jerking/bucking after driving for a while

[Jason_99ozGS]

About a week ago it got pretty cold for here with temps in near the 0 mark. My Laser would violently jerk under acceleration. I thought it was fuel cut (it was bad enough that I actually almost hit my head on the steering wheel). So I decided to change the boost from the 16psi I was running down to the stock 11psi. At 11psi I was still getting this jerking once I hit boost. Eventually the temps warmed up to around 30-40 degrees and I was still getting the jerking in boost at 11psi when I've ran 16psi @ 30 degrees with no problems before.

Anyways one night I had to drive about 20 miles on the highway. Before I got on the highway I was probably already driving the car for about 20 minutes. Once on the highway in 5th gear the car would jerk any time I gave the car enough gas for it to be at 0psi or more. I was often boosting 5psi just to stay at 65mph! Once I got off the highway acceleration was horrible! I decided to be easy on the car and shifted at about 3000rpm and the car felt like it had no power in any of the gears.

The car sat for about 3 hours and I made my return trip home taking it easy the whole 20 miles. Well during the last 5 miles the bucking got worse. It would do it when I was on the gas just enough to mantain my speed, when I let off the gas, and if I gave it more gas.

I thought it was a boost leak so I tested that the next day. During the test I first hooked the tester up to the turbo inlet and when I pumped air in with a bicycle pump it sounded like I had a leak coming from somewhere because I heard a slight whistle. Then I took of the hose that connects the the throttle body elbow and I blocked it off and pumped air into the system and everything help fine.

So was I doing the boost leak test correctly the first time? I held no pressure at all leaving the hose connected to the throttle body elbow, but with it off and blocked off everything held pressure.

Today I also changed the spark plug wires. I didn't change the plugs since they were changed less than 1000miles ago. So pretty much anytime (worse in 1st and 2nd gear) I hit boost I get the jerking... At the beginning of my drive everything is fine if I stay out of boost. After a long drive or hitting boost (which seems to accelerate the problem) the jerkiness begins

Mods are in my profile... Thanks for the help I appreciate it

 

[Patryk]

i would try replacing the spark plugs, and if that doesn't help then do the wires too. get NGK's

 

[Patryk]

oh i see u replaced it already, by the way same thing was happening to me like 1000 miles after replacing plugs. I put in those BOSCH PLATINUMS annd after 1000 miles they were shit. so i switched to NGK wires and plugs and they were all good.

 

[Enigma_Man]

You might possibly have a leak somewhere where an intake leak test might not show up.

Check to make sure that all of the hoses/tubes connected to the rubber turbo accordion intake thingy are there.

I've had the bigger BOV one come off before, and the car felt like that.

If you heard a leak when you first had it hooked up, I'd investigate that more too. It should leak very very slowly (or not at all) even with the TB hooked up.

-Jesse

 

[Jason_99ozGS]

Originally posted by Enigma_Man
You might possibly have a leak somewhere where an intake leak test might not show up.

Check to make sure that all of the hoses/tubes connected to the rubber turbo accordion intake thingy are there.

I've had the bigger BOV one come off before, and the car felt like that.

If you heard a leak when you first had it hooked up, I'd investigate that more too. It should leak very very slowly (or not at all) even with the TB hooked up.

-Jesse

Everything is hooked up the the accodrion intake... And with the Throttle Body hooked up it seemed like it was leaking air very very quickly. I could pump the bicycle pump like crazy and just hear what sounded like a leak and nothing would ever read of the boost gauge. So would this mean something could possibly be leaking past the throttle body such as the a throttle body gasket or intake manifold gasket?

Also to add to my symptoms: The car has a loopy idle now and if it neutral I can rev it up to about 5000rpm then it starts cutting out and won't go any higher.

Also my plugs are NGK's and like I said less than 1000miles on them. So I don't think it them. I try and stay away from BOSCH

Oh and if it is a boost leak somewhere past the throttle body, is it normal for it to get worse the longer you drive? Because eventually it gets bad enough that the jerkiness happens with normal driving.

 

[markbenbear]

I used to have a 1991 laser rs turbo and when i would step on the gas once i got up to around 3000 rpm and boost started building my car would buck and jerk. I tryed everything on that damn car but it turned out to be my TPS sensor it had gone bad and was sending bad signals to my computer. All you gotta do is buy a new one (130$ or so) then take off your fuel rail the tps sensor is bolted almost on the throttle body two screws hold it in take it off get a voltmeter and you have to adjust the tps sensor so it reads right This might be the problem hope it helps.

 

[gravityforce]

maybe timing related? cas?
I had a 91 Laser RS 4g63 nt that used to buck ,I tried decarbing ,new plugs of different brands, new wires. But now that I'm a little wiser I would have looked towards a cas or tps theory rather than all the other stuff I tried.
The Laser finally died on a road trip (Abq. to Phx.), it bucked real bad and would make a real bad burning smell (hard to explain the smell)
before it died .

I took the valve cover off to see if I could see something obvious and sure enough the head was in pieces...literally.
Dont know what that tells you but my timing belt checked out good so something was definitely wrong, I would take the situation really serious and not drive the car at all untill its fixed or else you might end up killing her .

 

[Jason_99ozGS]

Thanks for the help everyone. Today I swapped my friend's 90 ECU into my car and the problem was solved. I found out my Caps are leaking slighty and I'm getting everything taken care of now.

You can see a leak in this picture

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