Missing under boost?

batmanfc · 09-03-2009, 10:55 PM

Just got my motor put in. The car runs ok. I believe it still has a vac leak I haven't fixed yet but I don't think it is causing this. Whenever it gets into boost it misses bad. Pulls the best in first and second gear but still misses some. 3rd 4th and 5th are horrible especially up hill it almost dies. In 3rd 4th and 5th the miss isn't nearly as bad if its not under boost and it seems to have a little more power out of boost. Kind of thought that may be a MAF going bad? Also when under boost you can hear a noise that almost sounds like a pebble bouncing around in the intake. Its not real loud but noticable. It idles on its own but fluctuates between 750 rpm and 1000 rpm. It also takes it a few trys to crank. It will crank everytime you try but won't run and hold idle until the about the 3rd try sometimes a few more. Not exctly sure what it is. Thought I would ask and see and listed all these problems to see if it may all come back to one thing. I may still have a few vac leaks that I have to fix too. Don't know if that would cause all of that?

NoDOHC · 09-03-2009, 11:26 PM

You need to fix this issue before you boost the car, the missing is very dangerous for your engine.

A vacuum leak or a bad/mal-adjusted TPS could cause this.

The rattling noise is a puzzler (you never had this engine apart, did you)?

batmanfc · 09-03-2009, 11:38 PM

I have only driven it about 3 miles maybe not even that far since this has been happening. I was afraid it would kill it. I had to switch the TPS off of my old engine to this one. How do you adjust it?
The only thing I took off and put back on was the upper intake manifold, turbo and turbo manifold.

batmanfc · 09-04-2009, 03:35 PM

Could it be a leaky injector?

batmanfc · 09-05-2009, 07:29 PM

Maybe clogged fuel filter or bad fuel pump? Maybe even the oxygen sensor bad?

batmanfc · 09-07-2009, 03:13 PM

Here is a video of how it runs in all 5 gears. It will not pull a hill and in 4th and 5th it bucks horribly if you try to keep a steady rate of speed and rpm. It only misses when it is under boos. and still doesn't idle right. Also, in 5th it will not accelerate much if any in 5th.
http://www.youtube.com/watch?v=9OmkgQ0Jybs

NoDOHC · 09-09-2009, 08:48 PM

Does your boost gauge read correctly? If so, I doubt that it is your MAP sensor.

Check your AFM to make sure that it is level. Put a gauge on your fuel pressure so that you can watch it from the cab.

It could also be a faulty BOV (leaks only under boost) this usually makes the engine run very rich. (Leaks under vacuum make the engine run lean.)

batmanfc · 09-09-2009, 11:34 PM

Thanks I will definetly check that tomorrow and let you know how that seems to help.

09-03-2009, 10:55 PM	#1
batmanfc Rotarys Ruin Lives Join Date: Aug 2009 Location: Wise, VA iTrader: (0) Posts: 66 Rep Power: 16	Missing under boost? Just got my motor put in. The car runs ok. I believe it still has a vac leak I haven't fixed yet but I don't think it is causing this. Whenever it gets into boost it misses bad. Pulls the best in first and second gear but still misses some. 3rd 4th and 5th are horrible especially up hill it almost dies. In 3rd 4th and 5th the miss isn't nearly as bad if its not under boost and it seems to have a little more power out of boost. Kind of thought that may be a MAF going bad? Also when under boost you can hear a noise that almost sounds like a pebble bouncing around in the intake. Its not real loud but noticable. It idles on its own but fluctuates between 750 rpm and 1000 rpm. It also takes it a few trys to crank. It will crank everytime you try but won't run and hold idle until the about the 3rd try sometimes a few more. Not exctly sure what it is. Thought I would ask and see and listed all these problems to see if it may all come back to one thing. I may still have a few vac leaks that I have to fix too. Don't know if that would cause all of that? __________________ '88 Turbo II '89 GXL '07 Cobalt: DD

09-03-2009, 11:26 PM	#2
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	You need to fix this issue before you boost the car, the missing is very dangerous for your engine. A vacuum leak or a bad/mal-adjusted TPS could cause this. The rattling noise is a puzzler (you never had this engine apart, did you)? __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

09-03-2009, 11:38 PM	#3
batmanfc Rotarys Ruin Lives Join Date: Aug 2009 Location: Wise, VA iTrader: (0) Posts: 66 Rep Power: 16	I have only driven it about 3 miles maybe not even that far since this has been happening. I was afraid it would kill it. I had to switch the TPS off of my old engine to this one. How do you adjust it? The only thing I took off and put back on was the upper intake manifold, turbo and turbo manifold. __________________ '88 Turbo II '89 GXL '07 Cobalt: DD

09-04-2009, 03:35 PM	#4
batmanfc Rotarys Ruin Lives Join Date: Aug 2009 Location: Wise, VA iTrader: (0) Posts: 66 Rep Power: 16	Could it be a leaky injector? __________________ '88 Turbo II '89 GXL '07 Cobalt: DD

09-05-2009, 07:29 PM	#5
batmanfc Rotarys Ruin Lives Join Date: Aug 2009 Location: Wise, VA iTrader: (0) Posts: 66 Rep Power: 16	Maybe clogged fuel filter or bad fuel pump? Maybe even the oxygen sensor bad? __________________ '88 Turbo II '89 GXL '07 Cobalt: DD

09-07-2009, 03:13 PM	#6
batmanfc Rotarys Ruin Lives Join Date: Aug 2009 Location: Wise, VA iTrader: (0) Posts: 66 Rep Power: 16	Here is a video of how it runs in all 5 gears. It will not pull a hill and in 4th and 5th it bucks horribly if you try to keep a steady rate of speed and rpm. It only misses when it is under boos. and still doesn't idle right. Also, in 5th it will not accelerate much if any in 5th. http://www.youtube.com/watch?v=9OmkgQ0Jybs __________________ '88 Turbo II '89 GXL '07 Cobalt: DD

09-09-2009, 08:48 PM	#7
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	Does your boost gauge read correctly? If so, I doubt that it is your MAP sensor. Check your AFM to make sure that it is level. Put a gauge on your fuel pressure so that you can watch it from the cab. It could also be a faulty BOV (leaks only under boost) this usually makes the engine run very rich. (Leaks under vacuum make the engine run lean.) __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

09-09-2009, 11:34 PM	#8
batmanfc Rotarys Ruin Lives Join Date: Aug 2009 Location: Wise, VA iTrader: (0) Posts: 66 Rep Power: 16	Thanks I will definetly check that tomorrow and let you know how that seems to help. __________________ '88 Turbo II '89 GXL '07 Cobalt: DD

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