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94 GMC Sonoma fuel leak?


lamigra311's Avatar
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03-22-03, 02:15 AM   #1  
94 GMC Sonoma fuel leak?

I have a 1994 Sonoma, 2.2L, 5 speed reg cab, 112K miles. Upon start-up, I experience a rough idle and hesitation under hard acceleration. Under slow, steady acceleration up into higher RPM's the hesitation doesn't occur, somewhat like when an old air-cooled VW is changed from a vacuum distributor to centrifugal. When the engine reaches normal operating temperature, the hesitation disappears.

When I return to the truck after it has been parked, there is a smell of gas inside the cab. Upon looking under the hood, I noticed what appeared to be fuel ever so slowly seeping out of a part located on the top left rear of the engine. The part is about an inch and a half long, silver, somewhat cylindrical. It has a two-wire electrical connection, female, held on by a metal clip, going into it. Also, I can hear the sound of escaping air/fuel pressure at this location for a few minutes after shutting the engine off as I see the small drips of fuel. When the hissing air stops, so does the seepage.

I had a basic tune-up done last summer, which I believe was plugs/wires and applicable idle/timing.

Any idea what might be happening here?


Lamigra311

 
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WeldGod's Avatar
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03-22-03, 02:27 AM   #2  
Sounds like a fuel pressure regulator to me. It seems you have a vacuum/fuel leak there causing your fuel system to not have the correct pressure in it. But first I would try to replace any suspect tubing that could be causing your problem. Go to an auto parts store and ask for a fuel pressure regulator and see if it looks like the part you need. I am pretty sure it is.

 
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03-22-03, 06:01 AM   #3  
Joe_F
Sounds like the fuel injector to me and that the seal is leaking. Replace it immediately. Use clean motor oil on the seals when you install them.

Follow the procedure of the rail R&R in Autolibrary.org

 
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03-22-03, 02:57 PM   #4  
Thanks guys for your quick response.

Weldgod, it wasn't the fuel pressure regulator. I went to the local parts store, where they showed me a regulator specific to my engine. It wasn't the same animal as I was looking at under the hood.

Joe F., it doesn't seem to be the fuel injector(s) either. The entire fuel injection system/assembly does not seem to be leaking fuel.

Perhaps I can describe it a bit better, after a more thorough look at the thing.

It actually seems more like a fitting on the left rear of the valve cover. The two-wire plug that goes into it is oval in shape, about a half-inch wide. On the outside and inside of the connector/plug there is a tri-ribbed sort of gasket, I assume to take care of any seepage. The fitting itself (interior diameter) is not quite as big as my little finger. I removed the electrical connection/plug and can feel/see wetness (gas) on my finger. There are no external fuel lines or any lines going to this fitting. This fitting/doohickie is aft of the entire fuel injection assembly. Just aft of this fitting there is a valve that looks like a bicycle tube valve with a cap on it, just to give you an idea of the location of this thing.

After removing the plug/connector, I started the engine and it would not idle at all, and ran very rough as if starving for fuel. I could barely keep the engine running by careful manipulation of the accelerator. I put my wife behind the wheel to observe the fitting upon turning the ignition to on. I could hear the fuel pump, I believe, activate but saw/felt no seepage from the fitting. I had her crank it for a couple seconds but observed no fuel spitting from the fitting, just wetness upon checking it when she released the key. I haven't yet discovered what the other end of these two wires go to, there's too much extra trash in the way; I guess you darn near need a computer engineering degree or something to even raise the hood anymore. I'm probably in over my head on this one silly item, but I appreciate your comments and suggestions.

On an aside, while at the parts store, I discovered that a PCV actually exists for my engine. The last trip to the jiffy lube with my wife's truck (94 full-size GMC 4.3 Vortec) they replaced the PCV. They actually took the thing out and showed it to me. On all my previous trips to the local jiffy lube type folks, with my truck (2.2 Sonoma) the work order always said PCV was not applicable; however, I have not yet taken my truck to the same people that we took my wife's truck.

Do I actually have a PCV (Positive Crankcase Ventilation) and need to check/replace it? Perhaps another post...

I appreciate all your help, guys.

Neat forums ya'll have here, looking forward to some Q&A on some of the others.


Lamigra311
Detroit, MI

 
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03-22-03, 04:13 PM   #5  
sounds like a fuel injector to me also, there should be 4 of them that clip into your fuel rail the fitting you are describing is likely the fuel pressure test port, if you actually see gas inside the electrical connector portion of the injector you may have a bad injector.
pcv valve on this model is at valve cover underneath plastic hex nut that unthreads from valvecover revealing pcv valve.

 
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03-22-03, 06:02 PM   #6  
AAArgh!! It ain't the injector(s). On the left side of the engine there's this big box sort of thing, with a cable coming from down around the gas pedal, an air intake from the front of the truck, etc. The injectors ain't visible/accessible; there's just four plenums sneaking down to the block from this injector/intake manifold type stuff...

I wish I could access the injectors, but this little fitting is behind the fuel injector assembly/system

 
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03-22-03, 06:47 PM   #7  
have you went to the site below and checked under fuel systems they do show a few pictures and components that might help you determine what exactly is leaking.
http://www.cybrrpartspro.com/Manual%...delLookup.html

 
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03-23-03, 01:53 AM   #8  
It might also be an accelerator cam but itís a long shot. I donít even know if it is visible on your Sonoma but itís worth a shot.

 
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03-23-03, 04:48 PM   #9  
Joe_F
Original poster: You should get a service manual for your vehicle if you are going to do this type of repair. In this way, you can familiarize yourself with everything there.

Hit your dealer's parts counter and they will find the "mystery" piece on the parts computer and identify it for you.

 
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04-28-03, 05:29 PM   #10  
OK, gentlemen-

It was one of the injectors. After mucho procrastination until I got serious under the hood, I found it. The Haynes manual wasn't much help identifying the part, no good pictures of it. I actually went over to my neighbor's house and looked at his Cavalier of the same vintage. His engine is sideways, (mostly the same trash on top) so we could see a lot more, make comparisons, and figure the fool thing out. Got everything unbolted to remove intake plenum, in order to remove fuel rail, to access the injectors. Haven't yet removed rear injector, the one that is leaking under pressure.

My question is-

Could it just be one of the O-rings causing the leak? If so, replace the O-ring on that one for sure, but I should probably replace all O-rings for each injector while I have all the stuff stripped off? (Kind of like plumbing-when you repair the weakest leak with new, the next weak spot blows.) I plan on taking the injector down to local parts store to determine if it is good or not, can I determine upon close inspection after removal if it is good or not? I also suppose that if I replace the one injector, I should replace the other three also? I guess I'm curious if injectors are one of those things that when they go, they just go, throw in a new one. The tear-down was really simple to access the injectors, so if in the future another injector leaks/goes bad, I can get to it pretty easy also.

Thanks guys for your earlier responses, you were right on the money. It just took me a month and a transverse neighbor to put two and two together.


G. Downs
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04-29-03, 06:33 AM   #11  
Joe_F
If the R&R was easy, you might try the seals first and see if that helps your problem. If not, replace the injector.

They aren't that expensive, but if it's not bad, you should be OK.

They can be electrically checked for fault. See autolibrary or a GM service manual (I recommend you buy the latter if you're going to do any work on your vehicle).

 
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