chrisindub

iTrader: (1)

I have a really weird issue with my 92 sc400

It has 200K on it.

Runs great at startup, lots of power, enough to break traction in first and second gear. Shifts smooth through all the gears

Then after about ten minutes after it warms up it losses power about 50%. When you take off with wide open throttle from launch, it runs fine again. shifts through all the gears.

Anything less than full throttle, it runs like a four or six cylinder (no offense to sc300 owners who would leave me in the dust!), it has significantly less power, wont downshift.

If i turn off the car, it will run normal again about a minute or too, then it starts acting funny again.

There's no check engine light, exhaust looks clean ( no smoke ) No ticking, engine still sounds smooth.

I looked searched the threads, found many threads/responses, none similar to this one. I hooked it up to check engine codes at a friend's shop and it said the coolant temp sensor is bad, so im replacing that today. Otherwise i just thought about ingition system, fuel, cats.

Any advice would be much appreciated.

lmfod

So is it when coolant is on open loop?

chrisindub

iTrader: (1)

dunno, didnt check that, talked to lexus, they said its a sensor that has something do do with the fuel injection too, it was reading my coolant to be -29 degrees.

should have it in tomorrow

chrisindub

iTrader: (1)

Turned out my #2 trans solenoid was still shifting, but switching the trans into limp mode

So after about 20 min of driving , that car would get sluggish, accelerate poorly, not downshift, and the OD cancellation switch would stop working

Pulled solenoids 1 and 2, they seemed to be working fine, replaced them anyway.

Problem fixed

chrisindub

iTrader: (1)

Now the car bogs a little at low rpm, fine with WOT

Checked CEL codes.

O2 sensor and coolant temp sensor

Replaced them.....still bogs

chrisindub

iTrader: (1)

New CEL/Trac light on.

Code for MAF sensor.

Disconnected the mass airflow sensor and the car drives amazing, no bogging.

Read a lot about about people killing their MAF sensors with CRC cleaner, decided to try something different.

Pulled just the sensor out of the housing.

Cleaned all of the plastic parts by wiping them clean.

There are two sensor shafts that protrude out of the sensor body into the lumen of the housing.

I blasted them multiple times with short bursts of dust-off compressed gas and in particular all the grooves and opennings without letting any moisture build up. Just short blasts.

Put it back in, hooked it up, reset the ECU by taking off the negative battery terminal for a minute.

Drove it for 20 min, CEL/Trac light did not return and not bogging, FOR NOW.

A couple other things,

I tried resetting the ECU by pulling the EFI fuse for a minute as described in the forums, that did not reset it.

I was thinking about deleting the resonators and leaving the stock mufflers, what do you think? Too loud?

I'll post again in a week or so if the problem remains fixed

chrisindub

iTrader: (1)

started running like it's missing a cylinder or two now.

put in new coils, plugs, and wires.

no change after.

looking for a new/used MAF sensor to see if that works

SexCoupe

iTrader: (6)

Unplug the Maf again if it runs good that's your problem i can't believe u asked us about your problem tried to diagnose them and replaced all that stuff lol ask and be patient young skywalker

chrisindub

iTrader: (1)

Impatience is definitely one of my character defects.

I found an early 90's gs300 MAF sensor at pick a part, same fuji part number. Bought it for 6$ with a climate control cluster (mine's LCD is f'ed). Put it in. Car runs better, but still hesitating.

Runs awesome, no heitation, with the MAF unplugged.

I was reading that unplugging the MAF puts the engine in a kind of "safe" mode with a richer mixture, and ignores the sensors.

Makes me think maybe there is another underlying sensor or fuel issue that doesn't trip an engine code.

I'm just not sure if the used MAF sensor i pulled is also malfunctioning or if it's something else.

Going to check the resistance of the MAF.

Thinking about doing the fuel pump jump to see if that makes a difference.

With the fuel pressure checked, driving around it was like 34-42 psi on the street, during hesitation with the MAF plugged in.

MooJohn

Pull your ECU and check the capacitors. You can have lots of unexplained issues when they start leaking acid all over the place.

OG Dada

iTrader: (10)

I went through all of this also my man. I was never satisfied of the power output even though it improves whenever I replaced a part or adjusted a part. I recently tried Seafoam the other week and never been happier. Seriously though, it really improved my SC's acceleration and power and it gave me the power that I was expecting from a 250hp V8. After going through alot of parts, some where really for changing, some I wanted to change just to make up for the other parts changed, I really thought that the problem was with the entire manifold being so dirty so I wanted to try out Seafoam based on everyones suggestions. Don't over do it though, which alot of people keep on having problems with. 1 pint is enough, do the 1/3rd rule.

SexCoupe

iTrader: (6)

Get a Maf from someone with a known working one if the car runs good with it out I can't imagine anything that will fix the problem besides the ecu

chrisindub

iTrader: (1)

Have a friend who has an sc400 without any mechanical issues, i will try and convince him that a night out at spearmint rhino = him letting me borrow his MAF and ECU to see if that fixes anything.

I'll pull the ecu and check that first thx Moojohn

About the seafoam, i read a lot about where to put the stuff, and fouling plugs, etc. I just put in new plugs. Doh! So if i do do it, it's 1/3 in a full gas tank, 1/3 in crankcase oil, and 1/3 in the PCV valve? then oil change?
Thx Kingphilip

OG Dada

iTrader: (10)

Yeah, 1/3 full fuel tank, 1/3 crank case & 1/3 PCV valve hose. It's not true for the spark plugs to foul. I think the people who's saying that used too much and didn't follow the instructions, which is clearly written at the back of the bottle and even in their website. It's completely safe I would say since it's composed of the same additives that fuel companies use. Just take your time doing it for it to properly work and don't over do it. My experience with it have been so great that I'm really recommending it for people to try out. Like I said, if you check my threads, I've gone through a lot ever since I got my SC, this is the only thing that changed everything. My SC doesn't feel like it's hauling something heavy anymore, it can accelerate without any, I mean any hesitation at all and idles way quieter and steadier even with the heater/AC on.

scENFORCER

Interesting thread. I wonder if seafoam would fix my low idle issue as well. My car also feels like its hauling a boat recently..
I was considering replacing the ECU before though, thinking thats most likely the problem.