Gauges fuse blowing instantly on 1990 L98 automatic
 

Hey everyone,

The vette has been running horrible lately - hard starting when hot, flooding the engine on start up, idles around 1000 rpm, and even stalls at stop signs. Anyway, couldn't find any vacuum leaks or fuel issues. Did basic maintenance - oil change, new plugs/cap/rotor/wires, and new air filter. No change. Checked the fuses after reading some threads here and saw that my Gauges fuse was blown. Replaced it, put my keys in and turned to the on position, and the fuse blew again. Any ideas on what might be causing it to blow instantly? I know a lot of things are connected to the circuit, but I haven't heard of anyone getting issues without even turning the car on. Anyway, I'll be trying to look for any loose wires or anything, but I was hoping someone might have some quick ideas.
Thanks a lot,
John

Turning the key energized your electrical system...car doesn't need to be running.

What do you mean a lot of things are connect to the circuit? Do you mean normal systems as part of the vette or was something added to the circuit?

Also have you confirmed the right size amp fuse is being used? I have seen lower amp fuses used by people as a short term fix.

When a fuse blows right away it means a hot circuit is shorted to ground.

Whatever you do, don't put in a fuse that is rated higher then then called for, that could lead to a fire! Fuse are safety protection, they generally don't blow without a good reason.

If you don't have a service manual, here is the circuit:

Hard Starting when Hot... First item
 

It sounds like there are several things that are going on in your car.

The hard starting issue could/might be related to a bad temperature sensor on the engine. You see when the sensor fails, the computer might see a cold engine and try enriching the mixture by using the 9th injector otherwise known as the "Cold Start Injector". If it fails the other direction your car would think the engine is already warm which makes a cold start challenging.

I would check your temperature sensor (s) and verify their are operating properly. It is an easy thing to check with a volt-ohm meter. Some C4's have two sensors on them, one is for the Engine controls system and the other gives you a signal for your dashboard temperature indicator.

I did not study the page from the FSM sent to you but that fuse seems to have a far reaching power as it connects to the cooling system fans and other assorted parts. I would not use the car until I could sort out this issue. I would hate to over heat the engine and see you spend thousands of dollars over a fifty cent fuse.

Check the fuse to be sure that some previous owner did not tap into it for his stereo amplifier or something. That fuse on my 1988 Coupe is easy to find and trace. You need to follow the output and isolate the short you currently have that is blowing the fuses. I have tools for this but if you don't then you are going to have to find it the old way.

When faced with something like this I start with any modifications done to the car by previous owners. There are a lot of idiots out there who don't understand electricity. The one thing in your favor is that the fuse blows right away which makes the short a "dead short" which easier to find than an intermittent short. Using a decent volt meter you should be able to identify the location of the short without too many problems.

On my car there were several modifications on the fuel pump relay when I bought it. I removed them all and put it back the way the folks at GM designed it.

I hope that the short is easy to find and allows you to enjoy your Corvette again!

Sorry, what I mean by a lot of things connected to the circuit is that according to the FSM there are a lot of things connected. The right size fuse is in. Thanks for the advice. I understand that it's a hot circuit shorted to the ground, but I cannot figure out what it is. I was hoping it'd be a more common thing, but I guess not! Thanks again.

Thanks for the advice. I did replace the CTS before I realized the gauges fuse kept blowing. Something tells me that the issue is related, so I don't want to go around throwing parts at other problems until I figure out the fuse issue. I've been driving the car for 2 years and this just suddenly started. No changes to the car... I just woke up one day and it started acting this way. I've been unplugging everything I see on the chart and still can't figure out where the problem is. Thanks again

Thanks! I actually have the FSM. I've tried unplugging everything listed on the circuit to no avail. I think there are more things that are not listed for whatever reason.

Someone recently had those symptoms turned out his TPI sensor slipped and was way off.
Need to make sure it is .54 volts so the computer knows when idling ect.
Mine slipped to .76 volts after it started idling at 1300rpm, and I just reset it to .54 at idle.
Also check if your car automatically sets it( I think that started later on) that the sensor rises to 4.5 volts smoothly with a voltmeter attached to the two top wires. Good Luck

Next step is to unplug all the circuits from that fuse port. Maybe grab a 30 Amp Automotive Fuse Circuit Tester and plug in each circuit until the amps jump on the test...that will at least narrow it down to the suspect circuit. Normal draw on the car as whole without interiors lights on is about 20-30mA.

I'd be inclined to maybe move to the C100 junction block - in the FSM 8A-202-12. It's a nuisance for sure but it might be easier to maybe isolate the circuit with the issue. E6 is on the forward lamp harness and the balance on G2 engine harness - unplug one or the other and theoretically you've isolated all components. If neither isolated the issue and you still blew the fuse I'd think you then move inside the car.

Have there been any modification attempts to the cooling fan operation?

I had a 86 Vette that was blowing the fuse for the lights in dash and tail-lights. It was a wire that was rubbing against the lower steering column right before the firewall. Not sure if that is your problem but its a easy check. The wire was in a group.