Z32 twin turbo falling short of full boost

[junkyS13]

I was looking for wisdom from the Z32 experts.
my Z was running in the only way i can describe as heavy, if that makes and sense. If i change the plugs it will run great for a month or so, but then the boost pressure starts to drop and it feels sluggish. I fixed the temp sender (dirty) but I still have a problem with the speedo jumping up to 40 mph as soon as the car moves. I was told it was the speed sensor in the transmission but the cruse control works fine. I don't know if they have anything to do with my problem but just wanted to make sure they where known in case. I looked in to the possibility of a boost leak but then again why would it run good after I change the plugs? Would a boost leak cause the plugs to gas foul? Or should I be looking into some other problem? Just dont know where to start looking.
Any help is appreciated

Thanks
Kerry C.

info on the car: 1990 300zx twin turbo
hks hi-power exhaust
single front mount intercooler
JWT eprom tune for 1.0bar
Running 1.0 Bar
Race logic traction control power builder
still have cats

[NolimitZ32]

The power builder, is that a 2 step setup? if so it might be the culprit, might be messing with your timing and overtime fouling your plugs. Pull the codes (if there are any), check your base timing at idle (15* btdc), and make sure your O2s are switching. if all checks out then id really look at the power builder, it could be destroying your plugs over a short period of time (which after reading up on it seems like the most likely reason for your problems)

[junkyS13]

Thanks for the input. I have turned off the race logic and slowly I can see more boost pressure every day, but after the boost comes up to say .90 (avc-r is set at 1.0 bar) the boost will drop back down to around .75 bar. It changes from day to day but its going up so that's a good thing. I have set the boost to stock and it will not drop, it just pulls solid throw the entire RPM range. Still think I may have a boost leak but from what i read who doesn't.
Thanks for your help I will update if anything changes, bad or good (hoping for good)


Kerry C.

[NolimitZ32]

NP man, that's why we are all here, to help each other.

[300ZXttZMAN]

Also another good thing to try is to check your compression.

Also i have a question you say would a boost leak cause your plugs to foul...
Does this mean your plugs do foul everynow and then??? If so do they smell like oil or gas or a little mixture of both?? Also does your oil smell like gas??
Also have you ever seen your car stop reving meaning it will rev up to like 3k then act like thats the rev limit??

My car's plugs smell like a mix of the 2 and the oil smells like straight up gas... Which is why im doing a rebuild... My car's current (original motor has 108k miles) and 125 psi in all 6 cylinders

But its all good cause i have a healthy power plant in the works

Also OMG im almost at 1000 posts hahah

[DreamZ32]

Junkys13 - how do you like the race logic TC system? I've been thinking of getting it installed on my stage V z32, more for safety cause she likes to get sideways and I let my wife drive her sometimes (with me in the car) I assume you have it set up to cut the spark? How long have you had the system before the things went haywire? Any info would be great. Also do you think the system is knocking your timing?