boost problem. 6psi falling to 2psi....

[smg944]

well i have a pretty weird boost issue. it builds 6psi of boost by 4k rpms then falls to 2 psi by 6500 rpms. did a boost leak test and found a leak in the ic which i sealed. i still hear a slight leak near the intake manifold and the injectors. but doesnt seem like it would cause this much of a boost drop. i looked through some threads and didnt find a similar boost problem. i have read on some wastegate problems also so i checked the acutator and arm. everything seemed ok. any ideas of what it could be? thanks in advance.

 

[oldman]

ok here is something new. i did a timing check and when my cam notches are at tdc posistion, my crank notch is at 25-30* btdc. now, there is a white paint spot that reads tdc with the cam gears. is this how it is saposed to be or did someone paint the white spot on there? also how do i know the timing is not all messed up? my idle is a little low but seems to be ok along with my normal driving rpms. lasly could the timing be cause my boost issues?

If both dowel pins on the cam gears are at 12 o'clock when two white marks are lined up at 3 and 9, your timing is waaaay off. Also make sure to only turn the crank clockwise, never CCW.

 

[smg944]

yes the dowel pins are at 12 o clock, and the white marks on the gears at matching at 3 & 9. so this means i have to remove the timing belt and adjust the crank clockwise to match? could someone before me have just moved the crank pulley around and thats why that white mark is there on the crank pulley? on my rx7 the crank pulley can only go on one way so it will always match up. is that how the dsm is? does it have a key way or something?

 

[oldman]

The crank pulley only goes on one way via the dowel pin on the crank pulley, there are only two possibilities here.

1. The belt has slipped, which will explain your lack of boost.

2. The outer and inner part of the crank pulley has seperated causing the out pulley, where the timing mark is located, to slip.

the turbo spins freely with much shaft play.

This too could a part of your problem.

 

[smg944]

ok im going to take a look at the crank pulley, any easy way of getting to it? i was also thinking of removing the timing belt from the cams, leaving them at tdc, and then turning the crank to tdc. that should fix it right? i am just thinking that if it was off at the crank by say 4 or 5 teeth, wouldnt that effect more then just my boost? like my valves being bent or running bad all the time. the only effect other then the boost i have noticed is that it runs lean. the plugs are white. and i have a 255 pump with 550cc injectors. no reason for leaning...

btw, i meant to say the turbo spins freely and not much shaft play.

also, thanks to all for the help.

 

[oldman]

i was also thinking of removing the timing belt from the cams, leaving them at tdc, and then turning the crank to tdc. that should fix it right? i am just thinking that if it was off at the crank by say 4 or 5 teeth, wouldnt that effect more then just my boost? like my valves being bent or running bad all the time.

Alot of things can cause boost problems, bent valves included. This is exactly what I would do next.

1. Place the motor in TDC using the "rod in #1 spark plug hole" method (search before you ask) instead of using marks on the crank pulley, this will tell you whether the belt or crank pulley has slipped.

2. After verifying that timing belt was in fact what has slipped, re-do the timing belt properly, do not half ass the job. If non of the components like auto tensioner, tensioner and idler pulley, water pump........etc were replaced last time around (which very well can be the cause, especially the auto tensioner), make sure it happens this time.

3. After everything is put back together properly, you can then perform a compression test to see if valves are bent. 5 teeth is alot, I would say anthing beyond 3, bent valves are almost certain, let's hope you're one of the lucky few.

also, thanks to all for the help.

Use proper grammar and capitalize all that need to be capped from here on out when posting in tech sections, we'll call it even. Good luck.

 

[91etalon]

if the dowel pins are at 12 and the timing marks both line up at 3 and 9 i dont think your belt has slipped. I would check the timing with a timing gun followed by a compression check. you may be losing compression somewhere and not nessesarily through the valves so if compression is weird follow it up with a leakdown test.

 

[oldman]

if the dowel pins are at 12 and the timing marks both line up at 3 and 9 i dont think your belt has slipped.

Not exactly, dowel pins will always be at 12 when ever cam marks lines up at 3 and 9 since they're both fixed positions on the cam gear, the questions is the crank position while the cam marks/dowels are lined up.