• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

car only getting 15mpg. and a screeching noise from rear main/flywheel area

99GPGTP

99GPGTP

New member
Couple years ago the trans went out on my gtp, I finally got trans rebuilt and put back in case. While trans was out I had motor out and put new timing chain dampener and oil pan basket on motor. I put a 2500 stall converter in trans, bypassed radiator cooler for trans. Car wouldn't start before these repairs due to fuel pump p going bad after sitting for 1 year. I installed a AEM 320 lph pump. Also installed my ported supercharger housing with new pcv valve. After vehicle warms up I get a screeching noise in rear of engine after reading operating temp. Also my fuel mileage has dropped from 24mpg average to around 14.5mpg. My mass air is reading the same as my coworkers gtp. O2s is reading normal, my Lt ft is -11 and st ft is 0. Indication of running rich. Anyone have any idea what the cause is???
 


Check to be sure all your fluids are full, especially the trans. Of course it has to be fully hot to do so to get an accurate reading.
 
BillBoost37 said:
Fix the pcv in the charger.

There is an o-ring on the pcv, then a spring above it and a gasket on the cover.
Click to expand...
My pcv didn't have an o ring. There is a piece of plastic that the pcv sits on and and then the spring. And gasket and cover. I have eliminated the transmission by taking the torque converter bolts loose
 
99GPGTP said:
My pcv didn't have an o ring. There is a piece of plastic that the pcv sits on and and then the spring. And gasket and cover. I have eliminated the transmission by taking the torque converter bolts loose
Click to expand...

That is the problem, you need an O-ring. It seals the pcv so you don't leak full manifold vacuum to the crankcase all the time.
 


I rechecked. Car did have boring under valve. I replace with new one but still screeching. Can I put a rubber cap on pcv valve and take oil cap off and install a breather and see if fuel mileage goes back up and noise stops? If so what would that indicate that needs to be done.
 
This all started with the ported supercharger? The squeal is to much vacuum to the crankcase, your actually sucking the seal into the crank to hard. If your PCV has an oring, then the problem is on the other side. You may have plugged the front port so your not letting air in. Valve cover breather or just removing the oil cap will fet rid of the squeal.

Bad gas mileage could be your boost bypass valve being closed all the time. Are you sure you have all the vacuum line hooked up correct and the bypass valve is open at idle?.
 
BypassBypass valve is working correctly. I guess I need to pull my supercharger and blow air through the pcv port and see what's going on

My boos gauge shows around 18 inhg at idle and 10-11 psi at 6k wot
 
Did you use a gasket or RTV down to the LIM?

Gen 3 with L67 TB?

Take throttle body off and blow back the PCV passage with compressed air from a blow gun.

Also the squeal should go away if you take oil cap of.
 
Also...did you clean the entire casing of the supercharger after you ported it? The shavings get EVERYWHERE, including the PCV passages.
 


Yes I cleaned the housing good. Flushed the passages with the vat at work. I caped off the pcv with a rubbercap and it still screaches. Which makes no sense. I used a new felpro gasket from advance auto parts. The bypass valve is open at idle and and closes when u snap throttle. All vac lines and evap lines are hooked up. I'm a Nissan master technician for a living. Only thing I can figure is there is blocked port for the pcv system. The supercharger gasket has 1 hole where the supercharger has two holes at pcv. Why is this?
 
Does the squeal go away with the oil cap off?

You are either putting to much vacuum to crankcase through the PCV valve on the supercharger. (No o-ring or bad valve)

or

The PCV passage is blocked that goes from front of supercharger to the throttle body. This passage lets metered air into the crankcase.

Again, take cap off and the squeal should go away.
 
Last edited:
Take throttle body off. Find passage that blows back to front PCV passage of the LIM. Blow compressed air back passage. If you used RTV for supercharger to LIM sealing, you probable blocked this passage.

I think it is the bottom right in this picture.

5fa0eeda49f46661cc9827cc90d138b2.jpg


Or it's on the PCV side. You don't have an oring or it is cut/broken. PCV valve is stuck open.

If you can cap the PCV so no vacuum is going down to the LIM but your still beget squeal there is something going on with your gasket or LIM.

DO YOU HAVE ANY PICTURES?
 
Picture of LIM.

32e456de1a37b97aef03c376215811a6.jpg


Top right round hole above square air inlet is PCV passage from PCV valve

Below left of inlet is round hole that lets metered air into crankcase.

If either passage is some how leaking air to inlet you will get squeal.
 


Found my problem. Parts store was closed so I made a tb gasket. Forgot to cut out hole on tb gasket for pcv vent. Feel stupid now, squeal gone, just hope my fuel mileage improves now
 
I have drove car for 2 tanks and still average only 14mpg. Half is city driving and half hwy at 60mph. No check engine lights. I believe my problem is the 320lph fuel pump. Does anyone make a aftermarket regulator I can install and adjust fuel pressure
 
Did you port the lower intake?

Reread your description and you got a screach even when you capped the PCV valve. That tells me your getting manifold vacuum to the crankcase somewhere besides the PCV valve. With the PCV capped there is no vacuum to crankcase and it shouldn't have screeched even with the TB gasket.
 
sseilmnop said:
Did you port the lower intake?

Reread your description and you got a screach even when you capped the PCV valve. That tells me your getting manifold vacuum to the crankcase somewhere besides the PCV valve. With the PCV capped there is no vacuum to crankcase and it shouldn't have screeched even with the TB gasket.
Click to expand...

I have already fixed the pcv screeching issue. The only issue I have left is bad fuel mileage. Averaging 13 to 14 mpg
 
You must log in or register to reply here.
Back
Top