intermittent problem with breaking up at WOT in boost above 4000 rpms

[loki_]

details:
88 supra turbo 7mgte w/ stock ct26 turbo w/ turbo blanket


this issue only happens sometimes, no constants (outside temperature/how long the cars been on/etc) noticeable.

when in boost (stock 7lbs) AND above 4000rpm it feels like i'm starting to lose power and begins to sputter. boost gauge shows it holding at a steady 7-8lbs. Other times it will scream to 6000rpms without an issue.

If I go into 5th gear, at like 2000rpms, i can go WOT and make a solild and steady 7-8lbs without issue upto 4000rpms without boost jumping or the engine making a peep, so i don't think its a boost leak.

Would too big a spark plug gap cause that? intermittently? I'm running ngk 4644 plugs w/ ngk wires; everything is plugged in securely. Originally it was gapped to .029, then I regapped to .025, and it seemed to get a little better, and from my research, i think that going to .022 may fix my problem.


I'm going to try to regap this week, I was just wondering if anyone had seen an issue like this before.

 

[Flateric]

My bet is on your aging and likely crsipy CPS wiring or connectors. Even though everything can seem plugged in securely it can still be loose. It's a terrible location for wiring and connectors to live.

 

[suprahero]

I don't think there's any way you're blowing out the spark at only eight psi. Usually you won't have to lower the spark plug gap until maybe 17 or 18 psi. You may have a small boost leak or it's along the lines of what was stated by Flateric. Good luck.

 

[loki_]

thanks for that info, ill definitely keep that in mind. ill let you know how it goes

 

[loki_]

ok, so an update. the issue has become more consistent.

cold start, idle 1-2 minutes, car screams to 6000rpms, makes about 8lbs of boost, goes sideways and its great. This lasts for around 5 minutes. After about 3-5 minutes of driving, the symptoms start. At WOT, the car makes 6-8lbs around 3000rpms, but just falls on its face at 4000rpms. The engine is still smooth, it just is barely gaining any rpms and it almost feels like i took my foot off the throttle. Its still making 8~ lbs of boost. I'm not hitting fuel cut and I don't have any codes. I just replaced all of my hose clamps and thoroughly inspected all of my IC piping for leaks. warm and cold start are both ok and my idle is consistently smooth.

The symptoms are only present when the car is at operating temperature, above 60-70% throttle, and over 4000rpms. For the first 5 mins or so after cold start, everything is awesome and perfect.

I've been searching my butt off, researching about CPS, O2 sensor, TPS, AFM, coolant temp sensors, loose connections, codes, boost leaks. I'm not really finding anything specific to my symptoms. Any help with this new info would be awesome.

I busted out my voltmeter and haynes manual, and im going to go down the list and check my sensors when i get off today. I'm just hoping that someone can recognize those symptoms and point me in the right direction. thanks!!

 

[loki_]

(with the tab in the middle top of the airflow meter port)

_______|_______
[K1 Vc Ks THA E2]

my multimeter has 200, 2000, 20k, 200k, 2000k settings for resistance.

airflow meter
E1->Ks = absolutely no reading on any multimeter resistance setting with with the probes one way or the other
VC->E1 = 157 (on 2000k setting) or 156.6 (on 200k setting)
THA-E2 = 1.85 (@ around 70*F on 20k setting)

Would the lack of resistance for the E1->Ks/Ks->E1 cause my issue? Per the haynes manual, if any of the resistance values are outside those specified, the airflow meter must be replaced.

 

[topekamk3]

Could also be your injectors/injector resistor pack getting hot...since they are electronics they can heat up at random almost instantly and then other times be fine.

 

[tomsupra8683]

fuel pump is starting to fail i bet.Danm in tank pumps.

 

[loki_]

Could also be your injectors/injector resistor pack getting hot...since they are electronics they can heat up at random almost instantly and then other times be fine.

what can i do the prevent that or protect against that?

fuel pump is starting to fail i bet.Danm in tank pumps.

it would be ok for the first few minutes after cold start?

 

[suprastroker88]

my car did that before. except it did it whether it was cold or up to temp. i just changed my spark plugs and the issue went away

 

[loki_]

the plugs that are in the car were in it when i bought it, so their age is unknown. i pulled them to check the gap about a month ago, but i think im going to switch them out, just incase that were to be the issue

 

[Backlash2032]

Im willing to bet its either the coil pack wiring, cps wiring, or the spark plug wires

Heat = resistance which is not good. lol

 

[topekamk3]

what can i do the prevent that or protect against that?




it would be ok for the first few minutes after cold start?

about the only thing to do is try to replace the resistor pack...once electronics start to get flaky the best thing to do is replace them.

 

[87GWSupra]

How many kv are you getting out of your coils. They could be getting weak.

 

[carbongs]

I'm having similar issues with my 89 7MGTE Auto. It is very random and I've noticed if when it starts cutting out if you turn off the car and restart it will go away. I think there is a grounding issue for the coil packs, fuel pump starting to go out and possibly the tps going bad. The car sat for about a year before I bought it. This is why I think it is the fuel pump. Any ideas?

 

[Tpilover]

my car did that before. except it did it whether it was cold or up to temp. i just changed my spark plugs and the issue went away

My car was having the same problem and I swapped out the plugs and re-wired my ground on the coils. It pulls hard in every gear and idles better.