94 SC400 wont rev past 700 RPMs

[xzaticah]

Hi everyone.

it has traction control, 155K miles. all stock

the story goes: picked it up in a trade, hesitated and hard started. i replaced fuel pump and it fixed hesitaion on the road but still hard started. couldnt replace fuel filter due to rusted lines. i then ordered them, while waiting i drained the trans pan, put in new trans filter, washed and degreased engine bay, let sit for a few days, fuel lines came in put the fuel filter on.

right after i connected the filter started it, will idle nice for about 3 to 5 seconds then idle real bad. 300 to 600 rpms. almost like its running on a few cylinders. can not get it to rev up. it sputters and tries to die. figured i shorted something out, so a checked the AFM, both ignitors and coils, fuel pump ecu. i did the fuel pump ecu bypass and it made no difference. so then i changed the plugs wires cap and rotors. hard start is gone, but stilll runs super rich. the old plugs were black and i little wet. pulled one of the new plugs out and it was black and a little wet. all 8 of the old plugs are like that.

so im at a complete loss. i've been researching and been under the hood for many many hours. any help would be great.

 

[xzaticah]

No one has ever had a problem like this I see. Is it possible that all 8 injectors got stuck open or are worn and are not use to the more pressure that surging through them now because of new filter and pump? please any help, i have still been unable to solve this.

 

[stevechumo]

Check the fuel pressure regulator, or change out with a good one. Do you get sparks at all ignition wires?

 

[xzaticah]

Check the fuel pressure regulator, or change out with a good one. Do you get sparks at all ignition wires?

yes lots of spark. so kind of update and answer- rental fuel pressure test kit, used the banjo nut adapter and bolted it to the equilizer tube on the driver side next to the main inlet for the system. it reads 10psi. which is way low. im going to get some various fittings so i can hook the gage up the hardline thats in the engine bay before it gets to the rail. i ran all new vac lines to and from the fuel regulator and that sensor thing.

lets say it still reads 10 psi, is there anything in the tank that would leak. meaning, the line that runs from pump to the bottom of the tank? i just rechecked the pump. the hoses are new and its getting full power right to the end of the connector that plugs into the pump.

I was thinking it is the regulator. but no fuel was coming out of the return line, and as far as i can tell the regulater is connected to that return line. so right now im assuming its not it. but i will be reporting back. thank you for the advice.

 

[stevechumo]

If the injectors inject too much fuel, then it can be either bad injectors that are stuck open or bad regulator. If it leaks, then there's no fuel going to the injectors.

You can check the fuel filter, too. But if I were you, I'd replace the fuel filter and pressure regulator due to its age. If you can't find a good used OEM regulator, an aftermarket with fixed pressure rate can be used with some minor modifications. I believe it should be around 40 psi at the regulator.

 

[xzaticah]

If the injectors inject too much fuel, then it can be either bad injectors that are stuck open or bad regulator. If it leaks, then there's no fuel going to the injectors.

You can check the fuel filter, too. But if I were you, I'd replace the fuel filter and pressure regulator due to its age. If you can't find a good used OEM regulator, an aftermarket with fixed pressure rate can be used with some minor modifications. I believe it should be around 40 psi at the regulator.

i found the problem, its by-passing bad inside the tank. the hard line from the pump to the bottom of the tank right there at the very bottom. so the weld broke or the line down there cracked. so pulling oiut now and seeing what can be done. probably have to by a new tank??

 

[stevechumo]

You can find a used good tank for around $100. There're not too many demands on the tank. I just bought one a few months ago for $100 on clublexus.

 

[xzaticah]

ok, so it was the botton supply line, but it was in between the tank and the outside bottom line. it was spraying out that little hole that is there to help line up those banjo nut lines to the bottom of the tank. wierd. so it wasnt sealing and was filling up that small cavity and then spraying out the top. but the factory never had a copper washer, or gasket there to seal it. so anyways siphoned and but a copper gasket between the bottom tank and that deal that has the rubber gasket on it tighten it down and it runs amazing. i didnt do the fuel pump mod just did the jumper wire, but it runs better than when i tried that. it almost doesnt crank and its already firing up.

so my conclusion, an incredabily stupid design. they were probably high when they desided to design it like they did. anyways runs great. hope this can help someone else who might be experiencing the same thing to atleast check one thing off the list that you may not think of.