runs rough for few minutes after restarting when hot - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

Reply
 
 
 
Thread Tools Search this Thread
Old 09-26-2007, 12:10 PM   #1
Senior Member
Posts like a Northstar
Thread Starter
 
Join Date: Jan 2002
Location: southern California
Posts: 538
Thanks: 0
Thanked 0 Times in 0 Posts
billha is on a distinguished road
Default runs rough for few minutes after restarting when hot

On my '92 SSE */c, if the engine is warm and I shut off the engine to stop at a store for a few minutes, for example, the engine runs a bit rough for several minutes after I restart it. When it'* running rough, the idle rpms are stable and appear normal, but the boost gage jumps around a little bit more than normal (maybe 3/16" or so as opposed to 1/8" or so normally). After driving for a few minutes, the problem goes away and the boost gage fluctuations return to normal.

There are no error codes, and no other known symptoms.
I haven't used a scan tool to look at the measurements while the problem is occurring, but even if I did, I suspect that I wouldn't see any odd readings.
I doubt that the problem is heat related because it only happens after restarting when the engine is hot; it doesn't happen after starting the engine (cold) and driving while the engine is hot.

I'm wondering if maybe it'* the IAC sensor?

Have any of you encountered this before?
Thanks.
billha is offline   Reply With Quote
Old 09-26-2007, 12:18 PM   #2
Junior Member
Posts like a Ricer Type-R
 
Join Date: Aug 2002
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
willwren is on a distinguished road
Default

Pull the vac line off the FPR and smell it for fuel. Pooled fuel in the LIM can cause your symptoms.

A leaky injector can do the same. Does it hold fuel pressure after shutdown?

EGR leaks can change with tempurature as the metal expands and contracts.
willwren is offline   Reply With Quote
Old 09-26-2007, 12:25 PM   #3
Senior Member
Posts like a Northstar
Thread Starter
 
Join Date: Jan 2002
Location: southern California
Posts: 538
Thanks: 0
Thanked 0 Times in 0 Posts
billha is on a distinguished road
Default

Quote:
Originally Posted by willwren
Pull the vac line off the FPR and smell it for fuel. Pooled fuel in the LIM can cause your symptoms.
A leaky injector can do the same. Does it hold fuel pressure after shutdown?
EGR leaks can change with tempurature as the metal expands and contracts.
I checked the FPR several months ago, but I'll check it again.
Roughly how long after shutdown should it hold pressure? About a year ago, I replaced all fuel injectors with a used set that had 30,000 miles on them. Does a leaky injector take several minutes to builup normal pressure again?
I know that there are a couple of cracks in the exhaust manifolds (they've been there since I bought this car in 1999, but this problem just began a few months ago).
billha is offline   Reply With Quote
Old 09-26-2007, 01:55 PM   #4
Junior Member
Posts like a Ricer Type-R
 
Join Date: Aug 2002
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
willwren is on a distinguished road
Default

Building pressure is of no consequence. A leaky injector will have you running overly rich on startup.

It should hold at least 50% of initial pressure for the first 10-30 minutes after shutdown. Longer is greatly preferred. If it leaks down quicker than that, it could be a leaky injector or FPR.

The age or mileage on your injectors is also incosequential. How long they SAT before re-use is a major concern.
willwren is offline   Reply With Quote
Old 09-26-2007, 02:14 PM   #5
DINOSAURUS BOOSTUS

Expert Gearhead
 
BillBoost37's Avatar
 
Join Date: Mar 2005
Location: Enfield, CT
Posts: 41,391
Thanks: 0
Thanked 0 Times in 0 Posts
BillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of lightBillBoost37 is a glorious beacon of light
Default

The 97 FSM says they should hold all the pressure for at least 10 minutes. Not sure if your year is the same. At 50% pressure though...you are leaking down somewhere.
BillBoost37 is offline   Reply With Quote
Old 09-27-2007, 11:55 AM   #6
Senior Member
Posts like a Northstar
Thread Starter
 
Join Date: Jan 2002
Location: southern California
Posts: 538
Thanks: 0
Thanked 0 Times in 0 Posts
billha is on a distinguished road
Default

I pulled the vacuum line from the FPR and didn't see or smell any fuel.
The fuel rail held pressure for 10 minutes after the engine was turned off.
What should be checked next?
billha is offline   Reply With Quote
Old 09-27-2007, 12:19 PM   #7
Junior Member
Posts like a Ricer Type-R
 
Join Date: Aug 2002
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
willwren is on a distinguished road
Default

What is your fuel pressure peaking at?

When was the last time you cleaned the TB?

What is your fuel pressure when you get the hard-start condition?
willwren is offline   Reply With Quote
Old 09-27-2007, 12:26 PM   #8
Senior Member
Posts like a Northstar
Thread Starter
 
Join Date: Jan 2002
Location: southern California
Posts: 538
Thanks: 0
Thanked 0 Times in 0 Posts
billha is on a distinguished road
Default

Quote:
Originally Posted by willwren
What is your fuel pressure peaking at?
When was the last time you cleaned the TB?
What is your fuel pressure when you get the hard-start condition?
Unfortunately, I didn't use a fuel pressure gage because I don't own one, and I haven't yet done any testing while the problem occurs.
After the engine had been shut off for 10 minutes or so, I pressed the release valve and let the fuel squirt into a rag.
I cleaned the throttle body roughly 10,000 miles ago.
billha is offline   Reply With Quote
Old 09-27-2007, 12:30 PM   #9
Junior Member
Posts like a Ricer Type-R
 
Join Date: Aug 2002
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
willwren is on a distinguished road
Default

We're back to square one. 5psi will squirt fuel into a rag.
willwren is offline   Reply With Quote
Old 09-27-2007, 05:08 PM   #10
Senior Member
True Car Nut
 
Join Date: Jul 2004
Location: Grand Rapids, Mi
Posts: 5,656
Thanks: 0
Thanked 0 Times in 0 Posts
Archon is on a distinguished road
Default

My son'* '99 GP had enough pressure to shoot fuel out to the front of the car, but not enough to start it.
Archon is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
97 sierra runs rough in rain after tune up big carl 84 GMC/Chevrolet Truck/SUV 4 07-22-2013 11:17 PM
97 97 Bonneville rough idle after start then runs fine. Mattus Pontiac 12 11-24-2011 03:19 PM
Rough idle/running 15 minutes after shutdown Leonardo 2000-2005 55 04-20-2010 09:46 PM
Runs OK then idles rough after 15 min bobref 1992-1999 4 06-17-2009 10:02 PM
computer keeps restarting on its own LittleHoov Lounge 17 03-14-2005 06:57 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 01:19 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.