Still troubleshooting

[cubanman2]

I have a 93 sc400 and it is low on acceleration. I have been trying to fix my car for the past six months. So far i have changed spark plugs, spark plug wires, distro cap, distro rotor, front two o2 sensors, air filter, fuel filter, had my injectors professionally cleaned and balanced, battery, cleaned throttle body and intake manifold, hollowed out cats because they were clogged. Still my acceleration problem is there. I am getting frustrated with this car. I recently had my alternator checked and it is supplying low power. I am told that the lower power output is not enough to reduce my acceleration dramaticaly like it is now.What do you guys think? Also what else should i check or change on this car that could fix the reduced acceleration problem?


One more question, can my hollowed out cats be the cause of the low acceleration? I did it because they were clogged and i did not have the money to buy new ones.

 

[chrisman]

hollowed out cats may make your car run lean--among other things.. but whatever caused them to clog up is probably your problem... try disconnecting the bat for about a minute.. make sure there is no aftermarket radio or any thing which may supply power hooked up.. reconnect the bat, and drive the car and see if it runs differantly..
has it always seemed low on power, ar did it happen for no apparent reason?.. just from what you said, it sounds like the cam timing may be off.. did you change the timing belt? also, have you done a compression test?

 

[gloverman]

It sound like you should take it to a tune shop or competant mechanic. Here are some thoughts though. I agree with checking the cam timing and the TDC mark to ensure the timing is correct and that the front pully has not delaminated. Is the engine itself in good order? Are the valve clearances to spec? Have you changed the wheel size? A wheel with a larger rolling radiaus will redure acceleration. What are you comparing the acceleration to? What is your fuel flow and pressure. Is your fuel pump getting enough voltage? Is you ecu getting enough voltage. Has the ECU recorded any fault codes? Have you had it on a scanner to check live data? What is the mixture at? rich or lean? Is your transmission working correctly? Has the engine and trans got suitable oil in them? Is the rest of the exhaust in good order? Are there any restrictions in the air intake? Does your car have Traction control and is it working correctly? Is the engine running at the correct temperature? I could go on but I recommend you find a good mechanic to deal with and work with them to solve your problem, do some testing and remove the guesswork. Cheers

 

[Zuffen]

I think Cubanman 2 has pointed us in the rght direction.

The alternator is not doing quite what it should.

Low power to the battery spells low power to the ECU, fuel pump, igniters etc.

I suggest trying the following:

Disconect the battery when the car isn't running.

Charge the battery with a charger for a minimum of 12 hours (it would pay to check the battery is OK and will accept the charge.

Reconnect the battery and try it out.

The performance should drop off as the battery discharges.

An alternator re-build isn't expensive and it needs doing anyway so do it.

Can someone explain how a delaminated crank pulley will affect accelaration? The cam belt is driven from a gear keyed to the crankshaft which is totally separate to the crank pulley.

 

[cubanman2]

I fixed what caused my cats to clog. I disconnect the battery all the time to reset the compter. So thats not it. I had my timeing belt checked and it is good. I have not changed wheels, so that s not it. The valves specs, i have not checked but again i did not touch or modify anything. My car just one day did not want to accelerate with power like it used too. My car had great acceleration when i bought it. 8 months later this happend. The air/fuel is fine , the fuel pump is fine. I had my car specs checked with a mk2500 OBDI tester. My o2 reading are good. My ECU is good. My trans has plenty of oil, my car is running a little rich. No restictions in the air intake, The rest of my exhaust is good. No my car does not have traction control. The engine is at the correct temperature. I battery is in good condition.

I am a competent mechanic(Gloverman i did not appreciate that comment.)
I am asking for help because this car is different from the rest of the cars i have worked on.

Zuffen i tryed that already.

I was thinking it could be the EGR system. I read somewhere that if the EGR pipe is cracked it could reduce your power. I am also thinking it could be the MAF.
Does anyone have any other ideas?

 

[chrisman]

someone had mentioned the fuel pump.. i think the fuel pump on these cars has an ecu that runs them.. normally the fuel pump is run at a low voltage.. this makes it last longer and is quiter.. when you accelerate rapidly, it should go to high/normal voltage which increases the output.. you would need a fuel pressure gauge to check this one.. i beleive normally the press will be around the low 20s.. then will rise to the low 40s on accel.. im not positive on this info, but something to check..
if for some reason it is not working as it should, i do believe you would feel low on power..
the egr system re-introduces exhaust into the intake.. exhaust gas can not be re burned.. this-in effect- cools combustion.. by taking up space--kinda.. anyway, this may affect power, but the car would have trouble idling, and you would probably hear a cracked egr pipe..
also, i think what was meant by the delaminated front pully is that if you check it with a timming light, you may get an eronious reading.. the outer pulley may have moved in relation with the inner pulley..this may happen because on most cars there is a rubber ring that isolates the outer part of the pulley.. i guess it helps absorb harmonics..

 

[cubanman2]

The ECU is telling the OBDI tester that the pressure is ok and that the car is running slightly rich.That info rules out the fuel pump and ECU.

 

[cubanman2]

I don't think its the fuel system, i kind of ruled that out after i cleaned the injectors. I think it might be a cracked egr pipe, thus reducing accelelration or a leak some where. I just want ideas from people that have an sc400 for a long time and have worked on them.

 

[cribbj]

Don't overlook the obvious - are you getting full opening of your throttle body with the accelerator pedal floored? Several of my Supra colleagues have discovered their butterflies weren't fully opening!

Maybe a vacuum leak?

If you don't have a solid 12.5-13 volts going to your ignition, it may not be man enough to light everything off under load. As Zuffen pointed out, injectors are voltage sensitive too, and will operate more sluggishly at lower voltage.

John

 

[chrisman]

i think you should check your fuel pressure with a gauge-- not the obd tester.. you said it is still running rich.. how have you fixed the problem that clogged your cats? running rich would eventually clog your cats by getting them to hot.. and with the cats hollowed out, you check engine light would light up every now and then..does this happen?

 

[cubanman2]

I will check my throttle body again just to make sure but i think it is opening all the way. Zuffen might be right about the voltage, i do need a new alternator it is not working to it's full potential. But i was told by more than one mechanic that a low alternator will not cause the low acceleration i have. I don't know i might just give in and buy a new alternator.

 

[cubanman2]

Any other ideas i might have over looked?

 

[Muzza_NZ]

cm2,
this may be a dumb question, but have you checked you engine earthing strap? I had problems on another one of my projects, and it turned out to be a high resistance earth connection...

 

[cubanman2]

What is an earthing strap?

I have never heard of that.

 

[Zuffen]

Cubanman2,

Whilst your battery may be good if the alternator isn't giving it a full charge it can't give it's best.

A drop of 1volt in battery output will affect performance. The alternator usually doesn't drop voltage output rather ampage output. What happens is it can't keep up with the power demands of the car and the battery slowly flattens.

You could try charging the battery overnight and taking the car on a test run with the air and radio off to see if performance improves.

The engine has earth pionts at the rear of each head. There are brown wires/terminals bolted under 12mm bolts. Check they are tight.

The engine has a heavy gauge cable (battery cable size) that runs from the block to the chassis. It stands to reason this cable is OK or the car wouldn't be too happy starting. I'd check all the brown wires you can find and either check their tight and/or remove and clean them.

 

[cubanman2]

Earth points, i did not know that. I will check them. Also i found an alternator rebuild shop here in virginia. I might remove my alternator and have them fix it tomorow. I have not removed the alternator in this car before. Is there an easy way of removing it?

 

[Zuffen]

The alternator is fastened with 2x14mm nuts from the front.

Drop the serpentine belt by using a 14mm spanner to roll the tensioner pulley down to release the pressure.

Remove the battery cable at the battery.

There is a plug on the rear under a rubber cover and (I think) 1x10mm nut to remove to release the output cable.

Remove toward the front.

You may have to clear a few bits out of the way to get to it.

Refitting is the reverse.

 

[cubanman2]

I did not see any earth points. Are they connected towards the back of the heads? If so how far back, because i did not see anything connected to the heads. Also would it be easyer to get the alternator out from the bottom of the car? If i do it from the front it looks like i would have to remove allot of stuff.

 

[Zuffen]

The earh connections are on the rear of the heads. On the verticle rear foace. If looking for them they will be beween the heads and the firewall. Nice convenient place.

Removal of the alternator from underneath sounds easier. Never worked on an LS so don't know haw hard it is.

 

[cubanman2]

I removed tha alternator, but power steering fluid was all over it. I might have a leak. Is there an easy way to remove the power steering pump? Is this a common problem?