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Old 07-06-2011, 10:11 PM   #1
mears
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Default Vacuum leak at fuel injector

This is a continuation of my ongoing saga with my 2000 Malibu: http://www.garagejournal.com/forum/s...5056&showall=1

To briefly recap, I replaced the lower intake manifold gasket to address yet another coolant leak (previous fix was performed by a shop). After I got it put back together, I quickly discovered that it idled roughly and was throwing a P0300 (random cylinder misfire). Using a can of carb cleaner I did detect a vacuum leak around near the rear of the upper intake manifold on the passenger side.

Per recommendations on the forum, I decided to build the following smoke machine: http://www.garagejournal.com/forum/s...ad.php?t=91216

I got busy at work and put this on the backburner until I received my yearly registration bill and discovered that it was due for emissions. In its great wisdom, Colorado will not grant an emissions waiver or extension for a disabled vehicle even though two other vehicles are registered in my name. So now I’m back to tinkering with this thing to avoid fees.

I attempted to use the DIY smoke machine, and like some others, I ran into an issue with it spitting liquid. After getting comfortable with the amount of liquid it was spewing, I hooked it up, but couldn’t identify smoke escaping anywhere. I figured that since I was already pumping air in the vacuum system I might as well try the tried and true method of using soapy water. I quickly discovered that the source of the leak wasn’t the upper intake manifold gasket but the bottom of a fuel injector where it plugs into the upper intake. Oddly, I didn’t even remove the fuel rail when I performed the repair, so I was somewhat surprised by this development. The only thing I can think of is maybe some solvent got in there and ate away at a seal.

I imagine this is probably the root cause for my P0300. I’m far from a mechanic, but working at it, so I’m wondering what my next step should be. At a minimum, I’ll need to pop off the fuel rail and injectors and replace the o-rings. Should I also order a new injector or injectors?

Last edited by mears; 07-06-2011 at 11:31 PM. Reason: Englishes
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Old 07-06-2011, 10:33 PM   #2
DoyleDee
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Default Re: Vacuum leak at fuel injector

I wouldn't order new injectors unless it was running like complete crap getting too much gas. I don't know your financial affairs either...but, if it was me I wouldn't. Just replace the o rings and try it again after you cleared codes.
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Old 07-06-2011, 11:12 PM   #3
MechanicNamedJohn
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Default Re: Vacuum leak at fuel injector

Replace the o rings.
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Old 07-06-2011, 11:23 PM   #4
srmofo
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Default Re: Vacuum leak at fuel injector

just get orings but something to think about

typically a vacuum leak at the injector is only going to cause a misfire on one cylinder. all the extra air is only going into the one cylinder is why. Unless its severe enough to carry the misfire counts on to the next cylinder(s)
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Old 07-06-2011, 11:35 PM   #5
mears
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Default Re: Vacuum leak at fuel injector

Quote:
Originally Posted by srmofo View Post
just get orings but something to think about

typically a vacuum leak at the injector is only going to cause a misfire on one cylinder. all the extra air is only going into the one cylinder is why. Unless its severe enough to carry the misfire counts on to the next cylinder(s)
Damn, that makes too much sense Although, the leak was bad enough to cause hissing when pressurized at 15 PSI and carb cleaner did kill the engine when I sprayed it back there.
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Old 07-07-2011, 12:07 AM   #6
Lotek
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Default Re: Vacuum leak at fuel injector

Pull all the injectors as an assembly and replace just the lower orings, unless you have a fuel leak leave the upper ones alone. Before removing the rail blow the dirt out of the injector holes after covering the intake passages. Coat the orings with Vaseline to ease the installation. P0300 doesn't always mean random misfire, depending on the ecm software, a single cyl misfire will throw a p0300 instead of a p0302 to indicate the cylinder. You are almost there.
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Another example of when God turns to Darwin and says "I thought you were going to fix this s@#t".

"You keep using that word. I do not think it means what you think it means. "

"I have a hammer! I can put things together! I can knock things apart! I can alter my environment at will and make an incredible din all the while! Ah, it's great to be male!" -Calvin
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Old 07-07-2011, 12:40 AM   #7
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Default Re: Vacuum leak at fuel injector

I'm a bit late to the party, but....

A P0300 is a random misfire, which is something affecting all 6 cylinders pretty much equally. A look at your first thread shows that I missed this:

Quote:
Originally Posted by mears View Post
Plugs were all installed and I did double check that the connectors were tight. I'm sure this will invoke some groans, but I didn't need to gap since I'm using Bosch platinum plugs.
Bosch plugs often don't get along with GM ignition systems. I'd start by replacing those with a set of OE plugs (AC Delco 41-940). Check the plugs to make sure the gap looks equal on all the plugs, but don't gap the plugs or use a feeler gauge to check (you risk damaging them). I'd also replace the lower injector o-rings (pull the rail and leave the injectors installed), and don't forget to lube them up before re-installing the fuel rail.

If that doesn't help, I'd move on to checking out fuel pressure to make sure it's within specs, and taking a closer look at the ignition module/coils especially if it's starting to get up there in mileage.
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Old 07-07-2011, 07:11 AM   #8
nato
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Default Re: Vacuum leak at fuel injector

Not to hijack, but I find this interesting and i don't have enough "real life" info to find my answer yet, but...why as of seemingly recently, do most negative ignition symptoms seemed to be cured by OEM installed spark plugs?
I remember a few weeks ago, we had a '04 Chrysler Sebring come through our shop w/ a P0300 and also a specfiic code fault for one of the of the primary ignition coil circuits(can't remember the exact DTC# but it was pretty much like a 1-4/2-3 firing config.), anyhow....e replaced the coilpack and also r&r'd his OEM plugs w/ Autolite single platinums (our staple spark plug as long as most vehciles don't call for a double, triple or iridium plug).
It was fine for one week then came back, same multiple misfire, same ign. coil fault code. Wires were fine, they ohmed out alright, checked all four towers/cylinder outputs with an inline spark tester, all consistent and then stress tested the coilpack again---nothing found

My boss then decided. based on another situation that has been cured by OEM plugs, to remove the autloites and install manufacter-recommended OEM plugs (forget what they were, maybe Denso's?????????)

Problem solved....
WTF?!
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Old 07-07-2011, 07:35 AM   #9
Lotek
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Default Re: Vacuum leak at fuel injector

Quote:
Originally Posted by nato View Post
Not to hijack, but I find this interesting and i don't have enough "real life" info to find my answer yet, but...why as of seemingly recently, do most negative ignition symptoms seemed to be cured by OEM installed spark plugs?
I remember a few weeks ago, we had a '04 Chrysler Sebring come through our shop w/ a P0300 and also a specfiic code fault for one of the of the primary ignition coil circuits(can't remember the exact DTC# but it was pretty much like a 1-4/2-3 firing config.), anyhow....e replaced the coilpack and also r&r'd his OEM plugs w/ Autolite single platinums (our staple spark plug as long as most vehciles don't call for a double, triple or iridium plug).
It was fine for one week then came back, same multiple misfire, same ign. coil fault code. Wires were fine, they ohmed out alright, checked all four towers/cylinder outputs with an inline spark tester, all consistent and then stress tested the coilpack again---nothing found

My boss then decided. based on another situation that has been cured by OEM plugs, to remove the autloites and install manufacter-recommended OEM plugs (forget what they were, maybe Denso's?????????)

Problem solved....
WTF?!
I've been seeing this since the 90's, Mazda wanted to race the 323 in the Champion Sparkplug series, they shipped some cars with Champions to dealers to qualify. Started to see random ign misfires under load. The fix was to replace the Champions with the factory replacement NGK plugs. GM's don't like Bosche or gimmick plugs like splitfires, either AC or ND work, whichever the OEM used.
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Another example of when God turns to Darwin and says "I thought you were going to fix this s@#t".

"You keep using that word. I do not think it means what you think it means. "

"I have a hammer! I can put things together! I can knock things apart! I can alter my environment at will and make an incredible din all the while! Ah, it's great to be male!" -Calvin
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