Help... No power under full boost!!!

[Nissandriver714]

I have an 89 coupe, redtop sr with upgraded turbo, and full exhaust with no cat. The engine ran fine before, but recently under wot at about 4-5k rpm, i can hear sputter sound and popping noise coming from the exhaust and the car would kind of stumble and jerk. When this is occuring the car experience a lost of power. I also had a friend drove behind me when i went under wot and he said that he heard what sounded like backfire, and a little bit of black smoke coming out of the exhaust. i've open the spark plugs to check, and they're fine. Anything else i should be checking for. What do you think is wrong with my car??

please help, thanks in advance

[Pepperoni]

Search around, or even just look at these recent pages in tech talk; there's a lot of threads revolving around the same questions. I'd say check your timing.

[sr240mike]

Id say its either a boost leak, spark plugs need re-gapping, or your timing is off.

[Nissandriver714]

Yesterday, I re-gapped the spark plugs from .30 to around .28 and test drove the car afterwards, it was still sucky. However, after class today, I boosted it again and it felt all normal again. Could this be timing related? Can your timing be way off and set itself back on track again?

[silviasichigo]

check your intercooler gromets one might have a hole. A friend of mine has a S-14 with T518Z greddy turbo and he is tuned to about 400hp his car was doing the exact same thing wot at 4or5k and popping and sputtering we pulled into jomo and found one of his grommets on the hot pipe was cut enough to stay sealed at vacuum but leak at wot or under boost. he is boosting 1.5kg by the way. I am sure you are not near that but still boost is boost.

[97DubTruck]

has your setup been tuned? sounds like detonation.

[Nissandriver714]

has your setup been tuned? sounds like detonation.
Hasn't been tune, but I don't think it's necessary at this point yet. Everything else is still stock, except for a bigger turbo, and full 3" exhaust. It's been running fine prior to this incident which started happening a couple of days ago. Also, I do not know what detonation sounds like, but this sound came from the exhaust. What DOES detonation sounds like anyways?

[97SilviaRB]

What kind of "upgraded" turbo do you have btw?

[asbestos]

how is your fuel pump?

[Nissandriver714]

What kind of "upgraded" turbo do you have btw?
It's a t28/t3 turbo with .86 turbine housing.

how is your fuel pump?
Stock fuel pump is replaced with walboro 255 already.

The question still remains if someone can answer this for me:
1. Can timing be advanced or retarded by itself? I doubt it, but who knows?
2. Also, what's are the symptoms of spark plug being gapped too high, or too low?
Thank you all.