Help! Wont go over 50 MPH

[l81c3vette]

I just picked up this 81 vette. The engine has had some work done but no visible hi performance stuff such as ignition or anything like that.It runs strong, smooth and has all kinds of power. It ran like a top for a couple weeks. Now when the car gets to running temperature, the engine cuts out for a second and runs for a second repeatedly. You have to let the car get down below 50 miles an hour then it will run normally. I know its getting fuel because you can see the smoke from the unburned fuel coming from the exhaust which goes away when the car starts running right again. Im thinking its the coil but ive never owned a vette before so I thought I would check with the experts. Any ideas?

 

[wishuwerehere82]

Could be the coil.
Might be the advance module in the distributor, they need a good layer of thermal grease under the heat sink to prevent overheating.

 

[l81c3vette]

Could be the coil.
Might be the advance module in the distributor, they need a good layer of thermal grease under the heat sink to prevent overheating.

The coil looked fairly new but i found that the battery wire was pinched, and the connector doesnt lock down to the cap very well. Replaced the coil and there was no change. I will check into the advance module. The car had been sitting a couple years before i got it and ive driven it almost every day since. I was thinking the vacuum advance might have a problem but I havent messed with an older engine in so long i forgot how to even test it. Will update as I go. Thanks muchly

 

[GerryLP]

C3Vette,

Do you get any "Check Engine" light flashes or lit-up?

There is a ton of places where to look, but half of them should trigger a code. One of the easiest is to remove the O2 sensor, and check its condition. I have seen some original sensors eroded to almost nothing or with the louvers collapsed (which would prevent the sensor from sampling an accurate reading.

GerryLP:cool

 

[l81c3vette]

No check engine light, but thats not to say that it isnt working or disconnected. If the o2 sensor was bad, wouldnt it cause the car to run poorly at all speeds?

 

[6880 Mike]

Take her a shop you trust and let them scan the computer.

 

[topless82vette]

I've never seen a carbed computer controlled car not be able to exceed 50mph even when in open loop or have very bad fault codes they just tend to run rich is all and poorly but there speed is never affectd.

I think by the way you talk about "unburnt fuel" black smoke if you have a cat converted this excess fuel has melted it down is all. Probably partially plugged it and thats why it cant get over 50. Well, providing you still have one but I would run it at night and see if the exhuast changes color.

 

[l81c3vette]

you can see light smoke pulsing with the engine cutting in and out. Its light the engine stalls for a second, then runs for a second over and over as long as i try to give it gas. When you let it coast back down under 50 it will run normally and have plenty of power.

 

[GerryLP]

No check engine light, but thats not to say that it isnt working or disconnected. If the o2 sensor was bad, wouldnt it cause the car to run poorly at all speeds?

Perhaps, but it depends on the amount of decay it has.

Can you rev-up the engine in the "parked" settting to the engine speed in which it starts acting up with the speedometer at 50 MPH? The coil could be bad, for it has less time to charge at higher engine speeds, and if it is faulty, this could be causing a loss of spark at those engine speeds.

GerryLP:cool

 

[Dream Ride]

Sounds like the cat converter is clogged to me. My Dad had a 72 Cadi that did the exact same thing. Drove me nuts for a while because I'd never owned anything with a converter before. Changed it out, end of problem.

 

[l81c3vette]

The car is at my local vette specialist as we speak. They looked under the hood and i was informed that the distributor is not the original one to the car. The intake was replaced along with a reman qjet carb that is not computer controlled. This is an interresting issue and I will post what info i get back from them for everyone else as I think someone tried to do some go fast mods that arent working together.

 

[l81c3vette]

If i shift to neutral and try to increase the revs after the car is above 50 mph, it acts the same way. Any slower and it runs completely through the rpm range with no problems. Its like a rev limiter is kicking in but the car isnt red lining.

 

[Curtis]

maybe stuck EGR valve.

 

[l81c3vette]

Got the car back. It has a reman qjet that is no longer computer controlled btw. The diagnosis was a blocked filter in the front of the carb that I didnt even know was supposed to be there. The shop installed an inline fuel filter and the car is running like a top again. Thanks for all the help to everyone that replied.

 

[GerryLP]

And thank you for playing!!!!

Sorry! :eyerole It almost felt like one of those made-for-TV game shows...:Lotfl

I am glad that you found the culprit. When it comes to solving problems like these, there is nothing better than to have the vehicle in front of you.

Fuel filter, huh? Who would've thunk it?:confused I would have left that one for number 12 or 14...who am I kidding...#22.

Again, I am glad to hear you got through that one. Makes you appreciate the Vette even more when you get past the problems.

GerryLP:cool

 

[wishuwerehere82]

And thank you for playing!!!!

Sorry! :eyerole It almost felt like one of those made-for-TV game shows...:Lotfl

I am glad that you found the culprit. When it comes to solving problems like these, there is nothing better than to have the vehicle in front of you.

Fuel filter, huh? Who would've thunk it?:confused I would have left that one for number 12 or 14...who am I kidding...#22.

Again, I am glad to hear you got through that one. Makes you appreciate the Vette even more when you get past the problems.

GerryLP:cool

Then we play the WILDCARD.
Not original distributor, nor carb.
We throw the dice.......And Snake Eyes!!!
Sometimes you just can't do a proper job on the internet, without getting your hands greasy, but we'll still keep trying.

 

[GerryLP]

Then we play the WILDCARD.
Not original distributor, nor carb.
We throw the dice.......And Snake Eyes!!!
Sometimes you just can't do a proper job on the internet, without getting your hands greasy, but we'll still keep trying.

right-on, brotha!

GerryLP:cool

 

[JohnZ]

The shop installed an inline fuel filter and the car is running like a top again.

Hope it isn't one of those glass ones - they're a fire hazard.

 

[l81c3vette]

I paid 2500 bucks for the car, so i kinda expected some short cuts here and there.