2G Sensor issue?

[IIv SHaDoW vII]

Car 98 GSX with a FMIC/ NGR Bov/ big 16g.. manual tranny

At roughly 2500 rpms the car sometimes seems to hit a wall and will not accelerate no matter what I do (extreme hesitation).. If I continue to hold the gas in, it will eventually break free from whatever is stopping it and accelerate. This only happens while moving.
The problem happens more often when the engine is cold but the issue can be witnessed in both hot and cold weather..

I have had this issue since I got the car a year ago..
I have changed the plugs, wires, and turbo plumbing to no avail. I took it to a mechanic and he said there were no signs of boost leak.

No engine codes.

Other things I read that it could be some of this issue:
coil packs are cracked
throttle position sensor

Thoughts?

 

[delta448]

Your mechanic is probably either lying by saying he did it -or more likely, doesn't know what you're asking him to do other than visually inspect things.

Do you not have a boost leak tester? The one I use is the $24 one described here as "single pop gauged with tire valve adapter".

It's almost guaranteed to be a fueling issue if it's worse with colder temps.

If it is only happening upon spool-up, your culprit is most likely the BOV. It would need to be adjusted tighter so that it takes more vacuum/pressure differential to open it, -where it "blows-off" harder. Of course, you'd have no problems at all if it were actually recirculated like it should be.

Zero your fuel trims out as well by disconnecting the battery and then turning the headlights on for a couple seconds.

 

[IIv SHaDoW vII]

The mechanic is a trusted member of the dsm community and didn't charge me to look at it and he has a boost leak tester.

The issue happens regardless of boost.. I could be in boost or not in boost.. the issue occurs regardless.

What should I do if it is a fuel problem? Also, I replaced the battery about 2 weeks ago and it was left out of the car for about a day.. is it absolutely necessary to turn the headlights on? What exactly does clearing the fuel trim do?

Thanks for the input!

 

[blakkat]

I would be looking at your TPS or MAF to be honest. I would clean the MAF and check to make sure the TPS is at 0.5v at idle.

 

[delta448]

When you're in partial throttle cruise conditions and even during spool-up, that BOV may be floating open. Obviously, this vents measured air. Loosen the locknut and turn the adjustment on the top of the valve about a quarter turn at a time towards HARD until you're sure it isn't soft enough to float open. Are you using the lower nipple? If so, you may consider trying the valve without having that fast release nipple plumbed in.

Turning on the headlights is just a suggestion to ensure that you've drained all the residual power out of the system and cleared the ECU's learned memory. The fuel trims will probably work their way further against you over time as you drive more and more with this problem. If resetting them makes the car run better immediately after you do it, you'll know it's fuel related.

Another thing to check is your FPR and the vac line to it.
I'd hate to suggest a fuel pressure test, cause it's a huge PITA, but if all else fails...

Are you getting any DTC's? -Usually if the MAS is bad, you will set one.

 

[blakkat]

TPS will cause tip in acceleration problems. If it's not a closed loop related problem. Which is indicated by it running bad when cold. The only things to check are fuel pressure, spark, the MAF, the TPS and that's about it. I would start with these things.

 

[IIv SHaDoW vII]

The BOV was replaced when the FMIC was added and the issue was happening before it was installed. I recently replaced the battery and it was disconnected for over a day. The BOV is also recirculated as it should be.

I ran the code scanner just in case and it had stored code. I asked the original owner about it and he said the cat had been deleted...

I guess I will start with the TPS and MAF.

 

[LarryJoe]

Try changing your fuel filter.

 

[blakkat]

Report back with your results and we can go from there.

 

[delta448]

The BOV was replaced when the FMIC was added and the issue was happening before it was installed. I recently replaced the battery and it was disconnected for over a day. The BOV is also recirculated as it should be.

I shouldn't have assumed. My apologies.

I ran the code scanner just in case and it had stored code. I asked the original owner about it and he said the cat had been deleted...

Was P0420 the only code?

I guess I will start with the tps and MAF.

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[IIv SHaDoW vII]

Yea, no other codes were stored.. Sorry, I must not have finished that paragraph before clicking reply.

Also, thanks for the info.. Definitely helpful!

 

[blakkat]

Update? I'm interested to see the cause of this problem

 

[IIv SHaDoW vII]

Going to swap the TPS and MAF with 2 known working ones to test that part.

Also, found that the alternator has not been charging the system properly due to the tensioner bolt missing.. I ordered one from ebay and will post back once all these things are tried.

 

[blakkat]

Alright goodluck, let us know how it goes.

 

[yhype]

I had a Dodge Caravan pretty much the exact same thing as you described and the last thing I replaced was the O2 sensors and the customer hasn't returned with that complaint again so it might be worth a try.

 

[IIv SHaDoW vII]

TPS swap and alternator tensioner fix didn't solve the issue.
I still need to get ahold of the MAF to swap in.

Also, I didn't even really think of fuel filter.. wow.. noob mistake.. May try that next.
But wait.. isn't the fuel filter on the firewall on the 2g 4g63s?.. That's not gonna be fun to replace...

Also, might try the O2 sensor as well.

 

[blakkat]

Yeah just check fuel pressure it should be low if there's a restriction in the filter. Check your maf. o2 sensor should not cause a problem other than cruising and part throttle because those are the only times the car is functioning in closed loop. When it is in open loop the car will ignore the o2 sensor and perform fueling calculations based off of tables burned into the ecu. Ie X grams per second airflow or hertz in some cases is equal to x amount of fuel to make x airfuel ratio.

 

[IIv SHaDoW vII]

MAF may have been the culprit.. I will drive it around for a week and see if I can recreate the issue. After swapping in a new one, I haven't witnessed the issue yet..
Is it normal to be able to feel the transition from - to + vacuum? I don't remember this feeling with my GST but I also didn't have a big 16g. It's like I hit a flat spot for a split second right before boost kicks in.. It's only in partial throttle.. But it is like.. car accelerates.. and once 0 vacuum is hit, it flattens just enough to feel. Immediately after, it accelerates in boost as normal.