So since i was last here I sold my 79 and then went a few months without a vette and got bored.. so I found a 1985 with 65k on it. It was about 500 miles away and I drove it home. Now I'm trying to fix some issues I'm having and I'm looking for some advice here(as usual).


Issue 1. I am leaking greenish fluid from underneath when parked. It's been parked for a few months since i bought it and the puddle is pretty large but all of my fluid levels are where they should be. I was thinking coolant or possible water pump issue but I can't seem to find the leak and the coolant level is fine from the reservoir. I haven't started it since I found a puddle. It appears to be dripping from the pan underneath but it is not oil. I also thought possible power steering fluid but that reservoir is also fine…I am having a problem getting the air conditioning and heat to work not sure if that has anything to do with this...thoughts?


Issue 2…. When I drive like a grandma the car is fine…when I punch it the engine warning like come on…i checked it and it's the anti-knock sensor…the engine is not knocking. I looked on here and found that any loud bang will set that off…I replaced the sensor and that hasn't done any good. Also the car has an after market exhaust that is pretty loud…especially when you punch it…My thinking is that the loud exhaust sets off the sensor. I have noticed a slight decrease in power when the light comes on but after about 10 miles normal power resumes….it is possible to bypass this sensor? or any other thoughts on how to correct the issue?


Any ideas would be great..this is my first C4 so I'm just diving into this and trying to get this weekend warrior up and running.
Thanks all

 

Issue 1 sounds like it could be coolant. Easiest thing to check first is to pressurize the cooling system and then look and listen for leaks.
I had one that turned out to be the hose between the TPI and the block. It was a bear to find at first but once the cooling system was pressurized I found it. Take a look in the area between the back of the water pump and the block, that's where I could see old leakage had run down the block. Replacing that hose fixed my issue.

Admittedly this is only one of many potential leak points but it's not always the most obvious.

 

I agree with the above, get a radiator pressure tester and check for leaks that way. As far as the knock sensor, you do not want to disable it. The computer "listens" for detonation and pulls timing before you can hear it, saving the engine. If you have access to an OBD I scanner I would read the real time data and check to see if the computer is retarding the timing when you get on it.

 

Issue 1 sounds like a heater core to me.

 

Heater core more times than not will leak inside the car.



OP go to your local parts store and rent a pressure tester for your radiator and pump it up. It will show you how big the leak is and force (in most cases) it to leak so you can locate it without running the car and making everything hot and hard to touch.

 

Welcome and glad to see another '84 being saved!

Ditto what the folks said about pressure testing your cooling system. Best thing to do if the leak is not obvious.

Make sure your knock sensor is working. it helps control dentonation and if it's faulty you will run into issues and can harm your engine. The L83 is a typical SBC...take care of it and you will get years and years of use from it. Also, I highly recommend replacing the fuel pump as the '84 is known for needing more pressure than what the factory pump recommends. Use an '85-'91 TPI pump. It's a breeze to change out too...you don't even have to get under the car.

Later,

Lee

 

Welcome to the C4 section.

As to #1, you've already gotten good advice - pressure test the cooling system.
As to #2, have you gone through and checked the condition of the engine? For instance have you pulled and checked the condition of the spark plugs? The knock sensor may be operating properly and preventing detonation from occurring. Do a tune-up and check/adjust the timing. Check the condition and operation of the EGR system which can cause problems when it is not operating properly. Check also for vacuum leaks - the vacuum hoses are 31 years old if they haven't been changed and can be leaking air. And if you haven't already done it, get a factory service manual to aid diagnosis and repair.
As a last thought, did you torque the knock sensor to factory specs? For my '96 it is 14 ft. lbs. of torque to tighten it. I don't know what it is for the 1985 but if you over tighten it, you could affect it's operation and cause false knock.

 

Is your car equipped with the optional oil cooler? If it is then coolant is routed by pipes and rubber lines to the oil filter housing. My 91 leaked there and the fix was to replace both the rubber hoses. Cheap repair.

 

Thank you guys for the responses. Looks like I know what I'll be checking out this weekend. One last thing regarding that leak...if it is what you guys mentioned why wouldn't it drain the reservoir ?

Thanks again.

 

Coolant leak/check freeze plugs.

 

Ok so for an update….I have to go to my buddy's garage to get the tool to pressurize the system… but i did run the car today for the first time in months and figured out a few things…first the drip is coming down from right by the oil plug…makes me take a look at the diagram that corvetternow posted and i think its possible that's where the leak is. I let the car idle for about 20 minutes and nothing was leaking..the coolant temp went to about 255 and then the fan kicked on and stayed about about 235. There was no leak and the coolant reservoir stayed at the normal level. The only time I was able to make it leak was when i was revving it up and then i saw the slow dripping.

Regarding my second issue with the knock sensor…the sensor itself was replaced and it was given a tune up..all the sparks are new… i need to get the tools to get the real time data…like i said the exhaust is loud but also this coolant leak has got me thinking.. I know from my chilton manual (1-50) that you might need to remove the knock sensor to properly drain the coolant….now the knock sensor only goes off when you punch it…it is possible that when you floor it the coolant leaks heavy and that somehow sets off the knock sensor????


Any thoughts?

Thanks

 

First off the fans should come on way before 255, I think the ones in my 89 come on @ 215 & 225 ish, 235 is way too hot, even in our heat wave over the last few days. Either the gauge is reading wrong, or the fan turn on sensor is not working properly.
As far as the knock sensor being set off by the leaking coolant, I guess it is possible, but not probable. Those sensors are designed to go in a hostile environment and deal with all kinds of conditions. The coolant could have compromised the wiring and connections to the sensor, so maybe check that. I would also check the initial timing advance to make sure it is correct.
Where in Jersey are you ? Sometimes another set of eyes can help.

 

I'm up on the northern end of the state. The owners manual says that normal operation is between 190 and 255 so i thought i was in range I'm not sure what temp the fan is supposed to come on… it could be that it came on lower but i didn't notice because i was looking for the leak.

 

Ummmmm....No

You bought a 31 year old car. Check the knock sensor wire (it's a single wire sensor), check the connector for corrosion, and if those look good, replace the sensor. With the sensor out, it's a good time to drain/flush/refill the coolant.

Btw....The sensor will "hear" knock before it's audible to the driver.

 

With regard to your problems, I would add the following:

1. Get a factory service manual for your year. They are available on Ebay often in both print form and on CD. Make sure you get the final version two volume set with red covers as the preliminary white cover versions are also often sold. It will have very important diagnostic, repair and torque specifications. Don't waste your time on the Haynes or Chiltons manual - I have them but essentially for the photos. Otherwise they are a good fire starter.

2. I know I'm beating a dead horse but when installing a KS, proper torque is absolutely the most important thing. For a '96 it is 14 ft. lbs. I don't know what it is for your year. Did you install it and was a torque wrench used? If not, I would get a new KS and install it torqued to the proper value per the fsm.

3. The exhaust is loud. And you're right that may affect the operation of the KS. Do you have headers? If so, with headers, your underhood temperatures are probably higher. An if you have headers, I would consider wrapping your headers to lower temperatures and noise.

4. Were other performance mods made? Roller rockers, cam, etc.?
Roller rockers make more noise also and can affect KS readings.

5. Which leads up to the following idea. If there have been performance modifications, it may need a tune. The factory engine settings in the computer are for an unmodified stock engine. Changes to the engine may require changes to the engine management computer - knock may be occurring and the engine computer is doing it's job. And I agree with Patsgarage, check the timing. Plus, who did the tune-up - you or the prior owner? If the prior owner did it, I would check everything including making sure the proper spark plugs were used and gapped properly.

6. Check the engine temperature when it is warmed up. 255 degrees is too high before the fans kick in. Who did the coolant change? You or the prior owner? Was the radiator pulled, flushed out and the fins cleaned along with cleaning the a/c condensor fins and the area underneath the shroud? Was the engine flushed and completely drained? When I got my car in 2012, I did all of that plus a new thermostat, water pump and hoses - after 16 years I figured it would need all of that even though the coolant looked new.

7. I would inspect everything I could on the car for maintenance, repair and replacement. Maintenance is the key for C4s. I had a number of splitting and rotting vacuum lines on mine. Bad vacuum lines can cause running problems like you're experiencing.