Missfire At Randome Revs? Coils Ok ...then Check Afm Fix...

[Hesh]

hi guys,

thought id share this with you ...ive been having the dreaded hesitation and missfire at 4500 on my rb25de so i bought spitfire coilpacks and whilst that did resolve the problem i still had aintermittent missfire at random revs both on steady throttle and when accelerating.

id regapped the plugs to point 8 theyre new ish anyhow so didnt think that was the problem. checked allthe conections tothe cas and all looked ok ...so

i took the AFM apart ...

Edit: link didnt work so heres the abridged thread ....not all posts are my work....

"...Well, I've solved my misfire..

Around a week ago the wife's Liner began missing, stuttering and juddering like a poorly maintained lawnmower. The problem was intermittent, appearing at will for no obvious reason, all the simple things were checked, vacuum pipes and connections etc., all OK.

Checked coils and found 4 were around 100% over resistance value (2.0 ohms) and 2 were around 300 to 400% over! (4.0 + ohms) They also had signs of arcing from the transformer around the bobbin area, the two plugs on the worst of the coilpacks were a little fouled but checked out OK after cleaning. (NGK Iridiums)

I cleaned and replaced the plugs and proceeded to clean up the coilpacks, cleaned with carb cleaner and toothbrush followed by a good squirt of WD40.

I refitted the lot and went for a drive, all was fine and I was happy, until it all returned the next day!

This time I had an idea and soaked the coilpacks in WD40 for 30 minutes or so, (in a jug) I dried and refitted them but did not drive the car that day. The next day the car went well in the morning but started to play up again in the afternoon. I metered the coils again whilst cold this time, and found they all fell within the 0.6 to 0.9 spec, in fact they were all 0.7 exactly. I realised from this that as I had previously metered them whilst warm they had risen in resistance due to the heat, cold they were fine. Of course the arcing would still have deteriorated the performance somewhat even with the correct resistance. However another soaking in WD solved that problem and I ran the car like that for a few days until I got the Splitfires, on removal the original coils still looked like new and metered OK, well done WD.

The Splitfires made a very obvious improvement, response was up considerably, the car felt much more urgent at all speeds. There was another strange benefit, which indicates the original coils even when in spec are not very good. The remote start (Clifford System) has never worked in cold weather, which is a bit of a piss off as it has the auto cold start and charge system as well, which didn't work when it was cold! It would start if you cranked the engine for a second with the key and then tried again, no problem. But the whole idea was to prevent the engine freezing and to charge the battery if the voltage dropped below a certain point, due to low temps or whatever. This was fitted as we spend 4 or 5 months abroad each year and the liner sits in airport carparks, so a great comforter, when it works, which it does fine when warm but not when it's cold.

Strange thing is it now works first time every time, only since fitting the Splitfires, so a bonus!

However the Splitfires did not solve the misfire/hesitation etc, so on we go..

I then fitted a new O2 sensor as the next possible problem at a reasonable cost, again no difference, problem remained.

I then fitted a replacement ignition amp, no change so not that, so I turned to my final choice for the culprit, the AFM, glad I did as that solved the problem!

Note: Aside from the hesitation and stuttering, there seemed to be a considerable amount of white smoke from the exhaust from time to time when the hesitation got very bad, consumption also went from 20 to 16 mpg under very restrained driving conditions due the fault.

As stated earlier, this differs from the coilpack symptoms, which tend to be at higher evs or under load, this would happen at tickover as well or anywhere in between, occasionally stalling at lights etc. It would always start again straight off though, as it did every morning, and for the first few minutes driving was usually better than subsequently.

If you get these symptoms try the AFM first!

Having said that I'm delighted the problem pushed me to getting the Splitfires, they are awesome.

I now need to aquire a spare AFM, but I would like to establish if I can fit a better one than the original, and keep the used one I've just fitted as a spare.

Aitch"

post 2 ..

"Hope this helps, won't get time to put it all back together myself until my return in two weeks.

Note: Do not remove the socket housing as I did, after removing the 4 screws I pulled it away from the AFM body, breaking the connections to the pins, so now I don't know if there was a bad joint!

I assume so though as it cam away fairly easy.

The way to go is remove the square cover, which is set in with the usual mastic sealant. This needs cutting through with a stanly blade or similar and then prising out. The copper shield plate below is soldered in place at one point, careful if you lift it not to break the solder, it will take some resoldering due to it being a mass of copper. The circuitry underneath is mostly PCB mounted so difficult to service.

Having removed the side inspection cover the pins on the socket will need resoldering, apparently thats the usual fault."

pictures....

its the conections betweenthe plug inside and the circuit board that i soldered....

its easy to remove the plug...i took the back off first so i could be sure i didnt damage the pins ....

after taking off the fourscrews holding the plug onto the afm body i carefully lifted this off and cleaned the contacts ...then

soldered the joints once back in place to ensure a good conection .

resealed the back with some clear mastic type sealent and she runs soooo much better.....more urgency and will now pull happily in fifth from 2000 revs where as before she was flat as a pancake....

i even reached 120km an hour in third at 6000 before changing up to fourth .........so well worth doing this ...all in all it took a couple of hours and made a drastic improvement.

Edited January 15, 2008 by Hesh

[Hesh]

could some one reply ..tell me if the the links working please? works for me but then im signed in ...

[Eug]

thought i replied to this when you first posted. apologies Si.

yes we are unable to view the pictures without registering and having at least 1 post.

if you could copy and paste what you've written into your first post, and attach all the photos onto our database it might make it easier for everyone.

the AFM should always be the first (or one of the first) places to look for any sort of electrical power issue. as they are quite sensitive.

coilpacks normally degrade/crack after high temperatures, usually not experienced with NAs and more so turbo motors

[Hesh]

ahhh will do cheers Eug....

edit all done it should make more sense now ....i hope ....

Edited January 15, 2008 by Hesh

[Eug]

nice work on the troubleshooting there Si.

a bonus in getting response from the splitfires! i happily take back my previous statement to you.

i do agree though, your colder climate may have different effects to us here in Oz and might require extra maintenance.

[Eug]

nice work on the troubleshooting there Si.

a bonus in getting response from the splitfires! i happily take back my previous statement to you.

i do agree though, your colder climate may have different effects to us here in Oz and might require extra maintenance.

[Hesh]

cheers Eug. i dont know what the climate difference are going to do tothe cars, but i reckon it would definatly be worth a holiday over in your part of the world were the sun shines more than twice a year to find out! lol

I cant take all the credit. another forum member over here by the name of aitch has done alot of research into the pros and cons of the elctrical systems on his skyline...also an NA rb25. I merely folowed his lead and found it worked so shared my experience.

coilpack failiure here seems to be related to age. both det and de suffer the dreaded misfire. Also we often find that wrong/ bad plugs cause alot of bad running problems.

incidently (and alittle off topic) as we now have superspark coilpack distributor inthe uk i think 2008 will see some head to head testing of the various ignition systems vaialable for our cars, the results of which i'll obviously forward to you......