bad acceleration under boost
#1
Senior Member
Thread Starter
Join Date: Jan 2008
Location: Virginia
Posts: 506
Likes: 0
Received 0 Likes
on
0 Posts
bad acceleration under boost
I have tried everything in the world to try and fix my cars acceleration problems. Its an '88 TII with a full turboback and intake. I just recently put the engine in the car. It has an S5 engine with S4 wiring harness and ECU. Also the TPS and fuel injectors was from the original S4 engine. At lower RPMs lower than 2500 RPMs when trying to accelerate the engine will vibrate. More like a side to side shaking. The car also idles high around 1200 to 1300RPMs and when idleing also has the vibrating from side to side problem. At any rpm above 2500 the car accelerates fine with no miss or vibration. It runs a steady 7lbs of boost and has no vacuum leaks. My boost gauge shows about 15 or 16lbs of vacuum. I'm not sure if this is caused by bad motor mounts or a running issue. The mounts seem to be in good condition. The TPS has been adjusted correctly also. Any ideas would be great.
#2
Retired Moderator, RIP
iTrader: (142)
Join Date: Sep 2005
Location: Smiths Falls.(near Ottawa!.Mapquest IT!)
Posts: 25,581
Likes: 0
Received 131 Likes
on
114 Posts
did you test for vacuum leaks?
www.fighters-garage.com has a tester that is Cheap,.and it saved Me Bigtime when I had to diagnose my car.
www.fighters-garage.com has a tester that is Cheap,.and it saved Me Bigtime when I had to diagnose my car.
#3
Senior Member
Thread Starter
Join Date: Jan 2008
Location: Virginia
Posts: 506
Likes: 0
Received 0 Likes
on
0 Posts
I have checked for vacuum leaks 2 or 3 times now just to make sure and there aren't any. The problem just seems to have no solution. I will check for leaks again tomorrow just to make sure though.
#5
Senior Member
Thread Starter
Join Date: Jan 2008
Location: Virginia
Posts: 506
Likes: 0
Received 0 Likes
on
0 Posts
No vac leaks on the car. Turbo harness. The car was an S4 turbo but has an S5 engine. I used the S4 TII harness already in the car and the TPS and fuel injectors from the old S4 engine and switch them to the S5 engine.
Trending Topics
#8
Boost makes cars smile.
iTrader: (5)
Join Date: May 2005
Location: ...
Posts: 1,424
Likes: 0
Received 0 Likes
on
0 Posts
Hm..... Try cleaning out stuff? TPS, AFM, BRS, primary injectors, etc.
A way to check and see if it's the AFM by idling the car, with the AFM and TPS disconnected. When it revs through the problem zone, on the tach, there should be a very noticeable change. If not, then you've found your problem.
A way to check and see if it's the AFM by idling the car, with the AFM and TPS disconnected. When it revs through the problem zone, on the tach, there should be a very noticeable change. If not, then you've found your problem.
#9
Senior Member
Thread Starter
Join Date: Jan 2008
Location: Virginia
Posts: 506
Likes: 0
Received 0 Likes
on
0 Posts
I tried disconnecting the boost sensor to see if that helped but it didn't change at all.
I will try the AFM to see if that is the problem. The TPS is good and adjusted for sure. I actually disconnected it the other day and drove it thinking it may make a difference. What is BRS?
Hm..... Try cleaning out stuff? TPS, AFM, BRS, primary injectors, etc.
A way to check and see if it's the AFM by idling the car, with the AFM and TPS disconnected. When it revs through the problem zone, on the tach, there should be a very noticeable change. If not, then you've found your problem.
A way to check and see if it's the AFM by idling the car, with the AFM and TPS disconnected. When it revs through the problem zone, on the tach, there should be a very noticeable change. If not, then you've found your problem.
#11
Junior Member
Join Date: May 2005
Location: Virginia Beach
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
Put the car in gear with the hood up and accelerate slightly. If you see the engine lift excessively, you have your answer. Don't forget to this only checks one side. You will have to put it in reverse and repeat to check the other side. As far as the high idle. Could be a faulty or stuck idle air control valve or a vacuum leak. Remember, the vacuum leak doesn't have to be at the engine. It can be at the other end of the vacuum line coming from the engine. Ie, sensors, brake booster, or even a/c system.
#14
Boost makes cars smile.
iTrader: (5)
Join Date: May 2005
Location: ...
Posts: 1,424
Likes: 0
Received 0 Likes
on
0 Posts
Course, the ethreal cure-all for vac-leak finding is carb-cleaner.
With the engine idling, shoot a little bit around the rat's nest and known vac-line termination points....
DO NOT FOG THE ENGINE BAY
This **** WILL light if your exhaust manifold is hot!
You'll know if you find a leak when the tach either drops or jumps (depending on the mixture in the spray.
I've used this and the starting fluid method a million times on every kind of engine imaginable and it works. Try it and if there isn't any reaction - and you've done it right, then the vac-leak problem doesn't exist and you can debug, elsewhere.
With the engine idling, shoot a little bit around the rat's nest and known vac-line termination points....
DO NOT FOG THE ENGINE BAY
This **** WILL light if your exhaust manifold is hot!
You'll know if you find a leak when the tach either drops or jumps (depending on the mixture in the spray.
I've used this and the starting fluid method a million times on every kind of engine imaginable and it works. Try it and if there isn't any reaction - and you've done it right, then the vac-leak problem doesn't exist and you can debug, elsewhere.
#16
Senior Member
Thread Starter
Join Date: Jan 2008
Location: Virginia
Posts: 506
Likes: 0
Received 0 Likes
on
0 Posts
Put the car in gear with the hood up and accelerate slightly. If you see the engine lift excessively, you have your answer. Don't forget to this only checks one side. You will have to put it in reverse and repeat to check the other side. As far as the high idle. Could be a faulty or stuck idle air control valve or a vacuum leak. Remember, the vacuum leak doesn't have to be at the engine. It can be at the other end of the vacuum line coming from the engine. Ie, sensors, brake booster, or even a/c system.
Course, the ethreal cure-all for vac-leak finding is carb-cleaner.
With the engine idling, shoot a little bit around the rat's nest and known vac-line termination points....
DO NOT FOG THE ENGINE BAY
This **** WILL light if your exhaust manifold is hot!
You'll know if you find a leak when the tach either drops or jumps (depending on the mixture in the spray.
I've used this and the starting fluid method a million times on every kind of engine imaginable and it works. Try it and if there isn't any reaction - and you've done it right, then the vac-leak problem doesn't exist and you can debug, elsewhere.
With the engine idling, shoot a little bit around the rat's nest and known vac-line termination points....
DO NOT FOG THE ENGINE BAY
This **** WILL light if your exhaust manifold is hot!
You'll know if you find a leak when the tach either drops or jumps (depending on the mixture in the spray.
I've used this and the starting fluid method a million times on every kind of engine imaginable and it works. Try it and if there isn't any reaction - and you've done it right, then the vac-leak problem doesn't exist and you can debug, elsewhere.
No, I haven't switched the flywheels. It still has the OEM flywheel and counterweight that originally came on the s5 engine.
#17
Senior Member
Thread Starter
Join Date: Jan 2008
Location: Virginia
Posts: 506
Likes: 0
Received 0 Likes
on
0 Posts
I cleaned the sensors and AFM today and it didn't solve the problem. I double checked the engine mounts today also and they are tight and the vibration is still there. When the car is idleing the engine also vibrates and moves from side to side but had no miss and is still completely smooth above 2500 RPM. The only time it vibrates below 2500 RPM though is when I try to give it gas to acccelerate or maintain constant speed. When idleing and revving down it is smooth just under acceleration. Could worn transmission mounts and brackets cause this?
#18
version 2.0
iTrader: (17)
Possibly, may I also suggest that you check the exhaust too, ensure there are no leaks, especially around the cat. If you want to absolutely 100% determine there are no vac leaks, use a tester like the link above that hooks up to the turbo inlet, then with a press. regulator up to an air compressor.
#22
Senior Member
Thread Starter
Join Date: Jan 2008
Location: Virginia
Posts: 506
Likes: 0
Received 0 Likes
on
0 Posts
I have adjusted TPS correctly and the timing was perfect when I checked it. Adjusting the TPS made no difference.
#25
Senior Member
Thread Starter
Join Date: Jan 2008
Location: Virginia
Posts: 506
Likes: 0
Received 0 Likes
on
0 Posts