Idle dropping off/misfiring/not firing on all cylinders - SaabCentral Forums
*
Home Saab Pictures Saab Classifieds Saab Dealer Listings Saab Forum Saab Forum


Go Back   SaabCentral Forums > Saab C900, 1979-1993 & '94 Convertible (C=classic) > C900 Workshop

C900 Workshop Classic 900 (1979-1993 & '94 Convertible) Technical Forum.

SaabCentral.com is the premier Saab Forum on the internet. Registered Users do not see the above ads.
Reply
 
Thread Tools Display Modes
  #1  
Old 31st October 2005
Si's Avatar
Si Si is offline
Saab on the Brain!
 
Join Date: Jan 2003                                                
Location: 5225′34″N 00152′19″W
My Saabs: Sensonic NG900T, a gagle of rusty c900's
Posts: 5,975
Default Idle dropping off/misfiring/not firing on all cylinders

Can all of the above be caused by dodgy HT leads?

On the way back from my parents (about 160 mile round trip) i hit traffic on the M'way and when the car dropped to idle it stalled, then would start OK but as soon as i let the revs drop it would stall, managed to make it home(just, it died on the driveway) , then when it started it was only firing on 2/3 cylinders.

It was OK the next day, then after a short jorney (with no stalling) i started it again and is was only firing on 2/3 cylinders again, popped the bonnet and checked the HT leads, started it and it was OK again.

Please let it be the HT leads and not my Head gasket .

(ps did'nt think i'd risk the trip to USD the next day)
__________________
Psytuned 1997 900 Sensonic coupe turbo
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2  
Old 31st October 2005
Matthew's Avatar
Matthew Matthew is offline
Saab Mad
 
Join Date: Dec 2001                                                
Location: Gloucestershire, UK
My Saabs: 900 S Aero Turbo, 9-5 Aero
Posts: 14,069
Default

HT leads can cause a misfire.

Your car's problems sounds more like a failing AMM, but then the T8s don't have those. Chronic over-fuelling could cause those symptoms. Did you smell excessive levels of fuel?

Try checking electrical connections on components that have something to do with air mass/flow measurement for fuelling. The intermittent nature of the fault could point to a loose connection of some sort.

Also check that all inlet piping is secure and without leaks. When the inlet hose from my T16's turbo compressor exit popped off, the symptoms were very similar to those you describe.
__________________
The path of my life is strewn with cowpats from the devil's own satanic herd
Reply With Quote Quick reply to this message
  #3  
Old 31st October 2005
Si's Avatar
Si Si is offline
Saab on the Brain!
 
Join Date: Jan 2003                                                
Location: 5225′34″N 00152′19″W
My Saabs: Sensonic NG900T, a gagle of rusty c900's
Posts: 5,975
Default IC piping

The IC piping is always the first thing i check, mainly cos i blow them off so oftern, i even welded lips on the pipework to help keep it all together(it's no fun blowing a IC pipe whilst trying to overtake a HGV on the M'way) but i'm still getting charge seeping over 1 bar(maybe the Bypass valve?), but that's another story though!

If anything i think i'm suffering from running lean, it's nearly impossible to stop it boosting over 1 bar in the higher gears, all i do is touch the throttle and off it goes!

I'll pick up some HT leads tommorow, hopefully that will solve the problems.
__________________
Psytuned 1997 900 Sensonic coupe turbo
Reply With Quote Quick reply to this message
  #4  
Old 31st October 2005
Tomarse's Avatar
Tomarse Tomarse is offline
Saab on the Brain!
 
Join Date: Sep 2003                                                
Location: crewe UK
My Saabs: LPG '80 99GL, '80 99T 2dr, LPG '93 ng900
Posts: 5,677
Default

Check your dissy cap too, especially the little sprung contact at the top that runs on the centre of the rotor arm.
Went on my 900T and on my dads 900i within a couple of months of each other.

Is the oil non- creamy and it isnt running hot or bubbling in the header tank? I also hope it isnt your head gasket. Have you plucked up the courage to do it yourself now?
Reply With Quote Quick reply to this message
  #5  
Old 31st October 2005
Si's Avatar
Si Si is offline
Saab on the Brain!
 
Join Date: Jan 2003                                                
Location: 5225′34″N 00152′19″W
My Saabs: Sensonic NG900T, a gagle of rusty c900's
Posts: 5,975
Default Hg

I'm checking the oil/coolant constantly as i'm not running a rad fan at the moment, i'll pull over and switch the engine off if the temp gauge goes over 2/3rds (it has'nt yet though).

I am getting a bit of pop bubble and crack though, but i'm hoping that it's more to do with the leaking ex man and maybe a few air leaks in the zorst.

Have'nt had the loud crack on gear change since i reworked the intercooler pipework so it must have been something to do with the length of the pipework.
__________________
Psytuned 1997 900 Sensonic coupe turbo
Reply With Quote Quick reply to this message
  #6  
Old 31st October 2005
Tomarse's Avatar
Tomarse Tomarse is offline
Saab on the Brain!
 
Join Date: Sep 2003                                                
Location: crewe UK
My Saabs: LPG '80 99GL, '80 99T 2dr, LPG '93 ng900
Posts: 5,677
Default

Quote:
Originally Posted by Si
I am getting a bit of pop bubble and crack though, but i'm hoping that it's more to do with the leaking ex man and maybe a few air leaks in the zorst.
Thats how mine started - then over a month or two it got to be how it was when i visited you and then not long after my oil went creamy..
My exhaust manifold has a crack in and the exhuast is blowing round the joints and it didnt pop atall after i replaced the head.

You havent noticed the car giving out the odd belch of white/grey smoke/steam when youre giving it some have you? Thinking back - I think i know when my head initially cracked as i was thrashing it along the dual carriage way and was just overtaking someone when im sure i got 10-20 seconds of smoke/steam out of the exhaust. It still ran fine though.

I also did about 10-15 miles after the oil had started getting creamy and i noticed no difference in how the car ran from normal! (though i had pulled the APC fuse and did it on base boost)
Reply With Quote Quick reply to this message
  #7  
Old 1st November 2005
Si's Avatar
Si Si is offline
Saab on the Brain!
 
Join Date: Jan 2003                                                
Location: 5225′34″N 00152′19″W
My Saabs: Sensonic NG900T, a gagle of rusty c900's
Posts: 5,975
Default Head Gasket

I guess that some problems with the HG will only appear once the engine is hot?

I'll replace the HT leads & plugs and keep an eye on oil/coolant, keep my fingers crossed in the mean time.

Cheers
__________________
Psytuned 1997 900 Sensonic coupe turbo
Reply With Quote Quick reply to this message
  #8  
Old 2nd November 2005
16saabs 16saabs is offline
Saab on the Brain!
 
Join Date: Jan 2005                                                
Location: fakenham
My Saabs: 2x LPT convertible's, 1 x 900 SE
Posts: 5,840
Default

when were the plugs last changed(mileage) my father in law had a brand new talbot horizon(1993) and came on a 100mile journey and said he did not think he would get here?, car was running roughly. checked the plugs, and the gap was between 52-55 thou, should be 25, asked him when were the plugs last changed ?,the had'nt,17000mls on a set of plugs,what a -anker(yes father inlaw,also garage,as he had,had the servicing done on time/miles)new car??,things do need changing now and again. sometimes they might even look ok, but i had one go after 500mls.
Reply With Quote Quick reply to this message
  #9  
Old 2nd November 2005
Jezzadee's Avatar
Jezzadee Jezzadee is offline
Saab on the Brain!
 
Join Date: May 2003                                                
Location: Southwold UK
My Saabs: Yamaha FZ6 Fazer
Posts: 9,170
Default

Quote:
Originally Posted by Si
The IC piping is always the first thing i check, mainly cos i blow them off so oftern, i even welded lips on the pipework to help keep it all together(it's no fun blowing a IC pipe whilst trying to overtake a HGV on the M'way)
I used to get this about once a week. I tried a new rubber IC connector, new jubilee clips and silicon sealant in turn but it still kept happening. I too have had the dubious pleasures of getting from lane 3 to the hard shoulder in heavy traffic with the engine stalled. In the end I bought a silicon humped hose, 70mm ID, from Burton Power for 10. It has never come off since.
__________________
Go Dutch
Reply With Quote Quick reply to this message
  #10  
Old 2nd November 2005
Keijo's Avatar
Keijo Keijo is offline
Active Member
 
Join Date: Nov 2005                                                
Location: Helsinki, Finland
My Saabs: 99 -84 T16+MS2-extra, 96 -77b
Posts: 31
Default

A faulty ignition amplifier may also cause trouble when it gets warm enough.
Reply With Quote Quick reply to this message
  #11  
Old 3rd November 2005
Si's Avatar
Si Si is offline
Saab on the Brain!
 
Join Date: Jan 2003                                                
Location: 5225′34″N 00152′19″W
My Saabs: Sensonic NG900T, a gagle of rusty c900's
Posts: 5,975
Default Plugs

Will be doing the plugs with the HT leads at the weekend, i bought the car (parts car which i took the engine out) in May, i've been working through the service stuff gradually, only done about 2k miles on the engine since i've had it.

Alan/Craig, any idea whan the plugs were last changed??????
__________________
Psytuned 1997 900 Sensonic coupe turbo
Reply With Quote Quick reply to this message
  #12  
Old 5th November 2005
Si's Avatar
Si Si is offline
Saab on the Brain!
 
Join Date: Jan 2003                                                
Location: 5225′34″N 00152′19″W
My Saabs: Sensonic NG900T, a gagle of rusty c900's
Posts: 5,975
Default HT/Dizzy etc

I bought some HT leads today and fitted them, also noticed that when i'd put the new distributer cap on a few weeks ago i'd managed to do it upside-down , so it was'nt sitting properly, swapped that about aswell.

It's definitley improved, less backfiring, idles a bit smoother, no ***ps in the boost, not perfect yet though but i'll hopefully get a chance to do the sparkplugs tommorow and see if that helps.

Car has'nt stalled again..yet .
__________________
Psytuned 1997 900 Sensonic coupe turbo
Reply With Quote Quick reply to this message
  #13  
Old 5th November 2005
ShadowWorks's Avatar
ShadowWorks ShadowWorks is offline
Banned
 
Join Date: Jul 2005                                                
Location: Holographic Universe
My Saabs: The Black Night, 900T
Posts: 5,841
Default

A plug can fail, the insulator can break down and the spark goes into the casing and not down the shaft.

Lets hope its a nice cheap easy fix like that,

I am quite good with my spark plugs and check the gap and condition of them ever 3 months or so, infact that may explain my weak idle vacuum, my plug gap my be too large? time to watch the fire works and work on the old girl, nice night for it too
Reply With Quote Quick reply to this message
  #14  
Old 6th November 2005
Si's Avatar
Si Si is offline
Saab on the Brain!
 
Join Date: Jan 2003                                                
Location: 5225′34″N 00152′19″W
My Saabs: Sensonic NG900T, a gagle of rusty c900's
Posts: 5,975
Default gremlins

I've been driving around a bit and it still seems OK, but every nown and again when i accelerate hard the car stutters a bit as the boost picks up, usually accelerates, stuters for 1/10th of a second and then accelerates some more.

It may be more to do with the turbo/IC pipework/APC/Solenoid/Bleed Valve or cuffs as it seems to happen when i hit max base boost & the APC takes over.

Once i've changed the spark plugs i'll have to investigate it a bit further.
__________________
Psytuned 1997 900 Sensonic coupe turbo
Reply With Quote Quick reply to this message
  #15  
Old 4th August 2006
tonyw's Avatar
tonyw tonyw is offline
SaabNut!
 
Join Date: Oct 2005                                                
Location: Berkshire, UK
My Saabs: 1989 Saab 900i 8v Auto 4 door
Posts: 252
Default

Si, did you sort that stalling under acceleration out? dansaabfan is having similar problems.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the SaabCentral Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Display Modes

Posting Rules
You may post new threads
You may 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

Forum Jump


All times are GMT -4. The time now is 09:38 PM.



Powered by vBulletin® Copyright ©2000 - 2014, vBulletin Solutions, Inc.

top of page | sitemap | email us



copyright © 2003 - 2011 saabcentral.com, All rights reserved http://www.whiter.co.uk - valid xhtml - valid css
SaabCentral is an independently run website and is not affiliated in any way to Saab Automobile AB.


Garage Plus vBulletin Plugins by Drive Thru Online, Inc.