Hey guys,

Just got done with a trans rebuild/install and replaced a few things on my 04' SS motor while I had the drivetrain out. Car runs great other than a couple of things.

1. Car idles at 2000 RPM all the time. Talked to some folks and they say the PCV "tube" that snaps into the upper intake gasket might not be positioned correctly. This is a little black tube that looks like it could be positioned a few ways when installing the upper intake gasket. Anyone know what this tube is for? I can't find a thing in service info about it and at Rock Auto, some of the pictures of the upper intake gaskets available have this tube and some don't. My old upper intake had the tube and the Dorman upper intake gasket I just bought has it too.

2. Can't do a crank-relearn on the car now (with Tech2Win) because I get an error that says there is no 18X signal. Started to check into this and it looks like the crank sensor puts out a 3X signal and a 18x signal. When you look at your crank pulley there are 2 rings in it. One with 3 tabs and one with 18 tabs i think. With the scan tool the 3X signal varies with crank speed but the 18X signal stays the same all the time. I'm thinking I damaged either the crank pulley or the crank sensor when installing the crank pulley or the crank sensor when the engine was apart. I'm about 1/3 through the trouble shooting for not having an 18X signal and the wiring is checking OK at this point.

Any ideas?

 

1. vac leak is why i think you have high rpms at idle. just check all the lines. if you have the s/c engine, the pcv sits under a plate on the back side of the s/c, the 3 prong plastic thing that sits right behind the throttle body is very prone to breaking when you mess with it though. for the non s/c engine, the pcv sits under the map sensor. there is no tube that runs to the pcv on either engine. the tube you speak of should be installed like this....






2. Part 1 -How to Test the 3.8L GM Crank Sensor With a Multimeter

 

Awesome documentation on the crank sensor deal! I'll check out the crank sensor with those instructions and take a look at that tube inside my intake if I can't find any other vacuum leaks.

One thing I didn't mention either is there is the one scan tool function where you can command your idle I think either 25 RPM or 100 or 500 RPM up or down and when I tried that, the idle stayed at right around 2000 even though the scan tool said recommend or intended idle was 680 I think.

Thanks!

F-whupper

 

not all scan tools can make the rpm change.

 

Sprayed a bunch of carb clean around the upper intake and no change in idle. I'm going to pull the upper intake to make sure I have that plastic tube positioned right and put it back and see if that makes a difference.

I was using the Tech2Win GM Tech2 emulator software (from GM.) You can use it with GM's MDI or J2534 tooling like my company makes (Drew Technologies.)

Our company sells a product called a MongoosePro GM II cable that when installed on a Windows PC (preferably Windows 7) with a subscription from GM (at www.acdelcotds.com), you basically have the same capabilities as GM's MDI tooling that their dealers use. The Pro GM II cable is $495 from us and the short-term 3 day subscriptions for SPS, Tech2Win, or GDS2 (for the Global A body styles starting in 2010+) are $55 each or GM offers bundles and long-term subscriptions as well. They currently bundle Tech2Win and GDS2 to for $750 a year I think. With both of those subscriptions you can perform full diagnostics on GM vehicles from 1996 up until the brand new cars they make now.

Sorry for the partial advertisement for my company but I feel it's a good deal and use it all the time for my older GMs at home.

Thanks,

F-whupper

 

All set! Took off the upper intake, installed a new PCV valve, a new throttle body gasket, and repositioned the black tube that mounts to the upper intake gasket and idle is down to about 700 in gear.

The black tube tucks into a port where the PCV valve mounts to. One of those deals where I didn't pay attention when I took it apart and GM's service info doesn't mention it either. Most of the upper intake gasket kits don't include that tube because they must assume you re-use the original factory one.

I'll work on the 18X crank signal issue later on. The car runs too good to screw with it now!! My buddy at work says that eventually the PCM will throw a code for not having the 18X signal. GM uses both the 6X and 18X signals between the ignition module and the PCM.

I appreciate the help.

F-whupper