Fuel Starving Problem Sc400

[solaros]

Hello all,

I have a 1992 SC400 with 194k miles on it. Recently I have been having a very strange problem, when I punch the throttle in 1st or 2nd gear the car starts to accelerate and then dies, recovers and starts to go again and then dies in a repeated cycle until I let off the gas, if I drive more sedately it runs perfectly very smooth no problems. The problem persists through all gears, rpm ranges, driving conditions and I can even get it to do its cycle a few times in neutral by starting out in gear and bumping it to neutral. The problem is much worse however if the gauge indicates that I have less then half a tank of gas or I am cornering hard.

Now comes the fun part, I have already read all other posts pertaining to similar problems and tried all the possible solutions, and I do mean all, for example:

complete tune up, new NGK iridium plugs, bosch wires, new caps and rotors, air filter, PCV valve, oil change

replaced the fuel filter

new TPS sensor installed and calibrated

Opened the fuel tank and removed the pump and cleaned the pump filter screen and tested the pump. also removed about half a gallon of rusty brown water from bottom of tank with a syphon hose, the problem seemed to get alot better after that but its still there.

Tried the trick where u short the B+ and FP ports in the diagnostic port to test that the fuel pump computer is kicking the pump into the high speed mode with maybe a slight improvement but the problem persists. when I plug the jumper in I can hear the pump increase in speed so I know it is working.

I ran 2 cans of Sea Foam through engine as directed, 1can in tank, 1/2 can in oil before oil change, 1/3 of can into brake booster vacuum hose... Now its a much crisper hesitation.

For the past 2 years the check engine light has been coming on and going off randomly mostly on the highway with no noticeable ill effect, but since this problem started I pulled the codes (21 and 28) which indicated a failure in the signal from the main O2 sensors to the computer, so I replaced them and it made no difference the light still comes on and goes off when it feels like it. I dont know if this is related or not.

my best diagnosis as a mechanic says fuel starvation, but i cant figure out why. why is it related to the level of gas in the tank, why doesn't the CEL say anything useful about such a violent problem,

Does anyone know where their might be a place to attach a fuel pressure gauge to the fuel rail so i can see if its dropping?

Has anyone had this problem before and found a solution or is it something unique to me?

I have modified some things on the car that might affect this problem although nothing to the fuel system or engine. stock intake, filter, and MAF. Stock engine and ECU no piggyback FMUs or anything like that. I have deleted the rear main mufflers, New Engine and tranny mounts, New flex couplings in drive shaft, Supra 4.272 Tor-Sen LSD.

I am thinking either clogged fuel injector, pressure regulator, computer or sensor problem, or some weird combination of things causing the pump the suck air.

I am running out of things to replace and don't want to shotgun this anymore its getting too expensive. Any and all help would be appreciated!

-Jake

[dcfish]

Hello all,

I have a 1992 SC400 with 194k miles on it. Recently I have been having a very strange problem, when I punch the throttle in 1st or 2nd gear the car starts to accelerate and then dies, recovers and starts to go again and then dies in a repeated cycle until I let off the gas, if I drive more sedately it runs perfectly very smooth no problems. The problem persists through all gears, rpm ranges, driving conditions and I can even get it to do its cycle a few times in neutral by starting out in gear and bumping it to neutral. The problem is much worse however if the gauge indicates that I have less then half a tank of gas or I am cornering hard.

Now comes the fun part, I have already read all other posts pertaining to similar problems and tried all the possible solutions, and I do mean all, for example:

complete tune up, new NGK iridium plugs, bosch wires, new caps and rotors, air filter, PCV valve, oil change

replaced the fuel filter

new TPS sensor installed and calibrated

Opened the fuel tank and removed the pump and cleaned the pump filter screen and tested the pump. also removed about half a gallon of rusty brown water from bottom of tank with a syphon hose, the problem seemed to get alot better after that but its still there.

Tried the trick where u short the B+ and FP ports in the diagnostic port to test that the fuel pump computer is kicking the pump into the high speed mode with maybe a slight improvement but the problem persists. when I plug the jumper in I can hear the pump increase in speed so I know it is working.

I ran 2 cans of Sea Foam through engine as directed, 1can in tank, 1/2 can in oil before oil change, 1/3 of can into brake booster vacuum hose... Now its a much crisper hesitation.

For the past 2 years the check engine light has been coming on and going off randomly mostly on the highway with no noticeable ill effect, but since this problem started I pulled the codes (21 and 28) which indicated a failure in the signal from the main O2 sensors to the computer, so I replaced them and it made no difference the light still comes on and goes off when it feels like it. I dont know if this is related or not.

my best diagnosis as a mechanic says fuel starvation, but i cant figure out why. why is it related to the level of gas in the tank, why doesn't the CEL say anything useful about such a violent problem,

Does anyone know where their might be a place to attach a fuel pressure gauge to the fuel rail so i can see if its dropping?

Has anyone had this problem before and found a solution or is it something unique to me?

I have modified some things on the car that might affect this problem although nothing to the fuel system or engine. stock intake, filter, and MAF. Stock engine and ECU no piggyback FMUs or anything like that. I have deleted the rear main mufflers, New Engine and tranny mounts, New flex couplings in drive shaft, Supra 4.272 Tor-Sen LSD.

I am thinking either clogged fuel injector, pressure regulator, computer or sensor problem, or some weird combination of things causing the pump the suck air.

I am running out of things to replace and don't want to shotgun this anymore its getting too expensive. Any and all help would be appreciated!

-Jake

Get rid of the bosch wires to start and get OEM, Get the codes read when the CEL is on. Your o2 sensors probably need replacing.

[solaros]

wow was looking throught he forum and saw my own post, thought id tell the rest of the story. the reason it ran poorly when it was below half a tank of fuel was because the connections to the fuel pump were loose and shorting out, when they were wet with gasoline they made good contect and all was fine but then they dried off they stopped working. replaced the pump and harness and all is well again!

-jake