81 Engine Issue
Thread Starter
Intermediate
Joined: Jul 2006
Posts: 40
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From: Livermore California
81 Engine Issue
Driving to school today, my 81(auto) started acting funny at constant speeds and just off of idle. At constant speed the exhaust sounds rough, like a stutter in the cycle but rpm is unaffected. At low speeds(ie parking lots) where rpm is at/under 1100 rpm it stutters but is noticeable(car jerks and lugs) and then rpms drop to 400 where it picks up or dies altogether. If it dies it cranks for a while before starting. A quick shift to neutral and a tap on the gas during the 400 rpm spell does nothing to boost rpm.
Noticed this yesterday after I got gas. She was in the red on the gas gage so I'm thinking I may have sucked some crap into the filter cutting off gas when the fuel demand is not great. The low rpm stutter/stall is the bowl running dry. The problem with that idea is that it runs fine at idle, it also has its power after the low rpm issue leading me away from idle circuit/accel pump. The car is completely stock(CA comp intact) and no adjusting has been done.
After she cools down I'm going to check the filters. Is there another filter besides the one in the carb? Just started actually working on the car so I don't have an AIM yet. Any suggestions/ideas appreciated.
Rich
Noticed this yesterday after I got gas. She was in the red on the gas gage so I'm thinking I may have sucked some crap into the filter cutting off gas when the fuel demand is not great. The low rpm stutter/stall is the bowl running dry. The problem with that idea is that it runs fine at idle, it also has its power after the low rpm issue leading me away from idle circuit/accel pump. The car is completely stock(CA comp intact) and no adjusting has been done.
After she cools down I'm going to check the filters. Is there another filter besides the one in the carb? Just started actually working on the car so I don't have an AIM yet. Any suggestions/ideas appreciated.
Rich
Thread Starter
Intermediate
Joined: Jul 2006
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From: Livermore California
Thanks.
Can you tell me if theres one other than at the carb? Maybe on a frame rail or something?
Also, earlier in the week I reconnected two hoses to the gas canister(driver side fender) that our old mechanic had cut(probably to allow its removal). One hose connects to the air cleaner box and the other to the top of the carb(both are 3/8 hose). Could connecting them backwards create this problem? The vacuum diagram on the hood didnt seem to match up to the way the other hoses were connected on the canister so I made an educated guess. I had the check engine light come on at idle(stop-go traffic) before the connection and it went away after the fix.
Can you tell me if theres one other than at the carb? Maybe on a frame rail or something?
Also, earlier in the week I reconnected two hoses to the gas canister(driver side fender) that our old mechanic had cut(probably to allow its removal). One hose connects to the air cleaner box and the other to the top of the carb(both are 3/8 hose). Could connecting them backwards create this problem? The vacuum diagram on the hood didnt seem to match up to the way the other hoses were connected on the canister so I made an educated guess. I had the check engine light come on at idle(stop-go traffic) before the connection and it went away after the fix.
Last edited by Richieboy; Aug 29, 2006 at 05:09 PM.
Race Director
Joined: Jul 2004
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From: Scottsdale Arizona
Originally Posted by Richieboy
Thanks.
Can you tell me if theres one other than at the carb? Maybe on a frame rail or something?
.
Can you tell me if theres one other than at the carb? Maybe on a frame rail or something?
.
As for your "check engine" light, I really doubt that it's the vacuum hoses. Not sure what would be a likely cause on idle. I'll have a look through the service manual and see if anything obvious pops up.
Thread Starter
Intermediate
Joined: Jul 2006
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From: Livermore California
Thanks for the info. Pulled the filter and it looks clean, little specs-nothing big. Was hard to blow through but Im thinking thats the oneway valve in it. Going to pick up a new one tomorrow but I dont think its going to solve my problem.
Any other suggestions?
Any other suggestions?
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by Richieboy
Thanks for the info. Pulled the filter and it looks clean, little specs-nothing big. Was hard to blow through but Im thinking thats the oneway valve in it. Going to pick up a new one tomorrow but I dont think its going to solve my problem.
Any other suggestions?
Any other suggestions?
Did you use a compressor?
Also. Is it the stock Quadrajet carb?
Race Director
Joined: Jul 2004
Posts: 12,686
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From: Scottsdale Arizona
If it's hard to blow through, then it needs to be changed. Should flow very easily.
It occurs to me, though, that if it's running well at speed, this may not be the problem as it should buck at speed. The problem could be flooding instead. Easy enough to check this. Take the air filter cover off when it's idling and look down the primary tubes. If fuel is dripping (or flowing) in through the oveflows, then the problem is a gummed up (or sunk) float and valve. This would explain the "check engine" light as well.
It occurs to me, though, that if it's running well at speed, this may not be the problem as it should buck at speed. The problem could be flooding instead. Easy enough to check this. Take the air filter cover off when it's idling and look down the primary tubes. If fuel is dripping (or flowing) in through the oveflows, then the problem is a gummed up (or sunk) float and valve. This would explain the "check engine" light as well.
Thread Starter
Intermediate
Joined: Jul 2006
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From: Livermore California
Swapped out the filter. The stalling went away but its dropping to 400rpm when reved to 1100-1300rpm and then quick foot off pedal. Ill check the primarys tonight. Any other possible causes?
My toyota pickup did this a couple months ago and the igniter box was bad. The vette is HEI, could a similar thing be happening?
My toyota pickup did this a couple months ago and the igniter box was bad. The vette is HEI, could a similar thing be happening?
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Race Director
Joined: Jul 2004
Posts: 12,686
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From: Scottsdale Arizona
Originally Posted by Richieboy
Swapped out the filter. The stalling went away but its dropping to 400rpm when reved to 1100-1300rpm and then quick foot off pedal. Ill check the primarys tonight. Any other possible causes?
My toyota pickup did this a couple months ago and the igniter box was bad. The vette is HEI, could a similar thing be happening?
My toyota pickup did this a couple months ago and the igniter box was bad. The vette is HEI, could a similar thing be happening?
Did the issue with the "Check Engine" light go away? I had myself convinsed that the problem was elsewhere.
PS. I should listen to my own advice. I ALWAYS tell people to try the simplest, cheepest repair first. Many times it takes care of the problem. It's when we get too clever that we get in trouble.
Last edited by CA-Legal-Vette; Aug 30, 2006 at 09:13 PM.
Melting Slicks
Joined: Mar 2006
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From: Orange Park Fl
Those hoses you re-connected are the vapor recovery. If they get hooked up wrong, or if it is not functioning properly (a possible reason they were disconnected in the first place), it can vent fuel vapor into the air filter housing. This can cause a rich mixture that will foul plugs and cause it to run rough. Just a thought. God bless, Sensei
Thread Starter
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From: Livermore California
Originally Posted by a1sensei
Those hoses you re-connected are the vapor recovery. If they get hooked up wrong, or if it is not functioning properly (a possible reason they were disconnected in the first place), it can vent fuel vapor into the air filter housing. This can cause a rich mixture that will foul plugs and cause it to run rough. Just a thought. God bless, Sensei
All the wires to the carb look fine but It looks as if some of the seals are starting to leak. when moving the accellerator a little(1/16 inch) fuel kinds of bubbles out rather than sprays, but moving any more than that gives a spray. also looks dirty on top of the carb, maybe something is gummed up?
Bob: no compressor, just mouth, Stock comp controled Q-jet.
Thread Starter
Intermediate
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From: Livermore California
Red: Smokes out of here on startup, notice the dirt/gas between the secondaries. Its dirty like that at the bottom of the red arrow as well.
Blue: Im no expert on these carbs, far from it. Idles fine, move the accel. and fuel sprays in from the accel pump(green) and inside the blue as well(both sides). At the blue however, fuel wets the brass tips and then seems to go dry if accel is held still. Now, I dont know if they all do this and its atomizing before I can see it, or if its suddenly going lean. Anyway the wetness dissapeared and it started to run rough, held it there, got worse, right before it died I tried a blip on the accel. but it died anyway. Starts up and runs, still doing the 400rpm off throttle thing as well.
Thoughts, inputs, suggestions?
Kalway: No sacnner to scan anything
Thread Starter
Intermediate
Joined: Jul 2006
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From: Livermore California
Car is hard starting now and requires a few pumps on the gas to get it to start, then it limps along, another few taps gets it up to idle speed where it holds fine(normaly about 1/2 a rev w/o throttle starts it). Notice a puff of smoke out of the exhaust on start(due to added pumping I assume). This car is my daily driver so any help would be appreciated greatly. Rich.
Safety Car
Joined: Dec 2004
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From: San Diego CA
Really sounds like a bad sensor or the confuser is confused in some way. You really need to get the trouble codes from the computer and see what it's telling you is wrong. I stepped back from the computer controls on my '81 and went with a non-computerized setup so I'm not exactly sure how you pull the codes. However, I'm sure someone here knows how.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
You need a book on this thing. You check the codes by shorting pin 3 on the 4 pin plug to ground (or pin 4) and them watching the Check Engine light flash. I don't have anything here, but the flash codes are available on here somewhere, do a search.
found some info
http://forums.corvetteforum.com/show...=trouble+codes
found some info
http://forums.corvetteforum.com/show...=trouble+codes
Last edited by SIXFOOTER; Sep 1, 2006 at 02:03 PM.
Ill check the codes and get back to you. Thanks for all the help. Ill keep you posted.