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87 running very bad

bobmo

Active member
Joined
Apr 28, 2003
Messages
37
Location
Lancaster, VA
Corvette
1987 Bright red, 1974 coupe--Basket case
Hi all.
I had to take the '87 on Tuesday to a funeral, and it rained and snowed and froze. It was a very slow drive for 3 1l2 hours at about 40mph tops due to the weather.
The ride home was much better at 75+ though.
She ran well in both directions, except I noticed a bit of bucking in 7th (4+3) when I would try to accelerate from below 60.

Since it was so cold for the rest of the week I couldnt clean her up, and this morning I need to run to the parts house and decided to take the Vette. Temps in the 60's and sunny.

On the way out I noticed a much stronger bucking in the same speed range, and then I had less and less power in 7th, then less in 6th, then I had to drop out of OD and there was less and less power at 4th.

I looked over the engine when I got to the parts house but nothing looked amiss. Oil, water, all connections looked ok.

She started just fine and idled ok, but lurched a bit in first, and the rest of the ride home was hell.
Top speed of 53 on flat land, and the last 2 miles to the house, on some hilly small roads left me at a MAX of 43!

I am stumped as to where to begin.
Help!!!!

Thanks
bobmo
 

G Winter

Well-known member
Joined
Aug 21, 2004
Messages
2,177
Location
NW Iowa
Corvette
1990 red convert 6 sp
The first thing that come to mind is aircleaner. Could it have gotten wet? If it was at all dirty the dirt would cake , not good. Second is fuel filter.Is it backfiring ? Maybe dist managed to get wet inside, although that usually get better after it warms unless the cap is cracked . I tend to lean towards the cracked dist cap. Hope this helps.
:w
 
N

nyernga

Guest
My guess would be the catalytic converter......The symptoms are the same for a clogged cat.


Len:w
 

G Winter

Well-known member
Joined
Aug 21, 2004
Messages
2,177
Location
NW Iowa
Corvette
1990 red convert 6 sp
:duh Missed that one! That completely slipped my mind. I just moved that to the top of my list. Good call myernga.
0ne way to check that , with it warmed up run it up to about 2000 rpm in park or neutral. and see if it beginnes to lose rpm.. if it does. I would bet the cat is plugged .
:w
 

bobmo

Active member
Joined
Apr 28, 2003
Messages
37
Location
Lancaster, VA
Corvette
1987 Bright red, 1974 coupe--Basket case
Thanks for the help. I will be checking things this week and will let you all know what shakes out.

Sure hope its the airfilter, Nice easy fix.
I forgot to mention that after I made my trip through the snow and rain, I had a custom fit ice bra that stayed on the frontend for 2 days.
Wish I had taken a picture.

Thanks again
Bob mo
 
Joined
Jan 15, 2004
Messages
2,240
Location
Northern Indiana
Corvette
1987 Z52 Black Convertible
I would definetly start there. Do you have the original filter assembly? With mine having Ram Air I have to be real careful about when I drive the car, since the air filter sits down right by the radiator booster fan. Keep us informed.
 

Jeb

Well-known member
Joined
Jan 20, 2005
Messages
456
Location
Covington, Louisiana
Corvette
1987 Convertable
If it's a clogged cat, you'll probably see the tach climb while the speedometer goes down. I believe this is due to the computer trying to compensate for the reduction in exhaust flow. My '87 had the same thing and it happened all at once, not so gradually that you would miss it.

There's also a test your mechanic can run to check for a clogged cat so you can have him do it before you go to the expense of replacing it.

You might also see if the fuel cap is breathing properly and the fuel filter is clean. Either of these can produce almost the same symptoms.

Good luck!!

P.S. If it's a cat, it might be a good time to remove the pre-cats. From what I understand, current cat technology now makes them unneeded and with an up-to-date cat in the back, you can do without them. That's a plus but ask your mechanic to check the law in your state. Mine did and the pre-cats are history so I guess the Feds are in accord also.
 
N

nyernga

Guest
G Winter said:
:duh Missed that one! That completely slipped my mind. I just moved that to the top of my list. Good call myernga.
0ne way to check that , with it warmed up run it up to about 2000 rpm in park or neutral. and see if it beginnes to lose rpm.. if it does. I would bet the cat is plugged .
:w

No biggy....I've missed easier ones....;LOL
 

bobmo

Active member
Joined
Apr 28, 2003
Messages
37
Location
Lancaster, VA
Corvette
1987 Bright red, 1974 coupe--Basket case
Test complete

Finally the rain stopped and the snow, and the cold, etc. I changed the air filter, and it was in dire need of change. She started ok, and idled fine. I listened around the engine for any unusual noises, while she was warming up, and detected a strong and steady HISSSS from the passenger side by the EGR pipe.
The protective cover I have over the tube was blistering hot, and when I pushed on the tube the hiss stopped.

Next I did the rev to 2000 rpm. She had a hell of a job just getting to 2000, much less falling off. So my assumpion is that the CAT is plugged and the egr pipe leak (back pressure) is verifying the fact.

Next stop is the Dynomax Cat store.
Thanks for all your help.

Bob mo
 
Joined
Jan 15, 2004
Messages
2,240
Location
Northern Indiana
Corvette
1987 Z52 Black Convertible
Would a plugged cat make it bog down on take off? I have not done the 2000 RPM hold, but could my cats, or cat be clogging up resulting in it running bad?
 

Jeb

Well-known member
Joined
Jan 20, 2005
Messages
456
Location
Covington, Louisiana
Corvette
1987 Convertable
Yes. They get progressively worse very quickly.

A competent mechanic can check and see if you have an exhaust restriction. Mine went at about 95,000 miles so I removed the pre-cats and installed a modern cat. It was a lot, a lot, noisier, so I had them put new mufflers and a new rear Y-pipe with a crossover tube on her and she runs like a dream now and doesn't have too awfully much resonance.

On removing the precats. My mechanic checked to see if it would be legal and the answer here, in Louisiana, was yes. I don't know if it would pass a California sniffer or not.
 

Jeb

Well-known member
Joined
Jan 20, 2005
Messages
456
Location
Covington, Louisiana
Corvette
1987 Convertable
Vettefan87 said:
Is there a way I can check mine other then doing the 2000 rpm hold and see if it falls off?

I grabbed this off of another thread....

"If you suspect that your "cats" are plugged, connect an ordinary vacuum gauge to anything on the intake manifold that has vacuum when the engine is running.

With the engine running, raise the rpm to around 1500 rpm and hold it there for 20-30 seconds, if the vacuum gauge reading becomes lower and lower, a plugged exhaust is indicated.

It's simple, fast and accurate!!"

(I'm sorry I didn't also grab the author so if he's out there reading this, I apologize for not giving you credit.)
 

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