wesman85

I am a first time Corvette owner and absolutely love this forum! I have lurked for months searching for various issues and finding some great advice! I will certainly give back after I get some experience under my belt with my C3.

I could really use some help with a recurring problem I'm having with my 1982 Collector Edition. The engine will run fine, then all of a sudden it will run really rough, miss, backfire, and die. When this happens, the check engine light will come on and it will throw a TPS sensor error code. I replaced the sensor and tried adjusting it using a multimeter according to the factory manual instructions, but can't get the voltage to get below .6 volts, nowhere near the .516 volts (working from memory, don't have the target number in front of me). Anyway, I continued to drive it with the higher voltage setting and the idle is really high (around 1000 to 1300 RPM), but it runs ok. The only issue is the infrequent rough running and error code. The rough running started happening more frequent, so it is now at a repair shop. The mechanic told me something I already knew, saying the Check Engine light code says I need a new TPS sensor. My car has been there for almost a week and am beginning to think that this mechanic may not have the experience I need with an older vette. Any advice on what could be happening here? Another problem is the instrument gauge fuse will consistently blow if I accelerate hard. Are these two problems related? Could I have a bad ECM?

Any help or advice would be greatly appreciated! Also, if anyone knows of a good Vette mechanic in the San Antonio, Texas area, I would love to know! Cheers! Wesley

general69

i see two problems for a start.

1.) A bad ground system. Fix all grounds and add extras if your not sure,especially at the
the computer. the computer itself is grounded internally to it's case, but over the years,
working on computer controlled vehicles,especially pre OBD type such as yours,i used
actually have good luck by adding a ground wire to one uf the computer case screws.
2.) I have run into problems with many after market TSPs.
Take it back if you are able to (electrical components are tough to return once installed
and if you're not a business)
Take your test gauge with you to the parts store and test each one they give you until
you get close to the one you need (as close to .5v as possible.) Don't take the word of
the parts counter people that they're not available.They are. Some dealers can still
get good ones.

Good luck
General

jdp6000

You should be able to get a new TPS down below .525 so stuck at above 6 is weird. You sure you have the arm on the correct side of the handle on the TBI. Dumb question but I've heard of it being installed wrong.

The other possibility is the throttle shaft in the rear TBI is binding and stuck in a more open position. Look at the angle of the throttle plate in the rear TBI and compare it to the angle on the front TBI. They should be identical. CAUTION DON'T LET ANYONE POP THE CAPS ON EITHER TBI AND STAR MESSING WITH THE FUEL TO AIR RATIO.

One more thing. .600 should work fine. Your with in variance spec's. Question, when you took off the air cleaner to adjust the TPS did you reconnect the hose to the air cleaner that comes off the back TBI? Is the valve in the air cleaner working or leaking? Check to see if all the vaccum hoses are connected. If there is no change cap the hose that goes to the air cleaner to eliminate it as a possible vaccum leak. At .600 on the TPS with a minor vaccum leak you will get 1000 to 1300 rpm at idle.

As for ground and bad connection. Follow the wires around to the firewall. Where they pass through to the cab there are several large connectors. Remove the cap on the firewall pull the connectors out. Clean them real well.

Jim

wesman85

General and Jim, thank you so much for your awesome advice!! My 82CE is at a local shop, where the mechanic worked 20 years for a local Chevy dealership and then went out on his own. He seems to know his stuff. Anyway, I talked to him late yesterday and the problem is some sort of electrical short that he is troubleshooting. The problem with the instrument gauge fuse blowing is related to the TPS/rough running problem. I don't remember all of the tech specifics he told me, but he hooked up meters at the TPS and other places and drove the vette. He noticed that there is an intermittent voltage spike showing up at the TPS and I think he said the two IACs, which are also related to the fuse going out. I authorized installing a rebuilt ECM to see if that is culprit (cost was around 140, which seemed to be reasonable based on my research). He checked grounds and connectors to ECM and other suspect components and they were all fine. He said if it was a ground problem, that you would see an intermittent voltage drop, and not a spike which seemed to make sense. The voltage spike is what was causing my TPS to fry (this is the third one I have replaced). He said the TPS wire that should be receiving a constant 5 volts was getting spikes as high as 9 volts. He is installing the rebuilt ECM this morning some time, so I am keeping my fingers crossed that it will fix the issue! I will post an update when we figure out the problem! Cheers! Wesley

jdp6000

You didn't mention the voltage issue. Sounds like that should be the problem. ECM's are know to go. Let us know.

wesman85

Jim, you are so correct! I guess I didn't mention the fuse blowing issue because I didn't think it was related to the intermittent rough running.. the fuse would consistently blow for the instruments/gauges when I accelerated really hard, but the rough running engine problem didn't seem to coincide with the fuse blowing. The fuse issue was something extra I asked the mechanic to look into once he fixed the rough running issue. Something else I noticed too, I should mention and need to tell the mechanic, was I replaced the alternator when I got the vette. The replacement alternator always showed a high voltage on my gauge (charging just outside the red zone, probably about 16 +/- volts instead of 13 to 14 volts I'm used to seeing on cars. I actually took the replacement back and got it replaced under warranty, even though they tested it and it passed. I have to assume that the alternator (a remanufactured AC/Delco from AutoZone with a lifetime warranty) and voltage regulator are good. So why would the voltage be so high when the engine is running? Does the ECM also have a hand in controlling that? Sorry for all the dumb newbie questions.

jdp6000

Does it still show high?

Voltage at the alternator should match voltage at the battery. If you see 12-13 at the alternator and battery and the gauge shows 16. Something else is interfering. Not likely the ECM unless something inside is the cause if the short.

terry82

sounds like you have a guy who knows what he is doing .let us know how it turns out

LastC3AZ

Make certain all the basics are covered before you start chasing ECM related issues. More times then not, we find a vacuum leak somewhere in the system ..... without this part of the system working properly, signals are sent through the ECM to make adjustments to several areas ...
Check vacuum for leaks and/or connections
Change out your MAP sensor .... inexpensive, but a key player in the system.
Then you can move on to other areas .....

just my 2 cents ......

wesman85

Ok, I have an update. The ECM was replaced with a rebuilt one and that seems to have fixed the volt spike/TPS problem. The car is running great now, idles around 700 RPM, and seems to run much smoother. No more check engine lights or blown instrument gauge fuses! My only complaint is that it now has a hard time starting cold. One last electrical demon to exercise, something causing the fuse to blow for hazard light/horn/brake light circuit.

I have a question for those of you that own an 82 with Crossfire Injection: Can you tell me where the small black hose connects from the air cleaner temp sensor to the rear of the rear throttle body/injector? There are two possible places I see for it to connect, both have rubber plugs on them. The factory manual didn't show where this hose connects. (this hose was missing on my vette when I purchased it, so not sure how crucial this connection is, but apparently it helps maintain/mix fresh air with heated air for intake.)

jdp6000

One is always capped, it's for balancing the TBI's. one goes to the MAP the other goes to the air cleaner. I can't remember which is which. You need that for a cold start.

jdp6000

Just looked it up. Its the snaller of the three. Far right towards the center of the engine.

Jim

wesman85

Jim, thank you so much for looking that up and for your other advice! I had the hose connected to that port so lucklily it was the correct one!

The vette seems to be running good now, the only engine issue now is that is is hard to start and get going when its cold. Not sure what to do about that. The mechanic had my car for over a week and was still wanting to keep it to see how it was starting when cold, but I got impatient and picked it up. I will probably take it back to them so they can adjust it or whatever to fix that.

Last night, I took out the speedometer/tach cluster and put in a new printed circuit. Man, that was NOT fun. Took me way longer than it should have, but it was a great learning experience. Now, I can actually see what speed I am going at night!

Now, my next project is to see what is going on with the rear end. When I drive it, I can hear a noise coming from the rear end that sounds like I am running over seams in the road (like a regular faint knocking sound that speeds up with speed. I am thinking maybe the u-joints need to be checked? Also, there is an annoying squeeking/chirping sound that also speeds up with speed, but noticed that this sound goes away when I press on the brakes, so I am thinking it has something to do with rotors/brake shoes/calipers (sounds like it is coming from the right rear wheel). I am planning on removing the wheels and checking the brake pads and maybe going ahead and putting new pads on all four wheels. Brakes are working fine, so I don't think I will need anything else. Maybe putting some of that anti-squeek compound between the pads and calipers will make that squeek/chirp go away. Cheers! Wesley

jdp6000

Cold start problem could be for a number of reasons. Aside from that the engine sounds like its running right. You need a starter that cranks over really fast....does yours? Other possibility is carbon build up in the intake preventing fuel from reaching chambers fast enough. Try decarbonizing the intake with a good cleaner.

Rear end problems could all be related. Clicking, sqeaking, etc. Try to accelerate until you hear the noicse. keep one foot on the gas and use your left foot to gently apply pressure to the brake pedal....does the click and sqeak stop?

Jim