engine surging 3800 series 3 STUMPED

[brycefishersprix]

Hey guys i am a new member and im having troubles finding a surging issue my 05 prix is giving me.

 

99k and a na motor,

 

I have been noticing a lack of power and VERY slight surging on acceloration. I have searched numerous threads to point where i should look and cannot find a definitive place to start. I cannot find anyone with the symptoms i am having

 

Any morning i start the car no problems, runs great, then as it begins to idle. I notice a very faint studder like poor spark maybe one rough fire every minute or so. Im due for plugs so i figure old plugs are the culprit.

Yet, when i put it in gear i dont get any stalling or hesitation when i start going until maybe 1100 rpms then i feel a slight bunny hopping that irritates the hell out of me, it follows the rpms up to 3000 gradually getting worse as rpms increase. Also is present through 1st 2nd and 3rd BEFORE tc locks in. No issues when cruising or highway driving. Does also SEEM to go away when you mash it and downshift.

No codes and just replaced filter fluid and pcs due to hard shifting in stop n go traffic. Which is solved.

 

Now i noticed i can shut the car off and restart and the problem will diasapear only to return the next time i drive. But that isnt a feasable option for me. Please help!

 

I have cleaned the tb and maf, tapped on the tps while idling to no change. On a side note i checked for vac leaks, and found none with carb spray, but hear a "whush" noise when in the seat. Doesnt change pitch when revving but cant hear above 2500 rpm.

 

Can a vac leak cause all this?? I am planning on changing the plugs wires and tps jist to try. Any advise?

[alec_b]

I'd be leaning towards failing coil pack/bad wires/old plugs. Could also possibly be a bad MAF, cleaning them doesn't always make them better. I've cleaned suspect MAF's before and had them come out worse than before.

[brycefishersprix]

I was moreso curious as what other members have experienced this type of issue. Just because i dont feel like throwing parts at it. Lol but people whom have looked at it and or heard the description of my problem have said the same thing.

 

Just start with these, if that doesnt work then replace those, and yada yada yada.... lol i just dont have money to throw at it. Im in the process of moving and i HATE Moving... lol:roll:

[rich17]

I'd do plugs and wires asap. Clean all connections on electrical stuff and go over your vacuum. Also while running unplug the MAF and see if it gets better or worst.

[alec_b]

Weak fuel pump and/or clogged filter could do this as well. It'd be easier to diagnose if we had some scan data, specifically misfire counts and fuel trims.

[brycefishersprix]

Whats funny about the fuel pump, i think, is that when i have under a quarter tank and its running, i get alot of clicking noise coming from my tank until i refill, i dont really know the schematics for the vacuum lines but i am going go be doing the plugs soon. Im just still paying off the psc bill from two weeks ago lol. Will unplugging the maf cause sputtering if its bad? Or do nothing at all?

[alec_b]

Not sure about the clicking noise, never heard a pump do that.

 

The only time I've had the MAF trick work on GM cars is when they're literally SO bad that the car won't run. It will start and rev (sorta) with throttle, and die immediately at idle. When the MAF is unplugged they'll start and run but not really rev up.

 

If you unplug your MAF my guess is all that will happen is it will stall. Which doesn't answer much.

[brycefishersprix]

Well i hooked a scan tool up,

Read the live data and the tp angle was at 3% at idle no misfires in any cylinders in current or history. Unplugged the maf and it went off programmed charts until id plug it back in, when it would stall momentairily. Then idle fine. Checked themiddle plug just to get an idea of what they might look like. They are not corroded or wet or dark. Just look like theyve been through heat cycles. And was gapped at .060.

 

In the process of pulling off the connector, broke the clip holding it on do now its free to slide off if someone puts tension on it.

 

I kinda want to replace the maf when i do plugs just to experiment.

Sorry for the typos im on my phone and its a pita to type a story on touch screen. On the positive note. The clicking goes away now that ive filled my tank for 52.00 (outrageous!!) Any other cards up your sleeves? Any advise on the air noise i get, the "wush"? It sounds like from in tbe d seat.That its coming from the air box location but its so loud sometimes. Lol i feel like im being picky.

[runt]

Sure you are just not hearing the intake pulling air in? I know sometimes when I shut down my old '01 with the Wizaird on it it's make quite the sound on shut down but also made some extra noise on startup.

 

On the same '01 I had a problem where it felt like the car would lose all fuel for a split second and suddenly come back. I never really lost power per say it just cut fuel and came right back. Turned out it was a faulty MAF. I would do plugs, wires and even find a used MAF from a lower mileage car. I put a used on in mine and it worked great. Cleaning them seems to do little unless you are really careful and actually clean the contacts with a Q-Tip or something.

[brycefishersprix]

I believe its just the intake sucking air but the surging is not very noticable, but when it happens. Power loss is noticable in comparison to when it runs fine. For instance, if i am power braking to simulate load, it will jump to 1500rpm under load, then immediately drop to 1200 and flutter up and down a hundred rpms constantly Nd can hear it and feel it jumping

 

I got the paper here for the data log. I cant interperate it but here it is

Long term fuel trim -13 degrees.

Loop status closed

Maf g/s 5.03 and varies at idle

Tp angle 3%

Air fuel ratio 14.65 to 1 at idle maf sensor is at 2900 hertz at idle.

Knock retard at 0 when idling

 

Whatever that means. Lol i just know kr is not good.

[Garrett Powered]

thats not what you need. you must have a datalog with IAC steps and battery voltage. that and engine and vehicle speed. knock,LTFT, even maf afr and tps really has nothing to do with this

[brycefishersprix]

Hmm i wonder if i can do that with the "genisys 200" our shop has. I work at a subaru dealership but i dont think i can with that specific instrument, its pretty dated. I may just be having a brain fart but remind me what iac is, intake air... somethingorother.

 

Sorry its been a rough week!

[brycefishersprix]

I also think i have a bad valve in my fuel pump. The one kweping the fuel from draining back into the tank. Or something along those lines, anytime she sits for a good 3-4 hours or more, it takes like 1.5 seconds to start whereas anytime before that deadline of 3 ish hours, its turn the key and it immediately fires within half a second. Cound be unrelated or completely normal idk.

[Garrett Powered]

when you start viewing those ones you will see why they are important. you are not alone most people completely ignore the IAC even though it is how the computer controls the surging feeling you get when you are not manually changing the throttle plate position. it is a motor that actively meters air into your engine. the MAF only senses the output. IAC enters data so you want to make sure it works first. same thing with the voltage.

[Garrett Powered]

not to sound like that is what needs tuned, It can at least point to a possible solution, as can other engine data. I have been troubleshooting my cars this way, but now beginning to investigate the possibility of injectors being clogged as causing a hesitation or surging problem. I sent one set to witchhunter and having them flow tested and cleaned. so that is just to add another thing to consider.

[alec_b]

Were those your data points idling? Was it warmed up?

 

Your LTFT shouldn't be anywhere close to -13%. I'd be looking more for +/- 5% tops. With it running at -13% means you're running way too rich. Possible causes: false MAF readings, stuck injector(s), too much fuel pressure. However, the only one really likely out of those is the MAF. Injectors rarely go bad in these cars.

 

I didn't think to ask, have you pulled the vacuum line of the fuel pressure regulator? These are NOTORIOUS for going bad and can cause hard starts, sluggish running off idle, and basically all the issues you're having.

[brycefishersprix]

I have been getting piss poor mileage too. Its cold in north dakota. But warm lately (near 20s all week) i idke for 5 minutes before leaving and i average 14 mpg in town, and yes it was idling and almost to running temp when that datalog was taken, and i dont know where these lines are exactly i just got the car a few months ago and dont know every nook and crannie yet lol i have noticed a strong odor from the tailpipe too.

Perhaps you might be right and i will have to look into those!

[brycefishersprix]

Also i plugged and unplugged several times the maf during idle soon before the data log. Possibly affecting the ltft?

[brycefishersprix]

Just enlightened myself on LTFT and what the percentages are all about, now with my specific data, wouldnt it mean im running lean and too much air is entering the system? And a vac leak is more probable? Or am i confused whether negative LTFT means less fuel to compensate for air? Makes my thought process a little foggy trying to comprehend all this new info

[Garrett Powered]

just look at the afr. it says 14.65 at idle? that sounds pretty normal to me. 14.7 is what its supposed to be for gasoline

 

 

if you are worried about the MAF then thats easy, find out what Hz it normally should be at idle, then it should be the same as your reading. or have a new or good used maf and make sure the numbers are close.

[alec_b]

Fuel trims come in two flavors: Short Term and Long Term. Think of the short term fuel trim (STFT) as being instant adjustments that the PCM makes to the fueling, whereas long term (LTFT) is a "running average" of sorts.

 

If either trim is way positive, the computer is ADDING fuel, compensating for a lean condition (aka vacuum leak or weak fuel pressure). Negative trims mean the computer is REMOVING fuel. That's the reason I say check your fuel pressure regulator. It's much more difficult to have too much fuel than to have too much air.

 

 

I circled the fuel pressure regulator in red. Pull off the vacuum line and see if there's fuel in the line. If there is, it's bad. Easily swapped with a snap ring pliers and about 5 minutes of your time.

[Garrett Powered]

Just enlightened myself on LTFT and what the percentages are all about, now with my specific data, wouldnt it mean im running lean and too much air is entering the system? And a vac leak is more probable? Or am i confused whether negative LTFT means less fuel to compensate for air? Makes my thought process a little foggy trying to comprehend all this new info

 

 

That was even foggy in my mind. but from what I already knew in the past on it, and reading the posts here, actually starting to make more sense than it did.

[brycefishersprix]

This has been really helpful, now i understand my ft data! Lol now how do i go about checking the regulator? Thank god i have people who understand this car more than the gm dealer here. The sooner i get to mod my prix the better!

[alec_b]

I circled the fuel pressure regulator in red. Pull off the vacuum line and see if there's fuel in the line. If there is, it's bad. Easily swapped with a snap ring pliers and about 5 minutes of your time.

 

There's your instructions

[brycefishersprix]

Thanks alec alot. I will post results either tomorrow on my day off or wednesday in the shop on our "shop night." Lol