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General 1GB weird boost gauge readings

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mrc_wkr

Probationary Member
10
2
Jun 26, 2018
Columbia, South_Carolina
I recently purchased a '94 talon tsi (FWD) - it has an aftermarket boost gauge mounted in one of the center vents. originally when i purchased the vehicle the boost gauge was reading mostly at the absolute negative pressure (vacuum) around -30. WOT would push it to a positive pressure but idle, and anything other than WOT would read -30. i looked under the hood to see where the boost line was connected - it is a manual boost gauge with the vacuum line running through the fire wall.

the FPS has been deleted off the vehicle as has the EGR(still in place but a block off plate is behind it with no lines running to it) as well as the PCV. so the intake manifold vacuum nipple towards the right side was connected to a T fitting where one side went to the boost gauge and the other to the fuel pressure regulator.

i removed the T fitting and ran directly from the intake manifold to the FPR and then ran the boost gauge vacuum line from the E port (the one to the left of port P). once i made this change the idle boost psi went to between -5 and 0, WOT showed approx 15psi, and a feathered throttle showed -16psi.

I would have used the P port but the blowoff valve is connected to that. using the diagram from the forum post below i searched for the intake manifold port to connect the blow off valve but couldnt find it (i am thinking it is on the bottom of the manifold and i just didnt see it)
https://www.dsmtuners.com/threads/taboo-speed-shop-vacuum-diagram-and-removal-for-1g-and-2g.198327/

so at this point i believe i have a possible vacuum leak that seems to be occurring mostly at idle (previous owner said wastegate is set up for 12-15 psi, there is no wastegate solenoid just the ball/spring). or the boost gauge is no good. it is a no name boost gauge and part of the casing is disfigured from being forced into the vent.

the only other thing i believe worth mentioning is the blow off valve flange has a poor weld on the intake pipe to the manifold, but i thought i would hear a constant boost leak from there if that was the source. for what its worth the other ports on the throttle body are plugged closed. thoughts?

on a side note, when i turn the key to on position the CEL never lights up. i assumed the bulb was pulled so i pulled the dash cluster and swapped it with the low coolant (parthenon/lincoln memorial) bulb as that one works. when i swapped the bulb the low coolant indicator lit up (meaning CEL bulb was good) but the CEL still did not. i am assuming with DSM link you can permanently turn off the CEL ? my car is running a downpipe only so i know they likely turned it off for lack of o2 sensors but i figured they may have left it functioning for other errors.
 

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You shouldn't be using the throttle body ports for anything, maybe the P port for a boost gauge possibly but really they are too small of a pressure/vacuum source. There should be a dedicated nipple for the BOV on the intake plenum (front left facing the intake) along with a port for the FPR (front right)on a 1g. The PCV obviously goes on the lower larger port by itself. The only way there is no port for the BOV on your intake is if you had a non turbo intake or it was plugged for some reason. Most people T off of the FPR line. Do not T the BOV. Take a better picture of your intake from farther back. Once you get your lines correct then you'll need to do a boost leak test.
 
I would be hesitant to run any of my boost pressure sources from the throttle body ports. One of them actually stopped working one and I've read other people have issues with them as well. I have my BOV hooked to the port near the TPS and by boost gauge T-ed into the fpr line and they work great.
 
@Vegas smith @007jimmy thanks for the answers. i am waiting on the car to cool down i just got home from work and it is about 94 degress outside (columbia, sc) so the engine bay is pretty warm. i am wondering now too if it is an NA manifold - i stuck my hands all under the manifold last night and never felt a nipple present on the left side. i doubt anyone actually cares (other than me ROFL) but i will post what i find out here shortly.
 
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Here is the stock 1g turbo manifold.

Red- PCV
Yellow- BOV
Green- FPR

Behind the plenum is the brake booster port. That's it for the vacuum/pressure sources on a stock 1g turbo intake manifold
 
so my intake manifold is NA as it only has the red circle and the green circle above. the pcv valve is blocked off completely. as a "solution" to the pcv vacuum line the previous owner ran a line from one side of the valve cover on the back left to a catch can and back to the valve cover on the middle left. see the image below, they both have blue fittings where they enter the valve cover. my bov is running currently to the p vacuum line on the throttle body so it cant stay there. im thinking until i can get a turbo intake manifold i should run the BOV off the pcv line and use hose adapters to get the correct diameter. once i get the correct manifold i will promptly be using the correct vacuum line for the bov and connecting pcv back with a catch can.

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i will also be removing the braided covers off the rubber hoses when i empty the coolant and flush the radiator.
 
after further thought i think that the p vacuum port must be on the charge side of the throttle body, while the e port is in the intake manifold side of the throttle body. i swapped the bov hose with the boost gauge hose, bov on e and boost gauge on p, car started fine boost gauge dropped to around vacuum 25. i turned the car off and then swapped them back and then drove home. but if the e vacuum port is pulling from past the throttle body valve it would explain why i could see semi accurate readings with the throttle WOT or slighty open due to the vacuum being able to pull more air and at idle it would show around 0 to 5 because the throttle plate is mostly closed.
 
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