Hesitation Under Boost

[dope96clipse]

Ok I was asked to help do a turbo swap on a buddies practically completely stock 96 gst. did the swap (just another t-25 ) and everythnig works minus a small oil leak on the oil return line...but when driving the car it bucks underboost from 3k-5500. but when easy on the gas it goes all the way to 7k with out a hitch. the car only has a 190lph pump and the standard BCS mod. It acts like it has too much fuel but idk im lost. It doesnt puff any smoke at all and other then the bucking under boost works great.. anyone have any ideas? anything will be help full thanks

 

[VETDRMS]

I would lean toward it being a fuel related problem, there is a much higher demand for fuel under boost/load than there is slowly making your way up to 7000rpm. Your pump may be going out as in working order the 190lph pump is plenty for a T25.

If it was excessively rich you would have black smoke.

Also, have you done a boost-leak test after the swap?

 

[dope96clipse]

actually no i didnt think about that, the pump its self was put in about maybe a yr ago an 4,000 miles were put on the car, (motor blew) and was replaced, i just learned that the bucking actually started before the motor and turbo blew, the motor was replaced by a local mechanic but the turbo blew shortly afterwards (shavings in the turbo). Could sparkplugs and/or wires cause the problem?

 

[brodiedehass]

Could sparkplugs and/or wires cause the problem?

Yes, very possible. But I would do a boost leak test first.

 

[oldman]

Boost leak test !!! Probably the reason why the other turbo took a dump in the first place.

 

[dope96clipse]

Thanks, we replaced the plugs and wires, turns out the company who did the motor swap was rather shady and put some plugs in that werent meant for the car and it runs perfect now. and i looked at the old turbo, i guess when my freind blew the motor a peice of a valve hit the turbine and tore it to hell there were huge pieces of the turbine missing

 

[RalphC96]

I'm having the same problem. The day before it was running great no problems or hesitation now the next morning I was leaving for work I get onto the main road my bov goes off louder then it should. After that I get into 2nd and once I start making boost it hesitates and retards the timing. It sounds like I'm hitting 2 step but it won't let me build boost I leak tested it and everything is clamped down tight. I have no idea what's going on I have a 190lph with a T-28 Turbo and a FMIC .
It drives great as long as I don't go into boost but once I leave vacuum and try to make boost the car will hold me in that rpm. It's getting enough fuel because I'm running rich and when it happen black smoke puffs out.

 

[2gmitsueclipse]

I'm having the same problem. The day before it was running great no problems or hesitation now the next morning I was leaving for work I get onto the main road my bov goes off louder then it should. After that I get into 2nd and once I start making boost it hesitates and retards the timing. It sounds like I'm hitting 2 step but it won't let me build boost I leak tested it and everything is clamped down tight. I have no idea what's going on I have a 190lph with a T-28 Turbo and a FMIC .
It drives great as long as I don't go into boost but once I leave vacuum and try to make boost the car will hold me in that rpm. It's getting enough fuel because I'm running rich and when it happen black smoke puffs out.

Welcome to the site. So members can better help you out going forward, creating a profile for your car. For instruction, see this thread:

http://www.dsmtuners.com/threads/welcome-to-dsmtuners-now-go-create-a-dsm-profile.499707/


Tightening down clamps will not be enough. You need to pressurize the intake system. On this site, it is referred to as a BLT (Boost Leak Test). You should check out the links below to see this procedure in action.

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I do not remember if the video mentions it, but complete a BLT on a warm engine. In addition to intake pipes, spray warm, soapy water around the throttle body and fuel injector seals.

 

[Dsmkauai]

Probabaly wasn't the bov that made the noise, sounds like you blew a coupler or maybe vac line. Blt!! Is your friend

 

[Victor1]

Spark plug gapping used to cause a breakup in my car, switched to bpr7es and gapped to 28, however your issue seems different, boost leak is the first thing id check which i think it is

 

[Onizuka186]

Hi everyone, i also have a similar issue on my 2g gsx, since i changed the catback from stock to hks hi-power exhaust it sarts now hesitating at wot, its like it stop boosting for less than a second boost again and cut and boost again. when i sart the car and i drive it for 10-15min until it reach the proper temp and i wot its just fine, after some pulls it start to do that hesitation.
the exhaust has increase some psi. before with the stock exhaust it was just fine.
Ive noticed a leak right to the section where the exhaust is bolted to the cat (stock).
Is it possible it hesitate because of that leak?

 

[doubleclutch]

Hi everyone, i also have a similar issue on my 2g gsx, since i changed the catback from stock to hks hi-power exhaust it sarts now hesitating at wot, its like it stop boosting for less than a second boost again and cut and boost again. when i sart the car and i drive it for 10-15min until it reach the proper temp and i wot its just fine, after some pulls it start to do that hesitation.
the exhaust has increase some psi. before with the stock exhaust it was just fine.
Ive noticed a leak right to the section where the exhaust is bolted to the cat (stock).
Is it possible it hesitate because of that leak?

Sounds like fuel cut to me, but no one will be able to help you without knowing anything about what is done to your car. Please create a profile with a complete modifications list.

 

[Onizuka186]

the problem starts right after i installed the catback. with the stock exhaust the boost was 11psi and now after i installed the hks hi-power exhaust it boost to 13psi. Before the install it was fine. the hesitation is only at WOT and it occure after some pulls or when the car is warm after 15-20 min of driving.
Ive noticed a leak right to the section where the catback is bolted to the stock cat and probably make the o2 sensor reading a bad mixture. Ill fix that leak and replace the spark plugs with the bpr6es to see if it could be the problem.
BTW if anyone knows what could be the problem let me know

 

[2gmitsueclipse]

The exhaust leak you mention is unrelated to your problem. The rear or downstream o2 sensor is not used by the ECU for fuel adjustments. Have you completed a pressure test of the intake system as was suggested in this very thread?

 

[Onizuka186]

Ive not done a boost leak test yet. Ive not the tool to do it, im in Europe and here is something like 100$ just to make that test and i dont want to spend money for that but i will find a solution. What coupler size do i need to make the boost leak tester fit the 16g? Ill make the jafromobile's blt

 

[doubleclutch]

the problem starts right after i installed the catback. with the stock exhaust the boost was 11psi and now after i installed the hks hi-power exhaust it boost to 13psi. Before the install it was fine. the hesitation is only at WOT and it occure after some pulls or when the car is warm after 15-20 min of driving.
Ive noticed a leak right to the section where the catback is bolted to the stock cat and probably make the o2 sensor reading a bad mixture. Ill fix that leak and replace the spark plugs with the bpr6es to see if it could be the problem.
BTW if anyone knows what could be the problem let me know

Yes, that makes sense. Your boost went up which means your air fuel increased which means you could be running lean enough to cause fuel cut. since we don't have any idea what you have in you car it is pretty hard to diagnose.

We are trying to help but you aren't making it easy.

 

[2gmitsueclipse]

Ive not done a boost leak test yet. Ive not the tool to do it, im in Europe and here is something like 100$ just to make that test and i dont want to spend money for that but i will find a solution. What coupler size do i need to make the boost leak tester fit the 16g? Ill make the jafromobile's blt

All of the parts can be had at a hardware store. Unfortunately, owning one of these cars will be an investment on your end. Making the tool in the video provided should cost no more than $30 US currency. You will want to measure the compressor inlet on the turbo to figure out the appropriate sized coupler. Complete the test with the car at or near operating temperature for the best results.

 

[Onizuka186]

Yes, that makes sense. Your boost went up which means your air fuel increased which means you could be running lean enough to cause fuel cut. since we don't have any idea what you have in you car it is pretty hard to diagnose.

We are trying to help but you aren't making it easy.

I already updated my profile, you can see all the mods

 

[Onizuka186]

I noticed on the rear bumper in the top of the exhaust it is black right now, i clean it and after a few pulls its black again. Probably runing rich?

 

[doubleclutch]

I already updated my profile, you can see all the mods

I see that now, sorry about that.

Soooo what are you tuning with?

 

[Onizuka186]

Im new to the dsm community and i dont know how to use the dsmlink. The previous owner has installed the dsmlink but when i bought the car he didnt gived me the cable to plug my laptop on the car and he get rid of it now. So the only one thing i know is the launch control is set to 4500rpm and thats it

 

[doubleclutch]

The software is free, you just have to find a cable. You can buy them directly from ECMlink but they are pricey. Hard to know what is going on without it because we have no idea how the car is set up.

 

[Onizuka186]

The software is free, you just have to find a cable. You can buy them directly from ECMlink but they are pricey. Hard to know what is going on without it because we have no idea how the car is set up.

Does an OBD-USB cable works or do i absolutly need a ecmlink cable?

 

[Dsmkauai]

No you need there cable. You can try but doubt it would work right.

 

[2gmitsueclipse]

Im new to the dsm community and i dont know how to use the dsmlink. The previous owner has installed the dsmlink but when i bought the car he didnt gived me the cable to plug my laptop on the car and he get rid of it now. So the only one thing i know is the launch control is set to 4500rpm and thats it

You will need to pull the ECU to find out which version of ECMLink you have. If it is V3, then a replacement cable can be had for $45 from ECMTuning. If you have V1 or V2/2.5, you will need to source one privately.

If your not sure how to pull the ECU:

http://www.dsmtuners.com/threads/resolved-need-diagram-to-remove-ecu.253650/

Once you pull the ECU, remove the four screws located on the ECU case to remove the cover. With the cover removed, you will be looking for something like this:

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