SOHC hesitation and acceleration problem

[AndyG]

I have a 1990 240sx with a KA24E and i run 93 octane. It is a 5 speed swap but i dont think that has anything to do with my problem. My ECU is throwing a 55 which means all good.

Okay here is my problem... when i start from a stop i have very slow acceleration. When I get around 3000 in third you can feel it build up. if you are in second and let off the gas and let the revs drop you can push the gas and it accelerates fine. If you keep the revs up around 2000 when your at a stop it accelerated like a rocket. When I start my car with some gas and keep the revs up it is fine. Also I have HORRIBLE gas mileage sometimes as low as 10 MPG!

I have been trying to fix this since i got the car about six months ago. I have been all around zilvia and a bunch of other forums and i seriously need some help.

This is all I have done.

Clean MAF
New Fuel Filter
Check Fuel Pressure 34 at idle and 40 at throttle
Check TPS Voltage
3 new injectors
new IACV
New intake gaskets
Checked for vacuum leaks
Seafoam in gas multiple times
Cleaned fuel rail
Checked timing
New cap, rotor, wires, and plugs
Replaced CAT with test pipe
CTS
No itake leaks
new air filter


Maybe it is an ignition coil problem?
I dont know where to go next. please help.

[moso]

i would change my 02 sensor and my coolant temperature sensor. both can cause excessively rich conditions and neither will throw a code on older 240s

[AndyG]

i did replace both of them but my wire for my o2 sensor wire is shot... could that be it maybe??

[S133P3R]

Might want to reword that o2 sensor and give it another shot.

[AndyG]

Just finished rewiring my o2 harness and resetting the ecu and nothing. Same slow acceleration. Any suggestions? This problem sucks and in every other thread with similar problem the people either never fixed it or never posted the solution. Thanks!

[compactfean]

What is you're fuel pressure under acceleration? You might have to run the fuel gauge up to the windshield so you can see while driving, but if your fuel pump is going out it can cause this.

[AndyG]

Well with no load it is around 40 when I rev it. That's a good idea about running it to the windshield. I'll do that tonight and see what happens. Thanks!

[compactfean]

Yeah, just pinch it under the windshield wiper. I used to have to do this to diag cars that had a fuel pump that was ALMOST out. Let us know.

[AndyG]

I haven't found any hoses yet for the fuel pressure gauge yet. BUT, i picked up an air/fuel ratio gauge..

here is a video showing how it drives. It is showing it is really lean, but it freaks out and jumps between lean and rich.

anyway, another thing that worries me is when i let off the gas the gauge go so lean that it shuts off.. what could this mean?

sorry it is so shaky...it was hard to shift, drive, and record.

http://img444.imageshack.us/img444/2389/o4p.mp4

Any Ideas?

[S133P3R]

suggestion - Fuel pressure gauge. low pressure could result in a lean mixture. and no, not the fancy racecar ones that mount in your dash... they rent the "fuel pressure tester" at your local autozone / oreilly.

[AndyG]

This is what i got right now. it reads 36psi at idle and 40psi when i rev it.
I need to find some hose so i can test it during load like compactfean suggested.

[S133P3R]

Yes that would do it. Have you also checked the vacuum on the fpr?

[AndyG]

Yup. I feel like it is weak but i dont know. also no gas comes out so the diaphram is not messed up. it could be stuck open though.

[AndyG]

Well i got up this morning and the a/f gauge was consistently doing something different. It stays very rich.

Here is a new video. It is at WOT.
http://img59.imageshack.us/img59/1574/2wk.mp4

[AndyG]

Okay well i got a boost/vacuum gauge hooked up today. steady at 20 inches of vacuum. still running rich though....

[nando]

Im having the same problem on my 89 auto. swapped in another distributer cap and rotor and ran better but still has a bit of hesitation at low rpms. this is the second cap and rotor i have put in it, first one was when i bought it a bout a year and a half ago. next i'll try a fpr that i got ordered from auto zone hope fully i can get it in this weekend and see what happens. good luck man

[AndyG]

well mine used to be an auto untill i swapped it. let me know what happens with your fpr because i think that is where im going next.

[AndyG]

Well got a little update...

my vacuum falls very slow along with the revs. this problem is affecting every aspect of my motor.

I got some hoses to move my fuel pressure gauge so i will be checking that in the morning..

Thank you.

[AndyG]

Alright... fixed the vaccum thing because i mounted my gauge in the wrong place...behind the check valve instead in front of it.


anyway.. my fuel pressure was a little on the low side so i got a walboro. the fuel pressure is now back up.


It still has the same problem now with some jerking.

can someone please help me? this thing is killing me.

[compactfean]

At this point, test the coil and try a different fuel pressure regulator.

[AndyG]

thats what i was thinking about next.


how do you test the coil?

[compactfean]

I can't remember the exact procedure, just download the fsm at the top of the tech section and its in there. Its something like test center post to negative and should be between x ohms and xxx ohms.

[schassisonly]

I'm going to chime in here and say it could be the EGR (exhaust gas recirculation) system?

Maybe your EGR valve is stuck open or faulty. Could use a clean or maybe even a complete EGR system delete.

I had slight hesitation in my S14 DE, around 2000-3000RPM. I followed a trick where you plug up the vacuum hose from the EGR-BPT to the EGR Valve, and it seems to have solved the problem:

http://jull.net/s14-tech-guides/block-the-egr-valve

I do have a ECU 105 code for the EGR Valve Solenoid though, and the CEL on my dash is super annoying. Having the EGR system tucked up against the firewall is a total b**** to work on.

[AndyG]

Well, today i made some progress and i think i finaly found the problem.

The hesitation worked itself out...i guess the computer just relearned it.

I did a compression test and it was 150,148,150,150. is that good?

I tested the coil and the power transister via the procedure in the fsm. It says that resistance should be about .7 ohms but mine is ringht at 1 ohm. is that okay?

Also, in the FSM it says to put a timing light on the other spark wires.. Except for the first one, the light is flashing too slow and cuts out when i rev the engine.. they are just crappy autolite wires but they are new. Could this be the distributor or the coil???

It makes since that it is a spark issue because it is running rich.

PLEASE HELP.. im so close to solving this horrible problem.


and the egr system is functioning correctly...

[compactfean]

Coil is toast. I have had coils .1 ohm out of spec and be bad. Replace it and you will definately notice a huge improvement.

[AndyG]

Well, it was not the coil... it is still running a little rich and it still has slow acceleration....

I took out the distributor and it looked fine and was in the correct position.

Can anyone think of why this is happeneing? i am about to give up and take it to the crappy dealership... please help me.. seriously.

[compactfean]

Well that coil that your tested is still bad and I wouldn't run it unless you tested it incorrectly. Have you checked your fuel pressure under a load yet? Try another fuel fpr??

[AndyG]

ya that is true... but no i got a new pump so i didnt feel checking the pressure was neccesary.. ill check it under load this week.. I love this car but i have been actively looking for this problem about six months. its getting tiresome.

[compactfean]

The reason I say check fuel pressure under load is not because fuel pump but because fuel pressure regulator. I put a walboro 255 in a friends car because he thought the same thing and ended up being a torn diaphragm in the fuel pressure regulator......it was able hold good fuel pressure under idle but couldnt keep up in higher rpms. (which felt very random)

[AndyG]

Okay I will give it a try.


Also while driving it I have noticed the gas smell being present so I assume it is not running rich anymore!?