Resolved 2g Won't build boost and stutters under load

[Tim holmes]

I have a question, I upgraded my turbo from the T25 to the T28, bought a AEM true boost controller, installed controller and after installing it the car won't build boost in higher gear. Under load car will start to stutter. Is that boost cut or is my fuel pump going out?

 

[steve]

Since you played with both the turbo and the vacuum lines for the wastegate I'd suggest you perform a boost leak test to see if you're just leaking all your airflow away.

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[Tim holmes]

Since you played with both the turbo and the vacuum lines for the wastegate I'd suggest you perform a boost leak test to see if you're just leaking all your airflow away.

Welcome to the site. Please take some time to create a profile for your car.

It ran good until I installed the controller

Let me try to explain better I'll go from 3rd to fourth will hit 4500 rpm car will loose power and serge ore stutter under load

Boost stops at 9 to 10 psi I'm hoping you understand me not the greatest at spelling and at explaining by messaging

 

[steve]

It ran good until I installed the controller

Then to check try just running from the the pressure source directly to the turbo. That will cause the car to only boost to the wastegate spring pressure.

If it doesn't break up that way you know your problem is with how you have the controller set up.

What else have you done to your car? Injectors to go with the turbo? Something to tune with?

 

[Tim holmes]

Then to check try just running from the the pressure source directly to the turbo. That will cause the car to only boost to the wastegate spring pressure.

If it doesn't break up that way you know your problem is with how you have the controller set up.

What else have you done to your car? Injectors to go with the turbo? Something to tune with?

Nothing just Evo 9 blow off valve can't order dsm link I live in California what would you suggest in

 

[waltah]

It ran good until I installed the controller

Let me try to explain better I'll go from 3rd to fourth will hit 4500 rpm car will loose power and serge ore stutter under load

Boost stops at 9 to 10 psi I'm hoping you understand me not the greatest at spelling and at explaining by messaging

Surge or stutter under load, especially when boost has been increased the first thing to check is ignition.

The fuel/air mixture is an electrical insulator. When you push more of it into the cylinders (higher boost) the spark voltage to jump the plug gap must go up. That happens automatically -- the energy stored in the coil must go somewhere so for each spark the voltage keeps going up until the plug fires.

But -- what if the higher voltage (for higher boost) is enough to break down something else before the plug fires? Like a bad plug wire sparks through the insulation to the valve cover? Then you will get a miss and if it happens on more than one wire you might get a complete breakdown of power. With the cylinder not firing the exhaust volume won't be enough to push the turbo so the boost will stop going up.

And the bigger the plug gaps the higher the voltage has to go, meaning higher stress on the other ignition parts. Meaning either higher grade parts or more risk of failure. I know nothing about what the chaps who run 300, 500 and even higher horsepower in these engines use for coils, plug wires, and transistors but I bet it's not 'came on the car 25 years ago OEM.'

I used to wonder why people bought 8mm and 10mm plug cables. What's wrong with 7mm OEM cables? Then I spent a couple months figuring out why my GS-T 'hit a wall' at 8-10 PSI boost and after I changed the wires and gaped the plugs per spec I figured it out: the higher the boost, the higher the voltages. My car is stock but if you go much higher than stock, yeah, I could see cables with more insulation making sense.

The first thing I would do is check the plug gaps. The spec for the 2g cars is 0.028 to 0.031 inches. With increased boost -- the T28 -- I would gap those plugs at 0.028.

If the plug gaps are now over 0.031 and setting them smaller makes the engine better but not quite right -- maybe you hit the wall at 12 PSI instead of 9-10 --- then replace the wires next.

Edit -- To fix wrong #s for plug gaps.

 

[1990TSIAWDTALON]

The STOCK plug gap is .028"-.031".
Those of us that run high HP motors (500+) have used colder plugs and then necked down the gap to .018" (mine)-.024" just to clear that up. I have my gap very close because I run between 30 and 40 lbs of boost, which will try to blow out the spark. I am on stock coils and Power Transistor also. It is true, the more boost, the tighter you MAY need to run your plugs, but with the tiny amount of boost you are using, I would say to stay in the .028" area unless you are getting misfires.

 

[waltah]

The STOCK plug gap is .028"-.031".
Those of us that run high HP motors (500+) have used colder plugs and then necked down the gap to .018" (mine)-.024" just to clear that up. I have my gap very close because I run between 30 and 40 lbs of boost, which will try to blow out the spark. I am on stock coils and Power Transistor also. It is true, the more boost, the tighter you MAY need to run your plugs, but with the tiny amount of boost you are using, I would say to stay in the .028" area unless you are getting misfires.

THANK YOU! When I find myself saying "... I think" after a fact, maybe I should look it up?
I have corrected the error in my reply.

For comparison -- OEM recommended gaps:
non-turbo 2G -- 0.048-0.053
turbo - 0.028-0.031

Good to hear from someone with experience at higher boosts.

 

[Tim holmes]

Surge or stutter under load, especially when boost has been increased the first thing to check is ignition.

The fuel/air mixture is an electrical insulator. When you push more of it into the cylinders (higher boost) the spark voltage to jump the plug gap must go up. That happens automatically -- the energy stored in the coil must go somewhere so for each spark the voltage keeps going up until the plug fires.

But -- what if the higher voltage (for higher boost) is enough to break down something else before the plug fires? Like a bad plug wire sparks through the insulation to the valve cover? Then you will get a miss and if it happens on more than one wire you might get a complete breakdown of power. With the cylinder not firing the exhaust volume won't be enough to push the turbo so the boost will stop going up.

And the bigger the plug gaps the higher the voltage has to go, meaning higher stress on the other ignition parts. Meaning either higher grade parts or more risk of failure. I know nothing about what the chaps who run 300, 500 and even higher horsepower in these engines use for coils, plug wires, and transistors but I bet it's not 'came on the car 25 years ago OEM.'

I used to wonder why people bought 8mm and 10mm plug cables. What's wrong with 7mm OEM cables? Then I spent a couple months figuring out why my GS-T 'hit a wall' at 8-10 PSI boost and after I changed the wires and gaped the plugs per spec I figured it out: the higher the boost, the higher the voltages. My car is stock but if you go much higher than stock, yeah, I could see cables with more insulation making sense.

The first thing I would do is check the plug gaps. The spec for the 2g cars is 0.028 to 0.031 inches. With increased boost -- the T28 -- I would gap those plugs at 0.028.

If the plug gaps are now over 0.031 and setting them smaller makes the engine better but not quite right -- maybe you hit the wall at 12 PSI instead of 9-10 --- then replace the wires next.

Edit -- To fix wrong #s for plug gaps.

Thank you so much I got some NGK plugs I couldn't find 9,10 plug wires but did get some 7 but upgraded ons did not gap plugs because the parts place I got them from said that thay are pre gapped so farso good no more wall while building boost thank you sir

 

[waltah]

... the parts place I got them from said that thay are pre gapped so farso good no more wall while building boost ....

Congratulations! Glad it's fixed!

It would be good to check, though, to be sure they're pre-gapped for your car rather than one of the others that take the same plug.

New 7 mm wires should be fine. They fail when an oversize gap for the boost pressure you run allows the spark voltage to go higher than it should and the wire is degraded by age (heat) and maybe resting on metal.

'Resting on metal' should be impossible. This is what the 2g turbo setup looked like from the factory:

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There are five plastic supports in the spark plug valley; the three white ones are easy to see. There's a black one in the lower right corner that's on a metal bracket and holds two wires; another black plastic piece above there holds all four. The wires can't touch each other or any metal, also they're kept far away from other wires that could lead to crossfiring. The parts are hard to find but they're out there.

I expect the cover (says 'Mitsubishi' on it) is there to keep the wires cleaner/dryer in heavy going.

 

[Tim holmes]

Congratulations! Glad it's fixed!

It would be good to check, though, to be sure they're pre-gapped for your car rather than one of the others that take the same plug.

New 7 mm wires should be fine. They fail when an oversize gap for the boost pressure you run allows the spark voltage to go higher than it should and the wire is degraded by age (heat) and maybe resting on metal.

'Resting on metal' should be impossible. This is what the 2g turbo setup looked like from the factory:

You must be logged in to view this image or video.

There are five plastic supports in the spark plug valley; the three white ones are easy to see. There's a black one in the lower right corner that's on a metal bracket and holds three wires; another black plastic piece above there holds all four. The wires can't touch each other or any metal, also they're kept far away from other wires that could lead to crossfiring. The parts are hard to find but they're out there.

I expect the cover (says 'Mitsubishi' on it) is there to keep the wires cleaner/dryer in heavy going.

Yes I have the cover just not the wire holder I'll find one

 

[waltah]

Here are the part numbers for the three wire guides -- left to right in the photo:

MD121633 Clamp spark plug wires (White nylon, 3 notches, need 3)

MD300098 Clamp spark plug wires (metal bracket/black nylon, guides 2 wires, need 1)

MD190974 Clamp spark plug wires (Black nylon, guides 4 wires out of s.plug cover, need 1)

It seems to me that these are now out of production and nearly all gone: Is anyone making them?