2LT starts jerking when accelerating (1 Viewer)

[hetman]

Hi Guys,

I am new to the forum, although have been following it for a while now. I could not find solution to my problem, hopefully someone had similar issue and could point me to the one of possible solutions.

I own LJ78 with swapped engine and manual transmission. The original 2LTE is replaced with standard post 90' LJ70 2LT engine and transmission. I bought it like that and drove for a while. It turned out that turbo housing (near wastegate) was cracked what was causing underpower. So I replaced turbo (to non water cooled if it makes any difference) and re-conditioned injectors, engine does not black smoke now. When turbo delivers full boost @~2400 RPM or higher it pulls really well, no jumps etc. When turbo starts delivering pressure @~1800-2200 when I accelerate , engine starts jerking. It does not occur without boost or when driving steady. It happens only on higher gears especially 3rd and 4th under load. No big difference when engine is cold or hot.

I played with main fuel screw, nothing changed except to rich mixture and black smoke. Tried to tune fuel pump boost compensator to deliver more fuel during turbo spool up (diaphragm spring preload), it is a little better but did not resolve the issue.

Any thoughts?

 

[GTSSportCoupe]

If you're running higher than normal boost, it could be the fuel pin in the boost compensator is hitting fuel cut. This would happen at maximum boost/load situations which is what you are describing. The boost compensator can be adjusted for higher boost levels. Things like changing the spring preload, and moving the adjust cam on the top cover, etc. It is a bit of an art.

Maybe start by installing a boost gauge so you know where you're at.

 

[hetman]

I was thinking about boost and egt gauges. In my case the thing is that when turbo reaches full boost (above 2400 rpm) it drives and accelerates really well. It only happens in low boost mode when turbo lights up. Giving it more fuel does not make it better, I just get black smoke and too rich mixture.

 

[GTSSportCoupe]

I was thinking about boost and egt gauges. In my case the thing is that when turbo reaches full boost (above 2400 rpm) it drives and accelerates really well. It only happens in low boost mode when turbo lights up. Giving it more fuel does not make it better, I just get black smoke and too rich mixture.

Sorry, I did not read your description well enough. Bizzare problem. Maybe compressor surge on your turbo?

My 2LTE at high boost low rpm stutters a bit too, like it's lugging. As the rpm's come up a bit it smoothes right out and flies. These engines do seem to like to be between 2400-3200 rpm or so. More of a high revving diesel I guess. Not sure if this is at all related to your problem.

 

[renago]

Is your car loaded ?
If so , it might be underpowered for the load it has .
In other words , the power delivered at low rpm is too little for the needs .
Ergo you need to push and get full boost /power in order to overcome the need Of insufficient trust at certain rpm
I had similar sensation when with my 78 , fully loaded was cruising at low speed, say 20-30 km/h, in 3 gear, at very low boost.
Or If the car is very old and trasmissione has done a lot ok km with heavy weight , there could be a shaft with spin line in the transfer or gearbox that is worn , giving this sensation.
Very expensive to substitute.
Or you increase the power ,
or you change the final gear ratio on differential
or you stay lighter ,
or you get a bigger motor.

Just my 2 cents

Bye Renago

 

[hetman]

Car is not loaded, I actually try to keep it as light as possible. There is no issue with engine behavior without turbo boost, there is no power but car gains speed smoothly.

When I try to drive in 3rd gear at low speeds, yes everything vibrates and rattles, but no pulsation or engine jumps. Once it reaches 1800 RPM and turbo light comes up engine starts to kind of slutter or car gently jumping. Once it gets full boost at 2200-2400 RPM or more everything is fine again. This happens only in 3rd - 5th gear.

 

[renago]

Sorry , locks like you have a different issue .
Can't thing of any other solution.


Bye Renago

 

[GTSSportCoupe]

Car is not loaded, I actually try to keep it as light as possible. There is no issue with engine behavior without turbo boost, there is no power but car gains speed smoothly.

When I try to drive in 3rd gear at low speeds, yes everything vibrates and rattles, but no pulsation or engine jumps. Once it reaches 1800 RPM and turbo light comes up engine starts to kind of slutter or car gently jumping. Once it gets full boost at 2200-2400 RPM or more everything is fine again. This happens only in 3rd - 5th gear.

I think you just need to gear down a bit to bring the rpms up while under high load situations. The more you describe this, it sounds like the same thing I experience under the same conditions. Basically you're lugging the engine. EGT's will be really high in that situation too. Try to keep your rpms between 2400-3000 and the engine will be much happier.