Hello all. I'm a new owner of what I think is an awesome 1985 vette, especially for the price that I bought it at, but I've come across a problem that the previous owner mis-diagnosed. I'll give a description: car starts fine and quickly, I take it for a spin and it sounds like the engine has a miss (what the previous owner called it) but at the same time the engine misses, I lose electrical power for a quick second (radio goes off, dash blinks off and resets, headlights flash off). While driving it yesterday going about 35 mph everything shut off. I pulled to the side of the road and all of the sudden power came back, I hit the key and it started right up. The in and out is pretty consistent especially at higher speeds (it tends to do it more on the interstate than around the neighborhood, maybe just more noticable at the higher RPMs) I have experience turning a wrench, but no experience dealing with all of the electronics on the newer decades of computer controlled cars. I would really appreciate any help. PS-I just bought the service manual for the car from vettesforsale who posts here on the Forum.

 

It sounds like something isnt properly grounded. I believe a short would cause something to not work entirely, not off and on like you described it. I'm not sure what circuit it is, but have you tried looking up error codes?

 

Uhhhh...... good luck with that. It could be numerous different things. First thought is does it do it at all at low RPMs? If it is only at higher RPM's it could just be something simple like the distributor coil going out. If it dies all over the RPM range then I'd first get a Helms manual, about $75 on ebay, and then go over the grounds (they are listed in the manual) and make sure they are not corroded or degrading. The wiring on pre-'91 vettes deteriorates over time, I've read service bulletins for this but forget the exact reasoning. I had an '86 that had two wires in the main engine harness rub together so much that they started making contact, and it happened to be the one of the wires for the fuel injection. Took me and a mechanic friend forever to figure that one out.

 

Will there be any codes if I'm not getting a check engine light on? I've read the thread about reading them but didn't know if there was some type of indicator that would let me know if it was reading error codes. I do appreciate the help. I love the car and look forward to be able to get it on the highway and seeing what it's got.

 

Has anyone else seen this problem? It's like a total loss of all electrical (accessories and engine). Could a computer going bad kill everything?

 

I have seen it dozens of times on the big trucks we work on, never on a car, but we don't work on cars anyway. Your symptoms sound identical though, especially with the headlights going off. Check for loose battery primary cables and/or bad connections. Especially the negative cable ground to frame. That is the one most likely to have corrosion build up as it is also the hardest to get to and service. Hope that is all there is to it.

 

Do you happen to know the location where the ground connects to the frame? One thing that I've noticed, there's not a lot of spare room in the engine compartment of the C4. I'm used to the older Chevelles and Camaros that when you look under the hood you have to make the "big" decision, should I build a big block to put in there or rebuild the small block. I appreciate the info. I'm just hoping to figure it out before I have to give in and take it to the dealership. The money could be better spent on engine components.

 

Sorry, mine is 95 and totally different. Just check cables at battery first, visually, tug test, and that connections are tight. Then follow them back. I know there isn't much room, part of what we all have to get used to. Last 'hot car' I had was 64 Malibu SS Vert and I could practically sit in the engine compt to work on it.

 

Not sure about the early C4's but the later 80's have a number of grounds on the frame below the battery, corrosion tends to build up there. Id chck grounds/battery connections first rather than ignition.

 

First things first, forget about the computor. You got to do a good visual and make some basic resistance measurements. Take battery terminals off battery & look at all surfaces, were the bolts tight? Make sure the heavy wires that are molded into the connector (that go on the battery) are not loose or has any movement within it.

Check the other end of the cables to see where they go, tug, pull, see if anything moves that should'nt, any splices, check it out and if you have one of those switches that is in line with one of the battery cables to turn off power to the car, it could be bad.

Leaving the cables disconected from battery, make resistance check from end to end of each cable. While makeing resistance checks, move and pulll the cables and ends. For that short legnth of wire the reading should be zero or darn close to it. As your pulling, see if the meter reading changes, jumps or flinches. If it does, check closer.

If all is good you can connect battery and turn the headlights on and start moving wires around. I would assume you have a disconnect causing everything to dye. A single part, sensor or computor is not going to cause the entire car to shut down. Before you chase the weird stuff do some basics first. This should get you started systematically. See if this helps and let us know.

 

Check the fusable links that connect to the battery lead under the battery. it sounds like they could be corroded or one of the links may be burnt inside the outer jacket and is only losing contact intermittantly due to vibrations.
There are also two grounds to the chassis in this area that you should check for corrosion and the chassis to engine ground is there too.
If a fusable link is blown you can buy replacements from NAPA and replace them.

 

As far as the grounds go just trace the neg. battery cable, it doesn't go that far. Should connect on the rear driver's side of the block, and then also have a pigtail coming off it I believe going to the frame behind the battery. There is also a ground strap that goes from the block to the frame in this area as well. Also there are several grounds that connect to the block on the top driver's side of the Trans belhousing. You should atleast be able to run your hand down to that area from the top and feel if they are tight. You have two wiring harnesses in the engine bay. The engine harness and the Light harness. The grounds previously mentioned are the ones on the engine harness. The light harness runs up the driver's side frame rail and then across the front to the other side and has several grounds towards the front of the frame rails on both sides. You also have a ground spot for the rear harness behind the passenger seat under the carpet. Thats all I can think of, but there may be some more under the rear of the car, but I've never torn that area down so can't say where.

***This info is from a '90 auto car I've torn down. Your year may differ slightly.

 

I appreciate all of the input from everyone. Hopefully if the Army will let me get home before 7:00 tonight I'll get a chance to starting searching for all of these leads that you all have passed on to me. Again, thanks everyone.

 

First yank hard back and forth on both the negative and positive battery cable while someone watches the dash, or while the engine is idling and observe for cutout. Not often, but sometimes the connection between the cable wire and the cable end lug becomes corroded and intermittent. Do the same for the ground connection of the negative cable. I believe on the 85, the wire that supplies +12v power to the ignition switch comes from the large bolt on the starter motor and I would tug on this connection too, both the large positive wire and the smaller wire that goes to the firewall connector and then to the ignition. If the ignition wire becomes intermittent, this could cause your symptoms because almost every circuit in the car passes through the ignition switch and a loss of connection here shuts everything off. Engine running, you can lose the battery ground and the alternator will run the car, but if you lose the positive connection to the ignition switch, everything shuts off.

 

Let us know what the culprit is when you find it.

 

Well, I'm pretty much with everyone on checking connections-battery cables etc. very important, but I also think you should check your bulkhead connection-right next to the battery,disconnect the negative terminal of the battery-then just disconnect the bulkhead connection and look at the pin connections-if you see a whiteish/greenish look-blow it out, don't mess with the black stuff, it's an anti corrossive protection. And if you do check it-after connecting it up-take some sealer and seal the top and sides and make sure the cowl drip tube is not dripping on it-re-direct it if you need to.