Help?



Just made this QUICK, CRAPPY, POS MS PAINT DOOOOOOOOODDDLLEEEEEE to give an idea of what my car is doing. I do a lot of highway driving, but a few days ago when passing a car (going roughly 80 to pass) my engine had a very hard time getting up to 80 from 70 (see chart).

I've also posted several issues in the past about HP issues when the engine is warm - could this be related to that? If not, what on earth would cause jumpy acceleration like this?

 

How did you get the values for that chart?

 

I just made it with MS Paint to give an idea of what it would look like on a DYNO. Nothing is to scale.

 

On a dyno and real world, you wouldn't feel those spikes. A lot of my dynos have that and it's usually too much timing.


Ahh, so is it bucking or choppy, or just takes forever? 70-80 is not a real happy place for the 4AT in 3rd, at all.

It's only happy w/ 7100 rev cut and breathing mods (IM/MAF/I/H)

 

Its a very rough, choppy acceleration. And, it does take forever, so yes to both of those. Is this a normal issue for our cars then, or should I be worried?

 

Choppy isn't normal. By choppy is it bucking?

 

I guess both words pretty much work in this case. It doesn't ever decelerate with my foot on the gas I guess, but it definitely jumps up by a mph or two at a time. I don't remember the exact conditions, but my foot was to the floor, so I know the pedal wasn't moving when the car was bucking like that.

 

Surging is probably a better term rather than bucking, since bucking seems violent. My old 4th gen used to literally buck when low on fuel and getting on it, but I don't think this is the case. Misfire, you know I could throw out the common things, but yea weird.

 

I still don't understand the graph values.

Did you take a horsepower dyno curve and just change the values, from rpm and power to time and speed?

 

how about just taking a video instead of a homemade time vs velocity graph?

 

Damn that sucks how many miles is on your ride? Never felt nothing like that but when my rear cat was done for on the freeway a little Scion with exhaust will be right there with me like WTF!!

 

You can only feel it. Gauges say nothing by watching them.

And again, the graph is only a visual attempt to show what the car does. It is by no means accurate.

 

Random ***'d guesses:

-MAF (an intermittent signal could cause unusual driveability; also the source of all Maxima problems)
-Cats (Meow; they be clogged? any cat efficiency or secondary oxygen sensor codes?)
-Misfire (spark plug or coil pack issue under load; does the problem occur at WOT at the same engine speeds in other gears?)
-Some weird automagical transmission issue (for which I am useless; never owned one)

 

All sound logical - I'm almost positive my cats are clogged (lack of power when @ operating temp), and the transmission slips. No SEL for anything though. Should look into those sooner rather than later I guess.

 

More I forgot about:

-Knock sensor (could also cause power loss, but I don't think the ECU the re-advance timing quick enough to cause a surging or bucking)
-VIAS opening and closing randomly (don't know about feasibility of this failure, but sudden changes in air flow will cause surging)

 

Where did you get the chart man? I don't really understand that. lol

 

Jesus he said it's just a quick freakin paint representation, qualitative, not quantitative!!!111one

 

ITS A FUKKING MS PAINT DOODLE! lmfao!

There. My new 1st post should fix any confusion.

 

the vtec kicks in yo
j/k, whats that ripple? rev limiter?
slow acceleration at high rpm could be MAF.

 

In my experience, this could be MAF, Knock sensor, or Coils. Although the vias is an interesting idea, not the first place I'd look, but you could easily examine whether there is a vacuum hose leak with the system or use a vaccuum tool to check if the valve is opening/moving and staying in position.

My experience though with this symptom points to coil pack(s). Have you pulled and inspected? Isn't there a way to ohm them out to determine if they are going bad?

 

That speed with the 4AT is not high RPM.

And if it is surging, I'm putting $$ on coils.

Get a dyno, seriously, or codes, or find a local if you know any with an OBDII logging system.

 

I severely doubt knock sensor, as that would not cause "surging" power, it would cause a lack of power

 

... which my car has. Going to check all this out when I'm off on Tuesday.

Appreciate the input guys.

 

Nobody can say for sure until we know which code (if any (which would definitely be surprising)) is pulled

 

That's been my problem since the whole thing started a few months ago with my lack of power. The car has absolutely no codes. A friend of mine who owns the repair shop I go to even ran a diagnostic test that pulls codes from the car when it's running, but that didn't come back with any codes either.

My goal here is to at least narrow down what my problem is because I've already thrown several thousand $$ at this car to fix stupid ****. I don't want to start blindly spending money on sensors, exhaust parts (especially the cat or precats - which certainly are not cheap), etc that may or may not fix my problem.

 

Get a dyno

 

did your friend use the scanner that runs only check engine codes, or did he use the full car code scanner that can run ABS, etc?

 

Second one - he used a tool that he said pulls "running diagnostic threads" as the car is running. That found nothing.

 

in for vid