Frank Baker

1. Hello, I have an 87 convertable that was my father's I am having some trouble with. It will start fine, Idle for 20 plus min at 6 or 7 then the check engine light will come on and it is appearing to enter a limp mode. Inside there are symptoms of a short or ground issue. The seat belt light will sometime intermitenly come on and the dash lights will flicker. Sometimes when it gets hot the dash will go out and if I tap it it will come on. I have replaced the starter, flywheel, inspected and cleaned all the grounds I could find. Bought a new ecm and chip but put old one back since it preformed better, pulled the bezels and inspected all the wiring in the dash put in a new key inignition and replaced all components in the column, replaced the entire cooling system, checked the 02 sensor and light wires, had sensors checked and ordered a new ignition module, coil, cap and rotor for the tune up this week.This morning it has been idling good for an hour but last night the light came on again with no code. I had a mechanic check the ecm settings... I am lost!!!

Frank Baker

Car idled for over an hour then a few surges to 1100, check engine and limp mode. No codes and battery went to 10 volts. Alt checked and fine, new battery...

billschroeder5842

Welcome Frank-

You will need to pull the code to see what is wrong. Your CEL is telling you something needs attention and will give the code for troublehsooting and repair. This is an older CF thred. Scroll down and there is a video to watch.

https://www.corvetteforum.com/forums...ies-video.html

ctmccloskey

If your Oxygen sensor fails it will go right into "limp mode", have you tested the output of the O2 sensor? Contrary to what most people think O2 sensors can fail about every fifty thousand miles. When the car is running in the limp mode it can vary its RPM a bit more than normal. I would start there and check it's wiring connector while you are at it. If the O2 sensor gets oil or coolant on the sensor it will not work as it gets poisoned by the contaminants.

When you start the car it starts and runs on (open loop mode) settings in the ECM until it transitions into the "Closed Loop Mode". At this point the O2 sensor's readings will take over and the engine control over the mixture is much finer. If your O2 is bad then you get the engine warning Light as it can't control the mixture properly. It sounds like you might have installed a bad O2 sensor... I have had O2 sensors fail before and all I got was a warning light, no codes just limp mode in my Pontiac.

As for your Dash issues, we all have them until we speak with Bryan Thompson at BATEE.com. Bryan is "The Man" for Corvettes and their digital dashboards. He will either fix it for you or sell you the parts and let you fix it yourself. Either way he is an incredible resource for the Corvette world.

Seat belt lights and other little issues will take time to hammer each one out. There will always be little details that need to be attended to in our Corvettes. Go back and double check the O2 circuit carefully, I think that is part of the problem. Be sure to verify that your engine has a good ground strap that works, if the O2 sensor is not grounded properly it could haunt you. I was missing a strap that connected the exhaust to the rear of the car and when I installed the ground strap my antenna started working again.

I wish you the very best in solving your issues! Please write back after you have solved this problem so we can all learn from your car!

P.S. WELCOME TO THE CORVETTE FORUM

Frank Baker

I put in a new delco oxyagen sensor. Same issue no codes. Also did a full tune up with new coil and ignition module. This time ran for about an hour and drove about 2 miles before limp mode, I did notice the drive icon appeared while it was in park after the check engine light came on. If this is electrical any advice, all grounds checked, ecm and chip good.

Frank Baker

Hello,

I pulled the TPS and it read a code 22. I filled it up today drove it 5 miles, it idled for 30 min went to 900 rpms, check engine light came on, ran rich and died. Let sit 20 min started normal... what can I check next. I did fix the horn, turn signals and wipers this week. They were unrelated issues from warn parts or poorly done repairs. My father picked this up about 7 years ago and used it as a daily driver. He was correcting bad or neglected repairs and it was solid mechanically. When he got sick it sat for about 18 months and since we lost him I have no reference to the history of the car and am starting from scratch. He had a c3 also but he loved this car so I am determined to get it back on the road. I will take any sugestions or advice.

Thank you!

Frank Baker

I just noticed the oil temp sensor is not responding... I will check the connection and order a new one if necessary... the dash reading is "low" at operating temp. Updates soon.

Frank Baker

It is not stock, it is a hypertec chip. I also have one new in the box but both do the same. It did run well with it before. Should I buy a new stock chip?

Frank Baker

I have changed the ignition control module, rotor, cap and coil. I am upgrading the wires this week. All are delco parts. New ignition in the column with new signal components and harness. The car revs from a normal 6-7 to 9-10, CEL come on and it feels and smells like it is rich but no smoke. If I tap the gas, it will stutter in the 10 to 20 range and some times rev clean past that but always eventually stalls as I let off. This only happens after it is running for 1/2 hour plus. I am wondering if I should put in the new chip and see if it helps. I have a new oil temp sensor coming in and the sender is putting out the correct pressure for the oil grade if I believe the dash reading.

Frank Baker

I should also note, as the car is idling in park, twice I have noticed as the CEL comes on, the dash iluminates the drive icon. Is there a shift indicator sensor, I did inspect the wires in the console and they looked good... let me know your thoughts and I appreciate your time.

Frank Baker

It is the overdrive indicator coming on with the CEL but I have an auto. The fuel pressure was tested so the pump should be good and it will run and drive fine for 1/2 to an hour. It could be a catalytic smell I am mistaking for rich. Not sure but the last mechanic I had it at said everything was fine and it stalled in the parking lot. They went back through it and said they could not find anything wrong. I drove it home and it stalled in my neighborhood, always the same issue. CEL RPMs surge then idols low and rough until dies. If it was fuel related, would it run as long as it does before the issues? I am not against replacing the pump and injectors but I am starting to think it is an electrical short. Today the CEL flickered, and turned off for a sec when I reved it before staying on... I am lost here.

tequilaboy

Low voltage likely triggering reset, backup fuel and bypass spark. Try logging an event so that the voltage can be monitored to confirm, or try and repeat event at idle with a battery charger to maintain voltage.

Frank Baker

Ok, should I wait to the cel comes on and connect the battery charger while running? I found a few post that have very similar symptoms, overdrive light, surge and stall and it was ECM or ground related.

ctmccloskey

Hello again Frank,

I was not sure about the O2 sensor but it still has me confused. I installed a O2 sensor once that was bad from the factory and the car did very much what you are describing. These cars don't use the O2 sensor until they go into the closed loop. If the sensor is bad then your problem would not go away. Lets try a couple ideas, okay?

First, Disconnect the O2 sensor's wiring harness and measure the voltage that it is putting out, do this when the engine is running in closed loop mode or supposed to be. From what I have read these O2 sensors are very easily damaged. They are very fragile and on top of that they are also killed by getting most liquids that cars use on them. Coolant is deadly to O2 sensors as is penetrating oil and numerous other liquids used around cars.

Second, remove the O2 sensor and check for back pressure in your exhaust system. There should not be much back-pressure, if you feel any you might have an issue there. Catalytic converters have several failure modes, the one I experienced is when I left my car at a marina while on a multi state boat trip. I got back 6 weeks later and the car would start up but not rev above idle. I removed the sniffer cap on the emissions system when I saw it turn the little cap into a balloon when revving the engine. With the cap off I limped over to a gas station and removed the catalytic and broke the ceramic plate up inside of it and shook out all the pieces. Then we put the catalytic on the car and I drove 400 miles home the same day. My C4 has three catalytic converters, the two near the manifolds and the one beneath the car. Check each one with a infra-red thermometer. If any one is hotter than the others you might have found the problem.

Third, Check your engine for proper grounding. If the engine is not grounded properly that causes havoc on the ECM. Take a multimeter and check the battery voltage at the battery, now take the black lead and attach it to your engine. This means the red lead goes on battery positive and the black lead is touching hard metal on the block someplace. The voltage should be the very same, if not your engine has a faulty ground which means the control systems can't possibly be doing what they are supposed to. Your injectors have 12 Vdc supplied to them any time when the ignition is on, the ECM grounds the individual injectors to make them squirt. They squirt twice for each revolution of the engine, I believe. If you have a bad ground you might have a reason why your gauges are not reading accurately.

Fourth, this might sound weird but take a multimeter and set it on AC voltage and check the output of the alternator. Alternators make AC and then the diode bridge will switch it back to Direct current. If a diode or something else in the alternator fails you might have AC coming out of the alternator. The noise that this would produce would cause serious problems for the ECM and the rest of the car.

I rebuilt my Digital dashboard with the help of BATEE.com, many of the problems with my old dash were from bad grounds or electrolytic capacitors that have been used for twice as long as they are supposed to last. I found several bad grounds that added up to problems in the inside of the car. Corrosion on the post where the fusible links get their power was also a serious problem after letting my C4 sit for a couple years, that and corrosion on the fuses and fuse-block near the passenger door.

I too am running short of good ideas for you to try, lets go with these I listed above and see if anything changes. This is a interesting situation you have with your Corvette, it will probably turn out to be something right in front of us the whole time!
Best Wishes for a smooth running Corvette, all the time!

Frank Baker

Sounds good... I will try it all this weekend and let you know. I really am starting to feel like is is a ground issue. On a side note, I was shipped 7 spark plug wires this week... that is awesome... I have a new set comming.