Engine stumbles, unstable idle after WARM start-up

E

edwinn

97 Riviera owner
Joined
Jun 11, 2012
1997 Riviera - 3.8 Liter, L36 - 139,795 miles

I'm posting this question in TB because the problem hasn't been solved in other Buick forums. When starting a WARM engine (3800 Series II) the idle is unstable, rough and stumbles for 3 to 5 seconds, then smooths out. It runs GREAT otherwise and idles just fine at stop lights. Cold starts are no problem. The warm idle issue started this summer in June or July. I had the engine checked by GM Techs recently, and they reported low initial fuel pressure of 28 PSI (when it should be 48 to 55 PSI) then rising to normal. What is the likely cause? and how to remedy?

Thanks,

-Ed
 
Sounds like a leaky injector that dribbles after shutting it off. Does it blow black smoke when it clears it's throat?
 
earlbrown said:
Sounds like a leaky injector that dribbles after shutting it off. Does it blow black smoke when it clears it's throat?
Click to expand...

I don't think there's any smoke. You mean out the exhaust? I'll have to get someone to start it and look. All of this happens without touching the accelerator pedal. It just starts to an unstable idle, stumbling for several seconds, then smooths out. There's a smell of fuel from the left rear wheel well (not filler cap area) in the garage now and then. That's another symptom.

-Ed
 
Why I always run a section of clear vacuum line on my FPR

You may also want to look at this

 
Heisenberg said:
Why I always run a section of clear vacuum line on my FPR

You may also want to look at this: [media]Testing for a leaking, ruptured, fuel pressure regulator diaphragm[/media]
Click to expand...


Wow.. that's a great reply!

Here's my FPR, vac and fuel lines. It's pretty clean for a 97 w/140k.

Fuel_Vac_Reg.jpg



The topic is also posted in AF where one of the buds suggested to 'pull the Vac line and check if you smell fuel from the regulator port' but I didn't smell any fuel. The Buick Techs would have likely done that test.. yes?

Here's the discussion: (moderator.. I'm new so if this isn't kool, please don't beat me up)

http://www.automotiveforums.com/vbulletin/showthread.php?t=1090506


-Ed
 
Unplug injectors one at a time as the car idles. The car will run worse when pulling injectors that are functioning. When you pull one that is not working the car will continue its same behavior,rough idle etc. Then you have found your bad injector.
 
edwinn said:
Wow.. that's a great reply!

Here's my FPR, vac and fuel lines. It's pretty clean for a 97 w/140k.

The topic is also posted in AF where one of the buds suggested to 'pull the Vac line and check if you smell fuel from the regulator port' but I didn't smell any fuel. The Buick Techs would have likely done that test.. yes?

Here's the discussion: (moderator.. I'm new so if this isn't kool, please don't beat me up)

http://www.automotiveforums.com/vbulletin/showthread.php?t=1090506


-Ed
Click to expand...


Well - first of all - yes - clean engine for a 98 model.
You could eat off mine and I still found and occasionally find "issues"; i.e. leaking this or that, yada yada yada
So, we all know that clean does always not equal a functioning part.

Alot of the symptoms you are reporting on that AF forum still point me towards a FPR.
Techs checked - maybe so. Maybe not so.
Test it yourself - like in the video.
Don't simply trust your sense of smell.
Remember, ScannerDanner said you have to be patient with that test.

I'm not familiar with that ScanTool that ScannerDanner uses in that YouTube vid - but it looks like it tells alot.
He has another video where he explains fuel trim.
Also - You can pick up a FP gauge kit at Horrible Freight for like less than 20 bucks.
This will tell you alot.

For grins - I would hit the boneyard and find me a similar - FPR - just to try. I bet they charge you 5 bucks.
I'm sure they are full of late model GM w/ 3800 Gen II motors - and there are probably tons of donor equivalents cross over models.

I for one am not leaning towards not enough gas, i.e. bad injector, but leaning towards too much or too little gas at certain times - i.e. bad FPR.
Just a gut feeling
 
Actually - we have a forum for 3800 Gen II L67 Tech - so Charlie may move this over there.
Even though you are not L67.
But those guys know your 3800 Gen II motor better.

Are you L36 or L67?
 
That a clean Riv though.

I like.
Riv's never get their due.

That is the model Buick should really bring back.
All that smack talk about new GN's and GNX and they should really appeal to their base by bringing a state of the art Riv back.
Mark Reuss and his GN chair fetish. :confused:
 
Ed is heck with those arrows - but it's kinda cool.
He don't play when it comes to posting pictures! :D
 
I'm out. I ask pertinent questions trying to help people diagnose problems and get stupid answers.



Here's a hint though.... If you have a fuel smell next to a tire and there's an exhaust pipe next to that same tire, there's a chance the fuel smell is unburnt fuel fumes coming out of the damn exhaust pipe.
 
Ahhh..c'mon Earl.
I'll let you ask me some questions - and I might even give you some serious answers.
Don't go so soon - your plate is still full! :D

Oh heck - bounce over to that thread where we are screaming at the knucklehead from Canada who insists on paying 8 grand for 85 HA WH1 in primer.
That one is fun.
 
[quote="I'm out. I ask pertinent questions trying to help people diagnose problems and get stupid answers."
I noticed after a few bourbons.......stupid answers.......sound less stupid! o_O
Click to expand...
 
Heisenberg said:
Actually - we have a forum for 3800 Gen II L67 Tech - so Charlie may move this over there.
Even though you are not L67. But those guys know your 3800 Gen II motor better. Are you L36 or L67?
Click to expand...

Yeah I'm really new here and unfamiliar with the forums.
The discussion thread was already moved from ET to GTBT.

It's L36, see in orig post "97 Riviera - 139,795 miles - NS" or non supercharged.

BTW i have the 3-Vol set of GM service manuals, but there's nothing like discussion with experienced people.

-Ed
 
earlbrown said:
I'm out. I ask pertinent questions trying to help people diagnose problems and get stupid answers. Here's a hint though.... If you have a fuel smell next to a tire and there's an exhaust pipe next to that same tire, there's a chance the fuel smell is unburnt fuel fumes coming out of the damn exhaust pipe.
Click to expand...

How hold it Earl, let's not get frustrated. :cool: I see you've posted a LOT of stuff, and I did take seriously the 'black smoke' but I don't think smoke has EVER come out the exhaust of the Riv, but took an action item. How would one check for a dribbling injector (presumed into the cylinder?) I did replace #3 injector plug after a mouse got in there a chewed the wires.

You can smell fuel AFTER driving the car and pulling it into the garage, that is with fully warm engine and open garage door. One time after a fill-up (really topped-off) Carol and i smelled raw fuel VERY strongly that evening in the garage. The plan was to leave on a trip at 6:00 the next morning. The fuel smell is there after 'just driving around' and without putting fuel in the tank. I've haven't noticed it prior to March or April of 2013. There was a good amount of rear body, wheel-well, and undercoating work done to the car last year.

-Ed
 
I noticed after a few bourbons.......stupid answers.......sound less stupid!
Click to expand...
Lol.. Carol and I will go out shopping this weekend. Yeah if you go into a grocery store for a half dozen items, then come out and start it, THAT'S when the idle gets rough.. only for a ~5 sec but it sucks! Just going into the package store for a six-pack.. is enough time for a 'rough idle' restart. :)

-Ed
 
edwinn said:
Lol.. Carol and I will go out shopping this weekend. Yeah if you go into a grocery store for a half dozen items, then come out and start it, THAT'S when the idle gets rough.. only for a ~5 sec but it sucks! Just going into the package store for a six-pack.. is enough time for a 'rough idle' restart. :)

-Ed
Click to expand...

Still kind of think that is the classic symptom of the FPR leaking.
Although smelling fuel...hmmmm..not sure about where the vapors are escaping..but somewhere - right?..
 
edwinn said:
How hold it Earl, let's not get frustrated. :cool: I see you've posted a LOT of stuff, and I did take seriously the 'black smoke' but I don't think smoke has EVER come out the exhaust of the Riv, but took an action item. How would one check for a dribbling injector (presumed into the cylinder?) I did replace #3 injector plug after a mouse got in there a chewed the wires.

You can smell fuel AFTER driving the car and pulling it into the garage, that is with fully warm engine and open garage door. One time after a fill-up (really topped-off) Carol and i smelled raw fuel VERY strongly that evening in the garage. The plan was to leave on a trip at 6:00 the next morning. The fuel smell is there after 'just driving around' and without putting fuel in the tank. I've haven't noticed it prior to March or April of 2013. There was a good amount of rear body, wheel-well, and undercoating work done to the car last year.

-Ed
Click to expand...


That also kind of makes me consider the fuel vapor cannister...on your car - no idea where it would be.
 
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