1989 engine control issues
Thread Starter
8th Gear
Joined: Apr 2005
Posts: 8
Likes: 0
1989 engine control issues
I have been working on my son's 1989 Corvette. It had several issues. Engine temperature gauge would swing all over the place from "Lo" to over 230 and back in a few seconds. The engine would load up and run really rich when it hit the low end. Installed a new temp sender and that solved it.
Then I noticed that when I stand on it, often it will pull in a lackluster way for a few seconds, then suddenly pull really hard and take off for a few seconds, then go back down in power. Yesterday I installed the following:
New spark plugs
New spark plug wires
New throttle position sensor
I adjusted the TPS so I had 0.500V on the center wire with the throttle closed (key on, engine not running).
Took it out for a spin. It ran really well. Pulled hard and I barely touched the throttle. Then, on my way back from the test drive, it nearly stalled when I went around a turn. Got back to the driveway and noticed that it would idle at about 800 to 900 for several seconds, then suddenly drop to the point where the engine would almost die before the computer yanked the idle up to about 1100. It would quickly settle back down to 800 - 900, then it would do it again. After it did this several times, I cracked the throttle a little and then it felt like the engine was running on 6 or 7 cylinders. The whole car was shaking.
Have I got the setting for the TPS wrong? Any other suggestions?
My son recently bought this car, so there may still be a lot that needs to be replaced (has 174,000 miles on it).
Thanks.
Then I noticed that when I stand on it, often it will pull in a lackluster way for a few seconds, then suddenly pull really hard and take off for a few seconds, then go back down in power. Yesterday I installed the following:
New spark plugs
New spark plug wires
New throttle position sensor
I adjusted the TPS so I had 0.500V on the center wire with the throttle closed (key on, engine not running).
Took it out for a spin. It ran really well. Pulled hard and I barely touched the throttle. Then, on my way back from the test drive, it nearly stalled when I went around a turn. Got back to the driveway and noticed that it would idle at about 800 to 900 for several seconds, then suddenly drop to the point where the engine would almost die before the computer yanked the idle up to about 1100. It would quickly settle back down to 800 - 900, then it would do it again. After it did this several times, I cracked the throttle a little and then it felt like the engine was running on 6 or 7 cylinders. The whole car was shaking.
Have I got the setting for the TPS wrong? Any other suggestions?
My son recently bought this car, so there may still be a lot that needs to be replaced (has 174,000 miles on it).
Thanks.
Le Mans Master
Joined: Oct 2008
Posts: 9,758
Likes: 49
From: Houston Texas
I have been working on my son's 1989 Corvette. It had several issues. Engine temperature gauge would swing all over the place from "Lo" to over 230 and back in a few seconds. The engine would load up and run really rich when it hit the low end. Installed a new temp sender and that solved it.
Then I noticed that when I stand on it, often it will pull in a lackluster way for a few seconds, then suddenly pull really hard and take off for a few seconds, then go back down in power. Yesterday I installed the following:
New spark plugs
New spark plug wires
New throttle position sensor
I adjusted the TPS so I had 0.500V on the center wire with the throttle closed (key on, engine not running).
Took it out for a spin. It ran really well. Pulled hard and I barely touched the throttle. Then, on my way back from the test drive, it nearly stalled when I went around a turn. Got back to the driveway and noticed that it would idle at about 800 to 900 for several seconds, then suddenly drop to the point where the engine would almost die before the computer yanked the idle up to about 1100. It would quickly settle back down to 800 - 900, then it would do it again. After it did this several times, I cracked the throttle a little and then it felt like the engine was running on 6 or 7 cylinders. The whole car was shaking.
Have I got the setting for the TPS wrong? Any other suggestions?
My son recently bought this car, so there may still be a lot that needs to be replaced (has 174,000 miles on it).
Thanks.
Then I noticed that when I stand on it, often it will pull in a lackluster way for a few seconds, then suddenly pull really hard and take off for a few seconds, then go back down in power. Yesterday I installed the following:
New spark plugs
New spark plug wires
New throttle position sensor
I adjusted the TPS so I had 0.500V on the center wire with the throttle closed (key on, engine not running).
Took it out for a spin. It ran really well. Pulled hard and I barely touched the throttle. Then, on my way back from the test drive, it nearly stalled when I went around a turn. Got back to the driveway and noticed that it would idle at about 800 to 900 for several seconds, then suddenly drop to the point where the engine would almost die before the computer yanked the idle up to about 1100. It would quickly settle back down to 800 - 900, then it would do it again. After it did this several times, I cracked the throttle a little and then it felt like the engine was running on 6 or 7 cylinders. The whole car was shaking.
Have I got the setting for the TPS wrong? Any other suggestions?
My son recently bought this car, so there may still be a lot that needs to be replaced (has 174,000 miles on it).
Thanks.
Did you cross any wires? is the timing off? Was it doing this before the tune up? Have you pulled any codes yet?
Thread Starter
8th Gear
Joined: Apr 2005
Posts: 8
Likes: 0
No crossed wires. Replaced them one at a time.
Before the tune up and TPS replacement, the engine would not pull very hard, then suddenly pull really hard, then go back to not pulling very hard. When I stood on it, it would pull like my '94 Geo Prizm for several second, then go like a bat out of someplace unholy, then go back to Geo Prizm mode :-)
After the tune up and TPS replacement it ran like a scalded dog. It ran like a dream. It was at the end of the trip that it suddenly developed the idle issue, and then the shake.
I will readjust the TPS for 0.54 volts. Is it correct to measure this with the key on and engine off, or should the engine be running?
Before the tune up and TPS replacement, the engine would not pull very hard, then suddenly pull really hard, then go back to not pulling very hard. When I stood on it, it would pull like my '94 Geo Prizm for several second, then go like a bat out of someplace unholy, then go back to Geo Prizm mode :-)
After the tune up and TPS replacement it ran like a scalded dog. It ran like a dream. It was at the end of the trip that it suddenly developed the idle issue, and then the shake.
I will readjust the TPS for 0.54 volts. Is it correct to measure this with the key on and engine off, or should the engine be running?
Le Mans Master
Joined: Oct 2008
Posts: 9,758
Likes: 49
From: Houston Texas
No crossed wires. Replaced them one at a time.
Before the tune up and TPS replacement, the engine would not pull very hard, then suddenly pull really hard, then go back to not pulling very hard. When I stood on it, it would pull like my '94 Geo Prizm for several second, then go like a bat out of someplace unholy, then go back to Geo Prizm mode :-)
After the tune up and TPS replacement it ran like a scalded dog. It ran like a dream. It was at the end of the trip that it suddenly developed the idle issue, and then the shake.
I will readjust the TPS for 0.54 volts. Is it correct to measure this with the key on and engine off, or should the engine be running?
Before the tune up and TPS replacement, the engine would not pull very hard, then suddenly pull really hard, then go back to not pulling very hard. When I stood on it, it would pull like my '94 Geo Prizm for several second, then go like a bat out of someplace unholy, then go back to Geo Prizm mode :-)
After the tune up and TPS replacement it ran like a scalded dog. It ran like a dream. It was at the end of the trip that it suddenly developed the idle issue, and then the shake.
I will readjust the TPS for 0.54 volts. Is it correct to measure this with the key on and engine off, or should the engine be running?
Last edited by ch@0s; May 17, 2010 at 01:48 PM.
Team Owner
Joined: Jan 2003
Posts: 20,254
Likes: 221
From: Summerland B.C. Canada
If it has the original Multec injectors, they may be your problem as they are know problematic injectors. Ohm test them hot and cold, it may shed some light.
Check out FIC's sticky on Ohm testing them.
http://forums.corvetteforum.com/c4-t...questions.html
Check out FIC's sticky on Ohm testing them.
http://forums.corvetteforum.com/c4-t...questions.html
Thread Starter
8th Gear
Joined: Apr 2005
Posts: 8
Likes: 0
I have not checked the fuel pressure or the fuel filter yet. Considering how well it runs when I stand on it, I don't think it is a lack of fuel. I will change the filter and check the pressure, though.
I had read about the original fuel injectors on here and had already talked to a guy who everyone on here recommends for replacements. I have not ordered them yet, but that will be the next item on the agenda.
Both good ideas. Thanks.
I had read about the original fuel injectors on here and had already talked to a guy who everyone on here recommends for replacements. I have not ordered them yet, but that will be the next item on the agenda.
Both good ideas. Thanks.
