Suburban help

Please change the fuel filter!

---

Owner, Driver, Head Mechanic, and Janitor at Tower City Race Team, headquartered near L'Anse. Michigan.
Driver / CoDriver in Rally America, NASARallySport, ARA, AMS, UPMDA, Champ Off Road

https://www.facebook.com/TowerCityRaceTeam/
https://www.instagram.com/towercityraceteam/

It's already changed. About a month ago.

---

Francois

It may not ever show misfire codes until you do a crank position sensor relearn. Some GMs you need to do a crank relearn after you clear the check engine light.

It's fun! You get your scantool in the car, set up the procedure, then floor the throttle until it hits the rev limiter and then let off.

Sounds fun! But since it won't go pass 3k rpm floored it will be even funnier!

Well maybe that's why it won't go pass 3k?

I think I should buy my own scan tool I've been borrowing my friends ones too much recently. That's a good enough reason to buy a new tool me think!

---

Francois

Finally had time to hook up the vacuum gauge.

At idle, it reads a stable 17 in/hg, but the gauge is quite close to 1 psi when everything is off, so it might be 18 in/hg really. I rev it to 3000 rpms with about half throttle, it goes to around 20-22. I floor it, it gets to 0 as soon as the engine starts acting. But I guess since the engine is almost dying it makes sens.

Does that mean I don't have any restrictions?

At least I think we can clear the low compression or chipped valve options! If I can clear the clogged cat options, well then I don't have any idea what I could do next except a crank relearn and to change once again the fuel filter. Maybe I got a bad new one.

---

Francois

check the fuel pressure. Stop wasting your time changing parts and speculating, and test the basics. To run correctly it needs:
Compression, Ignition at the correct time, the proper amount of fuel, and the ability to exhaust the spent gasses.

You have stated that it does not run under heavy throttle or load. I would check in the following order:

FUEL PRESSURE! checked under load. You are describing a low fuel VOLUME problem to the T. The pump volume is enough to maintain pressure at idle and light load, but not enough volume to sustain pressure under high demand

Secondary ignition after the cap (those silly GM caps that put the wires on the correct side of the motor are notorious for crossfire) The spark will seek the path of least resistance, when the cylinder pressure rises, it will then seek its path to ground elsewhere if it can, causing the failure you describe.

Restricted exhaust, caused by the initial misfire damaging the cats.

BTW, I am the lead and driveability tech in a 10 bay shop, for the last 15 years it is all I have done. Please check the fuel pressure and report back.

^^^ That.

Quote
phlat65
Secondary ignition after the cap (those silly GM caps that put the wires on the correct side of the motor are notorious for crossfire) The spark will seek the path of least resistance, when the cylinder pressure rises, it will then seek its path to ground elsewhere if it can, causing the failure you describe.

Not going to happen on a 5.3.

I'd be dismayed if fuel pressure wasn't checked by one of the prior people to look at it. Not shocked, just dismayed. Like we say, it's not about finding out what it is, it's about finding out what it isn't.

And yes! It needs to be checked under load! Tape the gauge to the windshield and go for a drive. I had a box van recently that idled and drove around town great but wouldn't go over 50mph, just sputtered and stumbled. Fuel pressure was dropping to 20psi! (This on one of those bastard CFI fuel spider things that need 55-60psi to function at all) As it turned out, there was what appeared to be concentrated drywall rolling around in the bottom of the fuel tank, which ate its way through the sock and wore the pump vanes out. Weird one, because fuel pumps generally fail electrically, not mechanically, and they're all-or-nothing. (And it turned out the guy was driving around without a fuel cap for a month after he lost the old one, and the weird green limestone in the tank was dusty crap from the box van's side panels falling into the open filler... But he was able to put off buying a $5 cap for a whole month!)

Also, please do not mess with the MAF connector more than necessary... MAF terminal failures are depressingly common on modern GMs, for some reason they made them out of freeze-dried crackers or something. It's very, very easy to introduce a new problem by messing with connectors/randomly swapping parts out. This isn't an 80's German car with monstrously tough terminals! I think the terminals are only rated for four connections, but we've seen plenty "virgin" terminals fail.



Edited 1 time(s). Last edit at 11/06/2011 10:54AM by Pete.

Quote
Pete

Quote
phlat65
Secondary ignition after the cap (those silly GM caps that put the wires on the correct side of the motor are notorious for crossfire) The spark will seek the path of least resistance, when the cylinder pressure rises, it will then seek its path to ground elsewhere if it can, causing the failure you describe.

Not going to happen on a 5.3.

I'd be dismayed if fuel pressure wasn't checked by one of the prior people to look at it. Not shocked, just dismayed. Like we say, it's not about finding out what it is, it's about finding out what it isn't.

And yes! It needs to be checked under load! Tape the gauge to the windshield and go for a drive. I had a box van recently that idled and drove around town great but wouldn't go over 50mph, just sputtered and stumbled. Fuel pressure was dropping to 20psi! (This on one of those bastard CFI fuel spider things that need 55-60psi to function at all) As it turned out, there was what appeared to be concentrated drywall rolling around in the bottom of the fuel tank, which ate its way through the sock and wore the pump vanes out. Weird one, because fuel pumps generally fail electrically, not mechanically, and they're all-or-nothing. (And it turned out the guy was driving around without a fuel cap for a month after he lost the old one, and the weird green limestone in the tank was dusty crap from the box van's side panels falling into the open filler... But he was able to put off buying a $5 cap for a whole month!)

Also, please do not mess with the MAF connector more than necessary... MAF terminal failures are depressingly common on modern GMs, for some reason they made them out of freeze-dried crackers or something. It's very, very easy to introduce a new problem by messing with connectors/randomly swapping parts out. This isn't an 80's German car with monstrously tough terminals! I think the terminals are only rated for four connections, but we've seen plenty "virgin" terminals fail.

Teee heee!
Hey I's the cheapest bastid in rally. When I've had a cap go missing just pop into a big gas station and ask ''Yo! Adrian, youse guys see'd a gas cap?''
Works good, costs nuthin'

And man I'm glad I don't fawk with modern 'merikanskij crap.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Fuel pressure was tested twice, but I have to say I have no more faith in these 2 tests. One was done when the issue first happened. At that time the only way to replicate it was while towing, going highway speed and adding some load (passing or going up an hill). But according to that guy, the pressure was dropping to 0 (yeah zero!) at idle, even though it doesn't even miss a beat at idle... I think no fuel at all at idle would cause some kind of problem.

Then other one, it's my old italian part changer (I'm not gonna call him a mechanic anymore since he's not good at all to do a simple diagnostic. That's related to this truck and a coworkers one where he changed multiple parts before finally finding the problem). But I'm quite sure he didn't test it under load.

I'm gonna buy a fuel pressure gauge and see for myself. I was supposed to do it today but I had to work 12 hours, from 9 to 9. It's not that expensive and will be useful.

Pete, what happened to that van is almost what's going on with the truck. Around town it's fine, it even gets to 75, but you have to do so very gently. Give it too much gaz and it will run like shit. I never ran my truck without a gaz cap, but who knows if the previous owner did. I know that the plastic strap that ties it to the truck is broken. Maybe that's where everything started.

And I'm right at 3 connections with my maf right now. once to clean it, another time to test how it would run without it and one last time to try the other one. Well that makes it 3 on the maf and 4 on the truck side since I re-installed mine after. I'll stop messing with it right now!!!

thanks for the help!

---

Francois

BTW, most modern cars will run fine with the maf unplugged, that is a pretty good test.

fuel filter.... yours has a very simple plastic connector on one end, the other end threads on/off... rock auto lists a FRAM G8219 for less than $10. go swap out the inline filter already !!

Like I said, it was already changed about a month ago...

But I'll change it again if the fuel pressure is not were it should once I test it.

I know they don't last, but they should still last more than a month and less than 500 miles. But maybe it was defective new.

---

Francois

Quote
Francois
Like I said, it was already changed about a month ago...

But I'll change it again if the fuel pressure is not were it should once I test it.

I know they don't last, but they should still last more than a month and less than 500 miles. But maybe it was defective new.

Maybe there is so much crud in the tank it's clogging the filter almost immediately.

Quote
fiasco

Quote
Francois
Like I said, it was already changed about a month ago...

But I'll change it again if the fuel pressure is not were it should once I test it.

I know they don't last, but they should still last more than a month and less than 500 miles. But maybe it was defective new.

Maybe there is so much crud in the tank it's clogging the filter almost immediately.

I've seen that often enough.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.