Parts Catalog Accessories Catalog Tech Info Tech Forums
 
  Search our site:    
 Cart  | Project List | Order Status | Help    
Go Back   Pelican Parts Technical BBS > 1- Porsche Technical Forums > Porsche 944 Turbo and Turbo S

Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Writer/Teacher
 
CJFusco's Avatar
 
Join Date: Mar 2001
Location: Wandering Connecticut
Posts: 8,937
Garage
Send a message via AIM to CJFusco
Slight backfires (?)

A few days ago, I did a tune up on my car, replacing spark plugs, the wires, air filter, oil change... at (roughly) the same time I replaced the stock FPR with a 3.0 unit so I can safely run the LBE (=slightly more boost).

Since then, I've noticed that if I let off the gas abruptly in 1st or 2nd, I'll get a little bit of a backfire. In 2nd it's more of a muffled "burble", but in 1st its more of a "pop".

I know that high-performance cars sometimes have "burbling" from exhaust off-throttle. Is this what I am experiencing? Or is it something I need to address (such as running lean)?
__________________
Black 2007 Porsche Cayman S (snappy nickname coming soon): Daily Driver (at least until winter!). Garnet Red 1986 Porsche 951("The Purple Pig"/"Suicide Machine"):SOLD. Dark Silver 2009 Mini Cooper S ("Mighty Mouse"):SOLD. Alpine White 1983 Porsche 944 ("Alpine Wolf") :SOLD. Guards Red 1984 Porsche 944 :One-time parts car, SOLD.
Old 04-03-2007, 04:23 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #1 (permalink)
Ornery Bastard
 
Join Date: Sep 2001
Location: Bellevue, WA
Posts: 2,832
I've noticed that in a few chipped 951's. Seems pretty normal, but I'd do a Dyno run with a wideband O2 sensor and see how the mixture's doing. Be sure to measure at the test port and not the tailpipe because the cat will change the readings if you measure at the tailpipe.
__________________
Shifting is an art. Learn it, love it, live it.
---------
Silver 1998 Volvo S70 T5 <- Daily (Anja)
Guards Red 1986 951 <- Seattle car (Gretchen)
White 1976 914 2.0 F.I. <- Prodigal car, traded away then brought back again (Lorelei)
Old 04-03-2007, 06:28 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #2 (permalink)
Writer/Teacher
 
CJFusco's Avatar
 
Join Date: Mar 2001
Location: Wandering Connecticut
Posts: 8,937
Garage
Send a message via AIM to CJFusco
If I am getting combusting exhaust gasses in the exhaust, I am guessing that would be closer to running RICH than running LEAN, right? I am most worried about running lean and blowing the head gasket.
__________________
Black 2007 Porsche Cayman S (snappy nickname coming soon): Daily Driver (at least until winter!). Garnet Red 1986 Porsche 951("The Purple Pig"/"Suicide Machine"):SOLD. Dark Silver 2009 Mini Cooper S ("Mighty Mouse"):SOLD. Alpine White 1983 Porsche 944 ("Alpine Wolf") :SOLD. Guards Red 1984 Porsche 944 :One-time parts car, SOLD.
Old 04-03-2007, 07:08 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #3 (permalink)
Junior Member
 
yahoo's Avatar
 
Join Date: Mar 2007
Location: NorthWest
Posts: 5
backfire or postfire??? Isn't a postfire when the unburnt fuel ignites after the exhuast valve is closed? and a backfire when it ignites in the intake manifold? Correct me if I'm wrong.

And with a backfire/ postfire you are running lean. Thats according to Wikipedia
Old 04-03-2007, 09:29 PM
  Recommend this thread for the PelicanWiki    Reply With Quote #4 (permalink)
cold starter
 
JustinL's Avatar
 
Join Date: Aug 2004
Location: Edmonton AB
Posts: 276
You'll get a burbling popping exhaust if the mixture is too lean. You can get really loud bangs if the exhaust is hot and you're running it rich. Because it's off throttle, the cylinder pressures won't be terribly high like under boost, so I wouldn't worry about it too much.

When you upped the fuel pressure did you change your chip to compensate for the added fuel, or was your chip supposed to be used with 3bar fuel pressure?

EDIT-- In case that was confusing... you are supposed to be under a fuel cut with the throttle closed at RPM above 1600. You are probably getting popping because instead of having no combustion, you are getting a bit of fuel during overrun.
__________________
88 Turbo S Silver rose: Megasquirted fuel, assorted suspension upgrades, etc.

87 944 n/a: Microsquirted PnP, 284K miles, Fresh engine, Mild suspension upgrades, mildly lightened.

Last edited by JustinL; 04-04-2007 at 07:54 AM..
Old 04-04-2007, 07:49 AM
  Recommend this thread for the PelicanWiki    Reply With Quote #5 (permalink)
Writer/Teacher
 
CJFusco's Avatar
 
Join Date: Mar 2001
Location: Wandering Connecticut
Posts: 8,937
Garage
Send a message via AIM to CJFusco
I got the 951Max chip BEFORE getting the 3.0 FPR, and IIRC, the chip was configured for the stock FPR. This makes me think that the car is running a little RICH at low RPM/low gear off boost, because more fuel is being piped through.

I have noticed that I only get the pops when the car is warmed up, so that kind of goes along with the running rich theory...
__________________
Black 2007 Porsche Cayman S (snappy nickname coming soon): Daily Driver (at least until winter!). Garnet Red 1986 Porsche 951("The Purple Pig"/"Suicide Machine"):SOLD. Dark Silver 2009 Mini Cooper S ("Mighty Mouse"):SOLD. Alpine White 1983 Porsche 944 ("Alpine Wolf") :SOLD. Guards Red 1984 Porsche 944 :One-time parts car, SOLD.
Old 04-04-2007, 08:21 AM
  Recommend this thread for the PelicanWiki    Reply With Quote #6 (permalink)
 
Now Available for Ordering:   101 Projects For Your BMW 3 Series 1982-2000  [more info]
cold starter
 
JustinL's Avatar
 
Join Date: Aug 2004
Location: Edmonton AB
Posts: 276
Quote:
Originally posted by CJFusco
I got the 951Max chip BEFORE getting the 3.0 FPR, and IIRC, the chip was configured for the stock FPR. This makes me think that the car is running a little RICH at low RPM/low gear off boost, because more fuel is being piped through.

I have noticed that I only get the pops when the car is warmed up, so that kind of goes along with the running rich theory...
Yes that's right it's running rich compared to what it's supposed to (fuel cut) off throttle, but your AFRs are likely leaner than stoich. On throttle, you are also right, it's probably rich throughout the rev range.
__________________
88 Turbo S Silver rose: Megasquirted fuel, assorted suspension upgrades, etc.

87 944 n/a: Microsquirted PnP, 284K miles, Fresh engine, Mild suspension upgrades, mildly lightened.
Old 04-04-2007, 09:11 AM
  Recommend this thread for the PelicanWiki    Reply With Quote #7 (permalink)
cold starter
 
JustinL's Avatar
 
Join Date: Aug 2004
Location: Edmonton AB
Posts: 276
Quote:
Originally posted by CJFusco
I got the 951Max chip BEFORE getting the 3.0 FPR, and IIRC, the chip was configured for the stock FPR. This makes me think that the car is running a little RICH at low RPM/low gear off boost, because more fuel is being piped through.

I have noticed that I only get the pops when the car is warmed up, so that kind of goes along with the running rich theory...
Yes that's right it's running rich compared to what it's supposed to (fuel cut) off throttle, but your AFRs are likely leaner than stoich. On throttle, you are also right, it's probably rich throughout the rev range.
__________________
88 Turbo S Silver rose: Megasquirted fuel, assorted suspension upgrades, etc.

87 944 n/a: Microsquirted PnP, 284K miles, Fresh engine, Mild suspension upgrades, mildly lightened.
Old 04-04-2007, 09:23 AM
  Recommend this thread for the PelicanWiki    Reply With Quote #8 (permalink)
Old 04-04-2007, 09:23 AM
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 



All times are GMT -8. The time now is 01:19 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.