92 S13 FB w/ SR Blacktop -- Exhaust Restriction @ FULL THROTTLE

[jdm_master_X]

today i got my custom exhaust done. its 3" straight pipe from the turbo housing all the way back to the HKS muffler. the stock SR downpipe flange to the housing was used and the rest of the 3" pipe tube bent all the way to the muffler. im still using the stock turbo housing as well as the stock exhaust manifold. im using an HKS SMF on the stock rubber couplings and turbo elbows. and im using the stock T25 with SMIC. and im using HKS BOV (pre 1995 O.G. style).

the exhaust is amazing and spool time on the stock T25 is excellent, however, at full throttle the SR will hesitate and feel restricted after 3K RPM throughout all the gears. at half throttle or a little more, it can rev beyond 3K but once i punch the gas, the SR literally bogs and wont rev any higher until i release the throttle and run on engine vacuum. the idle is a little lower as well and bogs for a little during startup. oil and coolant was changed 2 days ago. the exhaust mounts and bushings wiggle, causing the exhaust to occasionally hit what i believe is the driveshaft or the transmission. what do you think is happening?

what im thinking is that the part of the new downpipe that uses the OEM downpipe and part of the 2.25-2.5" (?) is building up too much boost at full throttle, and builds excessive boost pressure at that part of the downpipe, creating that bogging feeling (thats where u can feel the hesitation and pressure buildup). in terms of the idle speed, i think that the engine isnt used to the backpressure reduction. im also thinking all the vibration from the unstable supports are causing this bogging. what should i do? is the exhaust routing a poor design for flow?

the routing of the piping is illustrated at the bottom. hope that helps the diagnosis. get back to me fellow NICO TECHS!

[180fan]

I'm more inclined to believe it's a TPS issue rather than a backpressure issue. Reason, the stock t25 turbo extension is 2.25" IIRC and it does not cause such problems.

[jdm_master_X]

could you explain in more detail why it would be the TPS? from my understanding it when you have a larger diameter pipe release gas into a smaller diameter pipe, it could create a backfire (i.e such as a 3" pipe connected to a muffler with a 2" inlet and outlet). would you know if by chance a defective blow off valve could be the cause because my friends KA-T ran at a nearly identical condition (except his didnt hold idle). i checked for boost leaks and vacuum leaks and the engine runs excellent compression across the board as well as 18 psi of vacuum and 7 psi of boost. i wish i could let u drive the car so you could see exactly what i mean.

[jdm_master_X]

another picture of just exactly how the flange looks.

[jdm_master_X]

okay i did some more research.

180fan, i guess your reasoning for the TPS was because the TPS isnt sending the right signal voltage to the ECU signaling the it to increase fuel and signal for faster spark. the MAF works of course because it holds a steady idle. i think the computer believes the car is still operating on vacuum or at a certain RPM (in this case, it doesnt operate past 3K @ full throttle). the car has all the obvious running well such as vacuum at 18 psi, compression 160 on all cylinders, MAF works and measures air (or else it would not hold steady idle or would die out. i was even able to drive home normally, applying on 75% throttle at most).

now what i would like to know is the the code that the ECU would throw at start-up. there is no MIL on my gauge cluster. also, does anybody know the reference and signal voltages for the TPS? and do the TPS and MAP have fuses i could check?

and on a final note. i would like to know if you all think that the MAP (manifold absolute pressure). i would like to know if that would also emulate or cause the problem. feedback? because the car believes might think its running on vacuum when its really running on boost, thus creating that pressure buildup at the turbo outlet. feedback anyone?

[180fan]

A small diameter pipe at 2.25" is the same size diameter as the one coming off of the turbo. I've also installed a 1" muffler for smogging days without too much of an issue. You're also stating a test pipe so that problem you're having isn't from a melted cat or anything else.

Reason behind the TPS, if it's not sending a signal to the ECU saying "hey ECU I'm now at WOT" then the ecu never realizes that. The MAP I don't think will do anything for you in this case. If you're trying to get rid of your MAFS then that's a good way to go but just getting a MAPS to see if that alleviates this issue is a bad idea.

[jdm_master_X]

okay just making sure before i go and **** with the sensors. i was just under the impression that the MAP sensor would also create such a problem because it is detecting engine load and signaling the ECU to raise fuel and spark.

by chance do you know where i could source the ECU fault codes? and could you tell me how to run the ECU in diagnostic mode? im running a J4 ECU. that way i know if the ECU can detect and isolate one of the sensors we mentioned.

oh by the way, what part of the bay do you live? maybe i could even show you the problem or solution one day...haha.

[180fan]

Dude I'm in SF. Like seriously in SF. The ecu you can put into the check mode by going to the ecu under the passenger kick panel and turning the screw on the back of the ecu clockwise (or was it counter clockwise...) then back and watch the blinking lights. You'll see short and long pulses, count the number of short pulses and count the short pulses.

You're running a map sensor on yours? It shouldn't be doing anything weird like that unless the sensor's going out.

[jdm_master_X]

well i dont even know if SRs even come with a MAP sensor. normally the MAF sensor signals the ECU to increase fuel and spark in response to engine load and speed. i dont think a MAP sensor is needed if a MAF sensor is already present.

do you know the voltage/resistance ranges for testing the TPS or MAF? im going to test them both tomorrow.

and do you know how a MAF sensor ties into this problem? picture this scenario. had i driven my car to San Jose on 7psi boost, and then gotten the exhaust on, the boost will increase significantly correct? do you know the measuring limit of the MAF? because im thinking that the intake velocity cannot meet the demand of the exhaust (its an HKS SMF on the stock rubber coupling and turbo elbow). maybe the MAF is sending the wrong values to the ECU. what do you think?

[rogoman]

well i dont even know if SRs even come with a MAP sensor. normally the MAF sensor signals the ECU to increase fuel and spark in response to engine load and speed. i dont think a MAP sensor is needed if a MAF sensor is already present.

do you know the voltage/resistance ranges for testing the TPS or MAF? im going to test them both tomorrow.

The SR20 uses a MAF sensor only.

The voltage readings are as follows:idle - 0.8 to 1.5v3000 rpm - 1.4 to 2.0v

[jdm_master_X]

3000 RPM @ WOT? how far open should the throttle be applied?

[jdm_master_X]

i talked to the exhaust guy and he said he clamped his electrode/ground to the turbo housing. is there any way it would have shorted out the o2 sensor? thats the only other load sensor i could think of.

still trying to test the sensors, but havent had time lately. im waiting on my friend to let me borrow his DVOM and sensors since this other guy i did SR swaps for is being a d!ck and wont let me get my tools back. ill let you know how it goes.

i still need to know if the TPS spec on the voltage is 3000 RPM @ part throttle, full throttle, or etc. and can i test the o2 sensor based on the spec of a 95 z32 TT o2 sensor?

97 200SX TPS spec will work?91-96 300ZX Twin Turbo o2 sensor spec will work?89-90 240SX (SOHC) MAF spec will work?

[jdm_master_X]

oh btw. my blow off valve seems like its broken. i noticed during the time of the problem, the blow off valve didnt seem to release boost surges from closed throttle. in neutral it still doesnt rev past 3K. any connection?

other than that im ready to start testing it. ill finally have the time this weekend. have a happy 420 everybody. haha

hey 180fan want some purp?

[rogoman]

3000 RPM @ WOT? how far open should the throttle be applied?

3000 RPM. Watch your tach!

[jdm_master_X]

drove my car again today to simulate the situation to a friend. now it goes through the entire RPM range at 1st and 2nd Gear, but the same problem for the rest. the night before i was testing it at rest in neutral and it didnt do it.

i checked the ECU today (car off), and the LED blinked code 55 for CONSULT Terminal Required. in any case, i finally obtained a DVOM so ill proceed with testing just as i planned. i printed voltage specs from the 97 200sx TPS, the 89 S13 SOHC MAF, and the 96 z32 o2. ill let you know the results tomorrow. thanks!!