351W popping @ 4000 rpm

[5.8mont]

I have a 79 fairmont with a efi 351W I recently rebuilt the engine and installed a vortech v1 s-trim. I had the car tuned and it ran decent for the first 100 miles, but would pop over 6000 rpm. My wide band showed it to be running rich so I had the tuner pull 5% out of the fuel. After that the car ran better but still popped above 6000 rpm, after about a week of this it started acting up in a different way. Now the car has a intermitent problem half the time it will run perfect and the rest of the time wont rev above 4000rpm without popping and back firing. If it is only part throttle when I get to 4000rpm it sounds like im hitting a rev limiter and wont pop, but if it is full throttle it starts popping. I just got my distributer rebuilt by msd and had them check out my 6AL box they said the box was fine. If anyone has experienced problems like this or has any ideas please help.

[Sleeper]

Jmans old car still looking good. what wheels you have on it now?

Good luck figuring it out until it starts doing it all the time. Check your plugs and wires just cause.

[Chas_svo]

My worst problem that was hard to find on a 6A was a bad connection or short inside. Let the car idle and wiggle the purple/green trigger wires into the box. If moving the wires makes a miss, you need a new box.

It really sounds like more of a tune issue, but I'd check this as it's easy to check and rule out.

[Sleeper]

Who did the tune btw?

[5.8mont]

I had true street tune the car. That box is new with the build so it better not be bad. I've been fighting this problem all summer and nothing I have done has helped. It has new plugs but could maybe use new wires. I've noticed when it happens the air fuel goes lean.

[5.8mont]

Jmans old car still looking good. what wheels you have on it now?

Good luck figuring it out until it starts doing it all the time. Check your plugs and wires just cause.

The wheels are 99 cobras but are polished so I think they are after market

[turbostang]

when a car 'pops' or 'missfires' - 99% of the time it will show lean, as the wideband is picking up raw oxygen that is pumped since it wasn't consumed and turned to waste like would happen in a normal engine cycle.

Is this engine a roller engine?

Have the plugs been verified to be 'good'?

have the injectors been checked?

Is the pop in the exhaust, or through the intake?

Does the fuel pressure rise 1:1?

[Sleeper]

You have anyway to datalog?

wtf you been brooks.

[5.8mont]

when a car 'pops' or 'missfires' - 99% of the time it will show lean, as the wideband is picking up raw oxygen that is pumped since it wasn't consumed and turned to waste like would happen in a normal engine cycle.

Is this engine a roller engine?

Have the plugs been verified to be 'good'?

have the injectors been checked?

Is the pop in the exhaust, or through the intake?

Does the fuel pressure rise 1:1?

It is a roller, the plugs have been replaced since the problem started, I already had a injector issue and replaced them with new 60# siemens-before this problem started, sounds like through the exhaust, I cant see the fuel pressure as the gauge is under the hood. I have been looking for a way to make it visable.

[5.8mont]

You have anyway to datalog?

wtf you been brooks.

No i dont

[turbos66coupe]

Like said above, make sure your fuel pressure is rising with boost. Make sure you have vacuum/pressure at regulator

[kingjason]

x2 on fuel pressure. How old is the gas tank in your car?

The reason I ask is that I had a 79 TA at one point I restored. Car had 23k original miles and it had been sitting in a field for 10 years. I replaced fuel pump, intake, carb, hoses etc etc and it still would'nt run right after about 30 minutes of driving. You could putt around all day, but if you put your foot down it would back fire and sputter at high RPM's. It was the stupid sock on the filter in the gas tank clogging up. I put an air hose on fuel line, popped the gas cap, and blasted air into the line for a minute. Got in the car and it drove perfect for a few days. Pulled the tank and cut the filter off and it never had another issue. I just ran two inlines at the front. It is always something stupid that will drive you crazy.

[turbostang]

It is a roller, the plugs have been replaced since the problem started, I already had a injector issue and replaced them with new 60# siemens-before this problem started, sounds like through the exhaust, I cant see the fuel pressure as the gauge is under the hood. I have been looking for a way to make it visable.

What plugs are you using? Gap?

If you are not, you should be using a 'non-extended tip' type plug.

[5.8mont]

I dont think it's the fuel tank iv had the car for years with spray and never had these problems. One of my worries is the fuel pump itself, as i bought it from on3.

I had been running autolite 3923s and was told to try motorcraft AGS32C they are on the car now.

[5.8mont]

And the gap is .028