LT1 diagnostics

[jpanek]

I'm going to take a look at a 1994, 86K miles, AT, and want to do a few diagnostics, but don't know the engine layout too well. Any help is much appreciated:

1) Where is a good spot on the intake to measure manifold vacuum?

2) How easy is it to disconnect the ignition coil from the optispark and short the spark to ground? I want to crank the motor for 5-10 seconds while watching starter motor current draw on a high resolution oscilloscope. This will show pulses during the compression strokes and reveal a poorly sealing cylinder.

3) The opti has been replaced at 80K. How can I tell if it is the new vented style?

4) I've got the CAC.com checklist and the c4vettes.com cold start checklist. Good stuff! Anything else I could look for as far as checking engine condition?

Wish me luck!!!!!!!

 

[jpanek]

I'm flying down there tonight to look at it. Haven't slept well in days......

 

[vettenick]

For a vacuum test-remove the passengers side injector cover, there's a nipple on the intake.
The coil wire goes right behind the water pump. It's really the only wire that can be removed.
If the distributor was vented, you should see a vacuum hose going to the intake hose, right behind the mass air flow sensor.

Good luck with the car!

 

[jpanek]

Thanks, vettenick!

I didn't get a chance to do anything intrusive to check the motor. The seller didn't want me messing with the coil and we didn't have enough time at the mechanic to do much except visual inspection and pulling trouble codes (none!).

Now that it's home I'll use your advice to check it more closely. The drivetrain was very strong on the test drive and the 900 mile trip home. Other than the battery cable connection being corroded enough to make the car look dead electrically once, the car is very nice.

I noticed the volts display was very erratic, 13-15 volts until I cleaned the battery terminals and cables. Then it was very steady at 14.2.

Watch out for dogs crossing the highway (I-95) in South Carolina. I went from 80 to 50 mph, swerved left/right, and had a big smile on as soon as the adrenaline went away. This maneuver was done with left hand on the wheel and right holding a coffee cup.

 

[vettenick]

Congratulations! Now you've been infected!
Power and ground connections are important on these cars.
If you need more help-we're here.

 

[Aaron]

Hello all,

I've been looking for a vette for a while and came across the CAC while searching through national ads. Great site, and you forum folks seem to know your vettes well.

I've been interested in an '84 Corvette for sale in my local area for a little while, and finally test drove it on Saturday. The car ran a little rough, but not bad. Although it's at a car dealership, the salesperson I spoke with advised that they hadn't done a tune-up on the car. His reason given for not having the car running optimum was that they just acquired it through a trade in and it's not a priority right now. (Where I live winter is well on the way and not too many people are currently looking for sports cars).

In any case, before I get ready to plunk down cash for the vehicle, I'd like security that I haven't purchased a grenade. I'm paying to have a diagnostics check done on it tomorrow at a mechanic shop I chose, but beyond this, do you have any advise about things to be aware of with this model?

Jpanek, I noticed your comments about the CAC check list, but didn't see it on this site. I broused through the "Tech Center" and referenced the C4 model years. Again, any comments about a check or test I should worry about with this model year corvette would be appreciated. Thanks!

 

[jpanek]

http://www.corvetteactioncenter.com/tech/buying.html

and there is lots of good info and a pre-purchase discussion at c4vettes.com (excellent section on cold start diagnostics)

Good luck!

 

[vettenick]

Wellcome Aaron!
The '84's had their share of driveability problems. Take the car on a long test drive (30) minutes to make sure it's fully warmed up. Make sure there are no codes stored. Maybe you should convince the dealer that you are a little concerned about the rough running, and that a tune up would be a plus in your decision.
The only other bad rap that the '84's get is the really hard ride that they give compared to the later models.
Make sure the trans fluid is clean also.
Also, check the underbody for damage in case someone bottomed out.
Engine leaks should be looked at closely.

Good luck!

 

[Aaron]

Right on. Thanks Vettenick.

I called the dealer earlier today to advise of an autoshop I had arranged for a diagnostics check at, and the salesmen proceeded to tell me he couldn't let the car go for the price we had agreed upon. ($5680). He commented that figure was a wholesale price (maybe, seems like a good price to get from a dealer) and that when his managers found out about it they got PO'd and notified him that a wholesale dealer from somewhere else had offered $6900.

Whatever, I'll keep looking I guess. It was an L83 (which I know was okay for its day but is fairly low output in todays world) with over 100,00 miles on it. I had in mind that I'd buy the vehicle and hope to get another year or two out of the engine, and at that point slip in an LTI gem under the hood. But I guess it wasn't meant to be.

Still, your recommendations would hold true for several year models I believe, so thanks for the reply. The quest continues . . .

 

[Aaron]

Hey Jpanek,

Just saw your post as well. Thanks for the hotlink and it looks like I gotta keep looking. But keep looking I will, until I find "The Deal."

Salesman mentioned a newer Camaro (hopefully not an obscene word on this forum LOL) but I'm going to keep looking for the two seater of my wants. The hunt is part of the fun of buying, right?

 

[vettenick]

Aaron, don't get down. There's tons of vettes out there that people are just dying to sell for one reason or another. Besides, there's one that has your name on it, you'll find it.

 

[Aaron]

Thanks Vettenick.

The dream is far from over. Might just take a little time for that really good deal. Up where I live it seems like everything costs a little more, so I might try to have a buddy of mine help find one and then drive it to Washington for me and put her on the ferry- I'm willing to go to somewhat elaborate measures. Where there's a will there's a way . . ..