Stumbling under load, particularly during low RPM - Defender Source
Defender Source  

Go Back   Defender Source > Defender & Series Technical Discussions > Defender Technical Discussions


Reply
 
Thread Tools
  #1  
Old March 27th, 2013, 10:15 AM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
Stumbling under load, particularly during low RPM

Symptoms:
When under load, particularly when going up a hill in lower RPMs or perhaps in too low a gear, my engine has started misfiring.

Background: I recently changed the coil to the Mallory 30451 which does NOT take the ballast resistor. I am running the Mallory Unilite distribuotr #4768901 and have been for many, many years.

Why did I change the coil? No reason other than I had it--the other was working fine. Did the engine skip before? Maybe a little, but never this bad.

I have checked the coil, wires, plugs, distributor cap and all seem fine and within spec. It may not even be related to the coil, but I did hear that misfires under load is often a weak spark. Spark looks good.

At higher RPMs, there is no skipping. Plugs look good--maybe a little rich. Timing is good, but I adjusted it from 6 degrees to 12 degrees and no change.

Reading up on misfires under load sounds like it could be anything from the plugs to the wires (I'm running magnecore, pretty new), to fuel injectors, fuel pump... long list.

But my symptoms are repeatable--I go up a hill in a slightly too low gear (or rpms under 2000) and my engine misfires.

This weekend I will rewire the old coil back in, but I have a sneaky suspicion it is not the coil---just because I don't feel lucky. If it was/is, then I will just leave it back in with the old ballast resistor...

Symptoms sound familiar to anyone?

thanks!
Reply With Quote
Sponsored Links
Advertisement
 
  #2  
Old March 27th, 2013, 07:55 PM
Roverchef's Avatar
Roverchef
Status: Offline
Jake K.
95 D90 SW
Member
 
Join Date: Jan 2010
Location: Deep in the Dirty South
Posts: 341
Here's a silly one to try before you get carried away replacing parts. Take the belt off the alternator and go for a drive around the block and see if your stumble is gone...yes the battery light will be on since it can't charge but you are not going on a road trip...just around the block. If it has stop'd stumbling then replace the alternator. If it still persists then look elsewhere and you have now tested the integrity of the diodes inside the alternator which can cause your symptoms if they are starting to fail(shit the bed)! Good luck and post up your findings for everyone else to enjoy.
Reply With Quote
  #3  
Old March 27th, 2013, 08:08 PM
rovertek's Avatar
rovertek
Status: Offline
chris
D130, 2001+99 p38
Member
 
Join Date: Jul 2012
Location: Long Island , New York
Posts: 500
Quote:
Originally Posted by Roverchef View Post
Here's a silly one to try before you get carried away replacing parts. Take the belt off the alternator and go for a drive around the block and see if your stumble is gone...yes the battery light will be on since it can't charge but you are not going on a road trip...just around the block. If it has stop'd stumbling then replace the alternator. If it still persists then look elsewhere and you have now tested the integrity of the diodes inside the alternator which can cause your symptoms if they are starting to fail(shit the bed)! Good luck and post up your findings for everyone else to enjoy.
ding ding i think we have a winner!! if that's not it i would defiantly look at the wires then check fuel pressure underload ... how many miles on it? check engine light? possibly sticky valve syndrome
__________________
No Mall crawler here
Reply With Quote
Sponsored Links
Advertisement
 
  #4  
Old March 27th, 2013, 08:09 PM
ukoffroad's Avatar
ukoffroad
Status: Offline
Chuck Yarbrough
67 IIA
Member
 
Join Date: May 2008
Location: Lynchburg,Va
Posts: 548
my classic was doing this, I had a vacuum leak on the advance and the weights on the dizzy were sticking.
__________________
Chuck
67 Series IIA
The parts falling off this vehicle are of the finest British craftsmanship.
Reply With Quote
  #5  
Old March 28th, 2013, 12:17 AM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
I converted the truck to a serpentine, so not that easy a check, but I can do a work around. I have replaced the pack in my alternator before, and that was/is almost always a consistent RPM that the condition happens at---in my case, though, it only happens under engine load. That said, I will check it out as well and I thank you for the advice. I have a two voltage regulator spares for the alternator (and some extra time) so I may just solder one in and see what happens. Thanks--

I am always up for more things to check from those that have also had similar symptoms. I called mallory today and they gave me several ohm checks on the coil (which all checked out) so I think the coil itself is cool. Oh the joy--trouble shooting continues!
Reply With Quote
  #6  
Old March 28th, 2013, 12:20 AM
ipgregory's Avatar
ipgregory
Status: Offline
Ian Gregory
'97 D90 ST #1008
Member
 
Join Date: Jun 2009
Location: Henderson, NV USA
Posts: 1,083
Registry
Quote:
Originally Posted by Davis View Post
I converted the truck to a serpentine, so not that easy a check, but I can do a work around. I have replaced the pack in my alternator before, and that was/is almost always a consistent RPM that the condition happens at---in my case, though, it only happens under engine load. That said, I will check it out as well and I thank you for the advice. I have a two voltage regulator spares for the alternator (and some extra time) so I may just solder one in and see what happens.
Chris,

If you can't pull the belt, why don't you just pull the wires off the alt temporarily. Same effect and allows you to exclude it or not. Easier than soldering in a new regulator pack?

Ian
Reply With Quote
  #7  
Old March 29th, 2013, 08:08 PM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
I found that my vacuum advance is broken, so I just ordered the new one. Not sure if that was it or not, but logic says probably not since it is a low RPM issue and typically the vacuum advance comes into play at higher revs. Still, it was a source of a vacuum leak, so at least that will be fixed (albeit a small one). Can't do much more testing till that comes in since I took it off and tried to patch the diaphragm but that wasn't possible. To be continued.
Reply With Quote
  #8  
Old March 31st, 2013, 05:26 PM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
Looked at my plugs and they seem really nice--did more driving and it does seem that the stumbling only occurs at about 1100-1200 rpm--not every time, but most, and this does seem to make sense that it may be the alternator as Roverchef so kindly pointed out. I'll dig into that avenue but it is what I am leaning towards as the stumbling doesn't feel like fuel delivery.
Reply With Quote
  #9  
Old April 1st, 2013, 05:03 PM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
Opened the alternator and checked all the diodes and capacitor and everything checks out a-OK. Leaning toward possible vacuum leak at the injectors, possibly. Not sure if that would cause it or not, but the alternator seems golden.
Reply With Quote
  #10  
Old April 1st, 2013, 05:17 PM
leastonce's Avatar
leastonce
Status: Offline
Jason England
D-90 White 95 SW #65
Site Team
 
Join Date: Jul 2009
Location: NYC
Posts: 6,078
Registry
Quote:
Originally Posted by Davis View Post
Looked at my plugs and they seem really nice--did more driving and it does seem that the stumbling only occurs at about 1100-1200 rpm--not every time, but most, and this does seem to make sense that it may be the alternator as Roverchef so kindly pointed out. I'll dig into that avenue but it is what I am leaning towards as the stumbling doesn't feel like fuel delivery.
TPS - Throttle Position sensor
__________________
Quote:
Soapy water / KY jelly, etc. is is basically a must. Yes, good idea to remove trim panels - only takes 5 more minutes to do so.
Car Camping Collective founding member and Chief Executive Officer
Cat Camping Collective founding member and Chief Executive Officer
Reply With Quote
  #11  
Old April 1st, 2013, 05:45 PM
Jonesy's Avatar
Jonesy
Status: Offline
Craig
87 D110 (Ruby)
Member
 
Join Date: Dec 2011
Location: Leesburg, VA
Posts: 4,445
Registry
yeah pull the idle control valve too and clean it...
Reply With Quote
  #12  
Old April 1st, 2013, 06:10 PM
leastonce's Avatar
leastonce
Status: Offline
Jason England
D-90 White 95 SW #65
Site Team
 
Join Date: Jul 2009
Location: NYC
Posts: 6,078
Registry
Could also be in limp mode if the temp sensor is reading wrong.
__________________
Quote:
Soapy water / KY jelly, etc. is is basically a must. Yes, good idea to remove trim panels - only takes 5 more minutes to do so.
Car Camping Collective founding member and Chief Executive Officer
Cat Camping Collective founding member and Chief Executive Officer
Reply With Quote
  #13  
Old April 2nd, 2013, 10:01 AM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
TPS and ICV are good--and don't get me wrong--the truck idles and drives great. Couldn't even tell something is wrong unless you are in too low a gear and then you get sporadic misfires. I know I have a slight leak around my injectors, right at the injectors themselves, so I am going to have to work on fixing that too... when I swapped injectors when I made the 4.6, I used those off a mustang per several peoples recommendations. They seem just a hair short and was hard to get them to fully engage both top and bottom without one side or the other leaking. When I spray starter fluid at them, there is a very slight change in idle, so I know that they have some leaks.
Reply With Quote
  #14  
Old April 2nd, 2013, 10:22 AM
o2batsea's Avatar
o2batsea
Status: Offline
Bill Adams
66 109 sw 94 lwb
Member
 
Join Date: Jul 2009
Location: kensington md
Posts: 6,502
Registry
You need the O ring kit. Also you might want to clean the injectors. When installing the injectors use a soapy water solution to help them into the bores. Leaks around the injectors=no bueno. This is probably the majority of your trouble, a vacuum leak.
The Mustang injectors are THE SAME as the rover ones. Only difference is in flow rate, which is determined by the orifice size on the end. The OE ones for Mustang are 19lbs/hour. You can get a bump up set that flow 24lbs/hour and on up to a ridiculous 120 lbs/h.
__________________
Bill Adams

1966 109 5 door wagon 300Tdi "spermaceti fueled"
1994 RRC LeWiB "ruining the air behind me"
1968 2A 88

All my troubles are Rover
Reply With Quote
  #15  
Old April 2nd, 2013, 10:59 AM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
The problem with the injectors wasn't the orings-- they just dont seem physically long enough for some reason, or the top fuel rail doesn't go down low enough-- either the top or the bottom of some of the injectors don't seat properly, just barely. I have to position them in the respective bore either slightly up or down. Anyone else ever have this issue?
Reply With Quote
  #16  
Old April 2nd, 2013, 12:45 PM
o2batsea's Avatar
o2batsea
Status: Offline
Bill Adams
66 109 sw 94 lwb
Member
 
Join Date: Jul 2009
Location: kensington md
Posts: 6,502
Registry
Hm. Prolly (guessing) that the fuel rail isn't seating all the way down. Yer using the old 3.9 intake on the 4.6, yes?
My theory is that when in low RPMs, under load, the air sneaking by the injectors is enough to throw the mixture out of whack. As the TB opens and more volume enters the engine, the amount of imbalance is proportionally lower and the engine smoothes out.
__________________
Bill Adams

1966 109 5 door wagon 300Tdi "spermaceti fueled"
1994 RRC LeWiB "ruining the air behind me"
1968 2A 88

All my troubles are Rover
Reply With Quote
  #17  
Old April 13th, 2013, 08:43 PM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
SOLVED. it was the Mallory Coil. It checks out fine with an ohm meter and it is the the Promaster e-Coil that specifically states NOT to use a ballast resistor. I didn't, and it the truck ran like crap. I put in the old coil/resistor and it ran fine. I hooked up the new coil and this time added the ballast resistor and the truck runs great. WTF? Am I going to damage this coil with the ballast resistor? The coil is only seeing 6v DC to the coil with this in place.

I'll call Mallory on Monday. Well, it just goes to show you, if it ain't broke on a Rover, don't friggin fix it...
Reply With Quote
  #18  
Old April 14th, 2013, 08:18 PM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
NOT solved. Friggn truck. Just less common now. No clue what it causing it, can't see any codes popping up, but there are times, particularly with wide open throttle going up hill, that I start to buck and think I am not getting fuel in the motor. Could be a fuel pump, not really sure. Gonna swap in another TPS and see what that does. Question--whenever I have lost a fuel pump, it has been all or nothing---has anyone had on that "slowly" failed, didn't just outright fail?
Reply With Quote
  #19  
Old April 14th, 2013, 09:28 PM
navydevildoc's Avatar
navydevildoc
Status: Offline
Neill Thornton
1984 D90 300 Tdi / 1965 Series IIA
Site Team
 
Join Date: Nov 2010
Location: San Diego, CA
Posts: 1,586
Registry
So you do still have the new coil with the ballast, or the old coil? I think you have narrowed the problem down pretty well.
Reply With Quote
  #20  
Old April 15th, 2013, 12:13 AM
Davis's Avatar
Davis
Status: Online
Chris Davis
94 NAS D90 6.2LS
Member
 
Join Date: Nov 2003
Location: Colorado
Posts: 2,504
I have tried several coils and still have the symptoms although they seem to manifest at different times and severity depending on the coil. And it isn't always when I am at full throttle or at a particular rpm or speed. It does seem to happy most when going uphill under load.
Reply With Quote
Reply

Lower Navigation
Go Back   Defender Source > Defender & Series Technical Discussions > Defender Technical Discussions

Tags
part

Thread Tools

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
300 Tdi Egt Q?????? Buckon37s Defender Technical Discussions 37 July 11th, 2012 11:26 AM
stumbling under load when hot..? revtor Defender Technical Discussions 0 May 5th, 2008 08:57 PM
Stumbling during acceleration and load Bozman Defender Technical Discussions 8 June 14th, 2006 08:02 AM
Low RPM knocking, ideas? OCD90 Defender Technical Discussions 6 September 30th, 2005 05:14 PM
The latest show-stopper: dies at idle, only runs above 2K rpm jaherring Defender Technical Discussions 34 December 23rd, 2004 07:05 PM


All times are GMT -5. The time now is 10:32 AM.


Copyright