Car shuddering under high boost, not making sense...

[TravisD62]

Hey guys,
My car is being weird since I got it back together, everything runs great and smooth when I'm boosting about 8psi but as soon as I try to turn up the boost, the car starts hesitating and shuddering, especially as the rpm's get higher. I'll try remember everything I've done to it here to give you a brief idea. It's a freshly rebuilt Jdm 7mgte out of a 92', the car has all brand new bearings and seals etc, mhg, arp studs, an o ringed block, bored out and polished heads, and is a 3.1 litre. I've got an HKS intercooler kit, brand new 60-1 ct26, HKS downpipe and catback, Intake, rc 550's, Lexus afm, apexi safc II, and that's all I can really think of at the moment. I didn't want to go to crazy with the safc so I have it pulling fuel 15% from 3000rpm to redline, my afr's before the safc were usually 9.2 in boost and are now about 10.1-10.4 and drop to a 9.8 in high rpm. When I try crank the car to 15psi the hesitating starts and I've noticed the boost gauge starts bouncing around. It'll drop from 15psi to 10 psi in a split second and bounce back up again. I'm thinking this is a boost leak of some sort but am really unsure, my pipes are all nice and tight and all hardpipes from the hks kit. Anybody have any idea whats going on? Really hoping it's not my turbo as it cost $800 for the rebuild and upgrade and doesn't have 1000km on it yet. The housing on the turbo and everything was fine with no cracks as well. Thanks!

Travis

 

[Backlash2032]

Sounds like fuel cut.. But isnt 15 psi a little low for FC with a lexus afm?

 

[the_shippey]

Are you still running the stock fuel pump?

 

[TravisD62]

It's definitely not fuel cut, doesn't feel as harsh and the check engine light doesn't come on right after for a second. I'm running a MKIV TT fuel pump. I'm starting to think fuel pressure perhaps? Do I need an afpr?

 

[the_shippey]

I would think it'd be a pretty big leak for it to drop 5lbs right away and the bouncing back up is a bit strange. You might be onto something with the fpr. I'd try getting one and see how that treats you. It can't hurt anything.

 

[TravisD62]

Yeah it's a very weird situation.... My car is also overheating like crazy now. This is weird too because even the littlest bit of acceleration makes it red hot. Pulling up to a stop light the needle would go about 3/4 of the way to the red area, as soon as I would take off and try get going with >10% throttle, it would bury itself in the red. It was a pretty hot day here today but it's still odd considering I've been driving the car for 4 days now with zero overheating issues. The HKS intercooler is blocking the rad off pretty good, and I'm missing the air diffuser under the engine bay, could these two things be causing this? Also noticed my heat doesn't seem to work in the car, it blows air fine but the temperaturew doesn't change.

 

[adampecush]

how do your oil and coolant look?

I have a feeling I know the answer.

 

[TravisD62]

Oil and coolant both look fine, I definitely don't think it's a bhg. At least it better not be..... Car still pulls hard on 10psi though? Would it do that with a bhg?

 

[radiod]

My car didn't show ANY lack of power @ 10 psi and it had a cracked head.

 

[hvyman]

I had massive amounts of power. half low on coolant. and my temp gauge said the temp was normal....

 

[TravisD62]

Oh my.
This motor has almost $15,000 into it and the rebuild. Not even 5000km on it, the block was o ringed and it has a mhg with arp's. If the gasket is blown I'm dousing this car in gasoline and burning it to the f*cking ground. This is its 3rd 7m FFS! jfhdsljgfhdjkslhglfjkdshgkjfdhsglkjfhdslkghfdsl;ghfkl;dsj!

 

[Backlash2032]

Check the coolant for combustion gasses. You can get a tester at pretty much any auto parts store.

 

[hvyman]

Uhh why was the hg o ringed? I think that there is your issue. Space between the cylinders is way to small. With the proper machine work just the mhg would have been a better option.

 

[TravisD62]

Space between the cylinders is causing overheating and hesitation under boost? I have no idea why it was o ringed, that's how the guy built it to be "bulletproof`. He`s been working on supras for almost 30 years and put out some wicked cars though... The heads have also been bored out and polished too, don't know if this helps the situation? He did this to ensure that the head gasket wouldn't blow, and was the one EVERYONE around here says to get your motor built by. Anyways, I just changed both fluids and checked for exhaust gas, and the head gasket is definitely not blown.... Any other ideas? And is there anything aside from changing the oil I should do seeing as the car overheated badly yesterday?

 

[hvyman]

Compression check.

Bhg will cause overheating.

 

[laotionracer101]

[video=youtube;YAxTTt7BDq4]http://www.youtube.com/watch?v=YAxTTt7BDq4&feature=related[/video]

Haha bud, my gs300 bhg'ed still ran strong. And had the same overheating characteristics. BTW how tight did you put the arps down?

 

[TravisD62]

Not 100% sure but I believe it was 80 ftlbs. Do you guys honestly think this motor would pop a head gasket after 5000km?? A factory motor with Toyota torque specs and an oem gasket I could see, but a proper rebuild with arp's?? Regardless I'll do a compression test tomorrow, see what I come up with.

 

[adampecush]

If its blown, chances are the o-ringing contributed.

Are you in Edmonton? If so, and the motor is toast, that makes 3 of us now...

climb aboard the group buy rebuild.

 

[te72]

I've seen head gaskets let go after only a few hundred miles... granted this was on a car with a penchant for breaking, so nobody was surprised. Have Rich with SIP Racing get you a quote for a long block. That's what I would be doing if I wanted a 7m built.

 

[TravisD62]

Ohhhh man that would suck. I'm in Calgary actually, but the motor was built by Raymond at Silverstone.... I guess I'm down for a group buy if this motors screwed. UGH.