i need help. i just bought a 1990 and it has several electrical problems. i am getting an (inflat rest) light and also a (sys warning). My tack is also registering way off what the rpm really is. My oil pressure reading is on zero as well as the tempature gauge going through the roof. The car sounds great and seems to be running well. I drove it home and saw the gauges and stopped driving it till i could find out what to do. I would think i would hear some pretty bad noises if it where about to blow but it sounds fine. The check engine light never came on when the oil pressure was reading zero. I bought it cheap and i knew it had these problems. Any help would be appreciated.

 

Welcome to the Forum and congrats on your new '90 vette.

Since you got it on the cheap due to these issues you would do well to invest ~$100 and get the GM Shop Manual set for your Vette from HELM. You can try e-bay but I didn't want to mess around with a used set of docs for my Vette.

For now insert a paper clip into the ALDL (to the right of the steering wheel under the hush panel) pins A&B (upper right), turn on the ignition switch and count the SES flashes. This will tell you what trouble codes the ECM has stored and may be a clue as to what some of the issues are due to. BTW, the ECM will initially flash three "12"s, followed by each trouble code three times, and finally three more "12"s to signify that last trouble code has been flashed.

Report back here with the trouble codes that you record.

The oil pressure issue could be due to the oil pressure sender located on the stalk to the rear of the intake base to the left of the dist.

The coolant temp issue could be due to a bad sensor in the front of the intake base just to the right of the TB.

The tach could be due to a bad tach filter, bolted to the top of the bell housing to the left of the dist.

Once you get these issues resolved we can give you some direction on freeing up some hidden ponies within your L98.

 

My 90 had a freaking out tach when I got it. I replaced the tach filter to no avail. Finally ordered a replenished instrument cluster from GM dealer and it works great now.

The SYS light means the CCM is having trouble communicating with one ore more of it's controlled systems.

Your oil pressure sender may be bad.

Your coolant temp sensor which is located just under the front of the throttle body next to the thermostat housing may need replacing. A false reading here will cause the ECM to not turn fans on as well as other troubles. You can avoid overheating in this situation by turning on your AC because it will activate your fans (providing they work) when sitting still or at low speeds which is when it will heat up anyway. (properly funtioning 90 will rarely overheat as long as it's rolling above 45 mph anyway)

The coolant temp switch for the "gauge only" is located inbetween the #6 and #8 sparkplug. Check it's wireing also.

Your air bag may have been deployed before. I'm not sure why that would light up unless there's a sensor problem or something. I've never had issues with mine.

You should pull your codes and see if and what you get. On a 90 the codes can be displayed on the digital dash where no counting of flashes is necessary. You jump pins A to G with the paperclip. If you need help with this PM me your email and I will hit you back with the method of pulling codes with a paperclip and reading them on your digital dash display and a list of codes and likely fixes.

Finally, you should go ahead and order a HELMS factory service manual for your 90 if you plan on keeping the car and doing most of the work yourself. They are expensive but worth their weight in gold to the DIY C4 owner.

Ooops, looks like 65ZO1 beat me to the reply.He must type faster. Oh well looks like our advise is simular.

 

thanks guys for taking the time to respond. i really do appreciate the help. hopefully i can get this thing fixed without going nuts.