mystery mid rpm misfire

I just need to run the bastrd for a while now , cost me a fortune recently and I dont want to break anything again!

Any thoughts on the genuine dizzy caps and rotors (silicon coated?) Ive got some fitted at the moment but althought its solved the damp starting feck ups it seems to have developed a very slight miss at idle which it didnt have before, you can only hear it when your head is at the exhaust sniffing fumes. Am I being to fussy for a 20 yr old range rover?

yeh you are, i'll swap ya.

Even more confused now.. i spent hours tonight double checking everything with the exception of fuel pressure reg, and afm (at airbox, checked out ok at ecu) it's all testing ok now
Idle still low after cold start settles down, i'm wondering if it's something breaking down once hot?? it drove spot on for 45 mins at the weekend, laning, before the misfire started playing up. the idle dropped out and stalled a few times but after a minute or so it sorts itself out
I havent physically checked the timing chain, it timed up really well with no 'dancing line' on the strobe.
More tinkering needed me thinks..
It's the two different probs that are confusing me most, the mid rpm miss definately feels like ignition but the low idle and stalling feels more like fuel starvation, that said when the starter was a bit slow the other day it flooded within 10 secs of starting and i had to have the plugs out to get it going again
got a copy of rave now, it says the fuel thermo only works by adjusting enrichment on hot starting?
Hopefully i'll fix it before i get the arse and take the hammer to it

Try the outer two pins on the AFM with a multimeter as kev said before and then tap the top of the AFM quite hard with your fingers and if the reading changes or you have the engine running and the revs change then you will have a broken circuit bord inside. Thats a trick Stuart taught me on his first visite.

I had almost identical problems with the misfire and huge loss of power which was getting worse week by week. Took it in to a trusted mech who after checking all the usual problems noticed the air box was not fastening tight. Inside the filter was not fittting right and as such the insulation from the bonnet lining was getting sucked in and clogging valves. All debris removed and all eight now firing for first time in a long while. Back in love the with truck....well for this week!

I think my range hates me, either that or it's female
I've not had much time yet to go further into it but the last 2 days i've used it it's ran bloody spot on I suppose i should be happy but i'm just waiting for it to have another fit
Gonna rip the plenium off tomorrow night and do all the bits in there to make sure it's ok..
I might have buggered it all up now anyhow, waiting for advice on cats and tune resitors etc
The middle box and one of the cats have been fecked for a couple of months after taking a whack while laning, as i didn't have spares to hand i cut the cats open pulled out the guts and welded em back up, then ripped out the middle box and put a straight thru pipe in it's place, still got the back box on but she sounds sweet now I haven't driven it yet tho guess it'll run like a 3 legged horse now

Lol, they are definatly female and have permanent PMT! :doh:

Pmt?
I got a feeling mines going through 'the change'

right, im in me workshop, kin freezin!! checked the afm. it was reading 2.54v Now reset to what kev suggested. Dunno what difference that'll make?

ripping the plenium orf to make sure all is ok in there. Starting to wonder why i love it so much... if it were a woman i'd just get rid like the last one

Lol yeah , I know what you mean.

I am going to try the old cap and or rotor again tomorrow-I know it will be ****e in the mornings but if that miss goes from the exhaust (as it wasnt there bfore the LR cap went on) then I will know two things:

1 you cant buy a cap that atually works

2 nothing else is broken (yet)

I thought yours were about sorted?
Let me know if yer new cap is ****e it'll save me spending a fortune at lr...

I didn't get too far tonight before i got frostbite but i got the plenium off, needs a bit of a clean and there seemed to be a fair amount of crap sitting on top of the ram housing which i assume has got through the air filter?
One very odd thing tho, the ram stacks were all over the place, 3 or 4 of em are loose and i assume through vibration have wiggled their way almost out of their seats the front one was so high up there's a clean ring on the underside of the plenium top!

Does anyone know if/how the ram stacks are secured in place? 2 of em are wayyy loose

Yeah she is running good its just that this exhaust missfire at idle I hate , I love and always have the sound of that V8 at idle and its always been good until now.

I have never been brave enough to take of the plenum, partly because I didnt know if you needed any gaskets to put it all back?

I wonder if my stacks are loose too? quite possible after 20 years!

I will be out there getting frostbite tomorrow as I have do do the oil and the plugs too :doh:

you don't need any gaskets for the plenium, it needs sealing back up with a silicone gasket poo. it's pretty easy to get off if you want to have a look in there. you need to drain some coolant out then just undo all the hoses off it.
What do you mean by exhaust misfire? It could be a small air leak in the system somewhere? mines got a tiny blow on the offside exhaust manifold and gives a little pop down the tube now and then

Might be that then , sounds like mine!

rustyrangie said:

I thought yours were about sorted?
Let me know if yer new cap is ****e it'll save me spending a fortune at lr...

I didn't get too far tonight before i got frostbite but i got the plenium off, needs a bit of a clean and there seemed to be a fair amount of crap sitting on top of the ram housing which i assume has got through the air filter?
One very odd thing tho, the ram stacks were all over the place, 3 or 4 of em are loose and i assume through vibration have wiggled their way almost out of their seats the front one was so high up there's a clean ring on the underside of the plenium top!

Does anyone know if/how the ram stacks are secured in place? 2 of em are wayyy loose

Click to expand...

As I understand it, the ram pipes are held in place with glue. I suspect a high temperature epoxy of some kind. I had one come loose and I used good old RTV to help hold it in and as far as I know it is fine.

Loose trumpets might well upset how your engine runs as it could have the effect of changing the length of the inlet tract. I don't know for sure but vaguely remember reading something somewhere about the trumpets - if you shorten them it moves the power band higher up the rev range or something.

As for your plenum - get it properly clean and make sure you clean around the throttle disc then check that the throttle disc is properly set. If you do a search of LZ you will find a number of references to cleaning your plenum.

Glad to see you have adjusted your air flow meter. I suspect you may find it will rev a bit better and your emissions should be better. You'll need to run round in it a bit to see if you are using less fuel.

Have fun!!

Just re-read a couple of the recent posts. The setting on your AFM may be out - you have an engine with cats so CO trim is set differently I think because the lamda sensors send signal to the ecu that then adjusts the injection pulse thereby adjusting the fuel mixture to achieve the correct output from the sensors on the exhaust. I don't rememeber if the sensors are in front of the cats or not but if the cat is damaged I susppect the sensors may well be shot as well, this could easily upset the running of your engine because the ecu isn't getting the right signal for the operating conditions (or something like that, maybe, I think!).

The setting I use is for a non-cat 3.9

There are a couple of guys around who would know for sure perhaps they'll take the time to set the record the straight. Anyway, I'll see what I can find/rememeber and get back to you.

Cheers for that Kev worried about afm setting now i've ripped the guts out of the cats last week as they were melted and broken up, the lambdas did test ok during the ecu tests but they look original so could be buggered?
I'll try an rtv the trumpets back in, one of ems well loose tho, in fact it's started wearing it's own groove into the plenium top
You're spot on with trumpet lengths, i;ve done a lot of dyno work with bikes and it can really make a good engine sing if you get em right and even 10mm can make a big difference. not sure how finnicky the v8 is though.

plenium all clean now
the throttle disc was out of spec, i couldn't get the stop screw to turn tho so i ermm well, filed it down worked a treat tho
just trying to get the bloody ram stack bit off the inlet, kin thing is well on there!

If you need a high temp epoxy I have access to Mazel metal which is the best thing for it, where are you located??

Oh bugger, i've done it now.. appriciate the offer fett, keep some ready for when they fall out again. lol... I'm in aldershot, not too far from you.

Just let me know m8 any time.

I got the oil changed the electric heater fitted and the leads checked and fitted a new battery to the BMW too but I didnt get any further , it was dark and raining and I was cold and tired!

Might have a play with the caps on fri or sat.

cool, let me know how you get on with the caps. I wouldn't worry about your miss noise, unless it bothers you, you'll probably end up with more nightmares getting the fannymoulds off and back on! besides most modern motors inject air into the exhaust nowadays to help reduce emissions so it'll probably help with them too, unitl it starts blowing properly