[Gearhead1124]

Whenever I step on the gas from a stop or from a slow roll the car hesitates. The longer I keep my foot in it the more it does it. If I keep my foot in it, it will eventually misfire. It will misfire on different cylinders. One time it was cylinder 2, I cleared it, then another time was cylinder 3. Occasionally at a stop sign she will shudder. Especially on an incline with my foot off the brake.

BUT if I accelerate slowly there are no problems. **** I can even floor it at 40 mph, she will drop the gear and take off no problem. Sounds healthy as ****.

So far I have changed the coil pack, wires, spark plugs (recently rechecked and good), the fuel pump, fuel filter, the fuel pressure regulator, the MAF, the TPS, and the Idle air control valve. I also completely cleaned the throttle body and checked for vacuum leaks in the intake.

She currently has a cold air intake, long tube hedders, a test pipe, and a cat-back exhaust. I’m using a mini-catalytic converter insert to dupe the check engine light.

What is wrong with her? I’m out of ideas.

 

[Circuitsmith]

What is wrong with her?

With all those mods I'd say it's not properly tuned.

 

[Gearhead1124]

With all those mods I'd say it's not properly tuned.

It ran fine will all the mods installed for over a year. No check engine lights and great performance. The hesitation came much after the mods.

 

[Circuitsmith]

Look at fuel pump pressure. What year and mileage?
Does it have adjustable valves.
Look at compression.

 

[AUTOSPARK]

Look at fuel pump pressure.

Before doing that I suggest you look at the O2 sensor voltages. If the hesitation is due to a fuel delivery issue it should show in the O2 sensor signals.

If I helped you fix it, why not...

Your support is greatly appreciated​

 

[Gearhead1124]

Look at fuel pump pressure. What year and mileage?
Does it have adjustable valves.
Look at compression.

I just put in a new pump with strainer. I haven’t checked the fuel pressure tho. It’s a 1999 Tiburon FX and it has 134,000 miles on it. I don’t know if it has adjustable valves. I haven’t run a compression test but I have put “Restore” in the oil since I noticed that the dip stick had moved out of place several times after putting it back, probably caused by blow-by.

 

[Gearhead1124]

Before doing that I suggest you look at the O2 sensor voltages. If the hesitation is due to a fuel delivery issue it should show in the O2 sensor signals.

If I helped you fix it, why not...

Your support is greatly appreciated​

I could do that. Although the oxygen sensor has been replaced with an oem. I don’t know how much voltage it should read.

 

[Gearhead1124]

I figured it out guys. I owe it to all of you to tell you what it was. The spark plugs were the wrong ones I.e they were not gapped properly. I put in “pre-gapped” plugs and it runs like a Lamborghini now. Such a stupid mistake. I wasted so much money on other parts. Check your plugs guy, check your plugs. Smh