2G sometimes it pulls, sometimes not

[Mike_GST]

Hello guys.

I looked around for threads like this, but none of them presents irregular working like mine.
I have now my '98 GST for one year and half and something is bothering me since ever.
My car sometimes pulls strong and sometimes not. No reason I can notice.
Same day, same temperature, same time, same conditions. I pull once, the acceleration presses my body to the sit. Then stop the car and pull again. The rpms goes up, the pressure gauge shows full boost, but the car has a very weak performance. In this same exactly pull, if I release and quick the accelerator, the car reacts full performance again! Pretty wird thing.

Everything in the car is stock. When I bought it, replace all the belts, spark plugs and fluids.
At first I was suspicious about the wastegate, that an erratic opening and closing could be doing that.
The car has VERY LOW MILEAGE, so being sitting could make some moving parts get sticky, I thought
Then I released that little rod that connects it to the actuador and moved with my hand right and left.
Very smooth movement! Is not the wastegate.

Well, I don't believe this problem is related to the air flow, neather from or to the engine. It couldn't be such a leackage on the lines, way to make the performance drop that much, without been noticeable in the gauge, which by the way, shows full boost.

Do you guys have any guess?
Thank you very much.

 

[bastarddsm]

Check the knock sensor. It's common for them to go bad and show phantom knock, and it will randomly pull timing.

 

[Anthony Aguilar]

If it's an auto it could be a torque converter

 

[chrysler kid]

I noticed my car did the same thing once, but it was a situation where I was in second gear at 10 mph and it seemed like the car just would never build boost even though the gauge showed 12 psi, it also did it in 4th when I thought I downshifted to second to pass slowing traffic

Knock sensor sounds probable but it's not really an every day thing I notice. I contributed it to an air density situation where throttle settings did not match air flow and the car pulled all timing and dumped fuel thinking there was possible sensor failure to prevent damage.

 

[Mike_GST]

If it's an auto it could be a torque converter

Anthony Aguilar, my transmission is manual.

I noticed my car did the same thing once, but it was a situation where I was in second gear at 10 mph and it seemed like the car just would never build boost even though the gauge showed 12 psi, it also did it in 4th when I thought I downshifted to second to pass slowing traffic

Knock sensor sounds probable but it's not really an every day thing I notice. I contributed it to an air density situation where throttle settings did not match air flow and the car pulled all timing and dumped fuel thinking there was possible sensor failure to prevent damage.

chrysler kid, I didn't mention that because this could be just a matter of personal feeling. But since you bring that up, it could be na important fact. I too feel it happening NOT when I press the throttle all the way down from "zero", BUT when I do it from 1500-2500 rpms, with the car already moving. So, maybe because of this, I feel the lack of power very mostly in 1st and 2nd gears. And again, sometimes it happens, sometimes not.

Check the knock sensor. It's common for them to go bad and show phantom knock, and it will randomly pull timing.

bastarddsm, the timming getting pulled could result in this behave, it makes sense. How do I check the knock sensor?

 

[miliman13]

By replacing it. Not cheap but a necessary expense.

 

[Mike_GST]

By replacing it. Not cheap but a necessary expense.

Hello miliman13. I just checked its cost in web stores. It's not that expensive if the problem is really related to that piece, but not cheap to throw it away. Those chinese OBD2 for android devices, for instance, costs 10% of this sensor. If there's a chance this scanners diagnose an erratic parameter straight related to that sensor, that would be a good deal. Any of you guys use OBD2? Can I diagnose knock sensor failure with it?

 

[bastarddsm]

Not sure on the 2g on my 1g id be using a datalogger to check for timing being pulled

 

[Lou98GSX]

Could it be your clutch slipping . How far does the pedal go before the clutch engages .

 

[Mike_GST]

Could it be your clutch slipping . How far does the pedal go before the clutch engages .

Dear Lou98GSX, if it was the clutch, I'd probably notice the rpms increasing fast with no consistence, right? But it doesn't happen this way, the rpms increase consistently, but lets say in slow motion, even with full boost. And as soon as I release and press the accelerator again, the car returns to its full performance.
My car is all stock with just 30k miles, no abuse at all, I don't think the clutch would get wasted so fast.

It may be something electrical, like the knock sensor, or the coil, or the cables, or who knows. The thing is how to check / inspect all of this, before spending money replacing parts that are working fine.

 

[chrysler kid]

If it is a consistent problem for you I would start by doing regular maintenance and cleaning of the intake hose (it tends t get filled with gunk from the valve cover breather vac line), egr, idle air control valve, new pcv valve, new air filter fuel filter etc. With mine being under partial throttle then going to full throttle when the engine is in a bog Im not concerned about it

 

[2gmitsueclipse]

Hello miliman13. I just checked its cost in web stores. It's not that expensive if the problem is really related to that piece, but not cheap to throw it away. Those chinese OBD2 for android devices, for instance, costs 10% of this sensor. If there's a chance this scanners diagnose an erratic parameter straight related to that sensor, that would be a good deal. Any of you guys use OBD2? Can I diagnose knock sensor failure with it?

I am not aware of a device like these that supports Mitsubishi's MUTIII protocol. ECMLink or EvoScan would work. The EvoScan option would be cheapest as you only need the software and Tactrix cable assuming your ECU is compatible.

 

[Chumpaumpalumpa]

Try only rolling on until 3k. Don't floor it under 3k. Do you have a boost gauge

 

[Utz_3]

Do you have an aftermarket boost gauge or are you going by what the stock gauge shows? Nobody has mentioned this, but maybe you have a boost leak? Especially if you still have a stock plastic BOV (those are very bad).

 

[Mike_GST]

If it is a consistent problem for you I would start by doing regular maintenance and cleaning of the intake hose (it tends t get filled with gunk from the valve cover breather vac line), egr, idle air control valve, new pcv valve, new air filter fuel filter etc. With mine being under partial throttle then going to full throttle when the engine is in a bog Im not concerned about it

I forgot to mention that I replaced all the filters too when I bought it 1,5 year ago. But cleaning all the intake hoses is something I can work with, just to make sure. Thanks.

I am not aware of a device like these that supports Mitsubishi's MUTIII protocol. ECMLink or EvoScan would work. The EvoScan option would be cheapest as you only need the software and Tactrix cable assuming your ECU is compatible.

Made a fast research on a brazilian fórum and the consensus is that all the 2gs that arrived here are OBDII compatible. Looks like the 1gs and early 2gs not! Those shity chinese bluetooth scanners for android devices can read fuel pressure and ignition timming (and tons of other parameters), something that will fill me up with informations about the fuel pump health and also the knock sensor. Nice! Gotta get one myself.

Try only rolling on until 3k. Don't floor it under 3k. Do you have a boost gauge

Sorry Chumpaumpalumpa, didn't understand your point. The GSTs models have a boost gauge stock on the dashboard.

 

[SomeGoFast]

I think what Chumpaumpalumpa and UTZ_3 are asking is if you have an aftermarket boost gauge instead of just the stock one to verify your factory gauge is correct. It could be a boost leak if your bov is not closing all the way.

 

[PlanZero]

My bone stock Tsi had the same issues. Got rid of the restrictive stock intake and exhaust and bpv and never happened again.

 

[Chumpaumpalumpa]

If you have sporadic spool (meaning it doesn't spool consistently every time) the ECU can get "confused" and retard timing then advance it and do some funny stuff. When I got mine I couldn't just floor it willy nilly. I had to roll on until 3500 and then floor it or else it would be very inconsistent. Logs said it was advancing timing then retarding it way back if boost came on late. It was a weird issue that didn't make much sense but fixing ALL boost leaks and finding a way to get a cooler air charge helped a lot with consistency.

 

[Lou98GSX]

If you don't have an aftermarket boost gauge then check the one on the dash to see if it changes or if it doesn't move when this happens . I would also try dropping the downpipe and drive it , to see if its something with the exhaust. You said that you changed the air filter ,did you replace it with a factory one , cause i have seen cheep auto part store ones collapse causing a restriction . Maybe drive it without the filter to see if that is the problem. Another thing you can check is to see if the turbo spins freely .

 

[GSXDNA]

I've had this problem before. Turned out to be a slit in a vacuum line. As the car heated up, the inside of the slit in the rubber hose would sort of melt and fuse together (it was close to the manifold), and seal air properly after it cooled down. But when the boost pressure eventually reopened the slit, I'd have no boost again.

 

[Mike_GST]

Thank you guys for sharing all your experiences and thoughts. Really good stuff!

Well, my boost gauge is the stock one. It can't be accurate like those aftermarket ones, but I think it does the trick about the turbo behavior. It shows boost the same way when pulls normal and when pulls weak. If there is a leak, it shouldn't show boost in the gauge, right? I know the OBD2 can read intake temperature and pressure. Maybe this way I'll have specific numbers and check if there's difference on this parameters between a regular pull and a weak one. The dealer is waiting for a picture of the conector under the dash to check if OBD2 is compatible.

About leaks or restrictions, eather the intake line or the exhaust line, it would make the car performance badly all the time, not randomly (actually I'm noticing a pattern, will write about it later). My BOV is stock too, that one made by plastic. I hear a lot of people complaining about this part reliability, but all of them using bigger turbos or tunning the stock wastegate to release pressure in higher values. Maybe it just doesn't suppose to work with pressure over the stock. I don't know how's the BOV internal mechanism. But if it is all mechanic, like the wastegate, a microscopic dust or rust wouldn't let it open and close smoothly, causing erratic performance. There's a chance! For instance, at first my boost gauge hardly touched the end of the scale; since I sprayed WD40 on the wastegate little axel, now I get the needle right on top of the gauge, ALWAYS.

About the pattern I'm observing, here it goes:

chrysler kid sad: "...I was in second gear at 10 mph and it seemed like the car just would never build boost even though the gauge showed 12 psi, it also did it in 4th when I thought I downshifted to second to pass slowing traffic" "...not really an every day thing..."

Parcial throttle to full throttle in low rpms.

Chumpaumpalumpa said: "Try only rolling on until 3k. Don't floor it under 3k."

At first didn't really understand what he wanted to mean, but turns out "parcial throttle to full throttle in low rpms"!

Chumpaumpalumpa said: "I couldn't just floor it willy nilly. I had to roll on until 3500 and then floor it or else it would be very inconsistent"

Again, parcial throttle to full throttle in low rpms... ...very inconsistent!!

I have to take my car to the road again in try pulls in differents rpms, to be sure this pattern confirms in my case, but it sounds pretty the same what I feel. From what I remember, pulls from zero, 1st, 2nd and 3rd gears, taking all of them until red line, my car never hesitated. The weak performance use to happen when I'm cruising in a low rpms and then floor the throttle. Turbo spools, gauge shows boost building all the way up, but the car accelerates very slow. Don't want to be repetitive, but this may be a very important fact: as soon as I release and floor the throttle again, the car wakes up immediately, just like that!

 

[BlueArcher]

The stock gauge doesn't exactly measure manifold pressure, it is a calculated value based on airflow entering the engine through the MAF... so no, I don't think it would appropriately show what you are experiencing, and I would expect it to read the same in both pulls even if you had a boost or vacuum leak.

 

[Chumpaumpalumpa]

The weak performance use to happen when I'm cruising in a low rpms and then floor the throttle. Turbo spools, gauge shows boost building all the way up, but the car accelerates very slow. !

That's exactly what I'm saying. Don't floor it at low RPMs. Go half throttle until 3500RPM then roll onto the throttle. See if that helps with consistency. Also the stock gauge especially in 2G cars doesn't mean squat really. It's more of a decoration. Like @BlueArcher said, its just calculated from what the MAF sees, not actual manifold pressure. You could have all your air spewing out of boost leaks and the boost gauge would still be pinned. Go do what's called a boost leak test. Here is how you do one:

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Now while doing the test, fix the leaks. Fix all of them. Even a small one can throw numbers off for the ECU. If you eliminate the boost leaks, then the problem isn't from that and we can move on to another theory knowing that a common issue has been fixed. If it fixes it, then you are done and the issue is resolved.

 

[Mike_GST]

If the gauge is based on informations of the MAF, I agree this is just a cosmetic tool.

Don't know what kind of air filter is on it, the first maintance was made by a Mitsubishi specialist. Only drove 3k miles on road since then. Will take a closer look to it. Thanks.

Will check the vacuum line too, thanks.

About the vídeo-tutorial, it shows they got 30psi, after fixing the intercooler. On a stock GST, what's the pressure I should look for as a target? As I'll have to work with the hoses, would't be worth replace them for new ones? What can you say about those dsm kits, made of colored silicon, probably chinese? They are not expensive, but still, is it good quality stuff?

What do you guys mean by "when engine is in a bog"? Couldn't even have a guess looking for it on the dictionary ha ha ha

 

[chrysler kid]

An engine bog would be described as a point in the rpm range where the engine is not able to produce the correct amount of power to rapidly accelerate.

An example of this would be trying to accelerate from a stop sign in third gear instead of first gear.