850 when warm).  As the engine began to warm up, the RPM increased a little and was closer to 1,600.  The AFR was initially around 12.5 at start up but slowly increased to where it was rather lean.  The average was probably around 15.5 but there were points it would spike much higher.  

The entire time the car was getting to temperature, the CL Status was OpenLP and it doesn't start learning until that states ClosedLP and the temp is above 180.  The temperature ultimately reached 186 but the CL Status didn't change to closed.  The idle also stayed at 1,600.  The AFR stayed rather high too and when I captured a few pictures it showed 16.8, 18.8, 16.6, and 17.1 (it was obviously changing rapidly so I took a few quick pictures in succession).

After letting the vehicle idle for a while at 1,600 RPM and above 180, I decided it wasn't going to switch to learn mode and turned the car off.  After researching it a little, I found that I need to adjust down the idle setting in order to get tuning to begin as my idle was too high for that to start.  I adjusted out the idle screen by a half turn, started the car, and it was still warm enough that it went straight to ClosedLP.  

I drove around a little amount found that the idle was still high (1,100) and didn't drop properly when I came to a stop.  That was because the IAC was better but still not set correctly.  The proper setting is between 2% and 10% and mine still read 0% which meant it was still out of range and the system couldn't then manage the idle RPM for me.  I turned out the idle screw another 3/4 turn or so and the IAC% was 4.  When the fans came on, it went to 9%.  The Sniper then controlled the idle properly at 850.

The car is running smoother at idle than I remember.  It seems to have really good throttle response.  I drove it another 18 miles (starting mileage at installation was 8535).  I'm rather impressed at how quickly it started and has been able to tune itself.  I'm quite glad to have the car running and driving again as it has been a while.  I moved to this new house a little over a year ago and have only really driven it 20 miles since because of the carburetor problems.

Holley Sniper Stealth EFI - Part 13 (Final Steps Before Start-Up)

The temperature has been in the low 30s or 20s all weekend with quite a bit of ice accumulation.  As a result, we have been mostly locked up in the house.  While the garage is cold, I've used a little Heater Buddy to keep the temperature to the point I can work off and on.

Over the weekend, I wired up a dedicated ground to the fuel sending unit.  I also filled a gas tank with 4 gallons of gas so I can add it to the tank when I'm ready to see the impact on the gauge.  I've not done it to this point as it will smell and probably not the best idea to have the heater going in those conditions.

I created a small mount for the fuel tank vent and ran it out of the old hole in the floor where the sending unit wires were originally routed.  It is mounted using the old exhaust hanger bolts so it is slightly close to the exhaust but not excessive.  I painted the bracket with more of the Kylon Matte Black paint.  The bracket already had holes in it but I figure having something that works for now is better than waiting for perfection in two weeks.  I can go back and make these various brackets perfect later if I choose.

I then worked to fasten the fuel lines along the underside of the car.  I used zip ties at the lower side of the fuel tank, made a couple of brackets around the axle (shown below), and then used some very large zip ties (#UL181B-C) that are super thick and made to hold HVAC ducting to hold the lines to the subframe connectors.

I still need to secure the line as it runs up the back of the transmission.  I also need to make a bracket which holds the fuel filter right behind the throttle body.  

Holley Sniper Stealth EFI - Part 12 (Sending Unit Adjustment)

This evening after work, I decided to add a little fuel to the gas tank and confirm the fuel gauge reads properly.  This is one of the few points that you have such a controlled situation you can determine exactly how much you have in the tank when the gauge reads empty or close to it.  I wanted to take advantage and set it up so that I had two gallons or so when it reads empty.

I added probably just under wo gallons to the tank and then checked the gauge but it had hardly moved.  I then added about a third gallon but didn't want to add any more.  At this point, the needle pointed to the lowest point of the E which is far below the empty hash mark.  I checked the sending unit and don't remember the exact ohm reading but it was below 70 so the sender was registering fuel in the tank.  

I pulled the sending unit, which is exceptionally easy since it is now on top of the gas tank.  It was at this point I was exceptionally thankful that I decided to use the rubber gasket on the sending unit instead of the cork gasket with sealant.  What I didn't know the first time I removed it was that I would remove it another 9 times before I decided to leave it alone.

The first adjustment was just to make sure that I had full movement of the arm where it would just touch the bottom of the tank when empty and would just touch the top when full... no change.  I then decided I would move the pivot point down just a little (1/8)" from the recommended setting... almost no impact.  This continued time and time again with little impact.  The sender is working as it reads 52.5 ohms with the three gallons it just doesn't correlate too much on the gauge.

I contemplated it all for a while and decided the gauge should really be set to read empty with three gallons.  Any more and it simply doesn't make sense to call it empty.  This time, I took it apart and confirmed the float would need to be about half under water before it started to move.  This really didn't change my approach much but confirmed that the two inches of fuel in the tank should be enough to move it reasonably.

I ultimately dropped the pivot a total of about 3/8".  I adjusted the arm so it would still just contact the top of the tank when full.  On the low side, it would initially attempt to hang lower than the bottom of the tank.  I adjusted the lower arm stop to match the bottom of the tank.  I then put it back in and the gauge pointed to the middle of the E.

I decided at this point that I was going to put just a bit more gas in thinking that I was perhaps at the tipping point of it moving rather rapidly to the empty hash mark.  I put about another gallon so I expect to have about 3.5 gallons in it.  With this amount added, the sender read 45 ohms and it is now pointing at the E hash mark.  

When the gauge is off or disconnected, you can see in the picture above the needle stop well below the E.  This is the beginning of the needle movement.  I expect that is where it starts when it is at 70 or so ohms.  This makes sense when you consider it but really empty is considered the bare minimum rather than what appears to be a quarter tank below it.  

I think when I actually fill it up, I should put in 4.5 gallons which would put me around 8 total and see what the gauge reads.  While I don't expect it to read a half a tank, that is what I'll have and it will be good to know what it reads.  I'll then do the same at 12 and then 16 gallons.  I'll try to take pictures each time just so I validate the gauge a bit more and know what I'm working with.  

Holley Sniper Stealth EFI - Part 11 (Tank Installation)

Today, I installed the new gas tank into the refinished Mustang floor.  Before doing so, I took advantage of the extra space to install the bulkhead fittings, fuel filter, and connected the fuel lines.  I need to fully tighten and secure everything but those initial tasks are far easier done without the tank installed.

 There was some original sealant between the tank and the floor which I emulated using some 3M butyl rubber strips (#08578).  This sealant is probably the best that you could get for this job.  That said, I hesitated a little using it as I know it will be an incredible pain if the gas tank needs to be removed in the future.

I bolted the new tank in place using a set of Scott Drake (C5ZZ-9002-MK) reproduction screws.  I used the replacement rubber filler hose that came with the tank as the original was hard as a rock.  I cut it to fit (3.5") and then installed it with a set of Scott Drake (C5ZZ-8287) clamps.

There are little vertical bumper pieces that can be installed below the rear bumper.  I've not had them in place and don't have interest in them.  I used reproduction bolts I had that matched the originals but used flange nuts on the back of each.  I did this in part to fill those holes but the two going down through the gas tank at the back at the car also serve as the ground for the gas tank and sending unit.  

With everything installed and tightened into place, I connected the sending unit, power to the pump, and a dedicated ground for the pump.  I then secured all the wiring with some 1/4" Tech Flex braided wire covering to help keep is safe.  I now need to find something that will cover the tank and help protect the lines and the wiring as I tend to put things there when going on long road trips.  

The following is what I have left before I could try to start up the car for a test drive:

• Confirm under hood wiring is secure
• Plug all wiring into the Sniper throttle body
• Connect the battery terminals
• Confirm fuel lines are all secure
• Confirm all fuel lines are tight
• Connect the fuel vent
• Connect throttle linkage
• Fill with gasoline

These are the things I'd like to come back to after the test drive is complete:

• Build a bracket for the filter behind the throttle body
• Build brackets to hold the fuel line under the car
• Insulation for the top of the fuel tank
• Rewire and dress up underhood wiring
• Run fans with the Sniper system