Bucking-Fishbite Under Load- Again and Ongoing

[BrentN]

Hi Folks- Its been awhile, but still having ongoing problems with bucking under throttle while warm and fishbiting at steady state at times.

Had my 99 out yesterday and under load (going up a 1600ft grade- Little hills in Oregon on the Coast range) at 55-60, the engine surged and bucked...I took my foot out of it and maintained the hill at a slower speed, but it definitely felt starved of fuel.

As I got to the end of my trip, a few times accelerating from a stop and performance was way down.

I am getting boost on the hills ( upwards to 7psi or so). I ran yesterday without my Kennedy boost fooler as I hadnt put back on and recalibrated yet after the IP was replaced.

Recent history- Last fall had the IP replaced, the optical sense ring had broken. Tech timed and set base timing. Starts and runs great, maybe a bit more smoke on startup than before, but it sits a lot.

Lift pump is a new GM. It is putting out barely 3psi with the engine off. Doesnt move the needle when the truck it idling.
Flow is good from the lift pump with engine off and engine doesnt sputter or die when I open the bleed handle while its running.

Engine Fuel filter is new.
Fuel is clean and new, tank was 3/4 to full at the time.
No sock in the tank.
When opening the fuel cap, I hear a "whoosh" - dont really know if it is pressure or vacuum.

Have experienced the problem prior to even replacing the IP.

Having been around in circles on this for the last several years, it just seems like it just doesnt get enough fuel for when there is a demand.

I did notice last night that it doesnt appear to have the Optical encoder Filter on it, which I thought was standard for the 99. But in any case, that might explain the fishbiting, but i dont think the load performance would be the case.

I am really leaning towards a higher volume, higher pressure lift pump as I am at a loss to explain the power loss issue.

It definitely did this after driving for the first 75 miles yesterday and getting it warm...I am going to try to take the fuel cap loose and repeat, thinking maybe the tank is getting a vacuum and not being pressurized....

Any thoughts?

[DmaxMaverick]

Replace the fuel cap. Revisit the diagnosis if that doesn't cure it. More often than not, it does. It's strange, to me, that some people will pass on the simplest, cheapest solution in favor for more complicated and costly wild goose chases. If it doesn't fix it, it was due for replacement, anyway ("whoosh" = bad pressure vents). Make sure the replacement is "Diesel Fuel Only". Gasser caps don't vent properly (they "whoosh", and cause bucking-fishbite).

3 PSI fuel pressure at idle is adequate. 4 PSI is the spec. If it doesn't stall when the bleed (or drain) is open, the LP is not likely your problem. A higher flow/pressure fuel lift pump IS NOT a solution. If a good OEM LP can't do what it needs to do at/near stock power levels, the problem is elsewhere.

Removing the fuel sending unit sock is not a solution. The correct sock should have NO affect on fuel flow. It not only strains the incoming fuel, and it decreases the fuel inlet velocity, which in itself, helps prevent plugging if a little garbage is in the tank. If it plugs, the problem is NOT the sock. If you have an aftermarket sock (such as a "gasser style") installed, all bets are off. Simplify things by doing it right the first time. The OEM sock should look like a mesh tube, with a flat end (which may include a flapper valve). Unacceptable aftermarket socks have typically looked like a slightly inflated, flat envelope, and these WILL fail with the slightest viscosity increase or debris.

Don't assume you have perfect fuel in the tank, even if it is relatively new. Pull a sample from the water drain (T-valve at the T-stat housing). Let is stand undisturbed in sunlight for a couple hours in a glass jar. Any water or debris should settle in that time. If it darkens, you have something growing in it (algae).

[BrentN]

DmaxMaverick- Thanks Much for the advice.

I will swing by GM and see if they have a new cap and as a short term measure at least loosen the existing one. If it will only be that simple of a solution, that'll be awesome.

I will pull some fuel into a mason jar this evening...Good trick on setting it in the sun for an algae check. Anecdodally, it is nice and green when I am opening the t-handle...no water or debris, but the sit for several hours test will certainly bear out if I have something in solution.

The cap is the original green cap and have had it on their since 2003 when I purchased this rig.

Like the fact that you had a cruze...I took the $ the VW was offering and made out like a bandit in getting the cruze...78k on mine, have seen 55.7mpg in the last month...It should do much better once it warms up before the AC has to come on

Thanks again for your fast response, that is what I love about this forum!!!

[DmaxMaverick]

A 15 y/o fuel cap is always suspect.

We loved the Cruze. Is yours a Gen 1 or 2 (2017+). 50+ MPG was a cake walk. Got over 60 at times (and 70 more than once) in the spring/fall. Just racked up too many miles too quick. New(er) car going at near twice the rate, but will probably keep it a bit longer. These things are getting too expensive to flip every couple years!

[BrentN]

I replaced the cap this morning...Proof will be in the pudding if it resolves it. Curious, the old cap and the new cap will allow air to be sucked through them, so I am not too optimistic that it will be resolved, but at least one more item checked off the list.

My 2014 Cruze is the 2.0, Not sure the Generation. It had a bit of turbo lag when I got it, a bit of hesistancy off the line, that unsure feeling if it was going to actually take off. The Kerma TDI Cruze Tune I got for it did wonders. Its the one that adds 35hp and 75lbs torque, it isnt the hottest tune, just perfect if you ask me.

In my current job I am putting on about 200 miles a day. It does seem to run about 10mpg lower in the morning when its cold, but the afternoon it really picks up. Seems to be more temperature sensitive than my 2011 Jetta TDI.

Its got 78k on it now. Going into GM monday for the 2nd level recall for Nox sensors. Had to return it to stock tune then will put back.

Thanks for everything.

I will let you know how it goes.

Brent

[Robyn]

When was the last time the injectors were serviced ????

Any codes showing ???

I agree with Maverick on the simple things first.


A flaky injector can cause issues.

The smokey start up is suspect.

Poor pop pressure on injectors and worn out nozzles can be a cause.

Normally on an OBD2 TRUCK a dropped cylinder will set a code...butttttttttttt you can't count on it.