Fuel System Issues?

[Riff Raff]

I'm wondering if it could be more related to voltage/spark/electrical problems, and not related to fuel issues??? Hope you find the gremlin(s).

[Dmitrikr]

Have them clean the MAF as well. Those symptoms were very similar to some problems I had when I first got mine (including running better with a full tank).

got four Isuzus last year in the shop with codes for both O2 sensors. But the problems were - MAF sensors on two; on other two-someone forgot to tight the clamp at air intake hose to plenum - created air leak not counted by MAF sensor

[vxcp]

I'm wondering if it could be more related to voltage/spark/electrical problems, and not related to fuel issues??? Hope you find the gremlin(s).

Will keep my eyes open -- known problem areas? Thanks.

got four Isuzus last year in the shop with codes for both O2 sensors. But the problems were - MAF sensors on two; on other two-someone forgot to tight the clamp at air intake hose to plenum - created air leak not counted by MAF sensor

Interesting. I did notice that a hose clamp was loose (now tightened) near the engine when cleaning the MAF today.

[Bob Barker]

It makes sense that if you were gaining air after the MAF it could take time to set off a code from the O2 sensor reading a "lean" (very dangerous) burn in the exhaust after an amount of driving. The car is adding a set amount of fuel to be burned with an expected amount of air that is actually greater than expected.

Did you have a chance to drive around with the air leak fixed yet?

[vxcp]

Did you have a chance to drive around with the air leak fixed yet?

Yes, I've driven it some and its running well. Really need to go on a one to two hour drive though. Hopefully I'll get a chance to do that later this week. Maybe I'll change the FPR first too.

[vxcp]

After cleaning the MAF sensor, tightening a hose clamp, and driving the vx around for a few days the bucking has returned. Guess I will be replacing the FPR next.

[samneil2000]

After cleaning the MAF sensor, tightening a hose clamp, and driving the vx around for a few days the bucking has returned. Guess I will be replacing the FPR next.

Sorry you're having so much trouble. I hope the fpr is your problem. Make sure you have or make the short allen wrench. It makes the job way easier. More or less impossible without it...

[Y33TREKker]

Something else occurred to me given the fact that the symptoms seem to reappear after you've been driving for awhile, and that is whether your u-joints could be involved. I don't know how likely that is, because as much driving as you've done while the problem has been happening, you'd think that if a u-joint was seizing due to lack of lubrication, it would have just totally let go and broken by now, but then again, they're built solidly for a reason so...???

Easy enough to stick some grease in them anyway, and unless everythings' been lubed in the last few months, it probably wouldn't hurt regardless.

Sounds like quite a few possible culprits have been eliminated though, so with a little more patience, it surely won't be that much longer before you get it figured out.

[Dmitrikr]

After cleaning the MAF sensor, tightening a hose clamp, and driving the vx around for a few days the bucking has returned. Guess I will be replacing the FPR next.

try to calculate the air volumetric efficiency before changing anything.
at least you can eliminate MAF, air leak, cat converter clogged problems.


explanation how to calculate efficiency

[Bob Barker]

What about the fuel cap? Is it gone bad? Mom had a bad fuel cap that would cause her driving issues in some other vehicle when I was younger.

[vxcp]

And the winner is the Fuel Pressure Regulator! Thanks for the help everyone! No more bucking.

[Bob Barker]

Yaaayyy for solutions!!!!

[vxcp]

Got this followup question recently:

Just curious, did swapping the FPR fix your gauge needle jumping around?

Heres my reply:

Nope that required changing out the in dash fuel and temp gauge unit ( p/n 8972114670 as seen here http://www.catcar.info/isuzu/?st=50&...fHxuaT09MDI%3D ). Took a few months to get the part in and think it had a $200 or so cost. I've seen on the forum that sometimes tightening a screw for the gauge behind the dash can fix the jumping needle.

You could also have a bad sending unit, but I had to get a new fuel pump and sending unit too, and those didn't fix my bouncing fuel gauge.

[djmdma02]

Got this followup question recently:

Just curious, did swapping the FPR fix your gauge needle jumping around?

Heres my reply:

Nope that required changing out the in dash fuel and temp gauge unit ( p/n 8972114670 as seen here http://www.catcar.info/isuzu/?st=50&...fHxuaT09MDI%3D ). Took a few months to get the part in and think it had a $200 or so cost. I've seen on the forum that sometimes tightening a screw for the gauge behind the dash can fix the jumping needle.

You could also have a bad sending unit, but I had to get a new fuel pump and sending unit too, and those didn't fix my bouncing fuel gauge.

Just my two cents... My fuel gauge is never right on (except at full) and I have no other problems (except a check engine light for the gas cap).

[vxcp]

Tonight my low fuel light came on. After driving 5-10 more miles, a light bucking returned for the first time since 2011. Filling up the gas tank fixed things right up. I only had to put 20.5 gallons into the VX, so presumably I had 2 gallons of gas still in the tank. I'm wondering if perhaps my fuel pressure isn't quite right. Is there an adjustment for our FPRs?