[Robofuzz]

My son and I recently started an El Camino project. It's a 1984 Conquista with the 305 and auto.

It's got some issues that make me think there is a massive vacuum leak somewhere and would appreciate some pointers on particular places to look.

Here's the issues:

1) At highway speed, giving it much more throttle results in predetonation noise. It seems like the timing on the motor is not changing correctly. Is the distributor vacuum controlled on a 1984 305?

2) The transmission does not kick down when you give it gas like above. Again - is this vacuum controlled?

3) The cruise control is inoperative. I know vacuum can cause problems for this.

4) The AC/heat vents only blow out of the floor and will not change to blow from the dash. Again - I know the vents are changed by vacuum actuators.

Any thoughts on where to begin looking? It seems like there must be a huge leak somewhere but I'm not hearing any typical vacuum noises.

 

[mrblanche]

The bad news is that the vacuum routing on these cars was pretty extensive when they were new. You need to know just what original parts are still on the car to know how to route the vacuum properly. But here are a few points to look for.

1. The PCV valve hose should be routed directly to the large vacuum inlet at the front base of the carb. It should not be T'd into any other line.

2. Be sure that any and all lines are connected properly to the vacuum reserve canister. Without that, you will have a big vacuum leak and the heater controls (among other things) won't work.

3. Check to be sure the vacuum line connected at the rear base of the carb is connected to the vacuum assist booster for the brakes. There should be a check valve in that line.

4. There are some little "spaghetti" hoses running from the passenger side of the firewall, near the heater and a/c container, toward the vacuum reservoir. Those little lines get damaged easily.

The transmission is controlled by a throttle valve cable that needs to be properly adjusted. That is what the third cable on the left side of the carb is for.

 

[darbysan]

To answer some of your other questions, in stock form the '84 distributor was controlled by the ECM, or "computer". Your distributor should have a 4-prong connector coming out toward the passenger side, connecting to the ECM. Do you get any "Check Engine" lights? Does the Check Engine light glow when the key is first turned to run? All questions to find out if a Previous Owner has disabled any of the ECM stuff.

It's common for folds to just start taking stuff off, think that will help give more power. The Vacuum Ball is just a reservoir of vacuum for the cruise and HVAC controls. See if it's still there, and has a line hooked up to it. Also look for a Pink Vacuum hose/line coming from under the HVAC unit in the engine bay. That should be hooked up to the vacuum ball, via a tee onto the line that connects to the ball. There should also be a check valve in that line just after it attaches to the intake manifold, to prevent loss of vacuum.

Your car should also have Th350 trans, which has a vacuum modulator on it that attached to the rear portion of the intake manifold, and to the passenger side of the transmission. If that is missing or unhooked, or if the kickdown cable previously mentioned is missing or not correctly adjusted, you transmission will not shift properly.

Do you know what carb is installed? Might show us a couple of shots of your engine bay, and we'll try and help you diagnose what's going on. An aftermarket carb, along with trying to use the stock Distributor, could be causing a lot of your issues.

 

[Robofuzz]

Thank you for the good info! I now have some places to start looking. Just glancing at the motor, I did see that it has a plethora of vacuum lines.

I will post up some pics with the air cleaner off when I get a chance this weekend.

I know the previous owner had the longblock replaced with a remanufactured 305 and the carb was supposedly rebuilt, both back in 2008. It starts and idles fine, the transmission seems to shift fine while accelerating smoothly and while decelerating and/or braking - it just doesn't seem to "kick down". But I haven't really gotten on the motor too much because of the predetonation noises from what seems like the timing not being adjusted correctly. I supposed that could also be a result of the timing being adjusted, but the transmission not downshifting to get with the program.

 

[Robofuzz]

I forgot to answer the question about the Check Engine light. The Check Engine light does light up when the car is started along with the other dash indicators (Seat Belt, etc) and then goes out like the other indicator lights.

 

[Keyser Sose]

check under the rotor in the distributor cap. I have seen the mechanism get so rusty/dirty that it wouldn't work properly anymore. There is no vacumn advance on yours, but there is still a centrifigal advance mechanism, and it needs to work smoothly.

oke:

 

[aeilenstein]

Hey congrats on you and your son working together on the car. When I purchased my car, the trans kickdown cable had been laying on the exhaust which melted the plastic sheath to the cable itself, making the cable not actually move. Of course your cable could just be too long for the car or need adjusting more rearward so the throttle lever grabs it to pull enough of it forward to engage the kickdown.