Hesitation during WOT

[WishDRFTR]

Heres what I got 1992 S13 Coupe, with stock block (KA) and S14 head (KA) and gnarly exhaust leak lol. I bought this car in pieces and am trying to get it back together and in somewhat of a running shape.

After I got the engine back together I've noticed that when I fully depress the accelerator the engine bogs and hesitates....then all of sudden it builds power and increases in RPMs. Almost like its waiting for something....

Now if I EASE into the throttle it'll build power like normal?!?!?!

I searched the forum and couldn't find a decent answer related to a KA24DE

I've checked TPS (seems good), and MAF (seemed good but cleaned anyway). Timing is set to 20 BTDC.

[Taylor008]

Check your ECU codes. Maybe a bad knock sensor? My car kinda acted like that when I went full throttle. New fuel filter or fuel pump is a guess if it's not the knock sensor.

[STEEZxIT]

Mine is opposite of yours, If i Floor it from a dead stop or atleast over 3K its fine.. but if i ease it from a dead stop, it will sputter up until it passes 2.5K RPM

I had the same problem as you from my old SR though, i never really figured out what was wrong, but i cleaned the MAF, TB, IACV. and also checked TPS. After that, problem went away.

[nismoman]

Check the timing

[WishDRFTR]

Last time I checked the ECU codes it gave me (flash, pause, flash, flash, flash) which I'm assuming is code #13? ECT code, I checked the ECT for resistance and just a hair on the low side so since the sensor was only $13 I threw on in the car just to see.

Light stayed off for maybe 2-3min of driving afterwards but came back on first time I went WOT. Maybe I'll check it again in a bit.

Nismoman - My Ignition Timing is set to 20 degrees BTDC (which AllData says is "spec"). I haven't checked Valve Timing (other than making sure my marks are lined up... I heard a compression test is another good way to check that?

Fuel has been a concern in the back of my mind seeing as I DONT own a fuel pressure tester... Viable cause?

[nismoman]

Did you backprobe the sensor with the ignition on the make sure it's sending voltage to the ecu? Might be a short in the wire if it's still throwing code with new sensor.

[WishDRFTR]

Did you backprobe the sensor with the ignition on the make sure it's sending voltage to the ecu? Might be a short in the wire if it's still throwing code with new sensor.

I'm going to do that shorty, as well as make sure the code is the same one as before.

Thanks for the help thus far!

[WishDRFTR]

Ok so I backprobed the sensor and it is sending voltage to the ECU. I also rechecked the codes and the only one I have is an EGR Temp Sensor code and seeing as how I dont have any EGR stuff I assume thats why its on.

Now, while I was at the shop today I borrowed a Fuel Pressure Gauge and check my pressure. With vacuum applied to the FPR I was reading 35-37psi (within spec) when I removed the vacuum source my pressure DID NOT CHANGE. AllData says that it should read 43psi.

Could this be a possible issue? I know poor fuel pressure will cause an engine bog HOWEVER my pressure with vacuum applied is good... I need opinions...

[WishDRFTR]

BUMPITY bump

[Taylor008]

When I removed my EGR I had reused the gasket hoping it would seal correctly. It didn't, and it would cause bad hesitation and irregular idle. New gasket and it fixed the problem.

I don't know what else it could be, just saying what happened to me. Check and make sure you have no air leaks.

[JDMRIDDAZ]

check voltage to the pump
wht/purple at f/p plug in back of car
if its low after start just rewire it...
and if its n/a w/ a bad exhaust leak will cause this
fix the exhaust

[WishDRFTR]

When I removed my EGR I had reused the gasket hoping it would seal correctly. It didn't, and it would cause bad hesitation and irregular idle. New gasket and it fixed the problem.

I don't know what else it could be, just saying what happened to me. Check and make sure you have no air leaks.

No EGR so deffinately no leaks there. Smoked tested the car and found a tiny leak in my PCV hose. Fixed it but its changed nothing.

[WishDRFTR]

check voltage to the pump
wht/purple at f/p plug in back of car
if its low after start just rewire it...
and if its n/a w/ a bad exhaust leak will cause this
fix the exhaust

I fixed the exhaust leak, turns out I left a bolt or two loose lol :D my bad!

now as far as your saying check voltage to the pump, your very unclear. Check for what voltage? dont you normaly check resistance on a fuel pump? And what do you mean by "rewire it"... Sorry, i just dont understand what your trying to say lol

I put a new FPR in, and that didn't fix anything. Nor did fixing my tiny vacuum leak. My fuel pressure still doesn't rise when I remove vacuum from the FPR so I'm gunna throw a fuel pump at it and see what happens.

[JDMRIDDAZ]

u use resistance to check fuel level sender and u check volts at switch wire on f/p plug at rear of car....

[WishDRFTR]

u use resistance to check fuel level sender and u check volts at switch wire on f/p plug at rear of car....

Ok, so I'm checking voltage of what? Obviously the fuel pump, but wouldn't checking voltage just tell me whether or not its working. Not if its weak. My car runs and drives, just has terrible throttle response...

[nismoman]

Make sure it's getting at least 12volts possibly a bit more when the car is running. It should never be lower than 12. Sometimes the connection is bad slowing the pump.

[WishDRFTR]

Make sure it's getting at least 12volts possibly a bit more when the car is running. It should never be lower than 12. Sometimes the connection is bad slowing the pump.

Ok, and I should check the wires mentioned above?

[nismoman]

That's right

[WishDRFTR]

That's right

Awesome, my meters at the shop so it'll be another day before i can check. That's for the help thus far!

[WishDRFTR]

Ok so I check voltage to the pump and it was PERFECT. I decided to buy a new TRE Performance fuel pump.

Now in case someone in the future comes across this thread I wanted to leave ya'll with this.

I replace the fuel pump this morning, and its fixed! CHECK FUEL PRESSURE!!! If the pressure is around 35-36PSI with vacuum to the regulator (its good) now remove the vacuum source, if it jumps to 42-43psi its good!! If your car does not do this, you've got a problem. Doesn't mean its a pump but its does mean its fuel system related.

Pressure gauges helps, but volume test is legit.