Hesitation during acceleration
Thread Starter
Instructor
Joined: Jun 2011
Posts: 205
Likes: 3
From: Great Mills Maryland
Hesitation during acceleration
I have a 94 coupe with the LT1 that I just got a week ago. I'm new to this type of motor, I'm used to big block Olds motors where I can actually see and change parts.
The car hesitates and/or bogs down when I try to accelerate from a stop went the engine is cold. Seems to work fine after it's warmed up but will bog if I jump on it too much. The car has 100k miles on it and I don't think it was well taken care off. I assume it has to do with the fuel system or throttle plate maybe. The engine may need a complete tune up? I pulled the easiest spark plug I could get to and it looked fine. I have new ones to install but looks like a day job. I know nothing about fuel injection. Thanks.
The car hesitates and/or bogs down when I try to accelerate from a stop went the engine is cold. Seems to work fine after it's warmed up but will bog if I jump on it too much. The car has 100k miles on it and I don't think it was well taken care off. I assume it has to do with the fuel system or throttle plate maybe. The engine may need a complete tune up? I pulled the easiest spark plug I could get to and it looked fine. I have new ones to install but looks like a day job. I know nothing about fuel injection. Thanks.
Burning Brakes
Joined: Feb 2009
Posts: 785
Likes: 3
From: Richmond Virginia
Assuming you're not seeing any warning lights and the ASR (traction control) isn't active at times. Some folks say the ASR feels like a "bog" and I agree. I'd start by checking fuel pressure first. These aren't exact specs for yours but they'll get you there.
42-47 psi ign on -engine off
38-42 eng. running
Spark plugs,wires air and fuel filters are all maint. items which should be replaced along with all the fluids being changed assuming you don't have service history on the car. Another possibility could be dirty injectors--but I'd check pressure first.
42-47 psi ign on -engine off
38-42 eng. running
Spark plugs,wires air and fuel filters are all maint. items which should be replaced along with all the fluids being changed assuming you don't have service history on the car. Another possibility could be dirty injectors--but I'd check pressure first.
Race Director
Joined: Apr 2003
Posts: 17,698
Likes: 1,667
From: moraga ca
The first thing I would do after buying a used car is do a tuneup; wires, plugs, cap, rotor, fuel filter, 02 sensors, check timing, oil, filters, etc. That usually will resolve any issues. If after all that, there are still issues, check fuel pressure and injectors.
Thread Starter
Instructor
Joined: Jun 2011
Posts: 205
Likes: 3
From: Great Mills Maryland
Assuming you're not seeing any warning lights and the ASR (traction control) isn't active at times. Some folks say the ASR feels like a "bog" and I agree. I'd start by checking fuel pressure first. These aren't exact specs for yours but they'll get you there.
42-47 psi ign on -engine off
38-42 eng. running
Spark plugs,wires air and fuel filters are all maint. items which should be replaced along with all the fluids being changed assuming you don't have service history on the car. Another possibility could be dirty injectors--but I'd check pressure first.
42-47 psi ign on -engine off
38-42 eng. running
Spark plugs,wires air and fuel filters are all maint. items which should be replaced along with all the fluids being changed assuming you don't have service history on the car. Another possibility could be dirty injectors--but I'd check pressure first.
I do need to do a tune up and change the mentioned parts, need to get a service manual first.
Thanks for the replies.
Le Mans Master
Joined: Feb 2005
Posts: 6,475
Likes: 565
From: Clearwater Florida
...... Don't waste money on a Chiltons or Haines ... buy the Helm factory service manual ... you can find them here occasionally or on the auction sites , or buy direct from Helm ........
Thread Starter
Instructor
Joined: Jun 2011
Posts: 205
Likes: 3
From: Great Mills Maryland
I wasted some on Haynes already, basically useless, should have known when I paged through it. Factory service manual the only way to go. Got one for my pair of Olds 442's and had gotten one when I bought my new 1988 C-4 coupe years ago.
Burning Brakes
Joined: Feb 2009
Posts: 785
Likes: 3
From: Richmond Virginia
[QUOTE The ASR, is that the unit that looks like it controls the throttle cable?
Yes on the drivers side fender well,there should also be a button to the left of the instrument panel to turn the ASR off which would be the way to check if that's what you're feeling. With the ASR on and active there is also a light which should flash saying "ASR Active" in the message center.The ASR shouldn't kick in on a stock LT1 except with hard accel. from a standing start/wet roads or tires in poor condition IMO. Manual trannies would be easier to loose traction and turn the ASR active. From your description the "bog" sounds pretty severe--I'm guessing you likely have other problems.
As far as getting a FSM try ebay they come and go there. They are year specific and you'll get more info with the 2 volume version than in the single preliminary edition
Yes on the drivers side fender well,there should also be a button to the left of the instrument panel to turn the ASR off which would be the way to check if that's what you're feeling. With the ASR on and active there is also a light which should flash saying "ASR Active" in the message center.The ASR shouldn't kick in on a stock LT1 except with hard accel. from a standing start/wet roads or tires in poor condition IMO. Manual trannies would be easier to loose traction and turn the ASR active. From your description the "bog" sounds pretty severe--I'm guessing you likely have other problems.
As far as getting a FSM try ebay they come and go there. They are year specific and you'll get more info with the 2 volume version than in the single preliminary edition
Burning Brakes
Joined: Feb 2009
Posts: 785
Likes: 3
From: Richmond Virginia
There's some good info here on fuel injection IMO whether someone is new to fuel injection or not. It's well written and easy for a newbie to understand. I've had a copy for years so i'm guessing they're still in print. I imagine other places like Amazon/ebay sell them--this just happens to be where I bought mine.
http://www.bentleypublishers.com/che...eng-82-01.html
http://www.bentleypublishers.com/che...eng-82-01.html
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Safety Car
Joined: Jul 2006
Posts: 3,696
Likes: 1
From: MA
With that many miles I would worry about the Optispark.
If you dont know what it is, You will soon enough.
Its the biggest problem with the LT1 motor.
To some it up its the distribiter unit for these motors and its in a real bad location,Under the water pump. Idiot engineers at GM on drugs to some it up.
If you dont know what it is, You will soon enough.
Its the biggest problem with the LT1 motor.
To some it up its the distribiter unit for these motors and its in a real bad location,Under the water pump. Idiot engineers at GM on drugs to some it up.
Thread Starter
Instructor
Joined: Jun 2011
Posts: 205
Likes: 3
From: Great Mills Maryland
[QUOTE=TWISTERUP;1578029471][QUOTE The ASR, is that the unit that looks like it controls the throttle cable?
Yes on the drivers side fender well,there should also be a button to the left of the instrument panel to turn the ASR off which would be the way to check if that's what you're feeling.
I'll have to turn it off and try it. Thanks.
Yes on the drivers side fender well,there should also be a button to the left of the instrument panel to turn the ASR off which would be the way to check if that's what you're feeling.
I'll have to turn it off and try it. Thanks.
Drifting
Joined: Jan 2010
Posts: 1,624
Likes: 48
From: Saudi Arabia
that's what I did ,
new plugs
new fuel filter
new fuel pump
cleaned injectors
changed engine oil
changed trans oil
changed map sensor " which was causing the same symptoms you have "
waiting list : new wires + optispark + o2 sensors
congrats on your new vette
Last edited by Mohammed_z; Jul 2, 2011 at 10:41 AM.
Thread Starter
Instructor
Joined: Jun 2011
Posts: 205
Likes: 3
From: Great Mills Maryland
With that many miles I would worry about the Optispark.
If you dont know what it is, You will soon enough.
Its the biggest problem with the LT1 motor.
To some it up its the distribiter unit for these motors and its in a real bad location,Under the water pump. Idiot engineers at GM on drugs to some it up.
If you dont know what it is, You will soon enough.
Its the biggest problem with the LT1 motor.
To some it up its the distribiter unit for these motors and its in a real bad location,Under the water pump. Idiot engineers at GM on drugs to some it up.
Thread Starter
Instructor
Joined: Jun 2011
Posts: 205
Likes: 3
From: Great Mills Maryland
Well I'm making my list of parts to buy and when I get the service manual, time to get to work. I guess since it's actually my 17 year old son's car, he will help. After driving the car, I got the fever again and need to get a car for me, a C-4 for sure. Thanks for the replies. I'll let you know how it turns out.
I need to upgrade so I can post pics.
I need to upgrade so I can post pics.
Drifting
Joined: Jan 2010
Posts: 1,624
Likes: 48
From: Saudi Arabia
here is how to change the opti , step by step
http://forums.corvetteforum.com/c4-t...-pictures.html
you can do these replacements without the need of the service manual , just search through the forum and ask here.
http://forums.corvetteforum.com/c4-t...-pictures.html
you can do these replacements without the need of the service manual , just search through the forum and ask here.
Thread Starter
Instructor
Joined: Jun 2011
Posts: 205
Likes: 3
From: Great Mills Maryland
Well I took the car out and turned off the ASR. Car didn't bog down, I assume the settings on the ASR are off or the unit under the hood is bad. Settings are probably built into the unit. The cover on the unit is loose, I'll take a look at it. When I lean over in the engine bay, the first thing I want to grab onto for support is the ASR unit. Thanks for the tips.
Pro
Joined: Apr 2000
Posts: 642
Likes: 3
From: Calhoun, GA / USA GA
Any update? I'm into the same issues with my son's 94 LT1. Starts & runs great under normal acceleration. Bogs significantly under hard acceleration. Just spent $5500 this summer on full tune up. Issues still there....
Thread Starter
Instructor
Joined: Jun 2011
Posts: 205
Likes: 3
From: Great Mills Maryland
$5500 is a lot to spend and still have the issue, you must have replaced everything or put aftermarket high performance stuff in.
Burning Brakes
Joined: Aug 2010
Posts: 951
Likes: 3
From: Placerville CA
My '94 tended to bog when accelerating uphill when the engine was hot. I pulled the EGR valve which was crudded almost solid, cleaned it out and the problem was gone. Can't say if that was the cause or not, maybe just coincidence. I also put in a manual fan switch to keep temps down, so that may have been a factor, too.
Anyway, it's good now. Best of luck.
Anyway, it's good now. Best of luck.
