Acceleration lag
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Instructor
Joined: Aug 2014
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Acceleration lag
Just got the vette inspected the other day so I decided to take her for a spin today. When I hit step on the accelerator and give it a good amount of gas it feels like it takes two or three seconds before accelerating. Is this normal for an l98? I have the stock 3.07 gears in it also. Thanks for the info
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Just got the vette inspected the other day so I decided to take her for a spin today. When I hit step on the accelerator and give it a good amount of gas it feels like it takes two or three seconds before accelerating. Is this normal for an l98? I have the stock 3.07 gears in it also. Thanks for the info
Thread Starter
Instructor
Joined: Aug 2014
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Safety Car
Joined: Aug 2009
Posts: 3,745
Likes: 275
From: Melbourne, Victoria, Australia
Just got the vette inspected the other day so I decided to take her for a spin today. When I hit step on the accelerator and give it a good amount of gas it feels like it takes two or three seconds before accelerating. Is this normal for an l98? I have the stock 3.07 gears in it also. Thanks for the info
You really need a shop manual, then you can diagnose and repair the vette yourself.
First thing to do is check the fuel pressure, the 85 has 24lb injectors and runs lower fuel pressure than the later models, you should have at least 34 psi. The later vettes run 38 psi.
You may want to drive the car with a fuel pressure gauge taped to the windshield, make sure it stays at 34 psi. If it drops on acceleration the fuel filter may be bocked.
Now the TPS throttle position sensor, with a multimeter measure the top and middle wire it should be set to 0.54 volts d/c
Disconnect the ecm connector next to the battery and reconnect to clear any codes, then start the car and take her for a drive.
Good luck, should be a simple issue like TPS sensor failing or fuel pump/ filter issue.
Drifting
Joined: Aug 2010
Posts: 1,704
Likes: 8
Same 85,same issue, the car has a lag when i flor the gas pedal for a rocket- launch.1-2 seconds lag before take off then she runs strong up to redline. It seems like a retarded spark advance or a misfire, thinkin about a worn out dizzy gear that miss some degrees of advance at lower rpms, but this is a long time issue...sorry if i post but same issue...
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
To address that lag I would look at:
-base timing: is it 6-8deg BTDC?
-TPS: is it 0.54Vdc at base idle (450rpm) or 0.65-0.68Vdc at normal idle (600-700rpm)?
-fuel pressure: does FP increase when you quickly open the throttle with the vac line connected?
-base timing: is it 6-8deg BTDC?
-TPS: is it 0.54Vdc at base idle (450rpm) or 0.65-0.68Vdc at normal idle (600-700rpm)?
-fuel pressure: does FP increase when you quickly open the throttle with the vac line connected?
Drifting
Joined: Jun 2013
Posts: 1,590
Likes: 60
From: ft myers FL/Munising MI
my 85 did that...timing was off....if you've eliminated fuel pressure as the cuprit and checked for vac leaks....go to timing/tps/ good luck 
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Thread Starter
Instructor
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Safety Car
Joined: Jan 2004
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From: Northern California
Disconnect the EST wire, (Tan wire with a Black stripe) located right next to the brake booster near the firewall.
Connect the timing light cables to the battery + and - and attach the other lead to the #1 spark plug wire. Start the engine and note the timing on the timing plate near the crankshaft pulley. Adjust the timing to 6* BTC by loosening the distributor bolt at the base of the distributor and turning the distributor in whatever direction needed to get the timing to 6* BTC.
Don't forget to reconnect the EST wire when you're done.
Connect the timing light cables to the battery + and - and attach the other lead to the #1 spark plug wire. Start the engine and note the timing on the timing plate near the crankshaft pulley. Adjust the timing to 6* BTC by loosening the distributor bolt at the base of the distributor and turning the distributor in whatever direction needed to get the timing to 6* BTC.
Don't forget to reconnect the EST wire when you're done.
Drifting
Joined: Jun 2013
Posts: 1,590
Likes: 60
From: ft myers FL/Munising MI
it helps to clean off the timing marks before you start...make sure you know where 6 degrees is on the mark...threre are examples here on threads....not all timing marks are the same...if you're asking how, it's certainly time to check it...probably going to be your problem.....if it's off, you'll need to reset tps/ min idle adjustment....then she'll go again...
Melting Slicks
Joined: Oct 2000
Posts: 2,158
Likes: 9
From: N.E. WA
If the FPR isn't seeing the proper vacuum at tip in, then it could hesitate due to a lean mix. I see the reference to the FPR as the accelerator pump shot on a carb. It shouldn't hesitate 3 seconds, but I'm hoping that was an exaggeration.
If the filter was plugged, I'm not sure it would run strong after the hesitation. Timing? I could go with that too.
As stated above, TPI cars should be quite responsive.
Thread Starter
Instructor
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Read online that driving the car in the overdrive setting will hurt acceleration. Maybe This could be the problem? Because I am always driving in overdrive. Or am I just completely wrong to even think that?
Melting Slicks
Joined: Jun 2013
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I don't think so. Over drive is definitely going to accelerate slower but if it was the kick down period from over drive you would see the RPMs go up when it kicked out of overdrive. This is a automatic or 4+3?
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Le Mans Master
Joined: May 2004
Posts: 5,866
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From: Hellinois
Finalist 2020 C4 of the Year - Modified
Mike1985, please don't think I am trying to hijack your thread, I have a similar problem and wanted to ask a question or two. My 85 has the 165 ecm upgrade and a whole list of other mods, today I was trying to get a very slight off-idle flutter to go away, not quite a bog but close. I was checking my timing which is supposed to be at 10 degrees advance in the tune. It was at about 9 so I loosened the dist. to put a little more in it, the dist. slipped and the timing went to 15 degrees and that engine came alive! I did not want to leave it there so I set it at 12, then kicked up the tps setting to .60 and that car has never ran like it does now. What I need to know, can I put it up to 15 degrees? can I leave it at 12? what is the best way to go here?
Safety Car
Joined: Aug 2009
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From: Melbourne, Victoria, Australia
It will be a simple problem, the ecm looks at the information from the sensors something not right can get the ecm in a knot trying to compensate.
Yes timing needs to be good, don't forget the harmonic balancer outer ring can slip. set the timing where the car runs best. advance It and if the car pings on acceleration back It of a touch.
Thread Starter
Instructor
Joined: Aug 2014
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Mike1985, please don't think I am trying to hijack your thread, I have a similar problem and wanted to ask a question or two. My 85 has the 165 ecm upgrade and a whole list of other mods, today I was trying to get a very slight off-idle flutter to go away, not quite a bog but close. I was checking my timing which is supposed to be at 10 degrees advance in the tune. It was at about 9 so I loosened the dist. to put a little more in it, the dist. slipped and the timing went to 15 degrees and that engine came alive! I did not want to leave it there so I set it at 12, then kicked up the tps setting to .60 and that car has never ran like it does now. What I need to know, can I put it up to 15 degrees? can I leave it at 12? what is the best way to go here?
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Mike1985, please don't think I am trying to hijack your thread, I have a similar problem and wanted to ask a question or two. My 85 has the 165 ecm upgrade and a whole list of other mods, today I was trying to get a very slight off-idle flutter to go away, not quite a bog but close. I was checking my timing which is supposed to be at 10 degrees advance in the tune. It was at about 9 so I loosened the dist. to put a little more in it, the dist. slipped and the timing went to 15 degrees and that engine came alive! I did not want to leave it there so I set it at 12, then kicked up the tps setting to .60 and that car has never ran like it does now. What I need to know, can I put it up to 15 degrees? can I leave it at 12? what is the best way to go here?
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
I can certainly get the tune changed but when I stumbled on to the effects of the advanced timing it got me to wondering. My engine is a crate motor from ATK Performance engines and it was dynoed at 435 hp. I have been trying to get a suitable idle and strong performance by staying with the stock parameters and it just was not working. I was amazed at what the 12 degrees advance did along with the higher tps setting so naturally I have to think that I am going to have to wander away from stock procedures a little bit. Also, I am using an LS style throttle body, (80mm) and the corresponding tps and iac and I can't find out if they react to the stock L98 settings correctly. Others on here have tried suggestions but they just don't seem to apply to my combination, either that or I am screwing something up.