Hesitating and stumbling over 3500 RPMs. Help! **Update**

[SrBigbutt]

Update....I decided to replace all my intake manifold side gaskets. So I now have new intake, EGR, Throttle body, and ISCV gaskets. The EGR valve gaskets looked to have been blown and it were loose. But all of this did nothing to my original problem. It may be running a little better. No more bucking, but still falls flat above 3500RPMs!!

It is nice to know that I have all new gasket all around on both Intake and Exhaust sides. But its frustrating to know that nothing I have done has done much to improve anything. So I'm now leaning towards Fuel Pressure. Maybe a faulty FPR? Any good way to test it?

 

[stolensupra]

If you have the stock fpr in place and your j tube has not been altered in any way the fpr is not likely (albeit not impossible) to be the culprit as the j-tube's restrictive properties act as a failsafe for a faulty fpr.

 

[SrBigbutt]

Still have the stock FPR and the J-tube has not been altered. Fuel pump is about a year old. It was just an OE replacement.

 

[stolensupra]

You are brewing a true mystery here man

---------- Post added at 05:54 AM ---------- Previous post was at 05:50 AM ----------

Ok. I read back through all the posts and had an idea. Are you using any kind of boost controller. and if not check the tube running from your wastegate actuator to the turbo compressor unit and test the wastegate bolts to see if they're tight, the wastegate for operation, and the wastegate shaft for any sort of damage or warpage. good luck bro.

 

[SrBigbutt]

Definately a mystery. No boost controller and i've replaced the wastegate vacuum hose and tested the actuator operation and it seems fine.

I hate throwing parts at a problem, and the funny thing is, pretty much everything i've replaced need to be replaced. But it hasn't been my main problem. Since I need to replace my front main seal, i'm going to look at timing again. Going to replace front main, oil pump seal, timing belt, water pump, tensioner and spring. Maybe my timing belt is stretched or something. Going to change it, since I don't know how old it is and be maticulous on setting timing.

 

[7mslider]

i don't know if this will help you or not, but a similar problem happened to me a few weeks ago. my car would run fine if i only gave it about a 1/4 throttle and didn't hit boost. when i gave the car wot and it would try to boost it would feel almost like fuel cut and not go over about 4k rpm. my fuel pump was only about a year old, but after i found nothing wrong with timing and spark i checked it anyway. what i found was a very dirty pickup strainer. even though the pump and strainer were new you put it in a 20+yr tank and it clogs fast. i would suggest dropping the tank and just taking a quik peek. after i got a new strainer and cleaned the tank really well i had no more problems. just an idea since you can't find anything else like i couldn't

 

[SrBigbutt]

May be a good idea. I dropped the tank when I first got it and it seemed ok. But you may be right. Wish you didn't have to drop the tank to get to the fuel pump.

 

[SrBigbutt]

Took the sending unit out and took a look and it doesn't look as nice as I remember! 8-( See some rusty stuff sitting at the bottom. Looks like I need to either clean it and or replace it. I'm leaning toward replacing it. Maybe I can have some luck finding a good replacement.

 

[7mslider]

what i did with mine was clean it out real good, and took it to a hotrod shop and had it sealed. it didn't cost but $150 and that'll keep it from rusting in the future

 

[jetjock]

1) This problem is often caused by a faulty fuel pump relay. Driving the car with B+ and FP jumpered is a test for that.

2) There is absolutely no need to drop the tank in order to test the fuel pump, suction screen, and filter.

 

[SrBigbutt]

I can try running it with the pins jumpered and test the relay. I will do that today. But most likely the strainer is clogged.

 

[SrBigbutt]

Tested the jumpered pins and it didn't have any affect.

 

[bombinuass]

Tested the jumpered pins and it didn't have any affect.

what do you mean no affect?

 

[SrBigbutt]

I drove the car with B+ and FP jumpered to test the relay as suggested and I didn't notice a difference. It still hesitated and lost power at about 3500 rpms. It felt the same jumpered or not.

 

[89turbosupraman]

I worked on a supra that had a very similar issue and after doing due diligence and testing/checking all the usual suspects it turned out to be the aftermarket intake. It introduced something in the intake path that the afm couldn't handle. The oem made the car run perfect.

 

[SrBigbutt]

I had the stock OEM intake on it when I first got it and started tracking down this issue. Only installed the Apexi Intake because it was such a PITA to remove the stocker when checking for boost leaks!!

 

[SrBigbutt]

Update....I installed a different tank on my Supra yesterday. And guess what. Its fixed!!!! Wooohooo!!! Fuel pump pickup was nasty!!! It was full of rusty muddy crap! Put new tank and strainer and now it boosts fine and no more hesitation. First time i've ever felt full boost!!! FEELS GOOD!!!! haha.

But guess what....now I have a new problem. 2 days before I put the new tank on, I noticed my car was smoking when I would get to a stop sign. It looks white/grey and smells like oil!! It doesn't always do it. But i'm guessing my turbo is on its way out! So one problem fixed and a new one presents itself!!

 

[bombinuass]

that sucks man

 

[7mslider]

glad you got it figured out. that was the same exact problem mine had. my turbo is on it's way out as well lol....time for a 57trim

 

[SrBigbutt]

Thanks, I should have checked that a long time ago. I was in denial!! Just sucks that my turbo starts to give out right when I start to feel what its capable of! haha. 57trim does sound nice.