engine boggs at high rpm (SOLVED)

yamayuki98

New member
hopefully someone on here has solve this problem already. okay. its drive just fine and idles just fine as long as i keep it under 4500rpm. once i take it above that the car boggs and kicks like a fuel cut. but no light and car continues to drive if i keep it under that rpm. boost is set at 10psi using tworus boost controller. gauged with blitz dual tt. no mods at this point on vehicle besides hybrid supra turbo. all suggestion are welcome.
 

yamayuki98

New member
sorry i should have made myself clear. the car has new oil, new plugs (bkr7e-11). i have both the magnecor 8.5kv wires and the stock (tried both). new rotor and cap. motor was rebuild with new factory valve stem seals, cometic 1.4mm mhg. fuel pump is supra TT pump brand new from factory (not used). fuel filter brand new (factory). timing is correct compression is right on. like i stated idles and drives just fine under 4500rpm. boost perfect too, problem only when i take it above that rpm. i know what boost cut is and its definitely not a boost cut because it does not throw a cel. sometimes the car would just stumble really rough trying to get up to 7k rpm other times it will bogg and throw me back and fourth and continue to climb but slowly. all suggestion welcome
 

Corey

Active member
Check your AFM? When did this problem start? What may have changed?

EDIT: What are you plugs gapped to?
 

Simba

New member
Fuel cut certainly does throw a CEL. However, it is pretty hard to mistake it with anything else. If you can rev higher, though it stumbles while maintaining boost, it's almost certainly an ignition or timing issue.

Usual stuff-- check for codes, check your base timing, plug gap, and coil.
 

bloodMoney

Active member
+1 on checking the base timing. I was set at 0*TDC and after 4k, the car would buck and spit fuel out of the exhaust. Once I set the timing back to 10*BTDC, it was fine. Pulls all the way up to the redline now.... No problems

~bloodMoney
 

yamayuki98

New member
thanks for the suggestion. it definitely feels like timing retard. i will check my afm on my days off. plugs are gap at .028. i also ran iridium non gap and still the same thing. timing is right on. no issue on ignition timing. a while back i had some issues running the walbro 255. i now changed it over to the supra tt pump after engine overhaul. fpr resistor on the ecu board was fried so i had to replace it. im wondering now if it could be that the fuel relay is not switching into hgih mode. ill try bridging fp/+b and put it in high mode to see if it helps. i will let you guys know this week sometime. and again thanks. all suggestions are still welcome
 

built2run

New member
hm, maybe check your pump relay for switching. check for boost leaks thats a good one. also make sure your tvis is opening
 

yamayuki98

New member
thanks for the suggestions. haven't the chance to diagnose it because my wheel bearings went bad. took it to a machine shop and they said hub needs to be replaced. quoted $192.00 just for the hub. i went online and got it off conecilli for $128.00 shipped to my door. still expensive though. back to the topic yeah, me thinks its also a boost leak somewhere. still using top mougnt. maybe need to check for vacuum. thanks i will try and get this sorted out asap once i get the hub and wheel back together.
 

jonahs_3sgte

New member
check to make sure your ignitor has a good ground and is the right 1 for your car
the wrong ignitor will make your engine cut off at 4500rpm
check the flapper door on your maf to make sure it moves smoothly
check for trouble codes?
try this...remove the vaccum line to your map sensor...plug it and see if it helps
 

TRDcelica90

New member
your spark plugs.. bkr7e-11 doesnt the 11 mean the gap is 1.1cm instead of the recommended 8mm?? that would give you a bit of a prob, but i wouldve thought it wouldve been during all driving conditions

just a thought
 

Corey

Active member
The 11 corresponds to a .044" gap or 1.1mm which is far to large for our application. But he said he gapped his plugs to .028" so i dont think that is an issue.
 

yamayuki98

New member
sorry to post so late. been working like a mad man. well, i'll be getting a couple of days off all to myself this week so i will check the compression. here is what i found out new. the engine seems to rev up to redline perfectly fine if i part throttle say around 85 percent, but if wot then it hesitates and struggles. so i test this by running wot and the minute its boggs i reduce the throttle slightly, the car picks up again and run all the way to redline. boost fine too.???
 

yamayuki98

New member
thanks everyone for all your help and suggestions. it turns out that the one vacuum that was not on the diagram (the one that comes out on the side of the throttle and hooks straight to the valve cover)was old and expanded so it kept loosing vacuum pressure. this line just happens to carry a lot of vacuum, a main line i believe. i hooked up a vac pump to it and notice that my vacuum was around 16-17, telling me that i had vac leak somewhere. so i started pinch off vac lines and came upon this particular one that was not listed int he diagram. sure enough when i removed it and plugged it with a new new vacuum shot up to 19 and stood there constant. took the car for a spin and viola. boosting and everything again. hoo-ray.
 

MWP

New member
Thats a tiny hose... im very surprised that a split in it would have that much of an effect.
Good to hear you found the problem though.
 

Rallly

New member
yamayuki98":1onb7af9 said:
thanks everyone for all your help and suggestions. it turns out that the one vacuum that was not on the diagram (the one that comes out on the side of the throttle and hooks straight to the valve cover)was old and expanded so it kept loosing vacuum pressure. this line just happens to carry a lot of vacuum, a main line i believe. i hooked up a vac pump to it and notice that my vacuum was around 16-17, telling me that i had vac leak somewhere. so i started pinch off vac lines and came upon this particular one that was not listed int he diagram. sure enough when i removed it and plugged it with a new new vacuum shot up to 19 and stood there constant. took the car for a spin and viola. boosting and everything again. hoo-ray.


Can you send a pic to ralllysport1@msn.com which vac hose it was please?
 
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