usmilret

As a new member here I am hoping share a few "technical issues" with this forum. Any and all help is welcome.

I recently got my hands on a 1982 Corvette. The Throttle bodies were black from backfiring and at first I didn't know why. I checked the timing and in the past someone set the timing way too far advanced. 25 degrees advanced. I can only speculate why. I reset the timing to 6 degrees BTDC and when I revved her up she was backfiring. That answered my question about the sooted throttle bodies.
I have been reading this forum.
1. I don't believe that the harmonic balancer has slipped.
2. The computer fires the cylinders.
3. the charcoal canister has a massive vacuum leak, I isolated the leak and the engine still backfires.
4. The engine looks to be on high idle and idles ~1500/1200 RPM.
I believe I resolved all vacuum leaks.
5. I will be looking into the EGR valve.
6. The HEI distributor looks newer than the car.

Interesting note the former owner says that the engine has been rebuilt .30 over. No paperwork.

toobroketoretire

Before setting the initial timing the brown 18-gauge EST wire behind the distributor MUST be disconnected so the ECM doesn't add any advance. Backfiring can be caused by an advance that is way too much or a valve that is adjusted WAY too tight or a leaking intake valve. Assuming there is no mechanical problem the EST wire not being disconnected is the likely cause.

usmilret

I know about the EST wire.
I also cleaned out the EGR Passages. The EGR now seals so no vacuum leak there. Idle dropped to 950 or so. Engine still backfires but only when the computer wants to raise the RPM. Doesn't backfire at idle.

As far as adjusting an intake or exhaust valve there are hydraulic tappets. Since the engine hasn't been running in 10 years or so it doesn't hurt to see if tappets are sticking. No engine sounds, ticks or knocks act.

I have a check engine light but no ALDL communication.

There is a replacement Engine Control Module.

ECT has been replaced earlier.

I think the prior owner or owners was snap diagnosing, replace this and replace that.

Any help is appreciated.

terry82

I would check the cam .the lobes may be bad.pull the valve covers and see if the rocker arms are moving all the same

usmilret

The Check Engine Light Stays On. Gages are not energized. Fuse to Gages is good.

Anyway back to troubleshooting.

mikem350

If the car has been sitting for 10 yrs make sure to check fuel system for gunk/water contamination

usmilret

OBD1 is repaired. DTC22 TPS voltage low is readjusted. Still high idle.

I am searching for gauges grounding terminal.

hugie82

it's not uncommon for a fresh engine to eat a cam lob. The valve will pop open a little bit , so idle and compression tests seem ok but rev it and it will run like crap.

usmilret

I have repaired most of the vacuum leaks and reset the timing. Reconnected the Vehicle speed sensor and repaired a battery drain. The 20 second interior lighting timing relay was shorted out. The corvette now runs close to normal.
The engine doesn't backfire any longer and the timing stays consistent. There is a lot of work to do to bring this corvette up to speed. The master cylinder needs a new seal to stop the brake fluid from leaking between the master cylinder and the hydro-booster. The 700R4 transmission slips a little when you get on the gas. Power antenna needs repair.
The mystery to me is why some of the gages are not working. The fuse reads 9.5 volts going to the gages, don't know if there is a corroded ground. If anyone has had experience with troubleshooting gages please chime in.
HVAC control switch "Vacuum manifold needs to be routed. All actuators are good to go and not leaking. This little problem seems to be a can of worms.
I am a bit disappointed with the lack of power coming from the engine.
The prior owners from before seems to have done a lot of higher quality work with the vacuum system.

usmilret

I want to thank the Corvette Forum for the information on crossfire injection balancing. This corvette needed it. She runs quite a bit better.

ddawson

Glad to see you are getting it sorted.

usmilret

Adjusted the minimum air idle and balanced the throttle bodies to 6 inches of vacuum using a manometer and readjusted the throttle position sensor. The engine now has plenty of power.

hugie82

If you are looking for a little more refinement, the hypertec stage 1 chip/prom really makes a difference for @$150
I've had mine for about 10 years now with no hiccups

7T1vette

Take the time for a "good to do" effort and find/open/clean/reattach ALL the ground points in the vehicle...especially those that are associated with the ECM. Also, pull the ECM connectors and clean ALL the contacts, coat them with non-conductive silicone goo, and stick them back together. After 30+ years, those connectors are not really "clean", anymore. This may save you a lot of grief in the long run.

usmilret

This is sage advice indeed and good to hear this on CF. For years I used to teach electrical troubleshooting in a classroom and hands on environment. Most do not think to check the ground. They will verify power and never address ground. Yes grounds do corrode and when they do then resistance builds up.

Here is how I check grounds.
1. Set the multimeter on resistance (Ohms).
2. Place one lead on the wire lead where it grounds, like the engine or the body.
3. Place the other lead on the ground itself.
4. If resistance is .01 ohms or less you are good to go.
5. If resistance is .02 ohms or higher remove the ground, clean, reassemble and check the resistance again. It should be less.

Some say the resistance threshold is .03. You can get away with that but I prefer the threshold to be .02.
Some types of grounds.
1. Battery lead to negative battery post.
2. Negative battery to frame.
3. Negative leads to body in the engine and cab area.
4. Negative lead to frame found at the power antenna.
5. Negative lead to frame just in front of the spare tire holder

That multimeter is a labor saver and not just for negative leads but positive leads as well.

You can also check cables from point A to Point B using resistance.


Setting the multimeter on Voltage Direct current, VDC.
You can also check for voltage drop and yes my 1982 vette has a lot of voltage drops. When you find a voltage drop along a circuit, disconnect any connections along the way, clean and reassemble, check for voltage drop again.

Power window switches had a voltage drop. I removed the fuse, cleaned the corrosion on the fuse blade and the receptacle. The voltage increased at the power window switch.

7T1vette

Good info, but most folks don't have a multimeter good enough to show "0.00" ohms for a continuity check. So, with whatever meter you have, FIRST touch the + probe to the - probe and see what ohms reading you get. You may have to wait for the reading to stabilize.

If the reading stabilizes, check touching the two probes together a few more times to see that the reading is repeatable. If so, use that 'probe test' resistance measurement plus .02 ohms as your "good" value.

If you have a meter that isn't capable of making such a precise resistance measurement, just remove and clean ALL of the ground points on the car.

usmilret

Can someone recommend a spindle and bearing kit that includes everything for install for a 1982 Corvette?
Thanks in advance for your help.