My 87 GN Build

[Mnt86SS]

Vacuum brakes? I had a stumble when releasing the brake a while ago, it was a bad diaphragm. If vacuum, plug the port off and see if anything changes. The computer will learn a vac leak and compensate while it can. Same with throttle shaft wear.
TIMINATOR

It does have vacuum brakes. I'll check it out when I get home

 

[Mnt86SS]

So I had some time to mess with it this week, and so far it's still running like ass.

Threw an LT1 Maf on it with a translator (I was gonna do this anyway, figured now was the time) have it set to ON ON ON OFF with the two tuning dials at 0 currently

Replaced the little vacuum hoses at the vacuum block, confirmed no leak

Checked vacuum line for brakes, no leaks. Even capped it off to remove the power brakes from the equation entirely.

Fuel pressure at idle with vacuum line on is 35psi, 45psi with line off

It'll idle all day in park, and has no issues idling in drive with my foot on the brake, but as soon as I let off the brake and the cars starts to roll the idle dips low and it shudders and dies.

TPS is set at .42
IAC at warm idle is 8


I did try unplugging the O2 just to see what it would do, and oddly enough it doesn't throw a cel for it. The scanmaster still shows O2 voltage and cross counts despite it being unplugged which is strange.

 

[Mnt86SS]

Ok I replaced my o2 sensor ,and now at idle I'm getting 800-060 milivolts which would indicate a super rich condition, right?

Double checked my fuel pressure, and it's 35psi line on and 45psi line off. I tried backing it down but no change

 

[jckcolarusso]

Your translator is set wrong you need to adjust it to the maf sensor I think it number 3 on the base setting

 

[Mnt86SS]

Ok I replaced my o2 sensor ,and now at idle I'm getting 800-060 milivolts which would indicate a super rich condition, right?

Your translator is set wrong you need to adjust it to the maf sensor I think it number 3 on the base setting

I have it set to 3 in base. The milivolts seem to fluctuate from about .180 to .600, sometimes climbing higher. Once you put it in gear it settles on the higher side, and stumbles and coughs when you take your foot off the brake and start rolling.

 

[salvageV6]

Looks rich from here in CT. Were the injectors cleaned or flowed after it sat?
I'd double check the chip programming if it's not on default etc. Double check the MAF translator stuff too.

 

[Mnt86SS]

Looks rich from here in CT. Were the injectors cleaned or flowed after it sat?
I'd double check the chip programming if it's not on default etc. Double check the MAF translator stuff too.

It seems to be idling rich at idle.

What's bizarre is nothing has changed from driving it 200+ miles to now. I literally drove 25 miles home from a car show, parked it, and the next day it developed this nasty stalling condition from an idle.

I replaced the vacuum lines at the block. The old ones were leaking a little, and the idle really changed spraying brake klean at the lines. It doesn't seem to have any leaks there now.

 

[Mnt86SS]

Update:

Got a smoke machine to really go over everything for vacuum leaks, and turns out I have a massive leak at the bushings the throttle body shaft passes through.

Just a quick search, and it looks like nobody sells them as a direct replacement. So I guess I'll take the old ones down to my napa guy and see if we can find a match.

 

[Sneaky_Pete]

There used to be a guy on here who rebuilt and ported stock throttle bodies. I don’t remember his name, but he had a website (I just checked it, it’s no longer up). I am wondering if he deals with G Body Parts directly now, rather than maintaining his own site. Anyways, here’s the link to the G Body parts rebuilt and ported unit.

https://gbodyparts.com/product_info.php?products_id=193

 

[V6sleeper]

There used to be a guy on here who rebuilt and ported stock throttle bodies. I don’t remember his name, but he had a website (I just checked it, it’s no longer up). I am wondering if he deals with G Body Parts directly now, rather than maintaining his own site. Anyways, here’s the link to the G Body parts rebuilt and ported unit.

https://gbodyparts.com/product_info.php?products_id=193

That would be Steve Monroe, i think he retired a few years back.

​

 

[GNONYX]

You can get the Throttle Body shaft seals at GBodyParts.com

GBodyParts.com

Do a search on Throttle Body, and you will read it's not a direct replacement

 

[Mnt86SS]

I grabbed the shaft seals, TB gasket, intake plenum gasket, valve cover gaskets etc etc.

Judging by how much smoke was pouring out of the shaft seals, this should fix it.

 

[Chuck Leeper]

Check the plenum gasket just under the t/b.

 

[Norman C Shibley]

Vacuum brakes? I had a stumble when releasing the brake a while ago, it was a bad diaphragm. If vacuum, plug the port off and see if anything changes. The computer will learn a vac leak and compensate while it can. Same with throttle shaft wear.
TIMINATOR

Did your problem occur when releasing the brake pedal? I have a similar problem but it does not occur when I release the brake. Only when gas is applied from a dead stop...and within a second or two you can feel a lack of power from the engine for a moment. It's not a misfire but almost like a momentary change in timing? Thoughts?