Fordmods Logo

Fordmods Advertising

Engine misfire at maximum load 

 

Page 1 of 1 [ 5 posts ] 

 
 Post subject: Engine misfire at maximum load
Posted: Thu Nov 03, 2016 11:59 am 
Getting Side Ways
Offline

Posts: 815

Joined: 1st Apr 2005

Gallery: 4 images

Ride: EF XR6 Wagon, AU2 XR6 VCT

Power: 148 rwkw

Location: Auckland
New Zealand

Hi all,

The car is a mildly-modified EF Falcon XR6 automatic.

Have had an occasional stumble at WOT for a while but has been getting progressively worse over the past few days and is now a full-on misfire. It occurs only at WOT from 2800 RPM (when it comes up on the torque converter) to 4000 RPM, so only at maximum torque/load. Once it is past 4000 RPM is pulls just fine to redline. I stumbles so hard that the revs are bouncing around a bit and even drop once or twice on the way up.

Drags are on tomorrow night, so I need to solve the issue quickly. I am working, so I basically have only tonight to sort it out.

It can't be fuel or injectors, as it pulls hard right out to 6850 RPM at WOT - at maximum fuel flow. I checked the AFR and it's 12.2 to 12.6 through this rev range, so definitely not leaning out.

I thought it might be the knock sensor detecting knock and pulling timing out. But I pulled out 3-4 degrees of advance and richened up 10% in the affected areas and it made no difference.

I checked the spark plugs and they look OK (white one side, tan/brown the other). Though a couple of them have bright white side electrodes which I haven't seen before. I have just picked up a new set of plugs to install tonight and hope that solves it, but I'm not confident, so need a plan B.

I did quick-and-dirty lead/coilpack test last night - testing two leads and the secondary circuit as one unit - and it seems fine. Cyl 1-6 was a total of 26k ohms, 2-5 was 20k, and 3-4 was 19k - all of which are well within spec in total: 9.2k for the coil leaves at most 17k total for the two longest leads. Could the coilpack be faulty anyway? I don't want to go through the cost and hassle of changing it unnecessarily.

It can't be a vacuum leak, as there is almost no vacuum at WOT, and a leak would make a poofteenth difference to total airflow at WOT anyway.

One earlier post mentioned unplugging the Cam Angle Sensor. Is it safe to try that, in case the CAS is dodgy? It shouldn't affect fuel in the batch-injection EF, but does the ECU lose it's ignition timing reference?

Anything else I should be checking? I will pull error codes as well to see if they tell me anything. Thanks for the help.

 

_________________

95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, SS Ind, BA ind, MLS, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip
01 AU XR6 VCT, Tickford body kit/alloys, Momo wheel/shifter, leather, QFM, SS Ind, BA ind, 3" airbox exit, Coby headers, no cat

Top
 Profile  
 
 
 Post subject: Re: Engine misfire at maximum load
Posted: Thu Nov 03, 2016 1:17 pm 
Technical Contributor
Offline

Age: 59

Posts: 6794

Joined: 22nd Jun 2005

Gallery: 8 images

Ride: EF Fairmont

Location: Campbelltown
NSW, Australia

I would have thought leads with the breakdown under load.

Could be the coil pack breaking down but unlikely.

With you AFR's, doubt a fuel telated issue. Sounds more electrical, plugs or leads.

 

_________________

SWC

South West Customs


Members of the SWC Stable, fordebgt93, TROYMAN, Benj, svo_matt, Mrs C, eb_fairmont, Total_tool, Terroristghia

Top
 Profile  
 
 
 Post subject: Re: Engine misfire at maximum load
Posted: Thu Nov 03, 2016 1:45 pm 
Getting Side Ways
Offline

Posts: 815

Joined: 1st Apr 2005

Gallery: 4 images

Ride: EF XR6 Wagon, AU2 XR6 VCT

Power: 148 rwkw

Location: Auckland
New Zealand

Thanks for that advice. I do have a brand new set of leads on the shelf for when these ones expire, so I might just replace them anyway.

Much obliged.

 

_________________

95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, SS Ind, BA ind, MLS, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip
01 AU XR6 VCT, Tickford body kit/alloys, Momo wheel/shifter, leather, QFM, SS Ind, BA ind, 3" airbox exit, Coby headers, no cat

Top
 Profile  
 
 
 Post subject: Re: Engine misfire at maximum load
Posted: Thu Nov 03, 2016 9:40 pm 
Getting Side Ways
Offline

Posts: 815

Joined: 1st Apr 2005

Gallery: 4 images

Ride: EF XR6 Wagon, AU2 XR6 VCT

Power: 148 rwkw

Location: Auckland
New Zealand

Update:

SWC, you were spot on! It was the plugs, even though they looked fine. Replaced them and it's all sweet again. So it's Night Speed Drag Wars at Meremere Dragway tomorrow!

Thanks heaps for the help.

 

_________________

95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, SS Ind, BA ind, MLS, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip
01 AU XR6 VCT, Tickford body kit/alloys, Momo wheel/shifter, leather, QFM, SS Ind, BA ind, 3" airbox exit, Coby headers, no cat

Top
 Profile  
 
 
 Post subject: Re: Engine misfire at maximum load
Posted: Mon Nov 07, 2016 3:35 pm 
Getting Side Ways
Offline

Posts: 815

Joined: 1st Apr 2005

Gallery: 4 images

Ride: EF XR6 Wagon, AU2 XR6 VCT

Power: 148 rwkw

Location: Auckland
New Zealand

It turns out that the ignition leads were also on their last legs and causing an intermittent misfire. Have replaced them and it runs like a dream now.

 

_________________

95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, SS Ind, BA ind, MLS, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip
01 AU XR6 VCT, Tickford body kit/alloys, Momo wheel/shifter, leather, QFM, SS Ind, BA ind, 3" airbox exit, Coby headers, no cat

Top
 Profile  
 
Display posts from previous:
Sort by  
 Page 1 of 1  [ 5 posts ] 

Who is online

Users browsing this forum: MSNbot Media, Yahoo [Bot] and 23 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

 

 

It is currently Fri Dec 09, 2016 11:01 am All times are UTC + 11 hours

 

 

(c)2014 Total Web Solutions Australia - Australian Web Hosting and Domain Names