HELP! GTFour hesitation under boost

[DonJuan]

Hey guys my brother is having a problem with his car, it is a 94 ST205 Celica GT4 WRC. We imported it a year ago and had no real problems with it. But now its got a massive hesitation when the boost.

Its weird, when the car is cold it only boosts a little (pretty sure its ECU controlled) and no problems, but when it warms up and it sees hard acceleration and boost the stock boost gauge goes all the way to the top of the guage and there is a massive misfire/hesitation. The car basically starts bucking. I changed out the plugs (pain the ass with top mount water to air intercooler), and the plugs looked a little dark, but otherwise fine. The distributor cap and rotor looked fine too, plug wires look new.

The only think I can attribute the change to is that a few weeks ago, regular gasoline was put into it by accident. I first noticed the hesitation a day or 2 later and 1/4 tank had been used. I dumped some octane booster in it and some 44k fuel system cleaner, but no change.

The car drives perfect under light boost and is still driven daily, and isn't throwing any engine codes. When the hesitation happens it also doesn't throw the check engine light or anything. No smoking or anything weird either.

Any ideas?

[SR240SX]

did you gap the plugs before putting them in? Is the car stock?

[sr20s14zenki]

Is it supposed to hit the top of the guage? Could it possibly be overboosting, causing fuel cut?

[RickDaTuner]

123345

[94_S14]

check fuel filter, fuel pump.

My friend has a JDM S14 and we noticed ALOT of sedament in his fuel tank, his car started with buckling to not even being able to go past 4000RPM under boost. What was happening was he was receiving all the boost perfectly but not NEARLY enough gas to make a propper mixture, thus no fire in that cylinder and massive buckling.

my idea to check aswell ^^

[sr20s14zenki]

Originally posted by 94_S14
check fuel filter, fuel pump.

My friend has a JDM S14 and we noticed ALOT of sedament in his fuel tank, his car started with buckling to not even being able to go past 4000RPM under boost. What was happening was he was receiving all the boost perfectly but not NEARLY enough gas to make a propper mixture, thus no fire in that cylinder and massive buckling.

my idea to check aswell ^^

Good point, it could be even an ailing fuel pump, ready to die. I have seen a few nissans do this as well. They dont completely die, they just dont have enough to maintain the pressure in the rail when the ecu demands more fuel.

[DonJuan]

wow thanks for the quick response guys!

Car is bone stock, no boost controller, not even a drop in airfilter. I didn't think you had to gap platinum plugs, just check em to make sure they were the same.

My first thought was that the wastegate was stuck closed, as when I did my SR swap in the 240, the wastegate was stuck closed.

Im gonna check the the fuel lines and filter. If the tank is full of crap, doesn't that mean that the filter could just be clogged too?

I sure hope its not the pump, cuz I don't wanna know how expensive that is gonna be.

[sr20s14zenki]

Pump won't be bad. Walbro drop in. Or a supra tt pump haha. I'm sure it's just your standard mount in tank pump

[Ashkente]

Originally posted by RickDaTuner



you start with basic stuiff, and clean the MAF sensor with some brake cleen, or some CRC Intake/MAF cleaner. and reset the ECU as well.

o

Gen3 3SGTE's are MAP sensored.

[94_S14]

Originally posted by DonJuan
wow thanks for the quick response guys!....

......
doesn't that mean that the filter could just be clogged too?

I sure hope its not the pump, cuz I don't wanna know how expensive that is gonna be.

Yep the filter may just be clogged, just check the pump to ensure it is not corroded or old looking. They are fairly cheep, maybe around $150 for a good 255lph.

To remove the residue purchase a drill pump from princess auto, connect to drill and run the hose on the bottom of your tank until you remove all the gas + residue.

[RickDaTuner]

Originally posted by Ashkente


Gen3 3SGTE's are MAP sensored.

i probably should have looked into the engine set up before posting huh. that makes my post pretty irrelevant then. But o totally agree with Fuel pump.

cheers.

[DonJuan]

Thx guys, I'm gonna pull the filter tomorrow and check everything all the way to the pump. Cant think of a better way to spend thanksgiving! I'll post up results.

Oh and Rick, I thought it was a MAP sensor, but with this car I wouldn't doubt if there was a MAF sensor too. Its got 2 rads, 2 water pumps, everything non essential is held down by 4 grade A bolts... no wonder it weighs more than the moon, but god damn Toyota makes a good rally car.

[texasnick]

Hey saw this thread a little late.

The st205 uses a MAP sensor....the AFM found in st185's is no more

First you need to jump E1 and TE1 ports on the diagnostic terminal next to the passenger side shock tower to get any stored codes. The light itself may not be lit up, but this car tends to hold on to old codes, some of which limit timing advance and boost. If you go to gtfours.co.uk it will give you a step by step on how to do this. Make sure there haven't been any CEL codes stored. If there are, make note of them and then pull the EFI fuse near the passenger tower for about 15 seconds to reset the ecu.

Fuel filter is where I would start as well. If you can, it might be worth checking the fuel pressure at the rail to see if the pump is giving out. autopartsway.ca carries a fuel filter for this car....I think they want around $40 for it. If you end up needing a fuel pump, as suggested above, just get a Walbro 255 and drop it in. They are quite inexpensive.

When it bucks, is it kicking out black smoke? I know plug gap is important on this car. If the plugs are gapped super wide (recommended is 0.8mm IIRC, double check), high boost pressure could be blowing one of them out. Also, what grade plugs did you buy? If you're thinking of changing the plugs again, do a compression test on the engine, just to be sure.

You should also change the dist cap / rotor. Makes a difference on a 20 year old car. I know it did on mine. It's a right PITA to change though.

Check that the wires are within tolerance WRT resistance. They tend to go bad after 20 years too. I don't remember the exact number they are supposed to be at, but you can find it in the BGB. If you don't have a copy, pm me and I'll email them to you.

Pretty sure the WG spring is open at ~7 psi on the gen 3 motor. Someone correct me if I'm wrong.


I feel your pain on changing plugs. I'm from the Honda world and I don't think it's ever taken me more than 20 minutes to change the plugs on a I4. This car took me around 3 hours (but that included some charge cooler cleaning / lagging as well), AND I still got that damned code 54 the first time it got chilly outside Even the simplist task is a serious PITA on this car.....but it's worth it

Good luck and pm me if you want a second pair of eyes.

Nick

[GT-FOUR]

You should have him join http://celicatech.com

But anyway, if it has 87 octane gas in it, that is the problem.

Knock response. Octane booster will not help.

Best advice, drive it until it is out of gas, then fill it with 94. Then, unplug the negative terminal of the battery for 1 min to clear the stored codes.

Youch, 3 hours to change the plugs! After some practice, you'll be able to do it in 15 minutes. (yes, with the WTA IC...I have 2 of them)

Aside from that, plugs / wires / cap / rotor. Get new OEM Toyota. I'd put money on those a million times before suspecting the fuel filter, pump, or residue in the tank.

[GT-FOUR]

Also, you are right, boost is electronically controlled. There is a Turbo-VSV that will limit boost when conditions are not favourable.

[JZS_147]

sounds like ignition to me.

[DonJuan]

did the fuel filter. $34 and a lot of swearing later it finally was done. Car still does the same thing though, although the filter itself did seem more restrictive than the new one when i was just blowing through it.

I guess its off to the check the fuel rail for pressure and price out some new wires. I sure hope it isn't the cap and rotor... Gonna drop the tank and do a pump too.

Just to clarify, the 87 octane gas as been burned out for months now. Its back to the 93.

[600rr]

Originally posted by JZS_147
sounds like ignition to me.

What i was thinking.
Even on my subi the same issues were occuring when i was trying to boost under WOT that was because the coilpacks were cracked. Try vac/boost leaks too.
Check everything ignition wise and maybe coilpacks and make sure you gap the plugs like texasnick said.

[Whitie_Bear]

damn code 54, i get it too...where does the coolant go ahahahah (yes i know about shrinkage in cold lol)

just a FYI, i had a 180sx that would buck and misfire horribly under high boost, it is highly modified (350 hp wheels) well highly modified for me, some think its fairly tame but anyways i chaned the spark plugs with the NGK copper ones (yes copper ones) gapped properly and i used 7 series temperature plugs as it fit the boost levels im running (Theres a guide somewhere) and this completely fixed my issue

i spent months in recoating the fuel tank, new pump, new filters etc. etc.

in the end $2.50/each spark plugs cured my problem...go with the easy stuff, although we all think about the horrible sand in the gas tank scenario, its extremely rare, check the stuff thats a no brainer
EVEN IF YOU JUST INSTALLED NEW PLUGS, install new plugs AGAIN, so many times ive been stubborn and said, i just changed my plugs last month so it cant be plugs, and then guess what..it was the plugs

long story short, you have some sort of firing issue, timing is off or something...my car hesitates on WOT full boost because my clutch is slipping (st205 gt4) and yes you would think the clutch would slip on starts or transitions, nope on the GT4 itll start slipping midway in 3rd or second gear once boost starts coming on strong

then you have the lovely job of dropping the engine to change a clutch...cars expensive, but 10 times the quality of any of the cars built here in those years

[DonJuan]

After alot of digging on Celica fourms, I found a thread where they same symptoms are described and the solution was a dying fuel pump! yay! Walboro pump is $120! YAY Shipping from the UK? Expected delivery January 27th? FFFUUU!!!

Will update when it gets here...