BrandonDrecksage

iTrader: (1)

I have a 01 denali. One day on the highway, it just shutoff. I started diagnosing and discovered that the manifold gaskets were shot. I replaced them with the quality metal gaskets. Car will start now, but my fuel trims are crazy. Both short term fuel trims are in the high teens idling. The long term were already pegged at 25%. I figured that meant i still had some leaks.

I them made a smoke tester out of a pump from harbor freight and a cigar, hooked it to the intake manifold. I discovered 2 more leaks. One from the egr and one from a line going to the fuel rail. I replaced the line and blocked off the egr. I then ran the smoke tester again and no other smoke came out from anywhere.

After this, my short term fuel trims both sides are in the mid teens and the long term is still pegged at 25%. I can drive it and the short term goes up in the high 30s. Around 1500rpms i can hear a whistle.

Is there any other line i should be checking? Intake manifold bolts are tight. I checked the pcv and the line going to the brake booster. What else can i check? Im not throwing any check engine lights, except the egr. I also cleaned the original maf and the replaced it.

Thanks

RB04Av

What is the fuel pressure?

BrandonDrecksage

iTrader: (1)

havent checked that. Low fuel pressure can cause messed up fuel trims?

RB04Av

Of course... if the wrong amount of fuel gets injected for whatever reason, the ECM will try to compensate for it by adjusting the duty cycle away from "normal".

Ls7colorado

iTrader: (3)

Sounds like low fuel pressure for sure, especially since it just shut off while driving one day.

BrandonDrecksage

iTrader: (1)

wouldnt low fuel pressure cause the opposite issue and have negative fuel trims?

It shut off because the intake manifold gasket gave out causing a huge vacuum leak. The car wouldnt run at all until i replaced that gasket.

Ls7colorado

iTrader: (3)

I've never, ever, seen a intake gasket give out and cause the engine to not run at all. Maybe a very very high idle but never cause it to shut off. Maybe something new I just haven't ran into yet, but that seems like it would have to have been a progressive condition that has slowly been getting worse for years.
Or someone loosened all your intake manifold bolts? lol

Low fuel pressure would cause a lean condition.

RB04Av

Positive fuel trim = the ECM is trying to add more fuel than it's programmed for at the factory; IOW trying to compensate for a lean condition

Never heard of an intake gasket causing a die-while-driving. Ever. Not any kind of motor. Now please note, I am NOT saying "your intake gaskets were fine", NOT saying "put your old ones back", NOT saying "intake gaskets don't matter", NOT NOT NOT NOT NOT NOT NOT NOT NOT. Only, that intake gaskets don't cause the situation you found yourself in. Which is to say, no matter what you found out about them or did to them, the underlying problem is still in effect.

More likely, your fuel pump died as you were driving down the road, and the fuel trims couldn't adjust rapidly enough. THAT will make a motor die while driving.

Check your fuel pressure.

BrandonDrecksage

iTrader: (1)

Im going to check it tomorrow. The gaskets were below the plastic that was holding them providing no seal. I also had 2 more vacuum leaks on top of that. My guess is all that unmetered air is what shut the engine down. Also, this happened 2 months ago and i still drive the truck everyday about 10miles without much issue other than the wacky fuel trims. It idles at 600 and accelerates fine. Im just trying to fix everything so i dont get stranded again.

RB04Av

No, it didn't; at least, not unless you were driving along happily year in and year out and everything was cool, and just all the sudden, all those things failed all at once all at the same time.

Possible: I suppose; LIKELY: not so much.

Check your fuel pressure. Again, NOT saying your intake leaks didn't matter, or whatever else; only, that they did NOT cause a die-while-driving. Die-while-driving is a SINGLE POINT OF FAILURE, some ONE THING that suddenly just decided to retire right then, that's UTTERLY ESSENTIAL to driving. Vacuum leaks … aren't. The vacuum in a truck isn't even all that high while cruising at highway speed anyway, so not much unmetered air would have got sucked in. Run-like-crap, maybe; idle-terrible, ABSOLUTELY; die-when-you-take-your-foot-off-the-gas, FOR SURE; die-while-driving-down-the-HIGHWAY, NO.

Especially not when after you've got it all "fixed", and the CAR ITSELF is telling you by way of wacked fuel trims IT'S STILL BROKEN. It might seem "fixed", because after the pump failed and the ECM had time to adjust itself to its new world order, the fuel trims have all gone as far as they can possibly go to one side, and it's feeding enough fuel that it seems OK; but if it was truly REPAIRED, as opposed to "fixed", the fuel trims would be back to near normal.

Check your fuel pressure. Should be high 50s, like 56 - 59 psi range.

BrandonDrecksage

iTrader: (1)

I understand the car isnt fixed. My point of this thread is exactly that. I also know it dying while driving isnt a single point of failure.

Fuel pressure with the keytin the on position is at 20psi with no bleed off. When i start it, it flutters between 15 and 22psi. Im honestly surprised this doesnt set a check engine light.

Is this a regulator or pump problem? Car always starts super quick. Im going to throw a new fuel filter in.

What are the next diagnosing steps?

Thanks.

Ls7colorado

iTrader: (3)

Probably a bad pump

G Atsma

Check pressure before the regulator.

RB04Av

Yeah most likely a bad pump.

You could try just changing out the regulator if it's only acoupla $$$ but somehow I doubt that's gonna give you much love.

I should also mention, be prepared whenever you DO get it straightened out, it's gonna SERIOUSLY RUN LIKE CRAP for awhile, until the ECM returns the fuel trims to near normal. In the meantime it's gonna DROWN itself in fuel.

And of course, ALWAYS a good idea to replace the fuel filter.

BrandonDrecksage

iTrader: (1)

if i undo the battery for a bit, should it reset all the fuel trims? I already ordered a pump, will start working on it tuesday.

RB04Av

Not sure, you could try it and see. That resets a bunch of stuff but just not sure about the fuel trims.

BrandonDrecksage

iTrader: (1)

Put in a new fuel pump. Had the battery unplugged for a few days. I started it up and it sounds different. I checked the fuel trims.all of them were at zero. Then short term started to go to -2 or -3 both banks. It did that until both long terms were at -8.3. Then the shirt term went to zero. When i rev it, they all go to zero and then return to the -8.3. The rpms would dip to the low 400s and then slowly recover to the high 5s low 6s. Any idea what that could be? Seems odd to me. My egr is blocked off now.

Thanks for the help in pointing me towards the fuel pump.

RB04Av

Sounds like it's MUCH better. FTs near 0 is a very good sign. When they go negative it's because it's rich, so changing the pump DEFINITELY had an effect.

I'd recommend driving it around for awhile, let it relearn itself; then see where it stands.

Is the FP up around 58 or so now?

BrandonDrecksage

iTrader: (1)

the gauge was reading 52. Since the long term ft is still 0, im not concerned about it. Its still going negative at idle to -8, but as soon as I touch the gas, it goes to 0. its still idling funny and low. It stalled out while in a parking lot turn today a few times. Im going to take the throttle body off tomorrow and do a good cleaning. Im guessing it hasnt been touched in a while...if ever and the car has 260k on it.

RB04Av

52 at idle is about right; when at high vacuum, the FP is reduced by the regulator (whether directly mechanical or electronic), such that the pressure differential across the injector stays roughly the same. 58 would be the target with no vacuum. Vac line disconnected if you have one that supports that. Can't recall whether the 01 does or not, I know the later returnless systems you can't quite do that.

Sounds like progress is progressing.

Probably wouldn't hurt to take the injectors out and soak them overnight in lacquer thinner. Take the O-rings off first if you plan to re-use them. Which I wouldn't unless they're near brand-new. If that makes a difference, consider replacing them. Any number of injector service places can either clean & flow-match yours, or supply you a set like that for your trade-ins, or whatever.