I just smoke tested the car and I have a pretty big leak coming from the spring/seal area where the throttle cable turns the throttle plate. Is this area subject to vacuum? My gauge is telling me I have a large leak but I haven't been able to locate any besides this.
What mods do you have? CAm? I doubt the shaft would cause that bad of a leak if your cam is stock. Have you rebuilt latley?
Poor valve sealing or worn out motor could be a issue if you can't find a leak.
What was it for the first 30 miles? Did you check the lifter preload? When I put a cam in my car I didn't check the lifter preload and it was hanging one of the valves open in #4. Car ran fine WOT but at idle it was like a big block with a monster cam and very low vacuum. It sounded sweet and would rock you quite nice, I kinda miss it.
When I did a compression test the cylinder was dead. So maybe you can start with a compression test. The lifter may have pumped up and is now hanging a valve open on you.
The motor is brand new, has less than 100 miles on it. Its a 4.3L stroker bored .050 over, with a 224/230 cam. So definitely not stock. It was making higher vacuum for the first 30 miles or so, and now at idle I sit right below -10 on the gauge.
I've got a similar cam and I'm only getting around 10 or 11 inches of vacuum at 1000 rpm idle. If you were getting 16 inhces and it suddenly dropped to 10, I'm betting it was because it was idling higher than it is now. What rpms is your idle set at ?
David
Dave,
Thanks for chiming in. I idle consistently at about 800-850. This is good to know though that you have a similar vac condition.
The only thing that I question is sometimes I will be sitting at a light and my vac gauge will read close to 0. This hasn't happened for a few days, so maybe I just need to drive it around some more to see if I can recreate this situation.
I think the Zero vacuum thing is just the gauge sticking. I'd suggest increasing your idle to 1000 rpms and you should get rid of the ocassional stalling problem. The guage on my turbo car is starting to stick at various readings and the same thing happened with my 91 last year.
I think mine got fouled up from years of using methanol injection. Nitrous will also cause them to foul up, because both are highly corrosive.
David
I took the car out for about 30 minutes of driving yesterday. I observed that it was pulling about 10-11 inches at idle, and about 9 when shifted into drive. I can get into about 5 pounds of boost relatively easy, but I have not observed the gauge reading 0 since a few weeks back. I am yet to really "get on it" with the new motor, as it has only about 100 miles on it.
Sound normal?
Yes, it does sound normal.
BTW...If your car is 89-92 the brakes will work fine with low vacuum, but if it's a 93-95 the brakes are more dependent on vacuum and they won't work very well without adding another vacuum cansiter.
David
The brakes are spongy, I am assuming this is why cause I bled them 3 times!